I wonder if the changes observed are a result of habitat clearance and
degradation more than just climate change.
Plumage coloration, moulting and body growth are all energy-intensive
processes. Food is the main source of energy for these processes. If there
is widespread habitat clearance and degradation, then maybe the amount and
quality of food available to birds is becoming more limited, in turn
limiting body growth and plumage coloration.
Moreover, in species that exhibit brightly-coloured plumages, those
individuals with the brighter and longer-lasting coloured plumage are
usually healthier birds (better nourished, lower parasitic loads, fewer
diseases). In other words, the bright plumage is a visual cue to
conspecifics of a bird's relative fitness and ability to breed. Perhaps the
smaller sizes and less bright plumages are a sign that birds are becoming
less healthy because of the extensive degradation and clearance of their
habitats.
Just a thought...
Regards,
Stephen Ambrose
Ryde NSW
>> Laurie Knight wrote:
>>
>> http://news.bbc.co.uk/earth/hi/earth_news/newsid_8560000/8560694.stm
>>>
>>> Climate linked to smaller birds
>>> By Matt Walker
>>>
>>> Editor, Earth News
>>>
>>> Songbirds in the US are getting smaller, and climate change is
>>> suspected
>>> as the cause.
>>>
>>> A study of almost half a million birds, belonging to over 100
>>> species,
>>> shows that many are gradually becoming lighter and growing
>>> shorter wings.
>>>
>>> This shrinkage has occurred within just half a century, with the
>>> birds
>>> thought to be evolving into a smaller size in response to warmer
>>> temperatures.
>>>
>>>
>>>
>>> <snip> ===============================
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>>> birding-aus.blogspot.com
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