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Monday, September 2, 2013

The chase is on!

Okay, back to Pelagic Week...and to Long-tailed Jaegers (Stercorarius longicaudus).  

On the 30 August 2013 boat trip, we saw over 20 Long-tailed Jaegers, but only one or two had long tails.  The two central tail feathers are extremely long and flexible but are dropped after the breeding season, so most individuals that we see in this area lack these dramatic feathers.  It's not a great shot, but here's a picture illustrating the long tail:


Long-tailed Jaegers are the smallest of the three species of jaegers (the other two being Pomarine and Parasitic).  They have a relatively small bill and narrow wings.  Note the contrast between the gray upperparts and the dark black flight feathers.  And look at the tip of the wing for an important characteristic: There are generally only 2-3 white shafts visible on the outermost primary feathers (see below and especially the following image).


Most of the jaegers we saw were subadults.  They had strong barring below the wings and on the tail coverts.


Some of these birds had dark feathering on the heads and breasts (as in the photo above), while others were quite pale (next image):


The following photo shows the same bird from above:


Long-tailed Jaegers are transequatorial migrants.  They breed on arctic and alpine tundra, but spend the rest of their life at sea.  Wintering concentrations of Long-tailed Jaegers in the Pacific Ocean have yet to be found, but one possibility is that they spend the nonbreeding season somewhere off New Zealand (Wiley and Lee 1998).

Although not as aggressive as their cousins, Long-tailed Jaegers do practice kleptoparasitism they pursue other birds until they drop their fish.  Long-tailed Jaegers have been documented pursuing terns and small gulls.  Below, a subadult jaeger is harrassing a flock of Sabine's Gulls:


A jaeger chase is always exciting and impressive to watch!
 

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