G'day Michael and all
There were some studies in the UK which stated
that chemicals in unleaded petrol were the villains behind the insect reduction
in big cities in the UK (I'm not so certain that this study is widely
supported or not). It may be that we're experiencing the same thing here. The
study which I mentioned in the previous posting involved a hell of a lot of work
on insect populations, life cycles and sparrow diet (anyone who has read
the paper would agree that the author deserves a medal for her ability to
observe the minutiae and wade through so much sparrow faeces). Sparrows may be
primarily granivores, but they do supplement with insects and insects play an
important role in raising young too.
I still don't think that it
is correct to cite a small population of raptors such as Collared
Sparrowhawks as being responsible for declines in birds. Especially, as
I mentioned in an earlier posting, that we have to take into account
that there are many more raptors in the country towns where sparrows thrive.
Neither sparrowhawks, or any other
raptors, are widespread enough in urban environments to account for the
massive and almost uniform disappearance of sparrows.
Importantly, the role of sparrows, along
with doves and pigeons, in most ecologies where they naturally occur
is to be food for raptors. Therefore, they have all of the breeding, clutch
size, behavioural and social patterns well in place to deal with a couple
of local sparrowhawks and then some. What sparrows might not have is
the ability to deal with some kind of change in local environments which does
not favour them in some way or may expose them to levels of predation which is
unprecedented for them. In this case, it could be a combination of environment
or competition of some kind and raptors but it would be one of the most unlikely
of scenarios that raptors alone are playing a significant role in the
demise of the House Sparrow.
Sparrows aside, half your luck for having a
breeding pair of Collared Sparrowhawks nearby.
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