> On Thu, 19 Jun 1997, Alex Appleman wrote:
>
> > Following on from Shane Raidal's commemts; raptors are hardy critters and
> > also
> > intelligent. There is evidence in North Queensland of black kites preying
> > on
> > the dreaded cane toad, flipping them over and feeding the legs and soft
> > underbelly to their chicks, avoiding the poison glands. We can only assume
> > that the kites ate poison in small doses, identified which part of the toad
> > was toxic
> > and are teaching their offspring how to avoid them.
Taylor writes:
>
> There is a summary of what is known about Cane Toads's effects on
> the Australian biota is a chapter in Mike Tyler's Australian frogs.
> He notes deaths of Kookaburra, a Crow species and two Bittern
> species as recorded as being killed by eating Cane Toads.
> This list probably reflects most the poverty of the data that
> Tyler could find.
>
> He also notes a number of bird species recorded as successfully
> preying on toads including Tawny Frogmouth, Whistling Kite,
> Ibis, Cranes, Swamp Hens and Herons.
>
> Mike Tyler also notes some native frog species posssess poison
> glands and native predators avoid these.
>
> So some possibilities are:
>
> a) Black Kites pre-Toad feeding techniques don't expose them to
> much toad toxin. Certainly if they don't tackle live toads their
> risks are reduced.
>
> b) Black Kites could (pre-Toads) detect and avoid the toxins. Cane Toad
> secrete cocktail of chemicals. Some of these chemical are only found in
> toads but perhaps Black Kites already could detect and would avoid
> one of the cocktail components.
>
> c) Black Kites have (pre-Toad) techniques for eating poisonous native
> frog species which have also allowed them to eat Cane Toads.
>
> d) New techniques were "discovered" by Black Kites (or other raptors)
> which allow them to eat toads and these have been communicated by
> observation among Black Kite populations.
>
> e) Immigrant Black Kites from Asia where Bufo species are native
> have brought suitable toad eating techniques to australia
> and these have been communicated by observation
>
> f) Black Kites (currently) eat Cane Toads and die and no one notices.
>
> I don't want to seem rudely skeptical but there are lot of claims
> about Toads but very little data.
>
Jim's Comment:
Thanks for the info. and in my opinion you are not being rude -- it is
enjoyable to learn about what facts are available. And, I would like to
add I am please that Alex brought up the issue of kites eating toads in
the first place. Now, if I may be so bold to add my two cents:
1) Given what you have stated about the toad eating habits of the asian
sub-species of Black Kites then we can expect that the Australian
subspecies would be pre-disposed to switch to eating cane toads once the
toad population reaches a high enough level. But, I wonder aren't cane
toads essentially nocturnal and kites diurnal?
2) Several other behavioural factors might be relevant. Alex's comment
about young kites being taught to catch toads may have merit given that
Black Kites are highly social for a raptor species. According to
statements in Penny Olsen's book on "Australian Birds of Prey" the
"gregarious" black kite travels in "small flocks, seldom singly, and is
one of the first raptors to arrive at fires" toeat carrion. If so, this
is where and when Kites could be introduced to the habit of eating toads
-- first dead ones then live ones followed by parents teaching young, etc.
However, it is my experience that young birds are more exploratory and
consequently, young are more likely to sample new foods than are adults.
Is true for raptors such as kites? I have no idea.
3) This arrangement would be ideal for the study of the cultural
transmission of a new feeding behaviour in a wild population. I know
there are people tracking the spread of cane toads into the Northern
Territory and these data could be used as a baseline to calculate toad
abundance.
I better stop here, I am getting a little out of hand <grin>.
Cheers, Jim
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