“Trapped” birds – how to count collision victims that survive the initial impact?

<This is an update to a post composed in 2013. We know a bit more now about injuries sustained by birds from window collisions. No, their necks still aren’t breaking and yes there still is a lot of beak damage. Brain hemorrhage can be difficult to determine from normal pooling of blood that can happen anytime a bird carcass lays on its back, however, so we might be overestimating brain injury incidence. Internal injuries, especially fractures of the coracoid (avian bone joining sternum to shoulder) that puncture air sacs, might actually be more common than generally appreciated. Stay tuned for updates from ongoing research in this area.

More important, wildlife rehabilitators have made strides in the treatment of birds that have collided with windows, including those that have suffered a traumatic brain injury. Thus it’s a good idea to keep handy information on your nearest rehabber and specifically seek their advice in advance for best practices in giving birds that survive an initial collision the best chance to make a complete recovery.

Here in Stillwater, OK we have two great options: Nature’s Vein Wildlife Rescue and Education (405-665-0091) and the OSU Vet Hospital:

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Now then, back to that old post . . .>

 

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Black-throated Blue Warbler in passage on a clear night, by Tim O’Connell

Several things can happen when a bird approaches a building.  Some birds approach and, seeing either a reflection of the grass, trees, and sky behind them or the grass, trees, and sky on the other side of a visual pass-through, simply collide with the window at whatever speed they were flying.  Many of these birds (Dan Klem estimates about 50% of them) will suffer a severe injury and die immediately.  Others might be stunned, knocked out, or otherwise impaired to the point that they cannot fly.  Of these that don’t die immediately, some will recover fully and some will die some time later, either because they are easy pickings for a neighborhood cat while in their dazed state or because they’ve suffered too much brain damage for “time” to repair their wounds.  Some birds will be dazed from the initial collision and able to fly to some more protected perch nearby where they will either recover on their own or ultimately die, but at least they are better protected from predators if they can make it to the relative safety of a nearby tree. Klem estimates that 50% of those that die from windows succumb to their injuries sometime after they leave the site of the collision.

I find these injured-but-not-dead-birds rather frequently: 56 individuals since I started paying attention during the fall of 2009.  As of August 2012, I’ve also been recording the location I first encountered each of these live birds.  Some of them look pretty rough when I find them, but if when I grab the bird it makes a fuss and tries to escape from me, I consider that it’s got a fighting chance to recover from whatever injury was so severe that it allowed me to catch it by hand.  These feisty birds I carry away from the building and place in some dense shrubs or low branches.  This way, the bird is out of the direct sun and has some better cover from predators while it regains its wits.  If the bird is, when I leave it, alert and able to perch strongly, I usually will not count it as a “casualty”; I’ll assume that it’s one of the ones that would have survived its ordeal.

Some birds, however, are neither feisty or alert.  Their bodies droop, their eyelids sag, they might be panting heavily, they can neither hold onto a perch or stand up straight in the palm of my hand.  The prognosis for recovery is very poor for these birds, and I have euthanized 3 or 4 of them in this condition, and counted them as casualties.

There is another category, however.  Some birds are found in fine physical condition:  active, volant, and apparently not dazed in the least.  They are, however, out of place, like the Eastern Wood-Pewee I found this morning perched on the ground, on a sidewalk, in an exterior alcove of the Noble Research Center.  These birds are “trapped” in the sense that they are in inappropriate habitat and, like a classic funnel trap, for some reason unable to figure out that they simply need to fly back the way they came for 100 m or so so they can clearly see how to fly around or over the building.  Instead, they might spend hours flying back and forth against the back wall of the alcove.  In this way, I suspect that some birds die from the stress and exhaustion of this experience, and that they might never actually strike the window with enough force to cause injury.  It is the shape of the building as much as its windows that makes it deadly for migrant songbirds. This could be one reason that the dead birds that I find are so often in immaculate shape: they are perhaps dying from cardiac arrest or exhaustion as opposed to trauma from collision.

So I consider trapped birds to be either of the following:

* a live bird that I am able to catch and move to a secluded location where, based on my assessment of its condition, I judge that it can survive the experience,

* a live bird that I am able to “shoo” or herd away from the building.

13 September 2013: trapped Eastern Wood-Pewee and Mourning Warbler

I had two trapped birds at the Noble Research Center this morning, both of which presented identification challenges because they were in good enough shape that I never got to examine them closely.  I first found what turned out to be a wood-pewee (and I’m assuming it’s Eastern) at the northeast alcove and then found a warbler I’ve identified as Mourning at the northwest alcove.  I was able to steer both birds away from the building so I am hoping that I won’t find them dead there tomorrow morning.

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Here’s the wood-pewee.  When I first came upon it, it was sitting on the ground, its long, low shape and attenuated bill had me momentarily thinking it was a swallow.  As I approached (within just a few feet) it was clear that I actually had a flycatcher, but it wasn’t until it flushed to perch on a nearby railing that I figured out that it wasn’t an Eastern Phoebe.

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This bird was intermediate in size between a phoebe and and Empidonax flycatcher.  It lacked the white throat of an Eastern Phoebe, it showed a bi-colored bill, and it did not wag its tail.  Relative to Empidonax flycatchers, this bird was larger and lankier, with a long primary projection, little to no greenish cast on the upperparts, no obvious eyering, and a dusky grayish vest.  All signs point to it being a wood-pewee, and I can only assume it’s Eastern as I wouldn’t be able to distinguish it from an extralimital Western in a photograph.  The buffy wingbars suggest a hatch-year bird. This is the first wood-pewee on the project, and here’s where Easterns have been reported this month:

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The Mourning Warbler on the northwest side of the Noble Research Center was also in good enough condition to fly off on its own, so I was left with my crude photographs to make the identification.  At first blush, the olive-green upperparts, yellow breast and throat, and grayish head suggested Nashville Warbler.  The structure didn’t fit well, however.  The bill wasn’t narrow enough for Nashville, and the pale lower mandible didn’t fit either.  The eye-ring seemed thin, and broken, unlike the bold, complete eyering on a Nashville.  The feet were big and pale, as opposed to a Nashville’s small, blackish feet.  The yellow throat pegged the bird as hatch-year, but I’m reluctant to call the sex.

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