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I'm with Denis on this. This sort of behaviour is fairly common.
Cases like this include things like sharks and gannets pursuing shoals of
fish, butcherbird and falcon pursuing the same small bird, etc. There is no need
for either species to be benefiting the other as an intention, indeed the
suggestion is rather odd. They are competing. Even though it is likely that
either will be more successful than they would without the other, because of the
escape attempts from the prey. When two hunter species are after the same prey
using different strategies, each tending to pursue the same prey in opposite
directions (towards the other) that can result in easier hunting for both
or maybe just one.
Philip
Hi John and others.
For what it is worth, I cannot support any
theory of altruism on the part of the Cormorants.
Intra-species co-operation yes. But
inter-generic altruistic behaviour?
I don't think so.
Opportunism of the Egret (Big Storky)?
Yes.
My brother Brendan recalls
seeing similar "co-operative fish-herding behaviour" on the Coast between a
flock of Little Black Cormorants. In that case, a "Reef Heron", (a.k.a.
Eastern Reef Egret (Grey Morph) (Yuck - do I really have to?) acted as
opportunist, on the rocks above the inlet. He reports that it caught 5 fish,
while the Cormorants were doing their fish-herding. Easy to explain that as
learned behaviour, or opportunism, without giving credit to the
Cormorants.
Can I please obtain a dispensation (from the
Nomenclature Nazis) to call them Reef Herons in future?
Cheers
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