Re: Long, long last gasp. (fwd)

[Dann Pigdon <dannj@alphalink.com.au>]

John Bois wrote:
> 
> If they come together in very large colonies at one time then they are an
> ephemeral resource (from a predator's perspective).  But what I'm not
> understanding is how, in normal times and population densities they avoid
> predation.  And, if they are accessible (because they're flying about in
> daylight--and, in any case don't seem to have a very effective hiding
> place) why they don't fuel a population explosion in predators?

For a start, a grey-headed flying fox (the most common and wide-spread
species) is quite a large animal. Not every raptor or python is up to
the challenge. Their eyesight allows them to spot predators before they
get too close, and living in large groups (ie. thousands strong even
outside of breeding times) makes for a excellant early warning system.
They are in constant communication with each other - to the point of
being deafening to us humans. In fact, in behaviour they're not unlike
flocks of parrots.

Where they damage valuble trees in botanic gardens (from sheer weight of
numbers while roosting), one method of encouraging them to move
elsewhere has been to make a lot of noise (banging metal garbage bin
lids has been popular). I never understood this strategy - a colony
makes a hell of a lot of noise at the best of times, so obviously they
can tolerate it. Needless to say, this method of dispersal never works.
Culling is out, since they are a protected species (and bio-terrorists
have threatened to poison one hundred-year-old tree in the Royal Botanic
gardens for every f.fox killed). Garden staff are thinking of capturing
as many animals as possible and relocating them to a new area a few
kilometres away, in the hope that as gregarious animals they will form a
new colony there. I don't fancy their chances of success.

> So what's going on?  Why are they extending their range and why do they
> seem to be unchecked?  I lived in Melbourne from 1950 until 1976 and
> didn't see a single flying fox.  

Many Melbournians still don't know they are around. Unless you know what
to look for, or have a large fruit or flowing tree in your backyard, you
may not get the chance to see them. In only live about 10 km from the
central business district (close to where the main colony is) and even I
don't see them every night. Now that the fig tree in the back yard is
almost ready to fruit, they have begun visiting again. I disturbed one
in the tree itself a few nights ago.

Keep in mind that I have NEVER seen a common pigeon anywhere near my
house, yet a quick trip into the city will reveal populations more
numerous than those of the f.foxes. I suppose you have to be in the
right place at the right time. :)

> How have they been able to manage this
> invasion?  Sounds like predator extirpation to me.  Or are we supplying
> them with better fruit now in Victoria.

One reason for extending their range may be that population levels
(fueled perhaps by fruit orchards to the north) are increasing to the
point where they must migrate to new areas. I don't buy this though.
They prefer native trees were possible, and in the wild tend to feed
more on nectar than on fruit. Raiding fruit orchards is an act of
desperation in areas where native trees have been felled.

I think it's more likely that f.foxes existed in temperate areas all
along, and were driven out by forest clearing for agriculture and
grazing early on. Now that the political climate has changed to one of
conservation and active revegetation, conditions may have improved
enough for them to return. They also require large trees in abundance to
roost, so maybe trees have now grown large enough after earlier forest
clearing to sustain them again.

At nights they spread out into the surrounding suburbs looking for food.
Backyard fruit trees, along with trees that flower outside of fruiting
times, seem to sustain them quite well. The colony increases in size
every year (usually by a few thousand animals).

I suspect that predators have as little effect on a well-established
f.fox colony as they do on city pigeons (even New York city has a
healthy population of raptors that prey on pigeons). Factor in
accidental (and deliberate) death by humans, and disease, and you'd
wonder how any species can survive in a large city. Yet f.foxes,
pigeons, rats, brush-tail possums - even foxes - manage to maintain
large populations in major cities. That's adaptation for you...

-- 
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Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
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