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

 

 

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20 June 2017 – trapped Carolina Wren

Today I came upon this stunned Carolina Wren at the northwest alcove. It looked pretty out of it but as I approached it perked up, clinging to the bricks.  I was never able to catch it and it ended up flying strongly to one of the oaks in the parking lot to the west, so I’ll count it as a survivor.

27 June 2012 – no casualties, but bonus Ag Hall wren

I found outside my own building yesterday a Carolina Wren that met its end at one of our windows.  This bird was in an advanced state of decomposition so I had potentially missed it for a few days.  (I don’t systematically search Ag Hall as I do the NRC.)  Conservatively, I will consider 26 June as the date of this bird’s demise.

Six-month summary: July–December 2010

Here is just a quick summary of casualties at the Noble Research Center from July through December 2010:


Very fat Mourning Warbler that never made it to the wintering grounds.

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.

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

1 August 2010 – Carolina Wren (scavenged)

Today I found the remains (4-5 incisor-snipped primaries) of a Carolina Wren. The feathers were fairly worn, so it’s difficult to tell if the bird had been there for a few weeks and I’ve been missing it, or if the kill was fresh but the feather weren’t to start with, i.e., the bird had not yet molted very worn feathers. If the bird had been in place for some time before being scavenged, I suppose that it was buried in a small pile of leaves that had accumulated in a corner at this spot. I always do check those leaves carefully, but I generally don’t dig through them for hidden victims underneath. That just doesn’t seem likely given that the “pile” in question is only 2-3 leaves deep and occupies the area of a standard coffee table book.

I’m leaning more, then, toward the idea that this was a more recent casualty, perhaps a bird with worn feathers that met its end yesterday and was scavenged in the early morning hours of today. Given my uncertainty about its time of death, I will just leave it in the database with the August 1st date.