I found a Clay-colored Sparrow in the northwestern corner entrance to the NRC this morning, following the first big front of fall with frost near Woodward. I left the bird in place and it was scavenged by the next morning.
It was a bit foggy overnight so perhaps that contributed to the casualties I found today: An AHY male Nashville Warbler in the southwestern alcove (fat = 3) and a Clay-colored Sparrow in the south portico (fat = 2).
The one bright spot was the second Nashville Warbler. It was stunned but alive. On my approach it perked up and flew off strongly.
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:
Top ten (eleven) species most commonly encountered as casualties at this site:
I found a trapped Clay-colored Sparrow today in the southwestern alcove. Upon release in the relative safety of a nearby shrub, the bird flew off another 5m or so to another shrub, where it perched strongly.
Less lucky was the Magnolia Warbler I found in the northwest alcove. This bird, a female with fat = 3, was just the second of this species documented on this project.
It was another big night for migrants here in the Southern Plains. I found dead Clay-colored Sparrows at the northeastern and southwestern alcoves, and a trapped Grasshopper Sparrow at the northwestern alcove.
Clay-colored Sparrow #1 was heavy with fat (=3) and looks to be a HY bird.
Clay-colored #2 had a fat score of 2, and some tiny red ants had colonized it by the time I found it. I left that one in place to check the removal rate.
The Grasshopper Sparrow was trying desperately to fly east from the northwestern to the northeastern alcove. It was really wearing itself out. Thankfully, it was easy to point in the right direction, and it flew well away from the building.
The night before last, we had our first real cold front of autumn push through, pushing overnight lows down to the 50s for the first time in months. I expected that yesterday would have been a big flight that would result in window collisions, but last night seems to have ushered in a bigger wave of migrants. I found two at the south face of the Noble Research Center this morning (providing additional evidence that the direction of the prevailing wind has little to do with where on the building birds will end up).
The first was this beautiful Clay-colored Sparrow (fat = 2):
Not far away was this Common Yellowthroat. She was very much alive, and I was happy to see her fly away strongly when I shooed her away from the building.
This bird was an ID challenge: She was very pale on the throat, breast, and belly, but her yellow undertail coverts were quite obvious. That pattern, and the fact that she was pumping her tail a bit, had me thinking she might have been a Palm Warbler. Her pale legs and the lack of white on the tail tips ruled out Palm Warbler, as did her lack of other plumage details that might have strengthened the link. Instead, she looks to me like a hatch year, female Common Yellowthroat, but from the “Interior West” according to Sibley: those are the yellowthroats that can lack yellow throats, unlike the eastern subspecies that should show a bright yellow throat in all plumages.
On a cloudy morning after a nighttime football game that shone bright lights on low clouds, there were birds left behind at the Noble Research Center. The first I found was this hatch-year Clay-colored Sparrow (fat = 2):
Then there were 3-4 birds trapped around the north entrance, including a House Wren. Is this the same little guy hanging around for weeks?
There was an obviously stunned Orange-crowned Warbler as well. The bird was sitting low and unresponsive, but it perked up when I picked it up.
The bird looks okay above. Had it remained this way I would’ve counted it as merely “trapped”. When I set it down, however, the bird did not fly away and it actually had trouble standing. For cases like this – in which a trapped bird has trouble standing – my policy is to consider the bird as a casualty. I’ll be interested in checking tomorrow to see if my suspicions are correct.
Yesterday’s Clay-colored Sparrow has been removed.
ASY-U, fat = 1
With sample sizes so small, any repeat of the same species in a week looks like a pattern. Here’s what eBird reveals about Clay-colored Sparrow migration this spring:
February 2012 records:
Yep, it sure looks like Clay-colored Sparrow migration kicked in this month, with birds passing right through Stillwater.
It was a busy morning at the NRC after a crisp and clear, moonlit night that must have supported a big local flight.
I first checked on the Grasshopper Sparrow carcass – still there.
Next, I noticed a trapped Lincoln’s Sparrow on the north side of the building. This bird was flying well and should be OK. In the west alcoves, however, were three more Lincoln’s Sparrows. One was moving fine, one I was able to herd away from the building, and one was stunned enough that I was able to catch it. I carried that bird around for awhile and it seemed quite perky in the hand. I released it in the dense cover on the south side of Ag Hall, and the bird flew strongly away from me. I will assume that it will be OK, so the tally will be 4 trapped Lincoln’s Sparrows with no casualties among them.
A fifth sparrow was not so lucky: this Clay-colored Sparrow I found on the east side of the NRC.
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
This blog focuses on window strike mortality of birds at a single building on the campus of Oklahoma State University in Stillwater, OK. The Noble Research Center (NRC) is a large, irregularly shaped building that presents expanses of glass on its north and south sides, as well as recessed alcoves on the east and west through which vegetation inside the building can be seen from the outside. Thus, all surfaces of the building present a hazard to migrating birds.
Preliminary examinations of this building reveal essentially zero window killed birds during summer and winter and no resident birds among the casualties. Instead, mortality peaks for several weeks during spring and fall migration, and the casualties are almost all migrant birds in passage.
I surveyed this building approximately daily from mid-April to mid-May in 2009, and was surprised by the species composition and number of individuals found. For example, I found dead Yellow and Nashville warblers, Grasshopper and Clay-colored sparrows, and Indigo Buntings. These are all common migrants in the area, but the NRC is located in an urban setting, with very little vegetation suitable for any of these species in the immediate vicinity. The dead represent birds migrating through at night, and perhaps mistaking the vegetation reflected in the windows as appropriate places to stop after a night of migratory flight. The most surprising find of the Spring 2009 window kills was a Cassin’s Sparrow – a species that normally occurs in the state about 3 hours west of Stillwater.