Today there was a House Wren in the southeastern alcove and an immature Ruby-throated Hummingbird at the main north entrance.
Birds on the move captured on Nexrad radar tell an important story on the evening of Sep. 23 to the morning of Sep. 24. First, watch migration blow up after local sunrise in the eastern US, and progress to the west.
As the night wore on, storms began to flare up in Oklahoma. Here in Stillwater those storms hit between 1:30 and 2:00 am on Sep. 24. As the storms expand, migration stalls: Birds put down to avoid the storms and for people on the ground, that’s a fallout.
Was there evidence of this fallout on the ground?
Well, there was a bonus Canada Warbler in that troublesome northeastern alcove of the Food and Agricultural Products Center. (This was in addition to a Mourning Warbler and a Wilson’s Warbler I found there on Sep. 21.)
There was a big flight of Nashville Warbler in Stillwater, too. Twelve were reported from Couch Park. I found one in the southwestern alcove and a Ruby-throated Hummingbird in the northeastern alcove.
The 40th casualty of 2019 indicates another unusually deadly year at the Noble Research Center on the campus of Oklahoma State University here in Stillwater, Oklahoma, USA. The fact that we’ve hit that benchmark in early September is especially disheartening. This hummingbird at the main north entrance earned the sad distinction of being number 40.
My walk to the Noble Research Center revealed two window-killed birds outside the Food and Agricultural Products building, a male Yellow Warbler and Ruby-throated Hummingbird.
I also found remains (wingtips) of the Summer Tanager and Indigo Bunting that were scavenged from the southwestern alcove.
New casualties this morning were a SY male Painted Bunting in the southwestern alcove and a male Tennessee Warbler (9.5g, fat = 1) in the northeastern alcove.
Same window, different day, same result: a HY male Ruby-throated Hummingbird whose first trip to the Neotropics was cut short by a pane of glass in the southeastern alcove.
This was the 370th casualty and 34th Ruby-throated Hummingbird found at the Noble Research Center since August 2009. Today’s casualty puts 2018 at number 7 out of 10 worst years for casualties at the NRC, and there’re still 3 1/2 months of monitoring ahead.
Casualty number two of the fall 2018 migration was this waterlogged Ruby-throated Hummingbird at the southeast alcove.
This Ruby-throated Hummingbird at the main north entrance is the first official fall migration casualty of 2018, a dubious honor.
Note how the window is a triple threat for migrating birds: It reflects vegetation behind, provides a pass-through illusion to the other side, and it contains a naturalistic rock garden inside visible through the glass.
In other news, the Black-and-white Warbler from 31 July was scavenged overnight, with 2–3 primaries and a single downy tuft all that remains. It lasted 9 days.
Well, here we go. Today marks the end of my 9th year conducting spring/summer monitoring for window-killed birds at the Noble Research Center. Tomorrow I begin year 10. Ten years of near daily monitoring of window-killed birds. Here’s a quick 9-year wrap-up:
- 40: average minimum casualties annually
- 360: total casualties (minimum)
- 64: species confirmed as fatalities
- 10: average number of days for birds to be removed/scavenged
Top ten (eleven) species most commonly encountered as casualties at this site:
- Lincoln’s Sparrow (45)
- Ruby-throated Hummingbird (29)
- Painted Bunting (24)
- Indigo Bunting (20) *tie* Grasshopper Sparrow (20)
- Mourning Dove (17)
- Clay-colored Sparrow (16)
- Nashville Warbler (14)
- Common Yellowthroat (11) *tie* Mourning Warbler (11) *tie* Song Sparrow (11)
There was a Ruby-throated Hummingbird in the southwest alcove today.
A sad bonus was this Blue Grosbeak at the Food and Agricultural Products Center.
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.)
As I’m about to head out for a conference this week, spring and summer monitoring comes to a close. I’ll begin August 2017 the 9th consecutive year of (mostly) daily monitoring for window casualties at the Noble Research Center on the campus of Oklahoma State University in Stillwater, Oklahoma, USA.
It’s been a busy spring.
Beginning Mar 1st, here’s what has turned up at the Noble Research Center.
- Indigo Bunting – 5
- Painted Bunting – 5
- Ruby-throated Hummingbird – 3
- Lincoln’s Sparrow – 2
- Mourning Dove – 2
- Nashville Warbler – 2
- Orange-crowned Warbler – 2
- Baltimore Oriole – 1
- Chipping Sparrow – 1
- Eastern Meadowlark – 1
- House Wren – 1
- Northern Parula – 1
- Tennessee Warbler – 1
- Yellow-billed Cuckoo – 1
That’s 28 individuals of 14 species, and damn, that is disheartening.
On the plus side, my commitment to checking almost every day has put me in position to save a few birds by getting them safely away from the building and taking them someplace secure to rest and recuperate for a bit. I can’t guarantee that all 6 of these survived the ordeal, but they seemed to be in good shape when I last saw them:
- Northern Cardinal
- Common Yellowthroat
- Mourning Dove
- Song Sparrow
- Yellow Warbler
- Carolina Wren
I found a dead Ruby-throated Hummingbird at the Noble Research Center yesterday and today I found another. Here’s a chance for me to identify, age, and sex this one correctly on the first try.
First things first – northwest alcove.
Okay, other than hummingbird what have we got?
Ruby-throated or Black-chinned? Wings reach tail tip (barely). It’s a Rubythroat.
Hatch-year or older? Bill corrugations? Buffy edges to feathers? Yes on both counts. This is a hatch-year Ruby-throated Hummingbird.
Male or female? The bird is reflecting kind of bronzy-gold rather than just dark green. Female a bit more likely . . .
Tail not notched or forked. That works for female and young male.
Throat spotted or no? Unspotted – more consistent with female.
Shape of p6? A bit more angular than adjacent feather tips but not sharply-swooped. Looks like female wing tip shape.
Does it have a brood patch?
It looks like it might, but it’s likely just another case of apteria similar to the July 22 hummingbird.
So, we appear to have a hatch-year female Ruby-throated Hummingbird, and I’m sad that she, too, met her end so soon after leaving her natal home.
On 22 July, I published the following post with a methodical and detailed explanation of how I determined this window casualty to be an adult female Ruby-throated Hummingbird. On July 23rd, I received a kind message from Sheri Williamson who gently explained where I had erred in my interpretation. Other than the fact that it was 1) a Ruby-throated Hummingbird and 2) dead, I had everything else wrong! Sheri literally wrote the book on hummingbird identification, so I’m delighted to have her input and grateful for the chance to learn from her.
I have now updated this post with Sheri’s interpretation explained in this blue font. Read on, learn, and enjoy. Thank you, Sheri!
In the midst of the hottest part of summer (105 F here today with a 111 heat index), I found this poor little hummingbird in the southeast alcove of the Noble Research Center.
Okay, but what hummingbird? It’s too easy to just assume “Ruby-throated” and move on. There is no obvious rufous coloration on the back or at the base of the tail to suggest one of the Selasphorus hummingbirds, such as Rufous or Broad-tailed. The wingtips not quite reaching the tail tip does suggest Ruby-throated. (Wing chord 46.0 mm on this one.) The next most likely candidate – Black-chinned Hummingbird – has wing tips that reach beyond the tail tip. So I begin with the suggestion that it actually is a Rubythroat, but it’s time to really examine it now. (So far, so good.)
The first thing to do is figure out how old the bird is. (Right here is where I mess up, and it’s all downhill from there.) Is it a hatch-year bird, i.e., one hatched this spring/summer? If not, it’s an adult: “second-year” if I can determine that it hatched in 2016 or the more general “after hatch-year” if I can’t. So, how do we determine age on a hummingbird?
The best way is to examine the bill for “corrugations.” Baby hummingbirds aren’t born with those long, pointy beaks. They start out shorter and kind of pliable, slowly lengthening and stiffening during the first few months of life. (This bird’s bill is 16.5 mm in length.) You can see this, too – although it’s difficult with my aging eyes. If there are corrugations along something like 50–90% the length of the upper mandible (the “ramphotheca” for you Ornithology students out there), then you can be certain it’s an immature hummingbird you’re examining. Adults will show usually 0% or, sometimes up to about 10% of the bill’s length showing those corrugations. What do you think about this bird?
All right, so this bird is an adult, i.e., AHY.
Nope! It’s a hatch-year bird, and that changes everything.
My other clue should have been that there are thin, buffy edges to most of the contour feathers. This is a bird in fresh plumage. An adult female should show much more feather wear at this time of year. Bill corrugations and buffy feather edges? This little sprite started life in a nest in 2017!
All right, so this bird is an immature, i.e., HY. That means it can be pretty easily sexed. (That part is still true, thankfully!) The most obvious feature for the North American Archilochus hummingbirds is the brilliant throat patch or gorget of males. This bird doesn’t have one, although it does have 3 red feathers in the gorget area and heavy throat-spotting all over the gorget:
That red looks ruby to me, too.
Okay, a few red feathers in the throat is not that rare among females. (Actually, Sheri indicated that it is really rare.) An adult male with so little red really would be odd. (True, but the rest of this paragraph is wrong-o.)
This bird looks like it might be an adult female, Ruby-throated Hummingbird. In fact, a second-year female hummingbird would be pretty unusual with that much spotting and red in the gorget. That makes me suspect that this bird was not born in 2016 and we’ve already determined that it’s not from 2017. That would mean that the bird is at least as old as a hatch-year from 2015. In other words, hatch-year is ruled out by the bill and second-year is unlikely by the spotted gorget. Yes, this is an after hatch-year bird, but it’s more specifically an after second-year (ASY) in all likelihood.
Okay, we now know that it’s a hatch-year bird. We also know that it’s got a heavily spotted gorget and already 3 ruby-reflecting feathers. It’s a boy! Yes, I mistook a young boy for a mature woman.
What else have we got?
Okay, the 6th primary feather on Ruby-throated Hummingbird has a weirdly-shaped tip. In males, it looks like a tiny Samurai sword has sliced off the tip, leaving it with a slightly concave shape that sweeps up to a rather dramatic point on the leading edge. (Although I don’t know for sure, I’m assuming that the shape of this one feather on the wing allows the males to make some kind of a mechanical sound for display.) On females – adult females – a shadow of that shape is present, too. It’s a less dramatic sweep to a point, but the 6th primary definitely looks lopped off at its tip, just like this:
According to the information in Peter Pyle’s identification guide, the feather shape on this bird is still a good match for an adult female . . . but it also is a good match for a young male. It’s still a boy.
The tail tips of female and immature Rubythroats of both sexes are just slightly notched or even straight across. Especially on females, the outer tail feathers have broad, white tips. Adult males lack the white tips on their pointed outer tail feathers, and the tail shape ends up looking strongly notched or even slightly forked. Here’s our bird’s tail:
Checks out for female Ruby-throated Hummingbird. (But again, also checks out for an HY male.)
But wait – if this is an adult female Ruby-throated Hummingbird in latter July, then she should have at least attempted to breed over the past couple of months. That means she should show a brood patch, just like this one:
It kinda means that, but again Sheri was a font of great information. To wit, that’s not a brood patch! Evidently, hatch-year birds of both sexes have apteria (portions of skin from which no feathers are growing) on the breast and belly. Experienced hummingbird handlers know this. Me? Not so much.
When I noticed what I thought was a brood patch on this bird, it colored everything else I thought about it. “If it has a brood patch, it can’t be a hatch-year bird.” “If it has a brood patch, it can’t be a male.” “If it has a brood patch, then those wrinkles I see on its bill can’t be the corrugations of a young bird’s bill.” My bias to weighting my opinion so heavily on something I was sure to be true definitely led me down the wrong path. I needed to apply better critical thinking than I did to avoid such a gaffe.
Which means . . .
There you have it: an adult female Ruby-throated Hummingbird. She had a nest and eggs at some point in recent weeks, though I can’t tell if she was successful with it. She had left her territory and might have been engaged in some local dispersal to someplace favorable for molt. She might also have been in the midst of her fall migration and, given our hot weather for the past couple of weeks I wouldn’t blame her. Either way, and whatever else might have transpired in her life as she alternated between winters in the Neotropics and summer in North America, she is another senseless loss to a window pane in our inhospitable human landscape.
None of that is true. Instead . . .
There you have it: a young male Ruby-throated Hummingbird. He was recently out of the nest and was likely on his first foray from his natal territory. Had all gone well for him, he might have ended up in southern Mexico or Guatemala or Panama. Had he survived the winter, he would’ve packed on as much fat as possible and zoomed out over the Gulf of Mexico some evening in the hope of making it back to the US after 18 hours or so on the wing. Then he would have kept going, orienting to an area probably not too far from where he was born, and prepared for a few months of pitched battles against his rivals and aggressive wooing of the ladies.
He didn’t get the chance, however. Like nearly a billion of his feathered comrades in the US each year, he fell victim to a stupid pane of glass while passing through a human-dominated landscape that can be fraught with danger for wild birds. RIP, young lad.
I was out of town from 21–30 June and no surveys were run during that time. On June 30th, however, I heard from Dawn Brown and Corey Riding that there were three casualties at the southwestern alcove of the Noble Research Center: a badly decayed Northern Parula (adult male), a female Ruby-throated Hummingbird, and a female (with brood patch!) Indigo Bunting. It’s possible that the bunting came in on the 30th, but the others were clearly killed prior to that date. (Photos by Dawn Brown.) This is officially the first Northern Parula found on the project.
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.
Another day, another window-killed hummingbird. This one was heading north when it met its end. This is the 10th hummingbird fatality, and the 180th overall.
Regular readers will note a very similar post from yesterday, and a superficially very similar-looking bird.
This one was more obviously a Ruby-throated Hummingbird. The following photo illustrates that the tailtip extends well beyond the wingtips.
Next, I examined the bill to look for corrugations indicative of a hatch-year bird. I can’t see any. This looks like an after hatch-year bird; plumage-wise, she’s female.
So I’ve got an AHY, female, Ruby-throated Hummingbird. I checked one last thing to clinch that identification – the shape of the 6th primary. Sure enough, it’s a perfect match for the shape indicated as “AHY/ASY” female Ruby-throated Hummingbird in Peter Pyle’s Identification Guide to North American Birds.
Today marked the inauspicious observance of the first window-killed bird at the Noble Research Center for fall, 2014. It was a hatch year Archilochus hummingbird at the southwest alcove that I have somewhat tentatively identified as a Ruby-throated. To nail down the identification as best as I could, I consulted David Sibley’s the Sibley Guide to Birds (2000) and Peter Pyle’s Identification Guide to North American Birds (1997).
Step 1 for identification of these hummingbirds is to confirm the age. As hatch-year hummers develop, their bills lose characteristic striations or corrugations over time. A hummingbird with these markings extending for > 10% the length of the bill can be reliably considered HY/SY (i.e., less than 1 year old). Here’s this morning’s bird (with bonus photo of hummingbird tongue tip):
The markings are evident over probably 90% of the bill length. This is a hatch-year bird.
The problem with the bird is that it presents some characters (admittedly subjective in some cases) that suggest Black-chinned more strongly than Ruby-throated. For example, there is low contrast between the auriculars and the throat, and that throat is spotted. Both of these are Black-chinned characters as rendered by Sibley. The flanks are dirty gray with just a hint of cinnamon – also suggesting Black-chinned. More pronounced is the relative length of folded wing and tail: If anything, the wingtips extend beyond the tail tip as opposed to obviously shorter than the tail as typical for Ruby-throated.
So it was going to take some measurements to help solve this puzzle. The wing chord came in at 46.5mm: that’s too big for a male of either species. So with that information, I knew I now had a HY, female hummingbird.
The length of the tail (24.9), culmen (18.8), and tail fork (0.10) – and the width of the outermost tail feather (r5, 5.2) offered no help in determining which HY female Archilochus I had. However, the shape of the outer primary (p10) and primary #6 (p6) were both in line with expectations for Ruby-throated. The photos aren’t great, but p6 is featured in the next two photos:
So, based on my analysis of the characters this bird presented, I’m calling her a Ruby-throated Hummingbird. The possibility of hybrids is very real for this species and Black-chinned, however, so I will be sharing this information with some more experienced folks to get some other opinions. Stay tuned!
Today, the Painted Bunting remains in place but the Ruby-throated Hummingbird carcass is fully gone. It lasted approximately 5 days.
At the north entrance, I flushed a small, olive-green warbler with noticeably long and yellow undertail coverts. The bird bumped the glass near me, but I was able to steer it away from the building and into some ornamental trees. I was unsuccessful at relocating it after that. My best guess is that the bird is a Mourning Warbler, given size, coloration, and the long undertail coverts. The spatial distribution of collisions now looks like this:
Both bunting and hummingbird remain in their approximate positions from yesterday, but the hummingbird has now been scavenged again. At this point, only the tail and undertail coverts remain.
I found a very fresh Nashville Warbler (HY female; fat = 2) at the north entrance and a Ruby-throated Hummingbird (HY male) just a few feet from the Painted Bunting carcass. The ants had gotten to the hummingbird, so I decided to leave it in place to see how long it lasts. Here is the warbler:
I often leave hummingbirds in place to check scavenging rates, but this one was so fresh I decided to pick it up and really study it. Of course, hummingbird identification, ageing, and sexing can be pretty tricky, and it’s taken me nearly an hour to figure out this bird with confidence. I learned a bit along the way, however, so that’s my reward.
OK, it’s a small green hummingbird in the eastern U.S. that is whitish below with some subtle streaking on the throat. That means it’s most likely a Ruby-throated Hummingbird. On the folded wing, I can see that primaries 1–6 are closer together than primaries 7–10. That, and some of the other measurements I took, ruled out Black-chinned Hummingbird.
It could be a female (HY or AHY) or an HY male. A closer look reveals a single gorget feather that has come in red. Case closed! It’s a HY male, right?
Well, not quite. Some AHY females can have a red gorget feather or two, so I had to be more careful in my identification. I needed to determine the age of this bird, definitively.
Some of the contour feathers on the crown and back were edged in brown. That should be indicative of an HY bird, but that’s a subjective criterion. It turns out that the most common technique hummingbird banders use for ageing is to look for “corrugations” on the surface of the bill. These are faint wrinkles on the bill that fade or smooth out as the bird ages. Did this bird on my desk have corrugations?
OK, kind of, I guess. But my inexperience with this character still made me suspicious. I could, however, determine the sex of this bird – definitively – by looking at the shape of the tip of primary #6 (visible in the top photo). In males, p6 is almost concave and sweeps up to an attenuated point; in females, that shape really isn’t there and the tip of p6 is more truncate or even rounded.
I see the attenuated p6. Now I’m convinced, it’s a HY male, Ruby-throated hummingbird.
Here is just a quick summary of casualties at the Noble Research Center from July through December 2010:
I detected 25 individuals of at least 16 species among the casualties. The complete list:
grasshopper sparrow – 4
ruby-throated hummingbird – 2
mourning warbler – 2
song sparrow – 2
Lincoln’s sparrow – 2
unidentified passerine (1 warbler, 1 sparrow) – 2
black-and-white warbler – 1
Carolina wren – 1
mourning dove (juv) – 1
least flycatcher – 1
common yellowthroat – 1
black-throated green warbler – 1
brown thrasher – 1
house wren – 1
red-breasted nuthatch – 1
white-throated sparrow – 1
field sparrow – 1
Because I was able to get to the NRC earlier each day during autumn than practical in 2009, I encountered more individuals that were stunned and “trapped” by the building for some time period without obvious mortal injury. Most of these birds are presumed to have eventually moved on, but it is quite likely that the house wren and one of the Lincoln’s sparrows on the “stunned” list were unsuccessful in their respective bids to escape from the confusion of the NRC, and are listed above. The bat represents the first mammalian “capture” by the NRC:
Lincoln’s sparrow – 5 (4 in one flock)
house wren – 1
common yellowthroat – 1
Nashville warbler – 1
grasshopper sparrow – 1
dark-eyed junco – 1
It’s dark when migrants like this Lincoln’s sparrow drop out of the sky and try to find a good spot in which to rest for the day. I’m beginning to think that most collisions are occurring in that last hour before sunrise.
It looks like Sep. 1 is the only day I did not check for casualties this month. Here’s what I found on the days I did check:
2 Mourning Warblers
1 unidentified warbler
1 Least Flycatcher
1 Common Yellowthroat
1 Black-throated Green Warbler
1 Ruby-throated Hummingbird
1 Brown Thrasher
. . . and no sign of the hummingbird feather today.
The hummingbird that I found on 21 September has been scavenged. A single rectrix remains. That’s interesting in itself: A tiny hummingbird falls victim to a window collision, ants attack the body quickly, but it lasts 6 days before being removed. Even after being scavenged, however, a single feather alerts me to the event. The identifiable cuckoo feathers from June remain in place; I wonder how long this lone hummingbird feather will be in evidence.
The Brown Thrasher is one of the most common and conspicuous migrants here in central Oklahoma, so I suppose it was inevitable to find one at the NRC some day. The bright yellow iris reveals this bird to be an adult (AHY). It was still warm when I found it.
I scored the fat on this bird a “1”, so it was a migrant (they breed here somewhat sparingly). What I don’t know is if this is one of our local breeders making its way south, or a bird from say, Alberta, passing through. It’s sad either way.
Hummingbird and cuckoo still in evidence.
The ants had gotten to this bird pretty quickly, so I left it in place to see for how long I can detect it. My guess is that it hit the window sometime during the day yesterday, rather than overnight.
On August 20th, I completed a full year of regular surveys for window-killed birds at the Noble Research Center. Here are some vital statistics for August 20 2009–August 20 2010:
I conducted (occasionally with help from assistants like Danielle Benson) 153 surveys over the full year of monitoring. This equates to an average of 2.39 days between surveys.
Coverage was irregular throughout the year. For example I did no monitoring in January 2010. For this reason, analysis of casualties by season must be viewed through the lens of dissimilarities in sampling effort among the seasons. I defined sampling effort as the number of surveys per days in a given season. I defined seasons as follows: Dec. 1–Mar. 20 (110 days) = “winter,” Mar. 21–May 20 (61 d) = “spring,” May 21–Aug. 19 (91 d) = “summer,” and Aug. 20–Nov. 30 (102 d) = “autumn.” The 11 winter surveys provided an effort of 0.10. This approximates 10 days on average between surveys. Effort indices were 0.87 for spring (53 surveys in 61 days), 0.44 for summer, and 0.48 for autumn. Thus effort was most consistent during spring with near daily surveys.
I recorded window strike mortality for 38 individuals of 22 different species over the year of monitoring. This rate of collision mortality places the NRC on par with other high-mortality buildings referenced in Klem 1990 and O’Connell 2001.
Of the 38 casualties, 5 were “local” (i.e., recently-fledged offspring of local breeders), 5 were “hatch year” birds (i.e., “immature”, or birds < 1 yr. old), and 28 were adults or of undetermined age.
Of the the 38 casualties, 8 were identifiable as male, 5 as female, and 25 were of undetermined sex.
As in O’Connell 2001, Neotropical migrants in passage comprised the greatest percentage of individuals among all casualties. The birds dying at the NRC are not local residents that commonly occur in the OSU campus. These are transient individuals traveling long distances that just happen to meet their end here. (Note that the number of resident individuals among the casualties is inflated by the fact that 5 of the 7 casualties were recently fledged mourning doves and northern cardinals.)
On at least four occasions, I encountered live birds that appeared to be trapped near a window but were not injured from a collision. These individuals are not included in the collision data, but they may have been had I not been there to flush them away from the windows and encourage them to move along:
9/22/09: Grasshopper Sparrow and suspected Swainson’s Thrush
10/19/09: Grasshopper Sparrow
11/2/09: Two Dark-eyed Juncos
6/21/10: Carolina Wren
The scavenging rate proved to be unpredictable over the year. For example, some carcasses left in place remained visible for several weeks and were untouched during that time. Others were identifiable only from feathers left behind of a carcass that, based on the timing of my most recent survey, had been scavenged just a few hours after the bird’s unfortunate collision. Further confounding the interpretation of scavenging rates, some carcasses were scavenged but readily identifiable feathers of the carcass were left behind and still in evidence long after scavenging. For example, the Yellow-billed Cuckoo that I found on 6 June 2010 was scavenged on 15 June. As of 3 September 2010, that bird’s primaries are still readily apparent at the location where I first found it on June 10th, approximately 86 days after the bird’s death.
I found evidence of 15 scavenged carcasses over the year. Thus, out of 38 total casualties, 39% were ultimately scavenged. (Of course, I collected the majority of the carcasses I found, most of which were fresh and in excellent condition and were photographed for entries in this blog. Presumably, a high percentage of these would ultimately have been scavenged.) Two carcasses were scavenged on day 0 and three were scavenged after just one day in situ. Four were in evidence for at least 30 days; the average number of days a carcass was apparent in place was 18.6 – nearly 8 times the length of time between consecutive surveys. Thus, the regular, frequent surveys provided ample opportunity to discover carcasses before they were removed or no longer visible. In addition, the most frequent condition of freshly scavenged carcasses of warbler-sized birds was a pile of remiges cleanly sheared off near the base of the feathers. Thus, even small birds were usually left in place after scavenging; this increased the probability that I would find the carcass even if it had been scavenged. Nonetheless, it is likely that at least some individuals were scavenged and removed from the site before I could document the casualty, so mortality rates calculated from my surveys must be viewed as underestimates of actual mortality.
The following table lists all the species found as window collision casualties at the Noble Research Center, 8/20 2009–8/20 2010:
Common Yellowthroat 5
Mourning Dove 5
Lincoln’s Sparrow 4
Black-and-White Warbler 3
Grasshopper Sparrow 3
Painted Bunting 2
Mourning Warbler 1
Gray Catbird 1
Wilson’s Warbler 1
Canada Warbler 1
Indigo Bunting 1
Orange-crowned Warbler 1
Song Sparrow 1
Nashville Warbler 1
Dark-eyed Junco 1
Sprague’s Pipit 1
Swainson’s Thrush 1
Orchard Oriole 1
Northern Cardinal 1
Yellow-billed Cuckoo 1
Ruby-throated Hummingbird 1
Carolina Wren 1
While I didn’t find this little bird until the 28th (I didn’t check yesterday), the state of decomposition suggested it’d been there for a bit.