In response to Michael's request for poison impacts on raptors, I have the
following information which was provided by raptor researcher Dr David
Baker-Gabb recently.
Makes useful reading on this issue.
cheers, Martin
Martin O'Brien
Wildlife Biologist
Threatened Species & Communities Section
Department of Sustainability and Environment
2/8 Nicholson St. (PO Box 500), East Melbourne 3002
Tel: 9637 9869
~~~~~~~~~~~~~
A. Poisons and raptors
Whistling Kites are vulnerable, but they are not the only species of
raptor that regularly eats carrion in Victoria. As a general rule,
raptors eat more carrion in autumn-winter when food can be scarce, and
prefer live prey in spring-summer (all those young rabbits, mice, birds
etc ). Moreover, in autumn, territory boundaries break down and juveniles
disperse in many species, meaning that many more birds are roaming over
wider areas and could be impacted by a poorly conducted poisoning
campaign. Hence poisoning campaigns in winter have the most potential to
inflict secondary poisoning casualties on raptors.
Whistling Kites forage/hunt by flying long transects looking for carrion
and small live prey. They generally fly higher than other raptors such as
goshawks and falcons, and keep an eye out for other kites or ravens
spiralling down to something interesting. As such they behave like
vultures in Africa and Asia. In this way, numerous birds can be "pulled"
into a single carcass. If this dead animal has been poisoned, then
several kites (eg 20+) can be exposed to secondary poisoning from a single
carcass. Whistling Kite numbers plummetted after the 1950s in southern
Australia when myxomatosis reduced rabbit numbers and pesticides such as
'Lucijet' became widely used on sheep carcasses to poison foxes, crows and
eagles. With the banning of such pesticides and more responsible
approaches by farmers, Whistling Kite numbers have partially recovered in
southern Australia.
Black Kites hunt/forage in a similar way to Whistling Kites, and are
similarly vulnerable to poisoning, but they are relatively uncommon in
Victoria, being mostly confined to the north-west of the State. Black
Kites could be poisoned during mouse plague control works or inappropriate
locust control works in the north-western wheat country.
Wedge-tailed Eagles routinely eat carrion, and I am sure that in your
travels you would have seen a dead one or two on the side of the road that
got clobbered by a car when feeding on a road-killed kangaroo or some such
delicacy. Wedgies hold large territories (eg 5km between nests) and so any
poisoning
activity is likely to only kill at most one pair of adults and possibly a
few roaming juveniles. Hence the impact on this species is likely to be
less than on Whistling and Black Kites.
Swamp Harriers eat a fair bit of carrion in autumn-winter. Tasmania is
the nation's stronghold for this species, and most of these birds migrate
to the southern mainland in autumn and return to breed in Tasmania in
spring. Poisoning campaigns in autumn-winter, particularly within 2km of
wetlands, could have an impact on several of these birds. For example, I
have recorded c.6 Swamp Harriers, 10 Whistling Kites and 20+ ravens
feeding from a single swan carcass over 2-3 days at Werribee.
White-bellied Sea-Eagles (threatened in Victoria) eat carrion, mostly dead
fish, but sometimes dead stock and rabbits, again mainly in winter. In
Victoria they live along the far eastern coast and the Murray River and so
only poisoning campaigns in these areas could have any possible impact on
them.
Brown Falcons eat carrion fairly often in winter. I have caught >20 in my
traps baited with dead rats and rabbits at Werribee.
Most other species of diurnal raptor have been recorded eating carrion,
but it is a rare event, and not generally an issue for poisoning
campaigns.
B. 1080 and birds
I think that you can discount the possibility of 1080 secondary poisoning
having any impact on owls as they hardly ever eat carrion.
There are some papers in the 1980s by McIlroy in 'Aust. Wildlife Research'
that later became 'Wildlife Research' on the susceptibility of raptors to
1080. In general they are not as susceptible as mammalian carnivores.
1080 used in meat baits for wild dogs may kill the odd Wedge-tailed Eagle,
but not much more than that. Whistling Kites and other susceptible
species are uncommon to rare near the upland forested areas where 1080
meat baits are broadcast.
The main area of possible concern is with secondary poisoning from rabbit
baiting in farmland, though I know of no cases of multiple poisoning from
this cause (which does not mean that it has not happened, but it is
probably rare). I don't know that it is an issue for raptorphiles to get
unduly concerned about. I am fairly confident that current modes of 1080
use are not a threatening process for raptors in Victoria.
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