Friday, March 13, 2020

Fri-D: Of Gulls and Bird Age-speak

[This is an egg. I dare anyone to dispute me. A Herring Gull egg, to be precise. It is not a bird, just ask the rule-makers at ABA. Eggs do not count as birds.]

Last Fri-D I wrote about bird ages. You might want to look at that one first before wandering through the images below. By the way, the chart at the bottom of that post needs a big screen or at least a landscape view on phone or tablet to see it all.

Large gulls are among those birds that take more than two years to reach full adult plumage. Eagles are another familiar example of taking a long time to become adult. Adult means capable of breeding; for virtually all birds, they are as big as they will ever be when they first can fly, but often look different than adults.

I think this matters, both for i.d. and for ecology. I got grouchy with my dear friend Pete Dunne when he used words like "immature" to refer to non-adult gulls in his gull book with Kevin Karlson, which he asked me to give a once-over before submission. As usual,  he pretty much ignored me.

Passing over i.d., what's the bit with ecology? Well, what are the two most common plumages you see in large gulls? Answer; first year/first winter and adult. Progressively less common are second years and third years. Why is that? Because birds start dying the minute they hatch, but adults stay in adult plumage until they die, sometimes after 10-20 years or more. So third year is the rarest plumage. This is why I think it is important for birders to age birds as carefully as they can. For example, what if someone looked at the ages of every American Kestrel, in the field or banded? We would be able to know whether the ratio of adults to first years was changing, and where, which would then tell us if the AMKE decline is about adults dying or about lack of nest success, or both, if we compared ratios over time. Presumably this information is "out there," but has it been analyzed? Maybe it has and I never heard about it.

Anyhow, here's how large gulls grow up in pictures. The baby things are from a gull colony somewhere near Avalon, Cape May County, NJ; the flight shots are from Gloucester, MA.

[Nestling Herring Gull. Downy, and still in the nest.]

[Fledgling Herring Gull, out of the nest, can't fly, very dependent on mom and dad.]

[Juvenile Herring Gull, with mom and dad in the background. Also first cycle, also hatch year. Male gulls are bigger than females, the reverse is true in birds of prey. This one's flight feathers are still growing in, and it could barely get off the ground.]

[First winter Herring Gull. also first cycle, also SY (second year) because it's February, after January 1 , which is when banders give birds their birthdays.]

[Second winter Herring Gull, also second cycle, also TY. In large (4-year) gulls, the second-years develop adult back color, helpful e.g. in picking a Lesser black-backed Gull out of a Herring Gull flock.]

[Third winter Herring Gull, also third cycle, also TY. In four year gulls, third years are very adult -like, but with different wingtip patterns and usually a tail band.]

[Adult winter Herring Gull, also fourth or later cycle, also fourth or later year (ATY, or after third year). Someone's going to get on me because this bird doesn't have head streaks so technically it's an adult breeding; gulls molt to breeding plumage early, this is from February.]

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