The surprising durability of wings

29 01 2015

While reviewing this month’s walk data, I came upon a resighted bird reported by Warren Mumford on his Cape Cod beach. The bird was nothing but a single wing and some gnawed bones, but still with a bright, shiny, aluminum tag affixed reading 588. I looked back through our records to determine when Warren first found and tagged 588, and was impressed to find that this bird has been on his beach almost a year, having been seen initially in March 2014. Here is a series of photos documenting 588’s decline:

First seen in Macrh, 2014. (photo: W. Mumford)

First seen in March, 2014, already just a set of wings. (photo: W. Mumford)

August 2014. (photo: W. Mumford)

August 2014. (photo: W. Mumford)

November 2014. (photo: W. Mumford)

November 2014. (photo: W. Mumford)

January 2015. (photo: W. Mumford)

January 2015. (photo: W. Mumford)

First off, I can’t resist even a mini-DBQ, so, can you tell what species this is? Second, this case got me thinking about how we count dead birds and how to account for their persistence (or lack thereof) on beaches. As I begin analyzing data from the past two or three years, I am interested in looking at these tagged birds in particular. Once we instituted the numbered aluminum tags, how many of them were resighted on later surveys? How many were never seen again? How does this differ across beaches? And moreover, 588 shows us how long wings can stick around. Who knows how long dead 588 was when it turned up on Warren’s beach in the first place? How long can a set of wings and a sternum drift around before landing on a beach? And if wings can stick around for so long, are they really useful in trying to track mortality through time? If a set of wings might be from a bird that died a year previous, should it be counted, for instance, in an acute mortality event, or should only intact carcasses be used for that?

Lucky for me, there are actual trained scientists with trained scientific minds who can help me sort this out as I tackle the data. We shall see what it all yields.



One response

29 01 2015

My first impression is female Eider Duck. The brown mottled wing coverts, the dull speculum with the white edges, the width of the sternum reminds me of an Eider. On the beach these wings can last for a long time, as proven by the pictures. But floating around in (sea) water they will last not very long. Maybe a week, most likely even much shorter. These pairs are most of the time the remains of a gull’s dinner and were consumed on land or close to the shore, in the tide line for instance and haven’t been floating around or just for a short time. When 588 was pictured for the first time I guess it was rather fresh, maybe a few days, a week, depending on the circumstances. Feathers still in good shape and condition and no discolouration at that moment. A good check is feeling the flexibility of the joints: still flexible in combination with feathers in a good state means fresh. The presence of red from blood is also a good indication for freshness. In dry periods the joints become stiff quite fast, and stiff joints but still good feathering means, not fresh, but not very old either. A good estimate requires experience and even then it is of doubtful reliability. It depends on so many factors: what was the weather in the days/weeks before: cold, dry, rainy, sunny, was it buried under the sand, was it scavenged or not, infested by maggots, etc, etc. But the latter pictures are definitely of wings that are dead for a long time and should not be counted in acute mortality events
We always cut the tips of the primaries when a carcass is counted to avoid the risk of doubling records. It is also a way to know whether a carcass is there for a longer period or not.

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