Song Sparrow finally gone. It sat untouched for 20 days.
No new casualties this morning, but the Mourning Dove was scavenged. Just this pile of feathers remains.
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.
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.)
No new casualties today, but I noticed immediately that the Mourning Dove carcass had been removed. Closer inspection revealed it to have been scavenged from its original location with remains scattered near the base of the building about 5 m away.
So what is scavenging rate all about, anyway?
The idea is that our detection of dead birds (or anything else) is imperfect. We can collect data and report that, for example, 50 birds died at a building. That estimate can only be a minimum, however. Our raw counts underestimate the true number of casualties because our detection cannot be > 100% but it can be far lower than 100%. Birds can collide but manage to flutter away and die outside of our search area. Some might be difficult to see against the substrate on which they land. Most important, some will be removed before we get there to find them. Cats, rats, opossums, raccoons, crows, etc. tend to be abundant in urban/suburban areas where most window collision research takes place and they can often remove a carcass before the investigator arrives onsite to conduct a survey.
For example, assume that the removal rate (whether by scavengers, human maintenance crews, etc.) is 25%. This means that, at best, the investigator is only predicted to encounter 75% of the casualties. That raw count of 50 dead birds? The detection-corrected number is actually closer to 50/0.75 = 67 dead birds.
Does that matter, though? I struggle to attach relevance to what the removal rate is for any given study. Is there some magic number of casualties that is a threshold for conservation action? Are there people for whom 50 dead birds wouldn’t register as important but 67 would? For comparing mortality rates among sites where removal rate might vary we assume that it is important to determine a separate removal rate for each site, but is it? Imagine 50 dead birds at our site with high removal of 25% compared to 50 dead birds at a site with low removal rate of 5%. That’d be 67 compared to 50/0.95 = 53. So? Would we really be concerned about 67 dead birds at one building but not 53 at another?
My final concern is the false sense of security that we’ve determined “the” removal rate. These rates are widely variable across space and time. We’re kidding ourselves to think that we’re improving our estimates of collision mortality by adjusting raw counts with a detection probability that is itself a moving target.
In my study, I’ve conducted approximately 86 removal trials over the past several years. On average, a carcass lasts about 10.5 days on the ground before it is removed. On average, I conduct a survey every 1.5 days. That gives me 10.5/1.5 = 7.0 opportunities to find a dead bird before it is removed. Ergo, removal rate is hardly noticeable in my study. Whatsmore, scavenging and removal are not the same thing. It is often the case – as with today’s Mourning Dove – that the carcass is scavenged but evidence remains. The Mourning Dove died on April 5th and was scavenged on the 15th. That’s 10 days. The remaining bones and feathers, however, might still be here weeks from now. On multiple occasions, I have found evidence of scavenging in the 24 hrs since my previous survey. For example, I check one morning and find feathers that weren’t there the day before. I refer to these as “day 0” removals, but the feathers are still there to provide evidence of the casualty for days and weeks after the event. The longest I have had feathers or other remains in evidence is > 90 days.
So I see scavenging and removal rates – and detection rates in general – as red herrings in our monitoring of collision mortality. Unless part of a well-controlled design to compare, for example, mortality from two facades of the same building, there’s not much to gain from collecting data to estimate such rates. There are, however, potential costs. Many avocational birders and conservationists collect data on collisions opportunistically, and their presumed lack of rigor in methods limits the use of their data for serious analysis. I maintain that those data are perhaps far more useful than we might presume because of an ill-defined obsession with calculation of detection as a study’s ticket to the club of legitimacy.
That southwestern alcove continues to get a workout this fall, but again, the unfortunate victim was found in front of untreated glass panes.
Today it was a hatch-year (HY) Nashville Warbler; sex undetermined with fat score = 2.
When I found the bird in position on the cement as indicated in the above photo, it had already been heavily scavenged by ants. I moved the carcass to a location on the grass on the north side of this southwestern alcove (see photo, top right) to set up a removal trial.
The Ruby-throated Hummingbird carcass from Sep. 5 has been removed.
I initially reported “no casualties” for September 7, but Chrissy Barton’s sharp eyes found one for me.
Some time between my survey that morning and Chrissy’s walking through that entrance around noon, a Ruby-throated Hummingbird – apparently another HY male, struck an untreated pane at the southwest alcove and died. Both it, and its partner from a couple of days earlier, were removed before I got back to check on the morning of the 8th. I recorded this second hummingbird as scavenged/removed on day 0.
The HY male Ruby-throated Hummingbird I found this morning means that, for 2016, a young male of this species was both the last casualty of “spring” (on July 11th) and the first official casualty of fall.
This bird was in the southwest alcove, illustrating the urgency with which I must complete my ABC bird tape treatments of the west entrances!
I found a presumptive HY male Ruby-throated Hummingbird in the southwest alcove of the NRC today. I left it in place for a removal trial.
I did not obtain photos of the bill showing corrugations. Instead check out the single ruby gorget feather and concave tip to primary feather #6 as indications of a male. The bird carried no fat.
The SY male Indigo Bunting I found yesterday has been moved, but not removed:
Presumably, this was a human moving the carcass from in front of the entrance to a more secluded location.
Today I found a Red-eyed Vireo in the southwestern alcove and an Indigo Bunting at the main north entrance.
The Indigo Bunting was a second-year male with zero fat and an impressive contrast of old and new feathers. I left him in place for a removal trial. The Red-eyed Vireo, an ASY female with a brood patch and no fat, is the first vireo I’ve ever recovered as a window-kill from the NRC.
I was away and unable to keep track of casualties at the Noble Research Center from 6/22–7/2. On my check today (7/3), the carcasses of Tufted Titmouse, House Finch, and Yellow-billed Cuckoo were all gone. (Actually, a cuckoo wing remains but it’s time to call the carcass as removed as it’s very unlikely to be noticed at this point.) The most conservative date to ascribe for the scavenging removal trial is 6/22 which gives unofficial removal times of 7 (titmouse), 17 (finch), and 32 (cuckoo) days.
This morning, a dead Tufted Titmouse achieved some grim and arbitrary notoriety as the 250th window-killed bird I’ve found at the Noble Research Center since monitoring began on 20 August 2009. She’s right near the entrance to the northwest alcove, and I left her in place to see how long it takes for her to be removed.
Like so many birds I find in June, this was a female (AHY) with a brood patch. This one had a faint stripe of mulberry juice down the front of her breast and little on her beak.
Intrigued by the pattern, I queried my database for June casualties, 2009–2016. Out of 22 window-kills, at least 8 have been females with brood patches (and additional 7 might have been but the data weren’t recorded).
With apologies for the 1) poor and 2) non-existent photos . . .
I found an ASY male Mourning Warbler (fat = 0) at the main north entrance this morning. He was waaaaay better looking than these photos attest, and I bet he was even more handsome in life.
In the northwest alcove lay a female (with well-developed brood patch!) Yellow-billed Cuckoo (no photo). I left the cuckoo in place, as the ants were already doing a number on her.
In scavenging news, the starling from 5/18 was both moved and eaten: I found a remnant pile of its larger feathers about 5m away from the bird’s location. Whatever picked it up had taken it south to the bushes in front of the northern entrance.
This was an odd find, both for species and location. In monitoring since 2009, this is only the second starling I’ve ever found, despite the fact that starlings nest on the NRC in spring and roost there year ’round. Starlings are pretty well urban-adapted, however, and I guess that explains the infrequency with which I come across them. They either know how to recognize glass as a barrier or they are so likely to perch on the building as opposed to flying past it that they’re more often at a safer “stalling speed” on the wing when they get close.
Except, of course, when they aren’t, and then they’re just as susceptible as any other passerine to death by window. That happened to this inexperienced youngster (HY) at some point over the past 24 hours. I left it in place for a removal trial.
The other weird thing as I alluded above was the location: left side of the main north entrance, close to where the building begins to curve on the east side.
I found this ASY male Swainson’s Thrush this morning in the southwest alcove.
Note the “booted” tarsus. On thrushes the tarsus is smooth, i.e., without a lot of obvious scaling. It’s sort of like the leading edge of the tarsus is wrapped in one huge scale.
The Painted Bunting lasted 2 days at the main north entrance; it has been removed.
The pictures tell the story:
We found 35 casualties at the Noble Research Center in 2015, plus 11 trapped birds. From 2010–2015, the NRC has averaged 35.5 victims.
I conducted 10 scavenging trials in 2015, with an average carcass survival time of 10.40 days. We ran 265 surveys in 2015, which works out to a carcass search every 1.38 days.
I’m always thankful for no casualties on a foggy morning following lots of audible flight calls overnight!
In other news, a fully cooked and mouthwatering bratwurst has been sitting in the grass on the north side of the building since last weekend’s tailgates. . .
The ants had already gotten to the bird, thereby complicating identification and encouraging me to leave it in place. The tail length and shape of p-6 suggest the more likely Ruby-throated Hummingbird, but the wing tips struck me as clubby and curved. Without better information to suggest otherwise, I’m recording this one as Ruby-throated.
As reported for May 30 2015, I had observed the beginnings of a pattern when I found the very first window-killed Tufted Titmouse on this project. That was the second titmouse I’d found on campus during the last week of May, and both were females with brood patches. In early June of this year, Corey Riding let me know that he had found a Carolina Chickadee dead at Ag Hall – that bird, too, was a female with brood patch.
Today, that emerging pattern got a bit fuzzier when I found just the second dead Tufted Titmouse at the NRC since daily monitoring began in 2009. This one was an ASY male with fat = 0 in the southwest alcove. So much for patterns, at least that one.
I left this bird in place where it lasted until Thursday, June 25.
Mourning Warbler carcass has been removed or was otherwise hidden from me this morning.
I’ve seen a lot of surprising things on this project, but this morning’s weirdness takes the cake.
First I came upon this fledgling Mourning Dove up against a door of the building. I don’t count local birds as trapped, but I still thought it best to move this bird to some trees not far away.
That’s not the weird part, this is:
It’s another female Indigo Bunting. Upon closer inspection, however, this bird was in worse shape than it should have been as an overnight casualty. The ants were enjoying it, but certainly they wouldn’t have had time to do more than process the bird’s eyes. This bird didn’t have eyes. It also lacked a beak, the base of the skull, and half of its thoracic cavity! It was floppy to the touch – no rigor mortis – but its feathers were only loosely attached. This wasn’t a bird that was so fresh that it hadn’t entered rigor mortis yet, this was a bird that had long since come out of rigor mortis to go soft again, i.e., something several days old at least.
Remarkably, the best I can piece together is that this bird is the same female Indigo Bunting that died on the north side of the building May 11th. It was nowhere to be seen on May 17th, but it reappeared today on the 18th at the south side of the building.
I’m at a loss to explain the movement and yesterday’s absence other than that this bird was scavenged and removed once, but not destroyed and eaten. Whatever took it then left it in this new location. Now the 6-day scavenging trial is about to be extended. Stay tuned . . .
No sign of any new casualties today, and no sign of the Indigo Bunting that lasted for 6 days.
Yesterday’s Mourning Dove had vanished without a trace today, so it lasted 1 day. I actually suspect that it was human intervention that removed it because predators so often leave feathers behind when dealing with Mourning Doves. This is one of those cases in which I would’ve missed the event completely had I not been here within 24 hrs of the collision.
I guess I spoke too soon yesterday: There was a beautiful, adult Mourning Dove dead along the south wall of the NRC this morning. Mourning Doves nest on and near the Noble Research Center, and I had a live bird very near this location yesterday.
I have a photo but the bird sustained a rather gruesome injury so I’ll not post it. I left the bird in place (after moving it about 1m out of the middle of the sidewalk) to conduct a removal trial.
Sometime between Dec. 11 and Dec. 16th – I’ll call it the 12th – the junco was scavenged. Of course, 2 or 3 of its rectrices remain in evidence, so it has been scavenged but not technically, fully removed. Those feathers might last for weeks.
The Clay-colored Sparrow from Oct. 13 has been removed after 9 days.