On the heels of an impressive southbound flight last night,
. . . I found two casualties this morning.
There was a HY Chipping Sparrow in the northwest alcove. The bird had evidently been stepped on or perhaps run over by a maintenance vehicle. I left it in place for a removal trial.
Also, near the main north entrance (actually at a west-facing facade in the corner) was a Mourning Warbler. The bold eyering and long undertail coverts looked tantalyzingly like a Connecticut Warbler. It was, however, an AHY-U Mourning Warbler. The bird was 13.5g and bulging with fat (3).
This was the 10th Mourning Warbler on the project.
I actually discovered it on my 8/20 survey, but this poor little bird on the 20th was already seething with maggots so I’m comfortable calling it an 8/19 casualty. This was a second year male. Check out the feather wear on his primaries. He was headed south to molt and then continue on further south.
Waterthrushes seething with maggots (ew), but still where I left them.
I’m sad for every casualty, but folks who know me know that there is a special place in my heart for the Pinnacle of Avian Evolution, the Louisiana Waterthrush. Today, not one but two of these splendid creatures met an untimely end in the southwestern alcove of the Noble Research Center.
I moved them off the sidewalk and into the nearby lawn as a removal trial. Both were evidently AHY-U.
My sadness, of course, is tempered by my scientific curiosity. Louisiana Waterthrushes are rarely encountered in passage. The routes and timing of their travels are largely presumed but seldom confirmed, and this is confirmation of both. Whenever two individuals are found at a window, it is tantalizing to consider that they were traveling together, perhaps “chip”ping every few minutes to stay in contact. If so, were these a mated pair? Siblings? From the same neighborhood? Did they leave from the same area or meet up somewhere along the way? Was this an agonistic encounter, with one chasing the other? Were they even together? Perhaps they hit the window hours apart, and were not traveling together but just using the same route?
With every observation, the follow-up intrigues.
Both hummingbirds gone now.
Both hummingbird carcasses still in evidence. The whole bird from the southeastern alcove has been decapitated, presumably by the ants.
The tail from the southwestern alcove made things a bit more interesting by being gone. I wasn’t too surprised by that because we had storms roll through overnight that I assumed would have blown that little bit of feathers away. So I started looking around just to see if I could figure out in which crack in the bricks it ended up. I couldn’t find it, but my more intensive searching did turn up these tidbits:
Aha! So it looks like yesterday’s tail was not necessarily from a hummingbird that had been scavenged. It looks more like a lawnmower got it. It also seems to have been a HY male, Ruby-throated Hummingbird.
Hummingbirds have been takin’ it in the shorts of late . . .
But what’s with the fractional hummingbird reference above? Well, “scavenging” and “removal” are not necessarily the same thing. Often I find the remains of a bird that has been scavenged, but there’s enough left behind that I am able to detect that a casualty has occurred. Those remnants – let’s say a pile of flight feathers left behind by a scavenging cat – can last in place for many weeks. Each time I survey for casualties I’m greeted at that spot with the information that a bird died there (or at least somewhere nearby) even though all the edible bits are long gone. We should be clear that scavenging isn’t the important rate to help us better estimate detection of window-killed birds, removal is. It’s only when every piece of that carcass is gone that I’m unable to detect the evidence of a casualty.
We see this played out all the time with hummingbirds. For some reason, the ants seem to get to the hummingbirds more quickly than they get to other birds. (I have some hypotheses about this, e.g., that hummingbirds are more often flying in daylight and might have lain in place longer than the night-flying warbler and sparrow migrants.) The result is that hummingbird carcasses are rarely in pristine shape when I find them, but they are still there.
Check out hummingbird #1 this morning from the southeast alcove. First, look how obvious it is to detect the carcass even from ~20m away. Up close, note that a good bit of her face has already been carted away, one ant-mandible-sized piece at a time.
This next one (or 0.33 of one) from the southwest alcove will put your observational skills to the test:
See it yet?
Oh, that explains it!
In this case, there’s a pre-scavenged hummingbird (likely also AHY-F Ruby-throated) that is represented by its tail only. But it’s still detectable and largely identifiable.
(UPDATE 10 AUGUST 2017: Today I found a head and wing near where I found the tail on Aug. 9. First, this looks much more likely as a HY-M than an AHY-F. Also, literal scavenging seems less likely. I suspect more that the carcass was chopped up by a lawnmower.)
Yesterday’s hummingbird is gone without a trace.
Fall 2017 monitoring is officially underway. Today’s clean sweep yielded zero casualties, thankfully.