Red-Tailed Hawk – Sculpted for Success in Predation

Ever since my first birding trip, I began to notice birds whenever I’m walking around. In the past, as I walked across my campus for class, the only birds that I would notice were either big or noisy ones, such as the great-tailed grackle or the American crow. Learning more about birds has helped me become more observant of the wildlife around me. Since then, I have spotted many different kinds of birds on campus, and the diversity is really quite amazing. Some of the many birds I have spotted on campus are:

Eastern screech owl, red-tailed hawk, cowbird, purple martin, ruby-crowned kinglet, American robin, European starling, house sparrow and the rock dove.

For this bird blog, I will be writing on one of the many birds I spotted on campus so far, and that bird is the red-tailed hawk (Buteo jamaicensis), which is the biggest and most majestic bird (in my opinion) that I have seen on campus thus far. But before I start, here is the “birding tip of the day”!

Birding Tip #2

Move around in small groups if possible and keep your speaking volume down so as not to alarm or startle the birds.

It was a sunny Saturday morning, and Houston was just beginning its transition from winter to spring. It was about 11 am, and I decided to walk around the inner loop with a friend to see if we could spot any birds that might be around on campus soaking up the morning sunlight. Stuffing my birding binoculars and my trusty camera into my backpack, I walked out towards the Sallyport to meet my friend. Although the sun was up, it was still somewhat chilly because of the wind that was constantly blowing against my face.

We began walking down the inner loop as we wondered what birds we would see. As we walked between Anderson Biological Labs, we noticed that there was a small group of people staring up at one of the trees between the Labs and the Rice Memorial Centre. When we reached the crowd, I realized that everyone was looking at a juvenile red-tailed hawk perching on a tree branch. The hawk was just sitting still on the branch, nonchalant towards the people watching it.

Upon closer observation, the red-tailed hawk’s beak was primarily greyish-blue in color, with a dash of yellow closer to the face of the bird. The giveaway observation that it was a juvenile red-tailed hawk was its white chest and white underparts with a brown breast band. As it was around 68 degrees Fahrenheit, the bird’s feathers were also fluffed up to stay warm. It sat still for about 5 minutes before flying off to one of the trees directly outside Keck 100. My friend and I then walked towards Keck Hall to observe the bird from a distance. At the second tree, it remained perched on the branch for about 10 minutes before flying off towards Duncan. Once again, we followed the bird and found it perched on a tree close to Duncan. It perched for about 10 minutes before flying off towards the Sallyport. As usual, we tried to follow it once more, but this time we were unable to find its new location.

I suspect that the hawk was actually hunting for food, perhaps an unsuspecting squirrel or a smaller bird; I assume this because the hawk stayed very still whenever it perched on branches. The only observable movements by the hawk was either shifting ever so slightly from side to side (even then, it was only a couple of centimeters each time) or moving its head in different directions, probably to increase its range of spotting potential prey movement. It would turn its head to look up, down, from side to side, or nearly all the way behind it. The hawk’s ability to rotate its head was amazing. At times, it would rotate its head close to 180 degrees. I believe that the reason for minimal movement is that it allows the hawk to blend into the environment, rendering it unnoticeable by its prey, thus allowing it to have the element of surprise as it swoops down to attack its prey. The largest movement that the hawk would make always happened just before it flies to a new location, which involved using its beak to “scratch” or preen its chest feathers. Another interesting observation I made would be that it always stayed in only one specific location for around 10 minutes and never more than 15 minutes.

Oh did I mention? At every location where the hawk perched, I did not see a single squirrel or small-sized birds. Not one.

Whenever the hawk flew from one spot to another, it would always push off from the branch and make a couple of deep wing beats before either gliding really close to the ground or soaring towards the sky. Because it glided so close to the ground, as it traveled towards the Sallyport/Academic Quad, I was afraid that it would crash into an elderly couple taking a stroll on the walkway. Of course, such an accident was extremely unlikely.

As a clarification, I initially could only deduce that the bird was a type of hawk, but I had no idea to what specific species it belonged. It was only after asking Dr. Cin-Ty Lee did he confirm that it was a juvenile red-tailed hawk.  Upon verifying the species, I researched more details on the hawk, and I found that the red-tailed hawk is actually a polytypic species in which at least one subspecies exhibits color polymorphism that is linked to geographical location as well. For instance, if you buy “The Sibley Field Guide to Birds of Eastern North America” (which is a great book for beginner birders that I recommend to all of you guys out there; here is the link to purchase it from Amazon: http://www.amazon.com/Sibley-Field-Guide-Eastern-America/dp/067945120X/ref=sr_1_1?ie=UTF8&qid=1302458922&sr=8-1), you will learn 6 different color variations of the red-tailed hawk, which the book tags to different region of American. For instance, the red-tailed hawks found in southwestern region of America typically have a darker upperside, a paler unstreaked underside, and a paler tail compared to eastern populations. On the other hand, western populations tend to be darker and more rufous, with 20% of the population being the dark morph variation. Judging from the book’s illustration and the photos taken of the hawk, I suspect that the red-tailed hawk falls under the southwestern category.

I was kind of disappointed that I failed to see any predator-prey action, so I decided to search the web for more information on some of the hunting patterns and related information on the red-tailed hawk. It turns out that as a result of natural selection, these hawks have actually evolved to become extremely efficient hunters; more efficient than what we perceive them to be. And if you ask me, nature has indeed “trained” them well.

It turns out that red-tailed hawks that are of a lighter morph tend to hunt and use perching sites that are relatively open while dark morphs often hunt in areas where perch sites are characterized by dense stem cover. It is not difficult to imagine why such a hunting pattern exists. Lighter morph red-tailed hawks that perch in more open areas stand out less than those that perch in sites with dense stem cover because  open areas are often brightly lit, enabling the hawk to avoid being seen by its prey. And the reverse is true for the dark morphs. Over time, hawks that perch in areas that allow them to blend in with the surrounding area are selected for by natural selection as these hawks are better able to hunt for food to survive as well as to feed their offspring so that they are all able to reach reproductive age to produce fertile viable offspring. This is in line with the hawk that I observed as well. The juvenile southwestern morph which I saw was of a lighter morph compared to the other variations, which explains why it is hunting and perching in relatively open areas such as the Rice University Campus during spring, where most of the trees do not have many leaves.

However, that’s not all; red-tail hawks are also able to differentiate and identify easy and difficult prey, and in doing so, they adjust their hunting strategy. In the event that they are targeting a prey that is difficult to capture and kill, such as a squirrel, these hawks are able to identify and target preys that were in markedly poorer conditions than those of the general population such as lower packed-cell volume and more physical defects. On the other hand, if they are hunting for easy prey such as chipmunks, then they do not discriminate between the chipmunks because they know that overall, the chipmunk is still an easy prey to overcome, even if the targeted chipmunk is considered to be above average in overall fitness when compared to its population. I just want to clarify out that there is no chipmunk population here on Rice University campus but in places where there is, the red-tailed hawk will not discriminate between the chipmunks when hunting for one.

Moreover, red-tailed hawks also have multiple methods of hunting for food, so that their prey does not get accustomed to a particular form or method of attack. In addition to perching motionless on a branch waiting for a prey to carelessly walk into the “circle of vulnerability,” red-tailed hawks actually spend 30% of the time hunting from the air as well, either by flapping around or soaring in circles in the sky.

In addition to all those traits, the red-tailed hawks are also well adapted to being able to co-exist with other birds of prey in the same habitat and region by hunting for prey that are least competed for. This is largely attributed to the fact that they are dietary generalists and are also highly opportunistic predators. If there happens to be another bird of prey in a particular habitat where these red-tailed hawks reside in, they are able to easily shift their prey choice to one that has lesser competition to form dietary niches with the other equally dominant predators in the region to ensure that they do not have to engage in fierce competition for food. One good example of a bird of prey that exists peacefully with the red-tailed hawks would be the great horned owls, whereby the diet of both birds has only a 50% overlap, which is actually quite a large dietary niche separation for two similar-sized birds of prey living in the same habitat. Studies have shown that whenever the red-tailed hawk lived in a habitat where great horned owls existed, the red-tailed hawks ate significantly more reptiles while the great horned owls ate significantly more invertebrates.

On a whole, I find hawks to be truly amazing birds, and I considered myself lucky to be able to spot and observe a red-tailed hawk on my bird walk around campus. I hope one day you guys will get the chance to see one in close range too!

In my opinion, self-taken pictures of birds are so much nicer to look at then random open-access pictures from the internet, so I highly recommend that you bring along a camera or invest in one so that when you go on birding trips, you can take pictures of the places you went and the many birds that you saw during your trips. If you’re looking for multi-purpose camera that is small and affordable for your birding trips, I suggest you check this model out: Canon PowerShot SD1300 IS. It is the one I am using at the moment. (Check it out at Amazon: http://www.amazon.com/Canon-PowerShot-Stabilized-2-7-Inch-Silver/dp/B0035FZJKI/ref=sr_1_1?s=electronics&ie=UTF8&qid=1302460682&sr=1-1)

I took many pictures of the red-tailed hawk, so if any of you guys want to see all the pictures I have taken, just drop me an email at yo1@rice.edu and I’ll send them to you.

In any case, here are some pictures of the red-tailed hawk which I took and some diagrams which details how well-designed the hawk is for hunting prey!

A juvenile red-tailed hawk perched on a branch by the inner loop on Rice campus

Here is the same red-tailed hawk rotating its head almost a 180° to check out for prey that might be behind it.

Here is a photo taken by my friend back in February this year of a red-tailed hawk’s successful capture of a squirrel!

Here is a diagram highlighting the observation that dark morphs tend to perch in sites that are less open while light morphs tend to perch in sites that are more open – Preston, C. R. 1980. Differential Perch Site Selection by Color Morphs of the Red-Tailed Hawk (Buteo jamaicensis)

This table shows that as the difficulty of capture for a particular prey species increases, the increase in the tendency of the red-tailed hawk targeting substandard individuals in a species for capture – Temple, S. A. 1987. Do Predators Always Capture Substandard Individuals Disproportionately From Prey Population?

This graph shows the three different methods by which the red-tailed hawks used to capture its prey. The graph also shows the amount of time spent on each method and the success to cost ratio – Ballam, J. M. 1984. The Use of Soaring by the Red-Tailed Hawk

And below are the references which I used to identify the bird and also to learn more interesting information about the red-tailed hawks for this blog post.

1)      Preston, C. R. 1980. Differential Perch Site Selection by Color Morphs of the Red-Tailed Hawk (Buteo jamaicensis) – http://www.jstor.org/stable/4085749

This journal article highlights the relationship between the overall outer appearance of the red-tailed hawks and their perching sites.

2)      Luttich, S., Rusch, D. H., Meslow, E. C., Keith, L. B. 1970. Ecology of Red-Tail Hawk Predation in Alberta – http://www.jstor.org/stable/1933655

This article discusses the relationship between the size and density of prey populations to the red-tailed hawk’s feeding habits.

3)      Temple, S. A. 1987. Do Predators Always Capture Substandard Individuals Disproportionately From Prey Population? – http://www.jstor.org/stable/1938472

This article shows that red-tailed hawks will tend to capture substandard individuals of a particular prey population depending on the prey-capture difficulty.

4)      Ballam, J. M. 1984. The Use of Soaring by the Red-Tailed Hawk (Buteo jamaicensis) – http://www.jstor.org/stable/4086604

This article discusses the uses and benefits of soaring by the red-tailed hawk

5)      Marti, C. D., Kochert, M. N. 1995. Are Red-Tailed Hawks and Great Horned Owls Diurnal-Nocturnal Dietary Counterparts? – http://www.jstor.org/stable/4163598

This article seeks to understand the similarities and differences of the diet of two birds of prey when living in the same habitat or region.

6)      Sibley, D. A., Cech, R. The Sibley Field Guide to Birds of Eastern North America. Alfred A. Knopf, Inc, 2003.

A great field guide to birds for beginner birders.

7)      Red-Tailed Hawk – Birds of North America Online – http://www.allaboutbirds.org/guide/red-tailed_hawk/id

This website provided an overall good introduction to the bird for all aspects. The distribution of the bird can be found here.