7 October 2019 – Two House Wrens and still learning new things

The two House Wrens I found this morning (one at the main north entrance and one in the northwestern alcove) were the 3rd and 4th casualties since August. I had only found 3 prior to August 2019.

August 2009–July 2019: 3 House Wrens

August 2019–October 2019: 4 House Wrens

24 September 2019 – Ruby-throated Hummingbird and Nashville Warbler; plus bonus birds

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.

 

August 2009–July 2019: Ten Year Milestone

Ahead of the official official ten-year anniversary of window collision monitoring at the Noble Research Center on August 20th, here’s a recap of my very first post from 7 September, 2009.

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Those were heady days, indeed.

Here are some basic things I’ve observed and learned, August 2009–July 2019.

With some occasional help when I’ve been out of town, we surveyed the perimeter of the Noble Research Center for window-collided birds 2,141 times. I’ve generally run surveys every day (usually within about two hours of sunrise) during heavy migration periods in  autumn and spring, scaling back to more like weekly surveys during the dead of winter.

Including 4 unidentified passerine remains, at least 414 individuals of 67 species died in window collisions at the Noble Research Center.

The most frequently encountered casualties were:

  1. Lincoln’s Sparrow 51
  2. Ruby-throated Hummingbird 36
  3. Painted Bunting 26
  4. Indigo Bunting 23
  5. Grasshopper Sparrow 20
  6. Clay-colored Sparrow 18
  7. Mourning Dove 17
  8. Nashville Warbler 16
  9. Mourning Warbler 15

Tenth is a four-way tie with 11 casualties each for Common Yellowthroat, Orange-crowned Warbler, Song Sparrow, and Yellow Warbler.

The spatial distribution of those casualties looks a bit like this:

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Collision casualties at the Noble Research Center, Stillwater, OK, 2017

Window treatments applied to selected panes in 2016 have, evidently, not contributed to a decline in collisions.

I plan to continue my monitoring at the NRC for as long as I can, and in the next 10 years hope to appreciably reduce the mortality here.

 

5 November 2018 – a pile of feathers and fruits

In a corner of the main north entrance to the Noble Research Center, I encountered this mystery today:

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And I’m all like:

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So let’s get to work on this.

First, this wasn’t here on Nov. 3 (Saturday), I did not check yesterday (Sunday), and when I found it today (Monday, the 5th) it had already been scavenged. I count examples like these as scavenging/removal on day 0.

Okay, so there’s a feather pile and a fruit pile. The fruit pile is on top of the feathers. The fruits show no signs of digestion, other than some of them having been opened and the pits are exposed. There is a single large pit inside a small fruit that is round and black with a highly glossy finish.

After much reading, comparing, consulting, etc., I’m pretty well convinced that these are chokecherries, Prunus virginiana.

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Paul Wray photo, Iowa State University

My guess? I think our bird gorged itself on chokecherries before undertaking a migratory flight that, sadly, ended at a stupid window. The scavenger burst the bulging crop of this poor bird but had no interest in the fruits (in turn, feeding my opinion on the scavenger). So the remnants of this event are a pile of feathers and a pile of chokecherries.

Ah yes – the scavenger!

Well, we know that on campus we have skunks, foxes, opossums, raccoons, and feral cats as the most likely scavengers. The most likely of those to turn up its nose at a pile of chokecherries? I’d say cat. A cat scavenger would also be pretty well supported by the clean shearing of the flight feathers from the wings, visible here:

So what’s the bird? Well it’s clearly a meadowlark, but whether Eastern or Western takes some additional work. As with the fruits, I’ve spent a lot of time reading, consulting, and comparing. Perhaps the best resource for this task was a blog post from Kevin McGowan ca. 2000. (I also couldn’t get the USFWS Feather Atlas to load.)

Everyone knows that Western Meadowlark shows a yellow malar and in Eastern Meadowlark this is whitish. Without the bird’s head this character was of no use to me, however. In fact, there were just three feathers in the pile showing any yellow at all. Two other character differences are more relevant. First, both species have white outer tail feathers, but on Eastern the outer two are fully white and the third is mostly white. On Western the white is less extensive and even the outermost feather isn’t always fully white. In addition, Western looks paler overall than does Eastern, with the pattern on its tail and in the folded wings over the back appearing lighter brown/gray with blackish stripes. On Eastern, those same areas are darker brown with thicker blackish stripes often joined at the center of the feather creating a fern-like shape instead of distinct stripes. What do you think of these?

I’m leaning toward Western Meadowlark as the original owner of these feathers.

So I’m reporting today a pile of feathers that I think was Western Meadowlark, scavenged by a mammal I think was a cat, and that the cat showed no interest in what I think was a pile of chokecherries in what I think was the crop of the meadowlark.

Challenges, thoughts, etc? I welcome any and all!

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31 July 2018: end of season wrap-up

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)

 

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9 July 2018 – Mourning Dove remains, and another note on scavenging and removal

I found a pre-scavenged Mourning Dove at the main north entrance today. This is another great example of the difference between scavenging and removal.

The carcass was scavenged even before I found it. The whole point of working to determine scavenging rate is a matter of detectability, i.e., that our raw counts will always underestimate mortality because some carcasses are scavenged before they can be found. But scavenging isn’t the issue per se, removal is. If the carcass is scavenged but not completely removed, then it is still detectable. Therefore, the act of scavenging was irrelevant to my ability to detect the carcass, and thus the event.

We can do some field trials with known specimens and determine that our observers detect, for example, 95% of the carcasses in their search area. We can also do removal trials by setting out specimens and determining what proportion of them are removed in a set period of time. For example, let’s say 25%.

If we do some window-collision monitoring and find 10 dead birds at a building, we can modify our estimate according to our imperfect detection rate: 10.00/0.95 = 10.53. That’s the detection-adjusted estimate of mortality. The removal rate of 0.25 suggests that another 2.5 carcasses were removed before they could be detected (or at least before 95% of them could be detected). Removal rate bias then bumps our estimate from the raw count of 10 to an adjusted count of 12.5. Factoring in the detection rate on that estimate increases our adjusted mortality to 13.16 from the raw count of 10 carcasses we actually found.

This matters naught if our objective is to highlight the total number of casualties. It’s is not the case that public outcry to help solve the problem of window collision mortality with be louder for 13.16 casualties than it is for 10. For comparisons among studies, however, it is important to have this information presented and standardized. If, for example, two sites are compared according to their respective landscaping or lighting influence on mortality, that analysis would be corrupted if there was an unaccounted stark difference in removal rate between the two sites. So it is important to quantify rates of detection and removal in monitoring so that our efforts can be of greatest use.

In this long-term monitoring project, I have approached removal rate differently. I leave some carcasses in place to determine for how long they are detectable. Some are removed before I ever find them; some are immediately scavenged but not removed so I can detect them for weeks after the event. Some are never removed and their feathers and bones can still be detected months afterwards. On average, carcasses in my my study last about 10 days on the ground, and I conduct my surveys every 1–2 days. This means that, on average, I have 5–10 opportunities to detect a carcass before it is removed.

That’s pretty good.

 

22, 24, 29, & 31 January 2018 – no casualties

Here’s a bit of a retrospective on the past year, though. I arbitrarily divide the calendar year into spring (Mar–Jul) and fall (Aug–Feb) monitoring. We’ve still got February to go, but my data aren’t likely to change much before the end of this next month.

The irony of having marked some windows in 2016 and seeing a new high count of dead birds in 2017 is not lost on me. I’m not sure what to think of that other than a standard admonition against drawing conclusions from just a year of data. Either way, 2017 was startling. My previous high count of 41 casualties occurred in 2010. The ensuing 5 years accrued fewer than 30; last year we were back up to 40. The 2010–2016 average was 37. Thus, the 61 casualties I found in 2017 was fairly shocking.

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12 August 2017 – Two Louisiana Waterthrushes

I’m sad for every casualty, but folks who know me know that there is a special place in my heart for the Pinnacle of Avian Evolution, the Louisiana Waterthrush. Today, not one but two of these splendid creatures met an untimely end in the southwestern alcove of the Noble Research Center.

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I moved them off the sidewalk and into the nearby lawn as a removal trial. Both were evidently AHY-U.

My sadness, of course, is tempered by my scientific curiosity. Louisiana Waterthrushes are rarely encountered in passage. The routes and timing of their travels are largely presumed but seldom confirmed, and this is confirmation of both.  Whenever two individuals are found at a window, it is tantalizing to consider that they were traveling together, perhaps “chip”ping every few minutes to stay in contact.  If so, were these a mated pair?  Siblings?  From the same neighborhood?  Did they leave from the same area or meet up somewhere along the way? Was this an agonistic encounter, with one chasing the other?  Were they even together?  Perhaps they hit the window hours apart, and were not traveling together but just using the same route?

With every observation, the follow-up intrigues.

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

 

 

16 April 2017 – Mourning Dove scavenged

No new casualties today, but I noticed immediately that the Mourning Dove carcass had been removed.  Closer inspection revealed it to have been scavenged from its original location with remains scattered near the base of the building about 5 m away.

 

So what is scavenging rate all about, anyway?

The idea is that our detection of dead birds (or anything else) is imperfect.  We can collect data and report that, for example, 50 birds died at a building.  That estimate can only be a minimum, however.  Our raw counts underestimate the true number of casualties because our detection cannot be > 100% but it can be far lower than 100%.  Birds can collide but manage to flutter away and die outside of our search area.  Some might be difficult to see against the substrate on which they land.  Most important, some will be removed before we get there to find them. Cats, rats, opossums, raccoons, crows, etc. tend to be abundant in urban/suburban areas where most window collision research takes place and they can often remove a carcass before the investigator arrives onsite to conduct a survey.

For example, assume that the removal rate (whether by scavengers, human maintenance crews, etc.) is 25%. This means that, at best, the investigator is only predicted to encounter 75% of the casualties. That raw count of 50 dead birds? The detection-corrected number is actually closer to 50/0.75 = 67 dead birds.

Does that matter, though?  I struggle to attach relevance to what the removal rate is for any given study. Is there some magic number of casualties that is a threshold for conservation action?  Are there people for whom 50 dead birds wouldn’t register as important but 67 would? For comparing mortality rates among sites where removal rate might vary we assume that it is important to determine a separate removal rate for each site, but is it? Imagine 50 dead birds at our site with high removal of 25% compared to 50 dead birds at a site with low removal rate of 5%.  That’d be 67 compared to 50/0.95 = 53.  So?  Would we really be concerned about 67 dead birds at one building but not 53 at another?

My final concern is the false sense of security that we’ve determined “the” removal rate.  These rates are widely variable across space and time.  We’re kidding ourselves to think that we’re improving our estimates of collision mortality by adjusting raw counts with a detection probability that is itself a moving target.

In my study, I’ve conducted approximately 86 removal trials over the past several years. On average, a carcass lasts about 10.5 days on the ground before it is removed.  On average, I conduct a survey every 1.5 days.  That gives me 10.5/1.5 = 7.0 opportunities to find a dead bird before it is removed.  Ergo, removal rate is hardly noticeable in my study.  Whatsmore, scavenging and removal are not the same thing.  It is often the case – as with today’s Mourning Dove – that the carcass is scavenged but evidence remains.  The Mourning Dove died on April 5th and was scavenged on the 15th.  That’s 10 days.  The remaining bones and feathers, however, might still be here weeks from now.  On multiple occasions, I have found evidence of scavenging in the 24 hrs since my previous survey. For example, I check one morning and find feathers that weren’t there the day before.  I refer to these as “day 0” removals, but the feathers are still there to provide evidence of the casualty for days and weeks after the event. The longest I have had feathers or other remains in evidence is > 90 days.

So I see scavenging and removal rates – and detection rates in general – as red herrings in our monitoring of collision mortality. Unless part of a well-controlled design to compare, for example, mortality from two facades of the same building, there’s not much to gain from collecting data to estimate such rates.  There are, however, potential costs.  Many avocational birders and conservationists collect data on collisions opportunistically, and their presumed lack of rigor in methods limits the use of their data for serious analysis.  I maintain that those data are perhaps far more useful than we might presume because of an ill-defined obsession with calculation of detection as a study’s ticket to the club of legitimacy.