Rock Pigeons: Rats with Wings or Thoroughbreds of the Air?

The rock pigeon (Columba livia) is one of the most common sights in cities around America. Toward the end of February, I sat in the shuttle pick-up area of the Orlando International Airport in Florida for what seemed like hours, waiting for the shuttle that would transport me to my hotel. But what was trying for my patience was fortunate for my bird-watching. While the airport is slightly removed from the more urban areas of Orlando, there were several pigeons to observe. As shown by this and the Rice campus, pigeons thrive in places other than the urban downtown areas with which people usually connect them. I saw approximately ten in the half an hour I sat waiting for the van.

Pigeons are considered by many to be rats with wings, but I have never really understood why. In high school, my history teacher and I developed an ongoing dispute over his insistence on shooting pigeons at his house. I remember that he sent me an article about a bridge on the verge of collapse. The hypothesized reason? The acidity and ammonia of pigeon excrement had caused the steel of the bridge to rust! I must admit, that is pretty bad, and the regularity of pigeon droppings is a nuisance. But other than small annoyance toward the ubiquity of pigeon waste, I have never felt the need for animosity toward pigeons that others have. (And apparently Mike Tyson agrees, although these aren’t necessarily rock pigeons in particular.)

Pigeons are such a common sight that we rarely feel the need to stop and watch them, which is a large part of the reason others find them so annoying, I can only presume. I realized, though, after consciously watching them and inspecting their physical characteristics, that they are actually quite attractive birds! And the cooing sound they make is fairly pleasant. The markings on each pigeon vary more than in other bird species, but in general their simple gray feathers are complemented by extremely iridescent teal and purple colors that are more extravagant than most birds so common. With their beady orange eyes, bright orange feet, and distinctive black bars on the wings, they are pretty colorful birds, although the eye is usually dominated by the majority color, gray. The pigeon isn’t underappreciated by everyone; however, they definitely have their devotees, although the most pigeon-crazy people are still not making a big fuss about the wild variety. There seems to be quite the dichotomy between opinions of feral pigeons and domesticated ones.

The pigeons matched the hustle and bustle of the airport, rarely staying still and almost constantly walking somewhere while characteristically bobbing their heads. They frequently made movements of scuttling sort, as well, as I noted in one bird that landed on a rafter and side-stepped until it decided it would rather be somewhere else and flew to the ground. I observed how they responded to external stimuli, mainly humans. There was little noticeable interaction between the birds. When headed in a general direction, they tried to maintain their course as long as possible despite looming interference from a human passerby. If it was absolutely necessary to avoid being kicked, they would hasten their steps and scurry to the side slightly. Only rarely would they agitatedly flap their wings and quickly move away. They generally displayed a lack of interest in attempting to significantly distance themselves from humans, which is interesting. It demonstrates that they do not need or desire to move far away from humans as quickly as possible. Few animals are as successful as pigeons are at adapting to human change in the environment and coexisting with us.

One interesting adaptation of pigeons, although not related to living with humans, is beak shape. Most pigeon beak tips feature a small hook, but why is it there? Turns out, it actually evolved as a mechanism for combating feather-eating lice infestations, which frequently afflict rock pigeons. The ancestors of modern pigeons were better able to damage, kill, or remove the lice while preening if they had this tiny hook on their beak, and since their infestation would be consequently less severe, they maintained better feathers than non-hooked conspecifics. Feathers are vitally important to a bird for many things, including maintaining warmth, evading predators, and attracting mates. Dale Clayton found that females significantly prefer clean males to males with high parasite loads, even though plumage damage is not visible and time spent grooming did not vary much between the two groups. So, birds with better feathers are better able to survive and reproduce, and therefore they have more offspring. Clayton and his colleagues decided to demonstrate the validity of this hypothesis for the existence of hook-tipped beaks. In order to test this, they caught 26 pigeons and trimmed the tips of the beaks. Over the course of the next 18 weeks, these birds developed lice infestations of a higher concentration than they had been prior to the beak-trimming. 13 of the birds, chosen at random, regrew their hooks. The feeding efficiency between both groups was not significantly different. The parasite loads, however, of these newly-hooked birds grew smaller (Figure 1), while they remained at similar levels for the hookless birds, indicating that the hooks are indeed useful in removing lice.

Rock pigeons may have evolved another way to combat lice. Some bird species have the uropygial gland, also known as a preen gland because it produces oil that the birds spread throughout their feathers during preening. The oil is important in maintaining plumage condition, preventing breakage and brittleness. The reduction of feather quality in the absence of this oil is potentially due to increased ectoparasite loads because the oil may have an insecticidal quality. A study performed by Clayton and his colleagues at the University of Utah was somewhat inconclusive, as captive birds with the gland removed did not demonstrate noticeable change in parasite loads, but lice raised in an incubator died more quickly on feathers with oil than on feathers without. The authors recommend further research on the matter. It would be quite interesting if something as seemingly mundane as feather oil served as the pigeons’ own personal insecticide!

Another curious feature of pigeons is their characteristic and consistent head-bobbing, which I alluded to above. (Although it actually occurs in 8 out of 27 orders of birds as well). What could they possibly get out of bobbing their heads so dramatically whenever they moved? There have been theories that the movement aids balance and depth perception, but Barrie J. Frost found in a study that it is primarily a visual response, rather than an equilibratory response. The motion was studied using high-speed motion photography. It was found to consist of two phases: one where the head is locked in space but moves backward relative to its body, and one in which it is quickly thrown forward (Figure 2). Interestingly, Frost had the pigeons walk on a treadmill, and head-bobbing stops! Since the treadmill acts to keep the pigeon in place, its environment remains relatively stable. The birds are still moving, but the scenery does not change, hence why it is perceived to be a visual matter as opposed to equilibratory.

Domesticating rock pigeons may have occurred as long ago as five thousand years. One of the things that they have become most renowned for is their homing ability, and so pigeons have been used to deliver messages during wars. They are even lauded as the “thoroughbreds of the air” for this characteristic. It might be easy to assume that they use visual clues from familiar landscapes to orient themselves, like humans and other animals. However, they also have a navigation system that is independent of learned landmarks, and so these visual clues are somewhat redundant, so it is difficult to determine what exactly the pigeon is responding to during its flight. One study found that birds allowed to preview the surrounding scenery before release returned more quickly, indicating that visual cues do in fact aid the pigeon’s homing system. Overall, exactly how this system works is somewhat of a mystery. Other potential cues include the Earth’s magnetic field, the sun used as a compass, stars, infrasound, a polarized light compass, and olfactory stimuli.

While watching the pigeons at the airport, I observed many physical attributes and behaviors of the birds. For most, I did not realize the underlying significance. Now I know pigeon’s beaks are hooked to help defend against lice, and they bob their heads to aid depth perception and balance. Despite being such a common species, there is still a lot to learn about rock pigeons!

References

Clayton, D. H. 1990. Mate choice in experimentally parasitized rock doves: Lousy males lose. American Zoologist 30:251-262.

This article explained how pigeon parasite load affects sexual selection.

Clayton, D.H.; Moyer, B.R, et al. 2005. Adaptive significance of avian beak morphology for ectoparasite control. Proceedings of the Royal Society of London B 272: 811-817. doi:10.1098/rspb.2004.3036.

I used this article to learn about adaptations of beak shape in response to lice.

Frost, B. J. 1978. The optokinetic basis of head-bobbing in the pigeon. Journal of experimental biology 74: 187-195.

This article discussed the reasons why pigeons bob their heads when they walk.

Moyer, B. R.; Rock, A.N.; and Clayton, D.H. 2003. Experimental test of the importance of preen oil in rock doves (Columba livia). Auk 120:490-496.

This article discussed the role of oil in the feathers of pigeons as a possible insecticide.

Wallraff, H.G. et al. 1999. The roles of the sun and the landscape in pigeon homing. Journal of Experimental Biology 202 (16): 2121-2126. doi: 10.1.1.136.4875.

This article discussed the roles of visual cues in homing pigeons.

Figure 1 (from Clayton et al 2005)

This demonstrates the impact of the hooked tip on lice.

a) Rock pigeon before trimming.

b) Rock pigeon after trimming.

c) Young pigeons with trimmed beaks (black squares) had more lice on average than young pigeons with untrimmed beaks (grey triangles).

d) Mean number of lice on adult pigeons. The hooks of all birds were trimmed for 17 weeks and at week 18, half the birds (gray triangles) were allowed to regrow them, while the remaining half (black squares) continued to be trimmed weekly. The birds with regrown hooks had fewer lice than the birds who continued to be trimmed.

e) Birds allowed to regrow their hooks (grey bars) tended to have a greater mass of feathers than birds trimmed throughout the rescue experiment (black bars).

Figure 2

Figure 2 (from Frost 1978). This demonstrates that, while the body is moving fairly evenly, the head moves in a pattern of quick movement forward followed by a subsequent “hold” position, where the head remains locked in space.

Figure 3. Distribution map for the rock pigeon. The dark red represents the approximate native range while the pink represents introduced non-native populations. From:

http://en.wikipedia.org/wiki/File:Columba_livia_distribution_map.png

Rock pigeons in their natural habitat. From: http://en.wikipedia.org/wiki/File:Rock_pigeons_on_cliffs.jpg

Adult rock pigeon. From: http://en.wikipedia.org/wiki/File:Blue_Rock_Pigeon_(Columba_livia)_in_Kolkata_I_IMG_9762.jpg

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The Amazing Red Shield: A Look at Common Moorhens

I watched the moorhens circulate about on the water surface of a pond at Brazos Bend State Park for quite some time, generally staying in the same place for some minutes and casually swimming to a spot within a few feet after they had finished with the first. The duration of the time I was there, most did not stray far from their original location, typically staying in the sections of the lake that had more plant material noticeable at the surface. Intermittently squawking and croaking, their primary activity was dipping their beaks into the water. I could not quite tell what they were eating. After looking it up later, they were probably consuming seeds of grasses and sedges and perhaps some snails. There was little obvious interaction between any two members of the population. At one point I saw a couple flap their wings and zoom to a different part of the lake (about five feet away), but that was the height of activity amongst the birds.

The bill was easily the most remarkable feature that enabled me to distinguish it from the American coot. Despite previously observing a multitude of these coots at another lake and having some time to get familiar with their characteristics, the two species are quite similar and difficult to tell apart, especially to an inexperienced birder such as myself. After some research, I discovered both are in the same family, Rallidae, which is composed of birds referred to as rails. Both are dark-feathered birds with triangular-shaped bills. I had decided to watch the common moorhen closely because the vast quantity of them would allow me to view a wide variety of behaviors. Thankfully, except for the yellow tip, their bill is red throughout, including its connecting frontal shield which extends from its upper mandible to its forehead. The coot’s, on the other hand, is almost entirely white with a black mark near the tip.

The common moorhen’s red bill is so conspicuous that it appears nearly fake. It looks to me like someone cut out an oddly-shaped piece of plastic, formed a muzzle of sorts, and slipped it over each bird’s face. I wonder how such a unique color and shield shape could have arisen evolutionarily? Perhaps certain shapes, sizes, and colors are selected for by some mechanism of natural selection. As a side note, to learn a LOT more about the process of natural selection (as well as other fascinating observations about the process of evolution), I urge you to read The Selfish Gene by Richard Dawkins, a must-read for any evolution scholar or enthusiast.

Having pondered about the curious shape and colors of the common moorhen bill on my own for a sufficient length of time, I decided to satisfy my curiosity and check out the primary literature on Gallinula chloropus.  Factors such as shield color and size are related to certain indices of body condition.  F. Alvarez, C. Sánchez, and S. Angulo determined that these variations are probably used as indicators of health to opponents of the common moorhens. This makes sense, as according to Stefano Fenoglio, Marco Cucco, and Giorgio Malacarne, this species displays a high level of intraspecies aggression, and the shield is displayed prominently during conflicts. Aggression is also associated with testosterone levels, and as might be expected, higher testosterone levels have been shown to be connected with larger shield size, thickness, and increased color. Interestingly, this is shown in both sexes. Reflecting on the behavior of the birds, this is expected as females are also very aggressive. Since competitors are the main audience meant to receive the common moorhen’s message of health and body condition, sexual selection is not the primary reason for variation; however, since organisms base their choice of mate largely on their level of health and quality of body condition, the color of the shield is also a method for signaling to potential mates that they are a great choice. So sexual selection also does play a role in the color, shape, and size.

According to the Alvarez et al paper, conspicuous coloration is often a sign of the individual’s condition because “only the more healthy individuals can afford the costs of developing such coloration.” Because of this, coloration is a very honest signal, as lesser fit birds cannot afford the cost of producing a shield with a more intense hue. A positive correlation has been discovered between shield size and body size in females, and researchers discovered a negative correlation between hue and body size in males. There was also a general trend between larger shield size and a better leukocyte index (figure 1), which indicates that bigger shield size is an indication of stronger health.

As is often true with science, these results are by no means infallible. A study performed by Fenoglio et al, mentioned above, found little significance in the red coloration of the bill and shield but found that yellow color intensity was a strong indicator of the health status of the birds, while the first study I mentioned found little meaning in the results from studying the yellow portion of the bill.

Quite interestingly, the Fenoglio et al study mentions that overall, there isn’t a significant difference between bill and shield coloration between males and females. They suggest that this is due to equal participation in brooding and parental care between the sexes, and so sexual selection has worked equally between males and females. I noticed while observing the birds that there did not appear to be drastic differences between the shield colors of male and female birds, and it appears that this difference does not exist because both sexes are doing the selecting.

One aspect the other papers touched on but did not delve into were the relationship between these indicators and disease. The Fenoglio 2004 study found a negative correlation between frontal shield redness and bacterial presence, while the yellow portion of the bill showed no correspondence to any bacteria. The researchers concluded that the frontal shields act as a signal of health, where the shade of red indicates the level of presence of cloacal bacteria (figure 2).

During my trip to Brazos, I spent some time observing common moorhens at one particular body of water and its surrounding areas. The number of individuals I saw was immense. It gave me much time to note the differences and similarities between the frontal shields and bills. Overall, the range in size, shape, and color of the shields was not extremely wide, but there were certainly noticeable differences among individuals. While the answers are not definite, it appears that the size and color of the bill and shield are expressions of health and fitness, meant as a sign to potential competitors for resources. The variation in shields between individuals is significant and meaningful in their interactions with other common moorhens.

Alvarez, F. , Sánchez, C. and Angulo, S. 2005. The frontal shield of the moorhen: sex differences andrelationship with body condition. Ethology Ecology & Evolution, 17: 2, 135 — 148. doi: 10.1080/08927014.2005.952260

This paper explains the correlation between size and color of the fleshy frontal shield with sex and with certain body indices

Fenoglio, S., Cucco, M. and Malacarne, G. 2002. Bill colour and body condition in the Moorhen Gallinula chloropus. Bird Study, 49: 89-92. doi: 10.1.1.158.6095

This paper also explained the correlation between size and coloration of the shield and of the bill with body indices, but with different results.

Fenoglio, S., Cucco, M., Fracchia, L., Martinotti, M.G., and Malacarne, G. 2004. Shield colours of the Moorhen are differently related to bacterial presence and health parameters. Ethology Ecology & Evolution 16: 171-180. doi: 10.1.1.158.7771

This paper discussed the relationship between shield coloration and presence of bacteria.

Loncarich, F. and Krementz, D. 2004. External Determination of Age and Sex of the Common Moorhen. Wildlife Society Bulletin 32: 655-660. doi: 10.2193/0091-7648(2004)032[0655:EDOAAS]2.0.CO;2

Used this for background info for the common moorhen.

Eens, M., Van Duyse, E., Berghman, L., and Pinxten, R. 2000. Shield Characteristics are Testosterone-Dependent in Both Male and Female Moorhens. Hormones and Behavior 37: 126-134. doi: 10.1006/hbeh.1999.1569

This paper provided the information for the section on testosterone.  

Figure 1


Figure 1. From Alvarez et al 2005. This graph depicts the correlation between a more favorable (lesser) leukocyte index and a larger frontal shield area in male common moorhens.

Figure 2

Figure 2. From Fenoglio et al 2004. This graph depicts the relationship between bacterial presence and the red color of the shield.

Common moorhen, adult plus young, in its native environment. From http://www.flickr.com/photos/dariosanches/1808855073/

Common moorhen adult. From http://en.wikipedia.org/wiki/File:Kokoszka(Grzecho_Lukasik).jpg

Distribution map for the common moorhen. From http://www.sdakotabirds.com/species/maps/common_moorhen_map.htm

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The American Crow- The fraternity everyone wants kicked off campus

Author: Christopher Rizk

It was a Monday evening as I drove towards a city park in Alabama; as I approached the park I thought my radio signal was getting weaker because there was an annoying and increasing background noise.  The instant I turned off the car I realized that the problem was hardly the radio but rather several hundred American crows, Corvus brachyrhynchos, making cawing sounds that blended together into an unbelievably loud rumble.  The crows had turned what used to be a relaxing park into a place guaranteed to induce migraine headaches upon arrival.  As I stood there, I realized these crows were just like that one obnoxious college fraternity that everyone wants gone but just can’t get rid of.

After my failed attempt at relaxation in the park, I went home and read about the American crow only to find out that they were in fact very similar to college fraternity boys in many aspects.  Along with the noise pollution and disturbance that crows and frat boys create, they are both willing to sleep anywhere and eat anything.  The American crow is willing to eat just about anything from mice to grain and settle anywhere from forests to parking lots.  This allows the crow to adapt and become successful in a myriad of unique environments.

As I walked through observing the crows I noted the sheer number and boldness of the crows.  As I would approach them, instead of fly away, the crows would just watch me as if trying to ask, “can we help you?”  It wasn’t until I was almost within arms reach that they would move away.  Richard Knight showed how crows living in urban areas are much less threatened by human presence then crows living in a near by rural area.  When threatened, the urban crows were more aggressive towards humans then the crows in the rural area.  The urban crows would also come much nearer to humans then rural crows (details in the chart below).

Just like the frat boys, the crows are social, stick together, and help each other out.  Typically crows will live together, forming colonies containing hundreds or thousands of birds.  As the crows form families, their young will stay around for a few years to help take care of the next generation of children, allowing the parents to get food.  Crows will also work together when chasing away predators or getting dinner.  When foraging, some crows will distract an animal from its nest as the other crows seize the goods from the nest.  In his paper, Marc Hauser shows how American crows recognize sounds made by predators and react in a similar and synchronized manner.  For example hearing the red-shouldered hawk led all the crows to fly away, whereas hearing the great horned owl lead the crows to “mob” the source of the sound and warn others.

Its no secret that teamwork goes a long way in helping these crows survive.  However, the fact that they are freakishly crafty and intelligent really helps them thrive in certain areas.  According to Carolee Caffrey and Louis Lefebvre, American crows have the ability to make and use tools for a multitude of tasks.  Most commonly, crows have been spotted making and utilizing probes made from wood in order to capture prey, reach a previously inaccessible area, or bore holes.  These crows are also remarkably clever in utilizing their surroundings.  American crows have been known to drop objects, including walnuts, from various heights in order to break them open. In a BBC special, David Attenborough showed just how ingenious these crows can be.  In order to safely consume the walnuts, the crows would perch on a power-line directly above a road crosswalk, drop the walnut in the middle of the crosswalk, wait for a car to run over the walnut, wait for traffic to stop, then walk along the cross walk with humans and consume the walnut until traffic resumed!!!

At this point the American crow seems basically unstoppable, they eat anything, live anywhere, are very intelligent, and work together.  However, the American crow took a significant hit to its population upon the introduction of the West Nile virus into the United States.  According to Robert McLean, the American crow is almost guaranteed to die upon infection with the West Nile virus.  The virus usually kills the infected crow in about a week.  Although the exact mechanism isn’t known, infected crows were able to infect healthy crows through contact (most likely through sharing food, or grooming).  Luckily crows aren’t able to transmit the virus to humans.  In his paper, Nicholas Panella discusses how crow deaths due to West Nile virus (confirmed via brain tissue) are actually a quite reliable biological indicator of West Nile virus levels in the area.  Michel Bunning was able to show that a significant number of crows could be saved via vaccination.  He tested four different methods of vaccination and found that administering an intramuscular DNA vaccine with adjuvant was able to save about 60% of the crows that were exposed to West Nile virus 10 weeks after vaccination (details in the chart below).  This is pretty impressive considering none of the unvaccinated crows survived.

Despite West Nile Virus’ attempt at wiping out the American crow, they are still going strong.  Some may consider the American crow a nuisance; as for myself, I can only say that I am greatly impressed with their resilience, intelligence, and resourcefulness.  Thus, it doesn’t look like this fraternity is leaving campus anytime soon, so buy a scarecrow or pair of earplugs.  If you want to read more about the American crow, the information I used in this blog can be found in the articles I have cited below.

Attenborough, D. 2007. Wild crows inhabiting the city use it to their advantage. BBCWorldwide.

This is a BBC video showing the crows ability to utilize their resources.

Bunning, L., Fox, E., Bowen, A. 2007. DNA Vaccination of the American Crow (Corvus brachyrhynchos) Provides Partial Protection Against Lethal Challenge with West Nile Virus. Avian Diseases. 51(2):573-577.

This paper discusses several methods for vaccinating American crows against West Nile virus.

Caccamise, D., Reed, L., Romanowski, J., Stouffer, P. 1997. Roosting Behavior and Group Territoriality in American Crows. Auk. 114(4):628-637.

This paper discusses group behavior with respect to foraging and nesting.

Caffrey, C. 2000. Tool Modification and Use by an American Crow. The Wilson Bulletin. 112(2):283-284.

This paper outlines observations of a crow making and using a wooden tool.

Caffrey, C. 2001. Goal-Directed Use of Objects by American Crows. The Wilson Bulletin. 113(1):114-115.

This paper outlines observations of crows dropping various objects and using tools.

Chamberlain-Auger, J., Auger, P., Strauss. E. 1990. Breeding Biology of American Crows. The Wilson Bulletin. 102(4):615-622.

This paper contains a lot of details about American crow breeding.

Hauser, M., Caffrey, C. 1994. Anti-predator response to raptor calls in wild crows, Corvus brachyrhynchos hesperis. Animal Behavior. 48:1469-1471.

This paper shows how the American crow can recognize and respond to predator’s sounds in a similar and synchronized manner.

Knight, R., Grout, D., Temple, S. 1987. Nest-Defense Behavior of the American Crow in Urban and Rural Areas. The Condor. 89(1):175-177.

This paper shows how the American crow adapts its behavior depending on the environment (rural vs. urban in this case).

Lefebvre, L., Nicolakakis, N., Boire, D. 2002. Tools and Brains in Birds. Behaviour. 139(7):939-973.

This paper has a lot of information about tool utilization in birds (with respect to the brain).

McLean, R., Ubico, S., Docherty, D., Hansen, W., Sileo, L., McNamara, T. 2001. West Nile Virus Transmission and Ecology in Birds. Annals of the New York Academy of Sciences.  951:54-57.

This paper discusses how West Nile virus may have been spread in the American crow population.

Panella, N., Kerst, A., Lanciotti, R., Bryant, P., Wolf, B., Komar, N. 2001. Comparative West Nile Virus Detection in Organs of Naturally Infected American Crows (Corvus brachyrhynchos). Emerging Infectious Diseases. 7(4):754-755.

This paper discusses how West Nile virus affects various crow organs.

Powell, R. 1972. Operant Conditioning in the Common Crow (Corvus brachyrhynchos). The Auk. 89(4):738-742.

This paper discusses the American crow’s impressive learning ability.

Powell, R., Kelly, W. 1975. A Method for the Objective Study of Tool-Using Behavior. Journal of the Experimental Analysis of Behavior. 24(2):249-253.

This paper discusses a combination of the American crow’s learning ability and use of tools.

Photo of an American crow, Corvus brachyrhynchos. Taken from Wikimedia Commons- http://commons.wikimedia.org/wiki/File:Corvus-brachyrhynchos-001.jpg

Photo of an American crow, Corvus brachyrhynchos, taking off. Photo taken by Dr. Gordon Robertson- http://en.wikipedia.org/wiki/File:Crow_taking_off.jpg

The above chart was taken from the 1987 Richard Knight paper on Nest-defense behavior. This chart highlights the behavioral differences between crows living in unique environments; specifically the way they can adapt to very different environments. As shown, urban crows did not fly or call when intruders (humans) approached their nests, whereas all rural crows did. Some urban crows even dove at the intruder, and were willing to come much closer to the intruders then rural crows.

The above chart was taken from the 2007 Michel Bunning paper on vaccinating crows against West Nile virus. As expected the placebo, adjuvant (alone), and oral vaccine had no effect. However, the intramuscular DNA vaccines with and without the adjuvant were able to protect 60% and 44% of the crows, respectively. The killed vaccine did a very poor job of protecting the crows (11%) because this is a form of passive (short term) immunity versus long-term immunity (conferred by the live strain).

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The snowy egret- looks can be deceiving

Author: Christopher Rizk

It was a Sunday morning at the beautiful Brazos Bend state park, when I heard a deep croaking sound.  Maybe because of the harsh sound and the dreary weather, I sought out the source of the sound expecting to lay eyes upon a hippo or some other large mammal.  Instead, I laid eyes upon a snowy egret, Egretta thula, a crystal white, majestic looking egret with black legs and yellow feet.  In disbelief, I listened as it proceeded to croak again and thought to myself “looks really can be deceiving.”

As pursued the Internet I realized that I wasn’t the only one who was awed by the beauty of the snowy egret.  As the snowy egrets approach their breeding season in March, they form a magnificent plume.  The snowy egret’s beauty actually earned itself a place on the 37 cent stamp, issued by the U.S. Postal service.  Unfortunately, not everyone was content with harmlessly admiring the snowy egret in the wilderness or on a stamp.  In the 19th century the fashion gods decided that the snowy egret’s plume would make the perfect addition to women’s hats.  So perfect in fact, that the plumes were more valuable then gold (by weight)!!  As you can probably imagine this almost led to the extinction of the snowy egret.  Thank God the Audubon society instituted laws to protect the great and snowy egrets, thus stopping this from happening.

Now these beautiful plumes that almost led to the snowy egrets demise had to be good for something, right?  According to Clay Green, these plumes may give the snowy egret a slight camouflage edge over the competition when foraging.  Green compared the effects of plume color between the snowy egret (white plume) and the little blue heron (dark plume) by quantifying how long the prey lingered in front of each bird and how much biomass each bird captured.  It appears that the white plume of the snowy egret did in fact confer an advantage when foraging in open water, most likely because it did not contrast with the background as the dark plume of the little blue heron did.  However the snowy egret did not have a significant advantage when foraging with a vegetative background (trees/forest) because regardless of the plume color, the plumes just blend in with the background (Graph Below).  Advantage or not, I still had no idea how the snowy egret captured prey in the first place.

As I watched several snowy egrets’ behavior throughout the day, I was a little confused.  Initially I saw one snowy egret standing around, not really moving just pecking at the water and looking around really confused, just like a kid who lost his mother in the middle of a park.  A little later I saw another snowy egret doing what looked like a bad rendition of Michael Jackson doing the moon walk, around a rather stationary ibis.  Later on I saw a group of four snowy egrets soar through the air and land near me.  They then proceeded to slowly walk around and peck at the water, in what looked like a coordinated fashion.

Thanks to Donald Kent’s paper on snowy egret’s feeding behavior, I was able to make sense of what I saw at Brazos Bend.  To my great surprise I found out that snowy egrets are actually not Michael Jackson fans- what I saw was probably typical foraging behavior.  Apparently snowy egrets have multiple feeding strategies including: standing, walking around slowly, and stirring the area with their feet.  I still wondered what the differences between these strategies were and which was the most popular.  Since snowy egrets consume many different types of food, they have several foraging strategies.  Although they can use any “strategy” to catch any type of food, there is a preferential strategy for each type of food.  When catching fish the snowy egret usually stands fairly still and goes in for the kill when it sees a desirable fish.  When they are in the mood for worms they usually adopt the “walking slowly” strategy.  In order to catch prawns they mix-up or stir the area with their feet.  Overall, the snowy egret is usually seen employing the walking slowly or foot stirring strategies.

Although my Michael Jackson hypothesis was foiled, I still had many questions: why was one egret foraging with an ibis, one foraging with another egret, and the third going at it solo?  Michael Erwin answered my questions and even more in his paper discussing the habitats of nesting birds.  Snowy egrets will forage for food alone or in small or large groups.  Most of the snowy egrets Michael Erwin observed were alone or in small groups.  What was even more interesting was that when foraging in a group, most of the time the group consisted of multiple species of related birds.  The average group consisted of about 10 snowy egrets, however the snowy egrets only comprised 39% to 55% of the group (the exact breakdown in the chart below).  The snowy egrets flexibility in group size and consistency parallels its many foraging strategies.   For example, when foraging in groups, the snowy egret was shown to most commonly forage with the glossy ibis.  Everything was finally starting to make sense: however, why the ibis?  Apparently, the ibis and snowy egret form a “Beater-follower” relationship in which both benefit through the team effort.  This comradeship isn’t limited to foraging either; the snowy egret is known to forage, fly, and form colonies with similar species.

Although women’s hat fashion may have taken a hit since the protection of the snowy egret, I must say it was well worth it.  What a tragedy it would have been to lose this bird for hats!  In case you want to read more about the snowy egret, the information I used in this blog can be found in the articles I have cited below.

Brzorad, J.N., Maccarone, D., Conley, K. 2004. Foraging energetics of Great Egrets and Snowy Egrets. Journal of Field Ornithology. 75: 266-280.

This paper has information detailing foraging behavior and what it costs the snowy egret energetically.

Erwin, R. M. 1983. Feeding habitats of nesting wading birds: spatial use and social influences. Auk 100:960-970.

This paper contains a multitude of information on snowy egret foraging behavior and social interaction.

Green, M. C., P. L. Leberg. 2005. Influence of plumage colouration on prey response: does habitat alter heron crypsis to prey? Animal Behaviour 70: 1203-1208.

This paper talks about the effects of the plume color on ability to capture prey.

Kelly, J. P., H. M. Pratt and P. L. Greene. 1993. The distribution, reproductive success, and habitat characteristics of heron and egret breeding colonies in the San Francisco Bay area. Colonial Waterbirds 16: 18-27.

This paper discusses the colonies formed by the snowy egret and other related species.

Kent, D. M. 1986a. Behavior, habitat use, and food of three egrets in a marine habitat. Colonial Waterbirds. 9: 25-30.

This paper tells all about the foraging behavior that the snowy egrets and other related species employ.  Also discusses habitat utilization.

Ohio Department of Natural Resources. Snowy Egret. , Web. 5 Feb 2011. <http://www.dnr.state.oh.us/Home/species_a_to_z/SpeciesGuideIndex/snowyegret/tabid/6761/Default.aspx&gt;.

Website containing a sound clip of the snowy egret and a few fun facts.

Photo of a snowy egret, Egretta thula, showing yellow feet and yellow upper bill area (not in breeding season). Taken by Johnath- http://www.flickr.com/photos/johnath

Photo of a snowy egret, Egretta thula, showing plume and red upper bill area (in breeding season). Taken by Len Blumin- http://www.flickr.com/people/9062441@N02

The above graph is taken from the 2005 Green and Leberg paper in Animal Bahaviour. Based on the three types of prey listed above, it appears that the snowy egret has an advantage due to its white plume color in open water (a). Although it may appear that the snowy egret also has an advantage in vegetation (b), it is not statistically significant. The advantages were based on the total biomass caught.

The above chart was taken from the 1983 Michael Erwin paper in Auk. This chart shows that the snowy egret (SNEG) will forage in groups ranging in size from 3 to more than 30 birds. It also shows that the majority of groups are mixed- meaning they contain multiple bird species with around 39%-55% of the group being snowy egrets. This chart highlights the cooperative foraging nature of the snowy egret.

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Don’t Mock the Mockingbird

With a classic lullaby, a best selling book, a chart topping pop song and a university run student publication, the northern mockingbird has sold its name to every corner of the industry. Yet, even with its ubiquity and name recognition, the mockingbird has been able to keep its private life hidden behind curtains–something Hollywood should learn from.  After a quick and non-scientific survey of the general populace, I came to the conclusion that outside of its more famous exploits, no one on campus had a clue who or what the mockingbird was! So today, as a favor to my readers and myself, I decided to do a little bit of my own “paparazzi-ing” to enlighten people to the world of this mysterious individual.

My first surprising discovery was how common northern mockingbirds (Mimus polyglottos) actually are. After walking just a few steps into the engineering quad at Rice University, I was able to find a pair of these birds hobbling across the lawn and flying around each other in quick fashion. They were physically inconspicuous – having a relatively small body size and a body shape that is very “thrush-like” but thinner; in fact, it was only when they opened their wings did their dull gray-brown coat give way to the glaring white feathers hidden in the folds of their wings. Yet, as they darted between bushes and grass while zigzagging around each other, it became obvious that their behavior was anything but “inconspicuous.” In fact, these birds were fairly loud and had a large variety of songs. But as a whole, the pair of lovebirds seemed to mesh perfectly together as they danced across the field. Of particular interest was the reappearance of the white feathers as they expanded their wings, a byproduct of their flight.

Taking my observations to more scientific sources, I found many studies on these bird’s andtheir songs, yet surprisingly little else. This piqued my interest since it isn’t very often we will see such an emphasis on one single subject. So what exactly is so interesting about the songs of these birds? It seems that these birds are like the you-tube stars of the bird world, they can cover any song by another bird and are constantly adding new songs and beats to their repertoire and annoying the casual by-passer. But what is astounding is that these birds have been found to have repertoires easily over 400 different songs, which grow as the birds age (Derrickson 1987). In fact, the size and quality of a male’s song repertoire is shown to have greater advantage in acquiring territory as they can deter other potential settlers with threatening bird calls (Howard 1974). Researchers agree that different songs and patterns are used for different purposes; burst singing was found to be most common in the fall when males and females were most territorial  (Logan, Budman et al. 1983). Most song patterns are used more for protecting territory, which is important for getting mates (Howard 1974).

Yet I was also curious about their lifestyle outside of just their singing. Digging through some archives, I came upon the finding that the northern mockingbirds are omnivorous feeders and often eat arthropods and insects close to the ground as well picking up fruits from trees (Breitwisch 1987). This completely explained why the pair that I saw was always hovering so close to the ground. Yet their unique behavior did not stop there, these birds also apparently do use flashing of wings to signal various messages (Sutton 1946) although their exact meanings aren’t always clear. Most of the time, flashing wing displays signaled warning against intruders and that you do not want to mess with these birds (Sutton 1946). Why you may ask? Because they WILL attack you! In fact, in a 1988 paper by Breitwisch, it was found that more aggressive birds were more successful in reproduction. The aggressive males showed greater ability to attract mates and protect their eggs because they were more prone to attack intruders (Breitwisch 1988). This pretty much means that we should probably stay away from these birds, and particularly not mess with their nests or their newly-fledged chicks.

After learning all this, my view of these birds has changed significantly. I always thought these birds were pretty song birds that didn’t really do much besides sing, but their mental and vocal capabilities are far beyond what I imagined and their aggressive behavior is definitely something to beware of. In short, if you didn’t take anything else out of this blog, just know that mockingbirds are basically the sirens of the avian family, they have a beautiful song but if you get too close, they might just claw you to death!

For additional information and pictures, I have placed some links and figures below.

Flickr (Open for commercial re-use): Northern mockingbird flashing wings

Flickr (Open for commercial re-use):  Northern mockingbird resting

Wikimedia Commons: Juvenile northern mockingbird

Fig. 2. The audiograph shows the sound patterns of the northern mockingbird. Each block represents one distinct pattern set of the mockingbird call. Image courtesy of Wildenthal 1965.

References:

Breitwisch, R., 1988. Sex differences in defense of eggs and nestlings by northern mockingbirds, Mimus polyglottos. Animal Behavior. 36(1): 62-72; http://www.sciencedirect.com/science/article/B6W9W-4KRFX07-8/2/7390675155798d9889b405f12c3692ff

Breitwisch, R., M. Diaz, R. Lee, 1987. Foraging Efficiencies and Techniques of Juvenile and Adult Northern Mockingbirds (Mimus polyglottos). Behavior. 101(1): 225-235;http://www.jstor.org/stable/4534598

Derrickson, K.C., 1987. Yearly and Situational Changes in the Estimate of Repertoire Size in Northern Mockingbirds (Mimus polyglottos). The Auk. 104(2): 198-207;http://www.jstor.org/stable/4087025

Logan, C.A., P.D. Budman, et al. (1983). “Role of chatburst versus song in the defense of fall territory in mockingbirds  (Mimus polyglottos).” Journal of Comparative Psychology 97(4): 292-301

Howard, R.D., 1974. The influence of sexual selection and interspecific competition on mockingbird song (Mimus polyglottos). Society for the Study of Evolution. 28(3): 428-438;http://www.jstor.org/stable/2407164

Sutton, G.M., 1946. Wing-flashing in the mockingbird. Wilson Ornithological Society. 58(4): 206-209;http://www.jstor.org/stable/4157522?seq=4

Wildenthal, J.L., 1965. Structure in Primary song of the Mockingbird (Mimus polyglottos). The Auk. 82(2): 161-189;http://www.jstor.org/stable/4082931?seq=5

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A Look at the Barbarous Butcher Bird – The Loggerhead Shrike

Standing, sweating in the hot Texas sun somewhere between Houston and Austin, I look out into the vast pasture next to the road. I can see miles and miles of open land, with the occasional tree and cows. A small bird is perched quietly on the power line. Approximately the size of robin, it has a hooked beak and large head. There is a black stripe that runs across its eyes and forehead, making it look like a masked bandit. Its appearance is striking: grey body, black and white wings, and a black tail with white stripes. Colloquially known as the “butcher bird,” the loggerhead shrike (Lanius ludovicianus) is a member of the predatory passerines and one of the most phenomenal birds.

The loggerhead shrike displays a remarkable and rather barbaric style of hunting. Unlike other birds of prey (like the hawk), the shrike does not actively forage. Instead, it sits and waits, perched high above the ground. When it locates its prey, it attacks and impales the poor animal on nearby thorns. Once secure, the shrike will tear off chunks to eat. Also, unlike other predatory birds, the loggerhead shrike does not have strong talons. For hawks and owls, talons are used for attacking, but more importantly, talons are used to anchor down prey. To compensate for a lack of strong talons, the shrike has learned to anchor its prey on thorns! To the shrike’s credit, though, it does have a disproportionately large head and a strong, hooked beak allowing it to attack larger animals than other birds of its size.

The shrike’s unique hunting style attracts attention from birders and researchers alike. How does the impaling behavior develop? Is it instinctual or learned? Susan Smith, at the University of Washington, has been studying this impaling behavior at the Columbia National Wildlife Refuge in Washington. She is interested in the ontogeny of the attack. After extensive observation of 5 nests, she reported that no adults made an effort to teach the impaling behavior to their offspring before the young left the nest at 16 days. Adults impaled their prey at the site of killing, and tore off pieces, which were brought back to the young. She compared the development of the impaling behavior between the offspring in the field and hand-reared birds in the lab. She notes that young shrikes go through a series of developmental stages before learning to impale effectively.  The first stage, “dabbing,” is simply manipulating an object by the beak: turning it sideways and placing it back down. In the next stage, “dragging,” the bird drags the object toward itself.  “Wedging” involves the bird dragging an object into a position in which the object is held in place. Finally, true “impaling” is accomplished when the bird uses thorns to hold the object (food) in place. Remarkably, the time it took the birds to reach these behavioral stages was similar in both the wild and captive shrikes. Smith concluded that the shrikes do not require any special experiences to learn the preliminary motor behaviors (ie, dragging), but need to learn to orient their food toward thorns for impaling.

One of the shrike’s keys to successful hunting is in using its powerful beak and strong bite to break the necks of small vertebrae. This allows the shrikes to attack and kill relatively large prey. Smith’s further research, using shrikes raised in the laboratory showed that by day 40, even inexperienced shrikes displayed the ability to attack the neck of small mouse-sized prey. Using stuffed mice as model prey, she observed the behavior of young shrikes when presented with the prey. All 28 of the study birds recognized and oriented toward their respective mouse. Only a fraction of birds attacked, but none lost attention. Interestingly enough, of the birds that did attack, some had never been exposed to the attacking behavior. From this, Smith suggests that shrikes have inborn abilities (visual, olfactory, etc) used to recognize and attack prey.

No matter where you go in the US, you can find loggerhead shrikes. Populations of shrikes can be found dispersed throughout the US and southern Canada. There are five main populations with wide breeding ranges. Rarely, do the breeding ranges overlap between populations. The shrikes’ movements from breeding grounds in the north to winter grounds in the south are not completely understood. Based on a compilation of banding data, Burnside confirmed that shrikes are partly migratory, with northern populations moving toward the southeastern US in the winter. Some shrikes are moving thousands of meters every winter. For example, shrikes banded in Saskatchewan were later found in Texas. That is a distance of over 2500 kilometers!

On my 3 hours drive from Austin to Houston, I only saw 3 shrikes. 50 years ago, however, the shrike population was burgeoning and I bet I would have seen many more. No one is sure exactly why the shrike has seen declining numbers, but much of the research on these birds has been driven by efforts to conserve the species. Special measures have been taken to understand and characterize the shrike’s breeding habitat, in hopes of maintaining the optimum environment for shrike breeding. Brooks and Temple at the University of Wisconsin thoroughly studied the habitat of shrikes in the upper Midwest. They found that shrikes primarily live in open, agricultural areas with grasslands. The shrike requires a relatively elevated perch site (average 2.3 m). Their research focused on 4 main aspects of the habitat, important to survival and breeding: herbaceous ground cover, potential and usable foraging habitat, and potential nesting sites. With these data, they developed sustainability indices to quantitatively assess an areas capacity to support the shrike.

Extreme measures are being taken in areas where the shrike population is especially low. In 1977, the San Clemente loggerhead shrike was listed as an endangered species. The population continued to decline as humans and feral goats habitually destroyed their breeding grounds. In 1991, only 14-20 adult of the population were left in US. A team of researchers in San Diego developed an artificial incubation and hand-rearing program in an effort to revive the population. The team had to take into account proper hatching conditions, diet, and re-introduction methods. The small, thin-shelled eggs must be kept in specific conditions. Without parental nurturing and care, the eggs have to be provided with a high-protein diet to allow for growth. Finally, the chicks must be able to survive back in the wild after being hand-reared. With a set of experimental diets, they tested their protocol on a non-endangered shrike population. They translated their research to the San Clemente population and were successfully able to rear 10 shrikes, which were released into the wild.

What a shame the loggerhead shrike population is declining so rapidly. It truly is an amazing bird. If its striking appearance wasn’t enough, it also has developed one of the most unique, yet successful, hunting techniques: attack and impale. I have yet to see this extraordinary behavior with my own eyes. However, I am going to pay much more attention to birds perched on tree branches and power lines. If I can find another perched loggerhead shrike, an attack is not far away. I just hope I am not the one the “butcher bird” is attacking!

References:

Smith SM. 1972. The Ontogeny of Impaling Behavior in the Loggerhead Shrike, Lanius ludovicianus L. Behavior 42: 232-247. http://www.jstor.org/stable/4533459

  • This paper describes Smith’s study into the impaling behavior exhibited by young shrikes. She talks about the general hunting patterns of the Loggerhead shrike, its physical characteristics, and her observations in the field and in the lab.

Smith SM. 1973. A Study of Prey-attack Behavior in Young Loggerhead Shrikes, Lanius ludovicianus L. Behavior 44: 113-141. http://www.jstor.org/stable/4533483

  • In this paper, Smith discusses her study of shrike attacks in the field and in the lab. She used models to elucidate how young shrikes attack prey.

Burnside, FL. 1987. Long-distance Movement by Loggerhead Shrikes. Journal of Field Ornithology 58: 62-65. http://www.jstor.org/stable/4513190

  • This paper compiles previous studies of banding and recovery of loggerhead shrikes during winter migration. It also includes maps of migratory patterns and breeding regions.

Brooks, BL and Temple, SA. 1990. Habitat Availability and Suitability for Loggerhead Shrikes in the Upper Midwest. American Midland Naturalist 123: 75-83 http://www.jstor.org/stable/2425761

  •  In this paper, Brooks and Temple characterized the breeding region of the loggerhead shrike and created sustainability curves for conservation efforts.

Kuehler, CM, Mcilraith, B, Lieberman, A, Everett, W, Scott, TA, Morrison, ML & Winchell, C. 1993. Artificial incubation and hand-rearing of Loggerhead Shrikes. Wildlife Society Bulletin 21: 165-171. http://www.jstor.org/stable/3782919

  • This paper describes the efforts taken by a team of zoologists to artificially incubate and hand-rear and endangered population of loggerhead shrikes.

Figure from Smith study on the ontogeny of shrike behavior (Smith, 1972). This graph shows the frequency of observed behaviors by captive (dashed) and wild (solid) shrikes as a function of age. The onset for these behaviors is remarkably similar even though the environments are different.

Figure from Burnside’s study of shrike movement (Burnside, 1987). The map depicts banding (open circle) and recovery (closed circle) sites for loggerhead shrikes that moved more than 100 km.Figure from Burnside’s study of shrike movement (Burnside, 1987). The map depicts the breeding zones for 5 populations of loggerhead shrikes: 1) L.l.ludovicianus, 2) L.l.migrans, 3) L.l.excubitorides, 4) L.l.nevadensis, 5) L.l.gambeli. Shaded areas are an overlap of breeding regions.

Figure from Burnside’s study of shrike movement (Burnside, 1987). The map depicts the breeding zones for 5 populations of loggerhead shrikes: 1) L.l.ludovicianus, 2) L.l.migrans, 3) L.l.excubitorides, 4) L.l.nevadensis, 5) L.l.gambeli. Shaded areas are an overlap of breeding regions.

Figure depicting suitability index curves for four elements on the loggerhead shrike breeding habitat: A) percent herbaceous ground cover in 25 ha land plot, B) percent potential foraging habitat in 25 ha land plot, C) percent usable foraging habitat in 25 ha land plot, D) number of potential nesting sites in .25 mile radius. (Brooks and Temple, 1990)

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The [Red-cockaded] Woodpecker Show

Walking amidst the towering longleaf pine trees and grassy undergrowth on a clear yet humid Sunday morning, my second birding trip (W.G. Jones State Forest in Conroe, TX) had a distinctly different feel than the previous overcast and rainy one at Brazos Bend. There was less crowding of shrubs and trees and the resulting open space made it easier not only to find birds but also follow them as they flew from tree to tree. Check out Figure 1 for a view.  W.G. Jones State Forest is known for its Red-cockaded Woodpecker (scientific name Picoides borealis) management area where habitat restoration via controlled fires is conducted (check out this video by user KennethKramm on YouTube for more info). Our walk around the longleaf pines did not disappoint as we saw at least 2 Red-cockaded Woodpeckers that day. My focus on this entry, however, will be on the Red-cockaded Woodpeckers cousin, the Red-bellied Woodpecker (scientific name: Melanerpes carolinus).

We were quite fortunate to see the Red-bellied Woodpecker here in southeast Texas as that is towards the edge of its range in North America (Figure 2). After getting to witness the white and black patterns of a Red-cockaded Woodpecker and a downy woodpecker, my eyes lit up as I saw the red nape of what I knew had to be a Red-bellied Woodpecker perched sideways several meters up on a longleaf pine. Although the namesake of a Red-bellied Woodpecker is a faint stretch of red feathers on its lower belly, this area is very hard to see so a much easier field mark is the red nape. Seeing as how this Red-bellied Woodpecker had a nape that extended over the top of its head, I knew it must be a male. While I wasn’t able to take any pictures, check out Figure 3 for a close up look of the creature I saw. Just as I was beginning to examine its barred back and red-orange face, the Red-bellied Woodpecker flew off and went to another tree. Fortunately, I was able to track it – at least for a while. Eventually I lost the bird and focused my attention on the Red-cockaded Woodpecker and Brown headed Cowbird (Molothrus ater) Anyway, let’s take a look at what the literature says about the Red-bellied Woodpecker.

An important aspect of a species’ survival is its ability to deal with competitors. A 1989 paper by Danny Ingold from Mississippi State University looked at the competition between the Red-bellied Woodpecker, the Red-headed Woodpecker (Melanerpes erythrocephalus)   and the European Starling (Sturnus vulgaris) for nesting sites in both rural and urban areas of Oktibbeha County, MS. Check out figure 4 for a picture of the Red-headed Woodpecker. Whereas many of the Red-headed Woodpeckers did not tend to breed at the same time as the other two species of birds and therefore were not always in direct competition with them, the Red-bellied Woodpecker and the European Starling had very close breeding times and tended to be in more competition. The Starling was generally the “winner” of this confrontation as it usurped more nests from the Red-bellied Woodpecker (Figure 5). Fifty-two percent of Red-bellied Woodpeckers nest cavities were usurped by the Starling compared to only 7% of the Red-headed Woodpecker by the Starling. Ingold suggests that this will cause selective pressure and result in a shift in the breeding season of the Red-bellied Woodpecker in east-central Mississippi as those Red-bellied Woodpecker who avoid nesting competition with the Starling will have a higher fitness.

But what if the Red-bellied Woodpecker in Oktibbeha County, MS don’t want to change their breeding season? Well they could just take a page out of the RWB I saw at Jones State Forest and just fly somewhere else, right? A 1999 paper by Grubb and Doherty looked at a phenomenon known as gap-crossing. Gap-crossing occurs when an organism crosses a large stretch of inhospitable habitat from one metapopulation to another. The researchers wanted to investigate what features of a particular species of bird correlated with its ability to gap-cross. They surveyed 47 woodlots in three counties in northeastern Ohio and recorded when a particular bird would arrive at a woodlot as well as leave a woodlot. Each woodlot was also measured and its geographical proximity to other woodlots was evaluated to assess how difficult it would be to go to that woodlot from another one. The researchers found that woodlot area was a large predictor of whether or not a bird would leave the particular woodlot, as those with a larger perimeter were less likely to have birds leave (check out Oram’s 1991 review of metapopulation theory and habitat fragmentation for a more in-depth look). The other predictor turned out to be the size of the bird. Unfortunately for the Red-bellied Woodpecker, it was in the middle of the pack of birds studied and the mean distance it traversed to go from one woodlot to another was only 200 meters (Figure 6).

At Jones State Forest we saw many different kinds of woodpeckers (downy, Red-bellied Woodpecker, Pileated Woodpecker, Red-cockaded Woodpecker) so let’s take a look at some research that considers how two different species of woodpecker – the Red-bellied Woodpecker and Red-headed Woodpecker interact with one another and how their behavior differs. A 1972 paper by Ann Reller investigates what behavioral and temporal activities of the two species of woodpecker allow them to coexist in eastern North America.  Particular interest was given to how they ration their time with respect to changes in the season and the environment. Reller found that what allows these two species of woodpecker to coexist is their niche segregation during breeding season. This allows one species fitness to be relatively unaffected by the others during breeding season, and although aggression does take place during non breeding season, it does not seem to be enough to warrant a significant advantage to one species over the other. Also be sure to check out Jerome Jackson’s 1976 paper which takes a deeper look into breeding differences between the Red-bellied Woodpecker and Red-headed Woodpecker.

Seeing the various kinds of woodpeckers was a fulfilling reward for a college student waking up at 6:00 AM on a Sunday morning. Their subtle differences in appearance are only the tip of the iceberg, as it is their niche differentiation that enables them to thrive alongside their cousins. Check out some more pics of the Red-bellied Woodpecker (figures 7-9)!

Fig 1. View of the Red-cockaded Woodpecker management area filled with longleaf pine trees. From user victoriabirder on Flickr (http://www.flickr.com/photos/pampered_oaks/5103504183/sizes/m/in/photostream/)

Fig. 2. Range of the Red-bellied Woodpecker. From Wikipedia (http://upload.wikimedia.org/wikipedia/commons/5/55/Red-bellied_Woodpecker-rangemap.gif)

Fig. 3. Close up view of a male Red-bellied Woodpecker. From user Sky~Soulshines on Flickr (http://www.flickr.com/photos/soulshines/3635727943/sizes/m/in/photostream/)

Fig. 4. Close up view of a Red-headed Woodpecker. From user rmaum on Flickr(http://www.flickr.com/photos/rmaum/2578981843/sizes/m/in/photostream/)

Fig. 5. A graph from the Ingold paper showing nest usurpations by each of the main species observed on each other. The primary victim was shown to be the Red-bellied Woodpecker by the European Starling (black box). The triangle shows nest usurpations of the Red-headed Woodpecker on the Starlings. The circle shows nest usurpations by Red-bellied Woodpecker on Red-headed Woodpecker.

Figure 6. A graph from the Grubb paper showing the relationship between body mass and the mean distance crossed from one woodplot to another for 8 species of birds in NE Ohio. The Red-bellied Woodpecker was near the middle of the pack.

RBWO = Red-bellied Woodpecker

DOWO = Downy Woodpecker

BLJA = Blue Jay

CACH = Carolina Chickadee

TUTI = Tufted Titmouse

WBNU = White-breasted Nuthatch

NOCA = Northern Cardinal

SOSP = Song Sparrow

Figure 7. Red-bellied Woodpecker close-up. From user majorbirds on Flickr. (http://www.flickr.com/photos/majorbirds/4751560715/sizes/m/in/photostream/)

Figure 8. Red-bellied woodpecker eating out of  a bird feeder. From user alibnyc on Flickr (http://www.flickr.com/photos/alibnyc/244316774/sizes/m/in/photostream/)

Figure 9. Red-bellied woodpecker on top of a dead tree while a loggerhead shrike flies nearby. From user Points in Focus on Flickr (http://www.flickr.com/photos/23589923@N05/4365556439/sizes/m/in/photostream/)

Sources

Grubb, T.M. 1999. On home-range gap crossing. The Auk. 116(3)618-628.

[This paper looked at factors that affected gap-crossing in different species of birds]

Link – http://elibrary.unm.edu/sora/Auk/v116n03/p0618-p0628.pdf

Ingold, D.J. 1989. Nesting phenology and competition for nest sites among red-headed and red-bellied woodpeckers and European starlings. The Auk. 106(2)209-227.

[This paper looked at the effect of competition on red-bellied woodpecker by the European Starling]
Link – http://www.jstor.org/stable/pdfplus/4087714.pdf?acceptTC=true

Jackson, J.A. 1976. Comparison of some aspects of breeding ecology of red-headed and red-bellied woodpeckers in Kansas. Condor. 78(1)67-76.

[This paper considered how differences in season and environment affected the behavior of the red-headed and red-bellied woodpecker during breeding season and non-breeding season]

Link – http://elibrary.unm.edu/sora/Condor/files/issues/v078n01/p0067-p0076.pdf

Opdam, P. 1991. Metapopulation study and habitat fragmentation: a review of holarctic breeding bird studies. Landscape Ecology. 5(2) 93-106.

[This was  a review paper that looked at metapopulation theory]

Link – http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.5.3536&rep=rep1&type=pdf

Reller, A.W. 1972. Aspects of behavioral ecology of red-headed and red-bellied woodpeckers. American Midland Naturalist. 88(2)270-290.

[This paper looked at differences in behavior of the red-headed and red-bellied woodpeckers]

Link – http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.5.3536&rep=rep1&type=pdf

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