28 September 2017 – Our first Savannah Sparrow, a trapped yellowthroat, and some bonus birds

Since Monday night, we seem to have received at least 5 inches of rain here in Stillwater.  That’s great as I’ve been lamenting the lack of even clouds for a few weeks. The system that brought the rain might have kept birds bottled up to our north because once it cleared last night (Wed.) there was one heck of a flight.

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Of course, attempts to correlate window collision mortality with big radar echoes of migrating birds are fraught with confirmation bias.  There are plenty of big flights that result in no dead birds on my rounds, and I’m a lot more likely to check “last night’s radar” on a morning when I find multiple casualties.  Today was one of those days.

I walked to the Noble Research Center on a route that took me past the long row of windows on the southern side of the Food and Agricultural Products Building, aka, FAPC. This is just across a parking lot from the NRC and I’ve made several incidental finds there.  Today, these “bonus birds” numbered three: an Ovenbird, a Common Yellowthroat (collected) and, around the corner, a female Indigo Bunting that had been there for at least a few days. So before I even made it to the NRC, I encountered 3 window-killed birds.

The yellowthroat was an apparent AHY-male, with fat = 2 and weighing in at 12 g.


At the NRC was another surprise.  Surprisingly, after all these years and considering how common these birds are as migrants and wintering residents, I found the project’s first Savannah Sparrow, in the northwest alcove.



There was also a trapped Common Yellowthroat at the main north entrance and another Savannah sparrow flitting around – through not trapped – just west of the southern portico entrance. The Savannah Sparrow was AHY-U, weighing 18g with a fat score = 2.

22 September 2017 – Mourning Warbler

I’m mourning the loss of another one today – this AHY female I found at the northwest alcove. She was fat (=3) and healthy at 12.5g.


This was the unofficial 315th casualty on the project and, for a new sobering record, the 44th this year. The previous annual high was 41. We’ve surpassed that already in 2017 and, for us, migration is really just ramping up.

1 May 2016 – Swainson’s Thrush

The longest stretch without a casualty in 6 years was broken this weekend, with the unfortunate Swainson’s Thrush below the first confirmed window kill at the Noble Research Center since 19 November, 2015.

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If you were in need of evidence to convince you that it is healthy individuals that succumb to window collisions, check out the fat deposits clearly visible in the furcular hollow and on the belly of this bird.  This bird was in the prime of life.

American Bird Conservancy report on window collisions

Sheppard, C. 2011. Bird-Friendly Building Design. American Bird Conservancy, The Plains, VA, 58p

The ABC has just released a report that really focuses on architectural and materials solutions to reducing window collisions. For more information, check here.


October 2010 Summary

I checked for casualties on 25/31 days in October, and encountered the following:

1 unknown songbird
1 House Wren
2 Lincoln’s Sparrow
2 Grasshopper Sparrow
1 Red-breasted Nuthatch
1 White-throated Sparrow
1 Song Sparrow

28 October 2010 – White-throated and Song sparrows

I found two sparrows this morning, a White-throated (fully dead) and Song (nearly dead).

Fat = 1, AHY-U

The Song Sparrow was still alive when I found it, but I was able to easily capture it by hand.

According to Dan Klem’s classic work, about 50% of the birds that are able to fly away from a window collision will ultimately succumb to their injuries. I don’t count “trapped” birds as casualties, but if I’m able to catch it, chances are its injuries are potentially life-threatening. In this case, I took the sparrow with me and carried it around for awhile until it had shaken the cobwebs off a bit. I released it near some juniper shrubs on the southwest side of Ag Hall, and it flew ~ 20′ into those shrubs. I will, however, consider it a “casualty.”

Is bird-safe glass on the way?

An astute reader directed my attention to an 8/28 article by Anne Eisenberg in the New York Times online Business Day section. The article describes the use of a new glass product developed in Germany, Ornilux, that holds promise for reducing window collisions because it is visible as a barrier to birds – its visible pattering, however, is largely invisible to humans, so the product could become popular for sustainable designs of homes and businesses.

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:

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.

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


Solutions for window collisions?

People often ask what they can do to reduce bird/window collisions. While the magnitude of the problem is great, there are somethings we can do to reduce the current – and future – carnage.

The basic problem is that birds don’t recognize glass as a barrier. Anything that communicates “barrier” to a bird solves the problem. Those old falcon silhouettes don’t really help, unless you put up so many that the glass is basically covered. Narrow strips of fabric or some other kind of opaque material will work but, again, they need to be covering probably more than 2/3 of the window area to do any good. Recently, some folks have had some success using UV markers or other colorings – birds can see them but humans cannot. But the jury is still out on how effective such treatments can be. Check here for a link to David Sibley’s blog including his own “field” trial of using a UV highlighter pen to make windows more obvious to birds.

The one product I’ve seen that really has some potential to reduce mortality around homes is Frank Haas’ “Bird Screen.” This is a netting product that can be mounted to an exterior window that should reduce mortality to zero while still allowing a clear view to the outside from inside. Even birds that fail to recognize the barrier with the screen down are safe – they hit a soft netting with enough give to allow them to roll away from the contact unharmed.

I’ve been asked about other structures that could be hung near windows to discourage bird strikes, and I can foresee how some things like this might work. The point would be to either draw attention to the barrier of the objects (e.g., hanging flower baskets?) in front of the window, or at least cause the birds to slow on their approach, rendering any collision that still occurred far less likely to be fatal.

For people with feeding operations, many birds hit windows when they take flight from feeders. The solution to this problem could be very simple: either move the feeders farther away from the windows or move them so close that a fleeing bird that strikes the window would not have enough room to get up enough speed for a fatal collision.
For larger buildings on major migration pathways, lighting can often play a big role in mortality. Check out the Fatal Light Awareness Program (FLAP) for information and resources.

New construction is a whole other ball of wax. New pitted or frosted glass products can allow a view to the outside from within -and bring in plenty of natural light – without leaving a clear reflective surface on the exterior. Construction that angles windows to reflect the ground, rather than sky or trees, can also be effective. Check out how Swarthmore College worked to re-design a science complex that included “bird-friendly” glass in its construction. Links to other examples can be found here.

One of the best resources for solutions to bird strikes can be found at Laura Erickson’s For the Birds blog.

Do I miss any birds on my counts?

Of course.

Any raw count of individual birds, bats, etc. that die from colliding with some structure is a conservative estimate of the actual mortality at that structure. Here’s why:

1) I could just plain not see the carcass during my check. Maybe it’s hidden by some vegetation, someone has kicked it under a bush, or the animal landed outside my search zone, say 10m from the building as opposed to the 2-3m zone I’m checking. Thanks to some of Dan Klem’s excellent work, we also have an idea that about 50% of the birds that strike windows but manage to fly away only temporarily stunned will also die, and potentially at quite a distance from where the collision took place. In fact, many bird deaths attributed to cats may actually be made possible by stunned birds that have hit windows.

2) Some predator has scavenged a carcass before I get there to record it. Cats, raccoons, opossums, skunks – any of these common predators would be happy to snatch a dead bird lying conspicuously on a sidewalk near a building.

3) Some human – perhaps someone doing a study like mine – has “scavenged” a carcass before I get there to record it. Groundskeeping crews do occasionally remove dead birds from sidewalks as well.

All of this means that if I count 50 dead birds around a building over the course of an observation period, that 50 is some fraction of the real total number of birds that died from colliding with that building during that period. Okay, but is 50 a large fraction or a small one?

I could calculate observer detection rate by having a partner place dead birds around the building and then going through my normal routine to determine how many I miss. Let’s say that I have a high detection rate of 95%, which is likely for my building because I have easy visual access to the entire perimeter. I would then modify my estimate of 50 by adding 5% (2.5) to my raw count. OK, so now we think that 52.5 birds died.

We can also test removal rate by putting out carcasses, chicken wings, etc. and seeing how many are removed over a set period of time. Let’s say that 25% are removed. We now add another 25% (13.125) to the estimate and conclude that 66 individuals died at the location, even though only 50 were actually counted.

But there are some problems with making these estimates. The first is that they greatly increase the complexity of gathering the data.

I’ve actually been a long-time opponent of Herculean efforts to quantify “removal rate” of carcasses around things. We invest a huge amount of time, money, and effort to do things like improve our accountability in detection a few percentage points. The real story is not whether 50 or 66 birds died by colliding with some structure, it’s that a lot of birds died by colliding with the structure. That’s the message that needs to get out; estimating that there were 16 more casualties than actually counted isn’t going to change anyone’s mind about the severity of the problem. What’s more, in cases in which detectability is low and estimating things like removal rates bumps up the estimate a great deal (say, 10 carcasses found but 100 estimated deaths), the public can become dismissive of the problem because they’re skeptical of the means used to derive the estimate.

The bigger problem, however, lies in attaching a static rate of removal to a raw count. Determining “the” scavenging rate is not only extremely labor and time-intensive, it’s silly. Scavenging rates likely vary over time at a location. It only takes one cat or crow or raccoon to learn that dead birds appear at the base of some building every night and the scavenging rate can change dramatically over a short time frame. Especially given that we study scavenging rate by placing food around the base of buildings, we need to be sensitive to how our own actions as researchers could be teaching scavengers about a reliable food source.

The solution? I advocate a healthy dose of common sense. If you check your building daily, you’re a lot less likely to have carcasses removed before you get there. If you leave carcasses in place after you identify them, you can get a sense for the removal rate by determining how long the carcass lasts. Right now, I’ve had three carcasses present at the NRC – all still plainly visible to me – that have been in place for more than 1 week. This tells me that scavenging rate is probably quite low.

Lastly, recognize that the number is not the most important part of the story when it comes to collision mortality. I’m far more interested in the species and life history composition among the dead birds I find. For example, abundant residents like starlings and House Sparrows are almost never counted among the casualties at a site like the NRC. In contrast, the great majority of victims are long distance migrants. So far this fall I’ve counted 7 victims of which 6 were Neotropical migrants – the 7th was a migrant too, a Grasshopper Sparrow. This is where I think the most interesting questions lie regarding collision mortality. The risk of collision varies by species, and this may mean that some species are disproportionately affected by window collisions.