Tuesday, March 22, 2011

Why is the tiercel taking care of the eggs?

If you were watching the UStream camera feed yesterday from the Franklin Institute, you may have noticed that for most of the day, it was the tiercel (dad) who was sitting on the nest taking care of the two newly laid eggs.

Where was the formel?  What was she up to?

John Blakeman shares some fascinating insight into the psychology of the hawks at this crucial time of egg laying:
"The tiercel's lengthy sitting upon the eggs (but it's not incubating yet at this early stage with another egg yet to come) is of no concern. Neither bird is yet in full incubation mode, especially the female. She almost surely has a third egg growing and descending her fallopian tube. She's already produced two eggs, which are physiologically demanding enough. She loses a lot of serum-mobilized fats, proteins, and some carbohydrates, along with an egg-full of plain water in the production of each of those first two eggs. Producing a third egg is particularly demanding, both physiologically and psychologically.
Frankly, she's just in no mood to be sitting around on the nest on eggs. It may be far more comfortable to be standing, to allow gravity to assist in the flow of the new, last egg down the fallopian tube. If she could have been seen today by any of us familiar with the distress formels express when making eggs --- especially the third and last one --- her attitude would been apparent. She sits with a subtle attitude of stress. She would be less alert, and slower in reacting.
She's eager to get that last egg formed and laid. When that happens, when she's relieved of the stress of egg formation, everything will change. Incubation will begin in earnest, with a profound compulsion by the formel to sit tightly and convey lots of body heat to the eggs across her naked brood patch under the feathers of her belly.
The tiercel, like fathers everywhere, just scratches his head trying to figure out the anomalous behaviors of his "eggnant" mate. Dutifully, he sits over the eggs and protects them. He'll be relieved when he can head off each morning to hunt for both his mate and himself. He's not much of a "nest husband." He really wants to be out there hunting and killing things for his mate. And his mate, when the last egg starts to descend into the internal cloacal space, will have a tremendous compulsion to get on the nest and begin another year incubating eggs and raising eyasses."
--John Blakeman


  1. John Blakeman always comes thru for us with wonderful information about the hawks. I love his word "eggnant". And thanks to sunny for keeping the blog going & up to date. J. Wlodek aka colibri or coli on chat

  2. Eggcellent piece of information.
    Once again, thank you John for keeping us informed.
    I eagerly await to hear more.

  3. I have to echo the thanks, to you, Della, for this great blog, to John for sharing his vast store of information, and to Kay for her incredible photographs. And, of course, to the Franklin Institute. Looking forward to "hawk season" keeps me going through the depths of winter.

  4. Wow John such wonderful information...so in keeping with the Franklin Institute. I'm looking forward to this being as exciting as the many eaglecams watched...But this even more so since I was raised in N.Philly and live in Bucks..
    Again so many thanks for what you do.