birding-aus

RE: nocturnal migrants

To: "" <>
Subject: RE: nocturnal migrants
From: "Conole, Lawrie" <>
Date: Thu, 16 Oct 1997 14:23:58 +1000
> 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 .........

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