How Can They Sit For So Long?

Dorothy asks E2 to get up so she can resume incubation (photo from the National Aviary falconcam at Univ. or Pittsburgh)

During courtship E2 is very active but now Dorothy has to plead with him to get up off the eggs.  Dorothy herself is able to sit for 12 hours in a snow storm.  How do they do it?

How do birds instantly switch gears from the frantic activity of courtship to sitting on eggs all the time?

They’re cued by hormones.  Here’s how:

  1. As day length increases after the winter solstice, a bird’s hypothalamus releases LHRH (luteinizing hormone releasing hormone).
  2. LHRH triggers the pituitary gland to release LH (luteinizing hormone).
  3. LH increases production of testosterone in males and progesterone in females.
  4. Testosterone triggers aggression, territoriality and sexual behavior.  It’s good at the start of breeding but doesn’t help raise a family.
  5. Progesterone is the “pregnancy hormone” that induces egg production.  It’s only needed for a short time since female birds are only ovulating and pregnant until they lay the eggs.
  6. On the day before incubation begins the hormones switch.  Prolactin, the hormone that promotes incubation behavior, rises sharply while the other hormones suddenly decrease.  In females, LH and progesterone drop off.  In males, testosterone has been dropping since egg laying began.  If the male shares incubation he has a sharp rise in prolactin, too.  On a graph this hormone switch looks like a sine curve.  There’s a moment where all these hormones are low, then prolactin takes off.

In peregrines, both parents have to be ready to incubate at the same time.  Their courtship rituals help get the couples’ hormones in synch.

This whole process may sound as if birds are at the mercy of their hormones but in every species reproduction is chemically tuned for success.  In humans for instance, progesterone and prolactin switch after delivery so that the mother’s body produces milk to feed the baby.  Individual animals whose hormones malfunction do not have live offspring.

So how do birds incubate so nicely?  In a word, prolactin.


(photo of Dorothy and E2 from the National Aviary falconcam at the University of Pittsburgh.  Today’s Tenth Page is inspired by page 448 of Ornithology by Frank B. Gill.)

10 thoughts on “How Can They Sit For So Long?

  1. Kate – In Rochester NY we have one tiercel servicing 2 females at different sites. Last year only 1 site produced a single offspring, but the female at the site south of downtown was a subadult. This year again both are being courted by the male, and he is copulating with both. Are the hormones in sync for all three? Can the prolactin switch be delayed if one female lays eggs and the other has not yet? In Toronto this tiercel’s father has successfully produced eyases at 2 different sites.

    1. If his father did it he probably can too. The real problem is that he has to court both females enough that their hormones get going. Not sure if he’s doing that well this year.

  2. I agree Kate, DC is young and not mature enough to handle both females. His father Jack didn’t start with 2 females until he was 7, so he had some experience by then and now is a good provider for both nests. I think Beauty and Pigott are both stressed especially after yesterday’s encounter with Pigott being DT and IN beauty’s nest. Not sure how this season will turn out but I believe Beauty is holding off on egg laying. She should have been ready by now. I’m no expert but just going by past history. DC has been stealing food from Beauty and bringing it to Pigott, (not good courting, if you ask me). I would be very surprised if both P and B lay eggs, hatch and DC provides for both at the same time. Will be an interesting learning tool in Rochester! Thanks for the great info, as always!

  3. Hi Kate. I have a question please. Does the age of the male (sub-adult) contribute to the amount of hormone he has? Does hormone production increase each year as the male grows older? Does the male learn incubation from the female or is it in the amount of hormones he produces? How much of their behavior is instinct and how much is learned? Yes, you are correct, that is more than one question. Thank you.

    1. Great questions, Cheryl. My knowledge of hormones is limited so I’m going to ask a bird biologist.
      Meanwhile, on your last question I have an opinion:
      Question: How much is instinct and how much is learned?
      My answer: The more we study this the more the instinct/learned continuum changes. There was a time when science said that animals didn’t think or have emotions & that they did everything by instinct, but now we know that corvids plan ahead and elephants mourn. Even if I had an answer from scientists today it could change in a few years.

    2. Cheryl, Dr. Anthony Bledsoe, who specializes in bird biology at the University of Pittsburgh’s Dept of Biological Sciences, provided some answers with this caveat: that he does not have much endocrinology training, and doesn’t know if research has been done in this area with Peregrine Falcon.

      * Does the age of the male (sub-adult) contribute to the amount of hormone he has?
      Probably. However, I think the males are reproductive at one year of age, and if that’s the case, then they would have normal hormones amount required for reproduction. [NOTE from Kate: Louie in Downtown Pittsburgh was reproductive at one year of age. He fledged 4 young with Tasha in 2003.]

      * Does hormone production increase each year as the male grows older?
      Not sure. I do know, however, that really older females increase testosterone production. We know this because, occasionally, older females exhibit male-like plumage attributes, which strongly suggests high testosterone levels.

      * Does the male learn incubation from the female or is it in the amount of hormones he produces?
      Almost certainly the latter [the hormones].

      * How much of their behavior is instinct and how much is learned?
      This is complex. For many behaviors in species well studied, both instinct and learning are involved.

  4. All such interesting information. I have a question, Kate. (surprise there…I know) D.C.’s dad Jake had 2 females. Do the offspring learn the 2 female behavior from the parent, or is it just something that happens?

    1. Birds learn from their parents. I imagine he observed his father & drew his own conclusions.

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