Spring/Summer 2017 was busy

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.

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Beginning Mar 1st, here’s what has turned up at the Noble Research Center.

Dead Birds

  1. Indigo Bunting – 5
  2. Painted Bunting – 5
  3. Ruby-throated Hummingbird – 3
  4. Lincoln’s Sparrow – 2
  5. Mourning Dove – 2
  6. Nashville Warbler – 2
  7. Orange-crowned Warbler – 2
  8. Baltimore Oriole – 1
  9. Chipping Sparrow – 1
  10. Eastern Meadowlark – 1
  11. House Wren – 1
  12. Northern Parula – 1
  13. Tennessee Warbler – 1
  14. 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:

  1. Northern Cardinal
  2. Common Yellowthroat
  3. Mourning Dove
  4. Song Sparrow
  5. Yellow Warbler
  6. Carolina Wren

 

 

13 May 2017 – Yellow-billed Cuckoo

Haley Butler tipped me off to this Yellow-billed Cuckoo she found at the southeastern alcove of the Noble Research Center on the afternoon of 12 May. By the time I got there to check on the morning of the 13th, the cuckoo had been scavenged, evidently by a cat.

21 May 2016 – Mourning Warbler and Yellow-billed Cuckoo

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.

 

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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.

25 September 2010 – Brown Thrasher

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.

A Year in the Death – Aug. 2009–Aug. 2010

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:

Effort.
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.

Data.
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.

I encountered more casualties during spring and fall migration periods than in winter or summer (though effort may have played a role in this result):

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.)

Non-lethal collisions.
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

Scavenging rate.
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.


Scavenged Swainson’s Thrush.

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.

Total data.
The following table lists all the species found as window collision casualties at the Noble Research Center, 8/20 2009–8/20 2010:

species number
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

O’Connell2001

10 June 2010 – two surprises

One interesting aspect of this work is that “lulls” of activity seem to be broken by periods of higher activity. To wit, I had just about convinced myself that there would be nothing noteworthy showing up by the windows of the NRC for several weeks, now that we’re well into June and all the migrants seem to have (should have) passed through or are busy nesting. I certainly did not expect the Yellow-billed Cuckoo and Black-and-white Warbler I found this morning:

The cuckoo might just be a late migrant. They’ve really only been around for the past 3 or 4 weeks as it is. But the Black-and-white has me intrigued. These birds come back and begin nesting in late March. Could this individual (a 2nd year bird) already have been involved in post-breeding dispersal? Was it on its way back south? Was it in poor condition overwinter, such that it was just getting back to its breeding grounds this late?