Greg and all,
There was a fairly long discussion around these questions in March
2002 - should be in the Birding-Aus archives. Apparently HANZAB
mentions Glossies feeding on the seeds of Swamp Oak (C. glauca) but
this seems to be only a rare thing. Looking at measurements of the
seed cones, River Oak has the smallest cones, Swamp Oak a little
larger, and slightly larger again (but smaller than other
Allocasuarinas) is A. diminuta which the Glossies feed on in the
Dubbo area. However, the late Judie Peet suggested that it's not the
cones that are too small for the glossies, but the seeds. She wrote:
"River Oak seeds are really tiny, less than 1/2 the size of
A.diminuta seeds which come from a cone of only about 10mm long.
Getting at River Oak seeds would be a lot of energy output for little
return."
Judie also observed that Dubbo Glossies differ from Glossies in other
areas by holding the cones at the stem end when feeding (as opposed
to the distal end). She had a theory this habit developed in response
to having to feed on the tiny cones of A. diminuta.
One of the main distinguishing features between Casuarina and
Allocasuarina is in fact the seeds, which are dull and pale in Cas.,
black and shiny in Allocas. Red-browed Finches often feed on the
seeds of River Oak (Cas. cunninghamiana). I suspect Judie was right
about the size of the seeds.
Cheers,
Carol
At 7:49 PM +1100 3/4/08, Paul Burcher wrote:
Greg
I think the fruits (?and hence the seeds) are too small. Also swamp
oaks grow on very poor saline soil so the nutrients are pretty low.
Similarly River Oaks grow on recent alluvium which also may be poor.
There is some paper somewhere about them choosing those fruits with
amongst their locally favoured Allocasuarinas that have a higher
nutrient content.
Paul
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