birding-aus
Hello All,
I posted a request for information about the Grey Butcherbird in respect of
the book being prepared on the Canberra Ornithologists' Group's, Garden Bird
Survey (GBS) and got heaps of replies. Thanks for that.
Now I have a specific question about the Laughing Kookaburra. It concerns
whether they compete successfully for nesting hollows against other birds. I
would imagine that they would be a formidable adversary for any other
species coveting the same hollow. However I may be entirely wrong. Do people
out there have any suggestions or insights on this? I'll explain the basis
of the question.
What is clear from the GBS is the significant decline in abundance of the
Laughing Kookaburra, over the 16 years of continuous duration of the survey
(data compiled so far is over 42000 records contributing to monthly
abundance counts of all species from July 1981 to June 1997). There is
nothing unusual about declines, increases and fluctuations for the whole
range of species but this one is harder to explain than most. It is hard to
imagine any human impact or any survey bias as contributing to that effect.
I can't think of any species that is a food competitor that has increased.
(Butcherbirds are much too rare to be a factor and the Pied Currawong status
has also changed but that is quite a complex story.) There is a possibility
that its decline may be due to it not competing well, for access to nesting
hollows with the King Parrots, Crimson Rosellas and Common Mynas, all of
which are now common here and all of which have simultaneously dramatically
increased their populations.
Can people shed some light as to which of these species wins out over nest
site competition?
This species also has a most peculiar annual pattern of abundance with two
peaks and troughs each year. This is unusual but it appears to be very
regular and very smooth, so presumably a real effect. The amplitude is
small, from a high in February, declines to a low in March then increases to
August, declining again to a low in November, then increasing to February.
The low spring and early summer pattern is probably due to birds breeding at
that time and tending to move away from suburbs and into the bush, or even
birds on nest not being counted. The April to June drop could be from
dispersal of young birds. As most records are counts of family groups, is
that a reasonable interpretation of the data?
If anyone has any comments can they send them to me please. Any good ideas
may possibly be published.
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