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Re: egg-sposure (was Re: egg laying rates)



 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?

Good questions, and while I'm away from home I can't check the answers.
However, I do know that brood parasites will often mount watch over suitable
nests waiting for an opportunity to slip in and deposit an egg, so a few
minutes may well do the trick.  As for egg-eating snakes, many snakes will
attack a nest with the parents still there and simply ignore their attempts
to drive it off.  Certainly egg-swallowing is not a rapid process and the
snake cannot carry the egg away first, to my knowledge.

>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... 

The point I was making is that such birds actually avoid brooding so that
the eggs will hatch simultaneously - this does not mean that they ignore the
nest altogether or do not guard it against predators.  Some birds can
disguise the nest quite well (eg by pulling water weeds over it as grebes
do), or rely on superb camouflage (many shorebird nests aer extremely hard
to spot because the eggs match the background so well).  If this fais the
birds may rely on "broken-wing" acts to lure predators away.

 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).

Possibly, but it could simply be that the brooding stimulus does not kick in
until there are no more fully formed eggs left in the oviduct.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net
Office: 130 Adelaide Street W., Suite 1940    
Toronto, Ontario Canada M5H 3P5