Parasitic Jaeger Life History

I decided, before I delve too much into these field observations that I should provide some background on the life history of this species, so here it goes.

Parasitic Jaeger, Stercorarius parasiticus

aka Arctic Skua or Parasitic Skua (American Ornithologists' Union code: PAJA)

Order: Charadriiformes

Family: Stercorariidae

Parasitic Jaegers are fast-flying and agile seabirds. There are two color morphs and an intermediate color morph between the two. The light-morph adults will have a brown back and mainly white underparts with a yellowish white on the head and a black or brown cap. Dark-morphs are dark brown all over and the intermediate-morph birds can be brown with some lighter brown or dusky white on the head. The Parasitic Jaeger has two central tail feathers that stream out and come to a point up to 7 cm from the edge of the other tail feathers. A Long-tailed Jaeger has much longer central tail feathers (15-16 cm) and a Pomarine Jaeger's two tail feathers are kind of spoon shaped.

They breed on tundra in Alaska, Northern Canada and Northern Eurasia; and winter in the oceans of the Southern Hemisphere. On the breeding grounds they feed on rodents, small birds, eggs, insects and even berries. In the winter time they obtain food by pursuing gulls and terns and forcing them to drop their food, again showing off their agility in flight. This is called kleptoparasitism, which may also be a reason for their name.

Pairs generally return to the same breeding territory each year, that site fidelity we have noticed. They typically lay two olive-brown eggs on a grassy depression on the tundra. I have noticed that they like to stand on higher mounds of dry tundra, but nest on ridges or small mounds that are surrounded by a wetter tundra. Through doing these field notes, I have also discovered that pairs are bi-parental, meaning they will both incubate the eggs. The incubation period is 25-28 days. The young will stay with the parents for a few weeks after fledging.

I was able to observe both pairs earlier today, and will be writing a summary of those notes tomorrow if I get the chance. I have also considered adding a third pair, if I can find their nesting territory. Part of the project I am working on is to set out artificial nests with real eggs, quail eggs to mimic shorebird nests, and monitor them as if they are real nests. We then use a few cameras to try to capture predators that come to the nests. On our most recent check, we had three camera nest predation events, and each was depredated by a PAJA pair at different time intervals. Meaning they probably have a nest nearby and have probably cued in on the cameras and getting a free meal. So, I would like to find out where they are, especially since it would be a pair that has been previously unexposed to my presence and could provide some interesting observations as far as defensive behavior.