The colony of grey-headed flying-foxes at Ballarat's Botanical Gardens is reducing in number as cooler weather sets in.
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Five hundred of these big bats were present in early April, then 250 later in the month, and 85 in early May.
At one stage, they were occupying ten different trees, but now just three trees are involved.
April is the usual month for dispersal to winter roosts.
READ LAST WEEK'S NATURE NOTES HERE: Why Ballarat's tree violets are not a tree or a violet
The wide wings of the grey-headed flying-fox are thin and uninsulated, and susceptible to hot and cold temperatures.
The Ballarat animals have been warming themselves on sunny mornings by expanding their wings to gain solar heat.
They have yet to experience a frost here, but a large colony in Bendigo has several frosts each year, apparently with no effect.
As well as the increasing cold, another contributor to the decline of our local colony is the fact that most local fruit trees have finished producing, leaving the bats with less food.
Habitat loss, and heat in northern colonies, have been attributed to the bats' movement to new sites - such as Castlemaine, Malmsbury and Hamilton, as well as Ballarat - this year.
While the Ballarat animals have used mostly deciduous trees for roosting, cypresses have been used elsewhere.
- Got a question for Roger? Use the form below, or send your question to rthomas@vic.australis.com.au, or send to Roger Thomas at The Courier, PO Box 21, Ballarat, 3353.
