I usually hear them on my way back from work at night. With a high-pitched keen, a small dark shape would dart through the black of the unlit IM (intramural) fields in the corner of my eye. “Are those bats?” my companion would ask. I never felt qualified to answer. Later that night, I am distracted by homework. Enter Bird Lab. So come along with me as investigate…
The stop and go life of the killdeer, America’s shore-less shorebird.
February 4, 2011 9:54 AM
They are outside. I peak through my window on the morning of a snowless-snow day to check for prospects and it is not long before I spot a lone killdeer, Charadrius vociferous, standing on the far side of the fields. Strange. In the evenings I always see them in flocks. Unperturbed by its solitude, the bird forages in the frosty manicured grass with intermittent bursts of speed and sudden stops. Dash. Pause. Dash. Dash. Pause. Almost Road Runner-esque with its seemingly disproportionate long leg but even Wile E. Coyote would be caught off guard by this bird’s ability to dart away from an at rest position. The killdeer and other ground feeding birds commonly use this start/stop method to stir up a meal. Only this bird does not seem to be having too much luck.
From the warmth of my room, my binoculars allow me to be close enough to see its characteristic two bold black chest bars. Most other plovers have only one bar. Julian Huxley, scientist and founder of Rice University’s biology department, suggests that the purpose of the second band is to compensate for the width of the first. The result is a disruptive pattern that breaks up the outline of the bird against its surroundings. This effect is especially important while nesting and while performing aggressive displays (Graul). Right now, the bars are moving up and down in some kind of personal rhythm. It is an interesting progression of movement: downward tail flick, upward head bob, dart forward and repeat. It used to be a common belief that killdeer only do this when a predator is around but this morning there are no predators in sight. Dash. Pause. Dash. Pause. A couple walks by in the distance, bundled up against the cold. The bird fluffs its feathers and preens under its wings before continuing its feeding ritual. It continues to move away from me and eventually disappears over the edge of a ditch on the far side of the field.
A short while later, the bird reappears on the other side as if it did not almost ruin my day. Dash. Pause. Dash. Pause. It suddenly takes off and breaks into shrieks. Before I have a chance to look around for the source of the disturbance, a yellow lab comes barreling into view, a silly grin slapped on its muzzle. The dog calmly sniffs at a lamppost for a while before taking another run at my bird. The killdeer swiftly takes wing from its position a few yards away to make some more alarm calls. Mischief accomplished, the dog goes off on the heels of the couple I saw earlier. The killdeer quiets and settles back down closer to my side of the field. Thus, I imagine, is the life of a bird: Always getting chased away by something bigger than you. I silently thank the dog and move my attention to the adjacent field to check for other birds. A few European starlings and dark-morphed pigeons strut about. A movement in the air draws my attention. I track it and am rewarded by another killdeer landing with its back to me, its golden-orange rump flashing briefly as it hits the ground.
As with other plovers, sex in killdeers is difficult to determine. Mundahl and others usually rely on positioning during copulation for sex determination. Unfortunately for me, it is not breeding season so I will just have to speculate. With Valentine’s Day approaching, I am going to say that the two birds, now exactly tail to tail, were a mated pair. If there were nests, they would probably be located in a gravelly area, which killdeer tend to prefer. The birds lay their eggs out in the open in a shallow hole in the ground. Shardein and Jackson found evidence that the parents take turns going to soak their bellies in water in order to keep the eggs under a certain temperature during hot weather. At all other times the parents regularly switch off incubating the eggs.
Mundahl also found that how the birds defend their nest depends on what stage of development the chicks are in. Females are generally less aggressive than male during all periods. Both are equally likely to perform the famous broken-wing act, an elaborate distraction display used by adult killdeer to draw predators away from their nests.
According to the study done by Conway, Smith, and Ray, killdeer nesting should occur near the end of March and into July. The study also did not have any of the plover’s common nest predators like ravens, crows, and gulls but because there are so many American crows are about campus I suspect the story would be different if a killdeer found a suitable place to nest here. I hope I’ll have a chance to see a chick later this year.
Now as I walk back from work I try to see if I can sneak close enough to the birds to see their markings in the dark. The fields are empty but for me and the birds. As I approach they scatter and finally, take off in amidst a flurry of feathers and a cacophony of shrill calls.
The killdeer is a plucky species, and very well adapted to the strange urban environments that humans so often create. But even so, for such a common shorebird, there are a surprisingly small number of in depth published resources available. Many of the most interesting abstracts I read on the Web of Science were mostly from unavailable theses published 30 to 40 years ago. There is however, a lot of research available on JSTOR. Here are the references that I used in this narrative:
Conway, W.C., L.M. Smith, and J.D. Ray. 2005. Shorebird breeding biology in wetlands of the Playa Lakes, Texas, USA. Waterbirds: Journal of the Waterbird Society 28:129-260. doi: 10.1675/1524-4695(2005)028[0129:SBBIWO]2.0.CO;2. This documents recent nesting patterns of various shorebirds, including the killdeer.
Graul, W.D. 1973. Possible functions of head and breast markings in Charadriinae. The Wilson Bulletin 85:60-70. doi: 10.2307/4160293. This source documents a study on the significance of plover markings.
Huxley, J.S. 1958. Why two breast bands on the killdeer? The Auk 75:98-99. doi: 10.2307/4082067. This source suggests the adaptation of the killdeers two breast bands.
Mundahl, J.T. 1982. Role specialization in the parental and territorial behavior of the killdeer. The Wilson Bulletin 94:515-530. doi: 10.2307/4161677. This documents the role of male and female killdeer during nesting and chick protection.
Sanzenbacher, P.M. and S.M. Haig. 2002. Regional fidelity and movement patterns of wintering killdeer in an agricultural landscape. Waterbirds: Journal of the Waterbird Society 33:16-25. doi: 10.1675/1524-4695(2002)025[0016:RFAMPO]2.0.CO;2. This describes the nesting locations and patterns of the wintering killdeer.
Schardien, B.J. and J.A. Jackson. 1979. Belly-Soaking as a thermoregulatory mechanism in nesting killdeer. The Auk 96:604-606. doi: 10.2307/4085560. This describes the parent’s feather wetting practices to keep their eggs at the correct temperature.
I could not find a distribution map that was free content to post here, but they can be easily found in places like Cornell’s AllAboutBirds site.
Here are a couple of the graphs from the studies I read:
And here are some pictures:The ones I saw were also foraging in short grasses like these. I would have taken my own picture but my camera is not powerful enough. Notice the red eye ring and double chest bar.”]
Baby Killdeer in Portland, Oregon (http://commons.wikimedia.org/wiki/File:Baby_Killdeer.jpg): Notice the single chest bar and the light colored rocks of its environment. Killdeer are precocial, meaning the baby birds are ready to run soon after they hatch. So rather than featherless, lizard-like creatures, killdeer hatch with a set fluffy feathers. They are born with only one chest band, making them easily mistakable for another plover early on. [Photo by Salvex Dodd. Click for direct link.]
Finally, here are some interesting video bonuses for making it this far. Take note of the distress calls: