At 14:00 16/10/97 +1000, John Leonard wrote:
>Tricky question here:
>
>Why do certain noctural birds migrate south in summer (I'm thinking of
>White-throated Nightjars and Little Bitterns, there may be other examples)?
>
>Because in doing so these birds are moving into areas where the biological
>productivity is likely to be lower, and the nights shorter, at a time when,
>as they are breeding, they are in need of more food.
>
>
John
here's my 2c
I think that its more complex than simply
tropics=plentiful food,
temperate = less productivity.
For example, my work on Noisy Pitta breeding showed that in Cape York
the breeding season was shorter, and with smaller clutches of eggs,
than down in NSW/sthnQLD. Part of the reason might be that in the
tropics - the rainfall is v.high but for a restricted season while
in the temperate areas there is a much longer period of productivity.
What is the limiting factor for productivity - temperature or moisture,
I think its more often moisture .... unless you're in the ACT!
peter
Dr Peter Woodall email =
Division of Pathobiology
School of Veterinary Science Phone = +61 7 3365 2300
The University of Queensland Fax = +61 7 3365 1355
Brisbane, Qld, Australia 4072 WWW = http://www.uq.edu.au/~anpwooda
"hamba phezulu" (= "go higher" in isiZulu)
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