> 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.
>
I'm not sure about the Little Bittern, but it could be argued that the
White-throated Nightjar moves into a region where it has few serious
competitors for food other than insectivorous bats. There are fewer
species of microbats down south, though perhaps not significantly fewer
individual bats. Temperate zones however have a plethora of generalised
small microbats, and few species of medium-large microbats (no Ghost
Bat, few or no sheathtail-bats, only one big freetail-bat) which might
otherwise be the main competitors with nightjars for large flying
insects.
Just a thought .........
===============================================
Lawrie Conole Newsletter Editor
2/45 Virginia Street The Australasian Bat Society
Newtown 3220 ph BH +61 (0)3 9669 9732
Victoria fax +61 (0)3 9663 3669
AUSTRALIA ph AH +61 (0)3 5229 4037
ph MOBILE +61 (0)419 588 993
===============================================
|
