Silver Gull Aerial Predation

To: "'michael norris'" <>, "'birding-aus'" <>
Subject: Silver Gull Aerial Predation
From: "Jon Irvine" <>
Date: Fri, 10 Dec 2010 09:08:57 +1100
Hi Michael,

It is interesting to note your take on this behaviour and whether it is
"natural" or influenced by human activity. I agree that light pollution and
gulls are a problem in our cities but last night's activity was based over
an area which is not affected by light pollution and the sun was only just
setting. The insects seemed to be emerging from areas of mangroves and the
gulls appeared en masse for approximately 10 minutes and then dispersed
again, before it was dark. I've seen other mass feeding events like this by
Silver Gulls during the day, for instance, when a very high tide flushes
leaf debris down the creek, the gulls sit on the water and pick over the
floating leaves for insects. This appears to be purely opportunistic
behaviour in that a few gulls start off feeding and, by doing so, gain the
attention of other gulls in the area that then come and join in.

>From an ecological perspective, I think the issue of "problem" gulls is a
complex one. Our pair of nesting sea-eagles certainly take advantage of the
gulls nesting on the sunken barges in the bay. There is no doubt that if the
barges and human food sources were not there, there would be far less Silver
Gulls in the area, but, as we have witnessed over the past three years, when
the eaglets are between 6 and 10 weeks old, Silver Gulls (adults and
full-sized immatures) form a large and important part of their diet. 

Jon Irvine

-----Original Message-----
From: michael norris  
Sent: Thursday, 9 December 2010 11:22 PM
To: Jon Irvine; 'birding-aus'
Subject: Silver Gull Aerial Predation

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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