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Ich bin ein Jaegermeister!

December 20, 2007

Lesson 1: Jaegers are not Gulls.

Lesson 2: No one knows anything about Jaeger ages.

These are the things I learned as I began to look at the Pomarine Jaegers in the NC Museum of Natural Sciences collection (granted, I kinda knew the first one). In order to get a handle on how to go about this Jaeger issue, I went straight to the very useful Birds of North America accounts put out by Cornell University, proving certainly that the august institution does far more legitimate things that run around looking for extinct woodpeckers (sorry, that was a low blow, apologies to the folks at Cornell). Interesting to note that the BNA account about Jaeger plumages, particularly Poms, was taken from observations of the NC Science Museum Jaeger skins. So I was in the odd position of determining information from skins using a document whose information was determined from the skins I was looking at. Obviously someone had done what I was doing but apparently hadn’t let the museum know what they discovered, so I had to do it again. Weird.

In any case, I was surprised to note that no one has done studies on Jaeger ages by following marked birds over several years as has been done with the other Larids. Turns out this is because 1) Jaegers nest in incredibly remote places in the far far north and 2) Jaegers don’t have regular breeding colonies they return to every year because their populations are geared to respond to outbreaks of Lemmings. Instead they follow the lemming populations around. So breeding Jaegers of all three species are practically impossible to predict, and then nearly impossible to reach. To that end breeding information is slim, and from that no one knows molt patterns, predictable plumage characteristics or ages.

Throw into all this the fact that there are three phases (Light, Dark, and Intermediate) and individual birds are not consistently one phase throughout their lives (i.e. a dark phase juvenile could end up being a light phase adult), and you’ve got a big flippin’ crapshoot. Between juvenile birds and obvious adults you can really only parse between early immature and late immature. Note the selection of immature birds to the below to get an idea of the variation I’m talking about. It’s wide is all I’m saying.

So this is all true for all jaegers, but the Poms have some interesting characteristics that are unique to them. Check out this spread wing on the right. One of the more reliable means of differentiating among the species of jaegers in all plumages, especially if you get a good look, is by counting the white shafts of the primaries. Poms have up to six white shafts on the first six primaries which shows up as a flash of white on the wing. Parasitics have four white shafts and Long-tails have only two. These spread wings are an especially good way to note this field mark.

Another thing I noted about jaegers in general and the Poms in particular are the enormous talons they have. I would consistently reach over to pick up the next skin on the tray without looking and prick my hand on these feet. While gull feet are largely benign, the jaegers have large, sharp nails that are really nasty-looking as you can see to the left. They certainly go a long way towards confirming the birds’ reputation as aggressive predators, which is actually pretty cool and part of the reason I like them so much. Poms are the largest collection at the museum as they apparently are the most common Jaeger species off North Carolina’s coast, but I’ll have more thoughts and pictures as I work through the other species after I return to the museum after the holidays.

  1. slybird permalink
    December 20, 2007 11:45 am

    Holy Jaeger Talons!! That’s awesome!

    Because you brought this awesomeness to my attention, I’ll let your dig on Cornell slide… this time.

  2. December 20, 2007 5:38 pm

    Bullet dodged, Nick…. ; )

  3. Anonymous permalink
    December 20, 2007 10:58 pm


    Do you have a cite for the idea that jaegers can change color phase as they age. I have never heard this before. It seems kind of unlikely and as you noted, apparently no one has done a marking study of wild birds. Did somebody raise some in captivity? I’m not sure how else one would know this.

  4. December 20, 2007 11:19 pm


    I agree it’s weird. I had heard it somewhere but forget where exactly, and was unable to corroborate it on the BNA accounts. I’ll try and get to the bottom of it.

  5. December 20, 2007 11:33 pm

    The phenomenon is mentioned in the Sibley guide where he states (and this is for Poms, p. 199) that while virtually all juveniles are dark or intermediate, about 90% of adults are light, implying some are going to change, but there’s no indication that there’s a way to predict which individuals will be the ones to do so.

    But you’re right of course, that with so little really known about jaeger life histories, there’s a lot that has to be assumed.

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