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Hi Roger,
Halfway through answering you I stopped to
check some of my references. This particular detail is not well covered in basic
ornithological textbooks that I have just looked at. This is not a comment about
Black-shouldered Kite, any more than any other
bird. HANZAB says for it that "copulation appears to
occur mainly during nest building". I would suggest to you that within a time
frame of days, copulation and laying events would be simultaneous, as in mating
would occur over the same set of days as egg laying and starting incubation (in
the case of raptors). This is why in my GBS Report breeding graphs, the timing
occurrence of copulation is grouped with the timing occurrence of nest building
and display. Birds will copulate several times over the egg laying period. Some
eggs will be fertile and others not. If your question is prompted
by wondering whether the copulation period precedes the egg laying period
by a significant amount, (in the way that copulation period precedes the birth
for mammals), the general answer is no it doesn't or not by much. Copulation may
start with courtship, whereas nest building may take several days. It is the
availability of the finished nest and the condition of the female, that would
determine laying time. The earlier copulations are probably recreational. This
would probably be pretty much the same for all birds unless there are birds (and
there may be), in which females have the capacity to store sperm (as some bats
do). As birds have a cloaca, I wonder how they would. Egg
production in birds is relatively quick and is nothing like a gestation period
in a mammal. It would not surprise me if Kiwis, that lay huge eggs
are slower than average. Of course some birds like copulating at times that
have little to do with egg laying.
Then again you actually asked about the timing of
sitting on eggs. This is one further step away from the timing of mating.
Most birds wait until a clutch is complete, before starting incubation. This way
all chicks hatch at about the same time. Most raptors (and presumably the BsK)
don't do that, starting incubation with the laying of the first egg. That way
the chicks hatch asynchronously and the last hatched tends to have a hard time
of surviving. I'm not sure what Black-shouldered Kites do. Maybe HANZAB can fill
in on that (though I can't see that mentioned).
Philip
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