Mar 23 2009

The Big Sit

Published by at 8:55 am under Nesting & Courtship,Peregrines

Female peregrine incubates her eggs at Gulf Tower, Pittsburgh, 2009 (photo from National Aviary webcam)When birders talk about The Big Sit they're usually referring to a one day birding event in October in which participants sit for 24 hours and count every species they see and hear from a 17 foot radius circle.  The goal is to get the highest count - and there are prizes.

I have never done a Big Sit because I'd go stir crazy sitting that long, so when I watch on the webcams as the peregrines incubate their eggs 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 33-35 days 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 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, 2009 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)

10 responses so far

10 Responses to “The Big Sit”

  1. Susanon 23 Mar 2009 at 2:29 pm


    I’ve always thought it was strange that they didn’t start sitting right away, as soon as the first egg is laid. It does lead to all of the eggs hatching closer together, but I think it’s remarkable that the first eggs survive being “on hold” for a while. Is there a time limit as to how long that first egg could go without being incubated, then grow normally into a chick?

  2. Kate St. Johnon 23 Mar 2009 at 2:57 pm

    I don’t know the time limit but I have read that waiting can reduce the viability of the first egg. On the other hand, raptor species that incubate immediately (bald eagles, for instance) have higher chick mortality because the first chick eats everything or kills his sibling.

  3. Joannon 23 Mar 2009 at 3:13 pm

    I see that Dorothy laid a 3 egg sometime last night or today. She doesn’t seem to be nesting yet so maybe she has more than 1 egg left to lay

  4. Elspeth Wissneron 23 Mar 2009 at 3:14 pm

    Kate – it looks as though there are now 3 eggs ??

  5. Kate St. Johnon 23 Mar 2009 at 3:17 pm

    Monday, 3:15pm. You all are so good at this! She JUST laid it in the last half hour. Here’s a picture:

  6. Elspeth Wissneron 23 Mar 2009 at 3:37 pm

    Thanks! I just happened to look earlier and she was off the nest, and I thought there were 3 – then next time I looked she was back and I couldn’t see!

  7. RAYon 24 Mar 2009 at 12:59 pm


  8. Kate St. Johnon 24 Mar 2009 at 1:35 pm

    Ray, yes there have. There’s a nest at the Monaca-East Rochester Bridge in Beaver County and there used to be a nest at the 62nd Street Bridge but the peregrines left 62nd Street when the bridge was under construction. We hope they come back.
    Other than those two sites people have seen peregrines at other bridges along the rivers but we aren’t sure any of the other sites have nests.
    Keep your eyes open when you’re near a bridge. Maybe you’ll find peregrines!

  9. Mary Ann Pikeon 26 Mar 2009 at 8:18 am

    I just saw Dorothy get off the nest at 8:15 am and there are 4 eggs now!

  10. Tracion 26 Mar 2009 at 2:47 pm

    I was thinking about what great teachers the Falcon’s are. I could not do a Big Sit either. For example, at the end of my pregnancy – I was so anxious for that kid to be out I was practically begging them to help him along (my son was 10 days overdue). In my mind – there was an end point and when it wasn’t met – I could barely contain myself.

    But wildlife simply lets things unfold in its own way and time. Whether one egg gets laid or four, and whether all survive or just one. It’s amazing.

    I am also struck by how Dorothy puts everything on hold, that would sustain ‘spirit’ in a person, and just does what she needs to. She sits and sits and sits on those eggs, without complaint. HMRPH – wish I could do the same myself! Do what I need to without complaining, that is!!

    The whole process for me, is enlighting and soothing. Everything unfolds as it should – if only we could let it.

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