23 March 2009
When birders talk about The Big Sit they’re referring to a 24 hour birding event in October where participants sit in a 17 foot diameter circle and count every bird species they see and hear.
I have never done a Big Sit but when I watch the peregrines incubating their eggs on the webcams I am in awe. How do otherwise active birds manage to sit there for four and a half weeks?
Peregrine falcons begin incubation when they lay their next-to-last egg in the clutch, then sit for about a month until the eggs hatch. Even then the work isn’t done. Peregrine chicks cannot immediately regulate their body temperature so the parents must brood the chicks for an additional week. All told, that’s five and a half weeks of sitting.
Tasha, the female peregrine at Gulf Tower shown here, began her Big Sit on March 17. (This post was written in March 2009.) Dorothy, at the University of Pittsburgh site, will begin in earnest when she lays her third egg. (Dorothy typically lays four.)
Who incubates the eggs depends on the species. Among mallards only the mother bird sits on the eggs but in peregrines both parents play a part. The mother peregrine incubates all night and most of the day. Her mate brings her food and incubates while she eats and flies a little to stretch her wings. Then she’s back on the eggs. How long her mate spells her and how often depends on the individuals. I’ve noticed at Pitt that E2 gives Dorothy a break at least twice a day: at dawn and in the late afternoon.
Because they incubate, both male and female peregrines develop a brood patch, a spot of bare skin with blood vessels close to the surface. The brood patch isn’t visible when they fly because nearby feathers cover it but it’s an opening for heat loss so it regrows feathers as soon as it isn’t needed.
Much as I like peregrines, watching them incubate eggs is about as exciting as watching paint dry. Barring an unusual event, there won’t be much to see at Gulf Tower until hatch day which will probably be April 19th. At Pitt, we’ll have some excitement as Dorothy lays two more eggs but she too will start The Big Sit.
News update March 23 at 3:10pm: Dorothy laid her third egg at about 3:10pm. If this is her next-to-last egg (which it very likely is) she has just begun her Big Sit.
(photo from the National Aviary webcam at the Gulf Tower, Pittsburgh)