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egg-sposure (was Re: egg laying rates)



Greg Paul (GSP1954@aol.com) wrote:

] I do not know of any bird that leaves its eggs exposed for more than
] a few minutes.

Ken Carpenter (crpntr@ix.netcom.com) responded:

} Sorry, not true.

I presume Ken meant only that some birds do leave their eggs exposed
for more than a few minutes (since I think we can all agree that Greg
knows what he knows better than Ken knows what Greg knows ;-) Sorry,
Ken, I'd have let that go, but Ron Orenstein (ornstn@inforamp.net)
gave me the opportunity to jump in when he came back with:

> Actually this is true for a number of precocial bird species;

I don't think Ken is arguing that it's never true -- he's only arguing
that it sometimes isn't.  Out of curiosity, Ron, how long does a bird
have to be away from its nest in order for a parasitic layer (e.g. a
cuckoo or a cowbird) to sneak in and lay one of its own?  And how long
does a bird have to be away from its nest for an African egg eating
snake to get in and devour the eggs?  I suspect that Greg's "a few
minutes" is too restrictive since the above-mentioned events occur
frequently enough for the animals in question to rely upon them.
Several minutes might be more accurate, don't you think?  Even using
your argument:

> it is a quite necessary adaptation for birds whose young leave the
> nest on hatching.

I think the birds could be away from the nest for several minutes.
Precocial birds don't just poof out of their eggs like Athena from
Zeus' head...  Anyway, if I'm reading you right, I suspect that most
such birds have some level of awareness as to when their eggs are
going to hatch and can modify their nest sitting behavior accordingly
(i.e. they don't have to monitor the eggs as closely just after the
eggs have been laid since at that time they're in no danger of the
eggs hatching unwatched).

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)