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View Full Version : Egg-laying in chickens vs. other birds


MikeS
12-08-2006, 01:48 PM
My GF and I were discussing eggs the other night, and the following question came up: Why is it that chickens lay one egg per day, continuously? Other birds don't, as far as I know.

The theory I came up with was that birds lay eggs until they have a certain number in their nest, and then something hormonal causes them to stop laying and start incubating; it's just that we steal chickens' eggs, and so they keep laying and laying. But would this imply that if I stole a sparrow's eggs, it would keep laying and laying as well -- is this true?

And what role do the males play in all of this? I know that the chicken eggs you buy in store are usually unfertilized; do other species of birds habitually lay unfertilized eggs?

Any enlightenment from ornithologists or other naturalists would be much appreciated!

bouv
12-08-2006, 01:52 PM
Selective breeding, I'm guessing. Same reason dairy cows produce milk all the time, and not just when pregnant and nursing.

Q.E.D.
12-08-2006, 01:55 PM
We just did this thread a couple weeks ago. As bouv states, it's basically selective breeding at work. Wild birds, even close relatives of domestic chickens, only rarely lay infertile eggs.

Q.E.D.
12-08-2006, 01:59 PM
Found it. Here (http://boards.straightdope.com/sdmb/showthread.php?t=396812) is the previous thread on this topic.

Colibri
12-08-2006, 02:07 PM
The theory I came up with was that birds lay eggs until they have a certain number in their nest, and then something hormonal causes them to stop laying and start incubating; it's just that we steal chickens' eggs, and so they keep laying and laying. But would this imply that if I stole a sparrow's eggs, it would keep laying and laying as well -- is this true?

This is in part the case. Birds will often keep laying until they have completed their clutch. If you remove eggs, they will lay additional eggs in an attempt to complete the normal clutch of the species. Unlike in domestic chickens, however, this won't go on indefinitely. Eventually the female won't be able to keep up with the high energy demands required to produce more eggs, and will shut off production. She may also stop for hormonal reasons.

I once had a pair of Zebra Finches I got from the psych lab at my university that had been used in behavioral experiments. I don't know that that was the cause, but the female was behaviorally screwed up. She would lay an egg in her nest, then within a day I would find it on the cage floor - she wouldn't incubate. But she just kept laying an egg every few days until she became exhausted and lost all the feathers on her head. She finally stopped.

And what role do the males play in all of this? I know that the chicken eggs you buy in store are usually unfertilized; do other species of birds habitually lay unfertilized eggs?

As has been said, although other birds will sometimes lay unfertized eggs by accident, the readiness of domestic chickens to do so, and to continue to lay indefinitely, is a selected trait.

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