Michael,
I agree that the availability of rubbish leads to over abundance of many
species, particularly at land fill sites. Although if the rubbish were to
disappear over night (or even over a longer period as silver gulls can live
~30 years) it would probably result in prey switching by the scavengers.
This may result in depleted insect and other prey taxa numbers while the
scavenger numbers correct themselves. THe birds may also become aggressive
as food resource become more limited. As some one else pointed out reducing
silver gull numbers may also impact on other fauna (notably predators
feeding on silver gull and other species competing for the same resources)
now dependant on the over abundance species as a food resource.
It is an interesting problem, but not one with an easy answer!
Cheers,
Ben
Date: Thu, 9 Dec 2010 23:21:40 +1100
From: "michael norris" <>
Subject: Silver Gull Aerial Predation
To: "Jon Irvine" <>, "'birding-aus'"
<>
Message-ID: <
>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Hi Jon
No - it's not good to see them catching live prey, especially at night.
German research has indicated, if not proved, that light pollution has
serious effects on insect diversity and abundance. For instance, the "vacuum
cleaner" impact sucks insects into the light and, for some species where one
sex does not fly, this means the potential partners die in disproportionate
numbers when they are killed by bats... and silver gulls....
And why are the gulls feeding on live prey? Because their vastly increased
numbers, and now all-year round breeding, in urban areas as a result of
trash means there are many more individuals short of day time food that need
to hunt at night.
I guess we agree the trash is the issue to be tackled. Ian Temby's work on
silver gulls in Melbourne includes accounts of roof top nests surrounded by
chicken bones. And estimates the damage caused by their excretions etc in
the millions.
Michael Norris
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