Michael Todd wrote, 08.07.02 -
> If the two calling populations are well separated it starts to become a bit
> of a problem, but what if two different calling populations abut. I guess
> that what is needed is knowledge of calls across the range of a species to
> see if the variation is clinal or sharp.
>
> Any thoughts on this?
May a non-taxonomist (and non-twitcher) offer a few thoughts? First, I
should declare that my sympathies are with 'lumpers' rather than
'splitters'. (A pox on he (or she) who split Corymbia out of Eucalyptus!)
But I do accept that in defining species one must keep firmly in mind the
purpose for which the taxonomy is to be used. If for twitchers, then by all
means split away, and swell the lists.
But on the matter of calls, it is probably necessary to distinguish between
birds that have to learn their songs, and birds whose repertoire is limited
to innate calls built into their neurones before they are hatched. With the
latter, if there is a marked difference in calls between two populations
that abut, this may indeed prevent them from interbreeding. If it does - or
appears to do so, which is all we can determine from field observations,
then the possibility of two species should be considered - and further
evidence sought.
Did not CSIRO discover a new species of raven by noting that certain
individuals had no reaction to the researchers' tape recording of the
mobbing call of the species they had assumed the ravens to be? My
recollection is that they stalked and shot one or more of the birds. And
examination of them in the hand then showed significant differences, and
following up on that it was found that their foraging, nesting, etc.,
behaviour was also different. Clearly a different species was involved.
But please don't go applying to your State fauna authority for a permit to
take specimens of our native birds just on the grounds that the calls are
different.
Many Australian Passerines have quite strong regional dialects, but it is
unlikely that separate species are involved.
To give you an extreme example, both species of lyrebirds show very great
differences in their vocalisations from place to place. The territorial
song, the gronking song, and the sequential mimicry of Albert's Lyrebirds on
Tamborine Mt, are all quite different from those of the ones at Binna Burra
in Lamington N. P., even though the two places are only a few miles apart.
But I'm confident that an individual from one area would quickly adapt to
the 'language' of the other, if moved. I don't think it could be suggested
that they are different species.
Male lyrebirds are strongly territorial in the breeding season. Play a
recording of his song in a male lyrebird's territory and he will assume it
is an intruding male and will react quite strongly. The late Norman
Robinson told me that when he played a Captain's Flat territorial song in a
Tidbinbilla lyrebird's territory, it caused no reaction at all. The two
populations had very different songs.
Norman wanted to test what would happen with Albert's. I took him to a
Tamborine Mt NP and in the middle of one lyrebird's territory, played a
recording of a territorial song of a Mistake Range Albert's, that being the
song with the greatest difference that I had on tape. The local male was
calling towards one end of his territory. We played the song intermittently
for a couple of minutes. It got no reaction at all. He just kept on with
his normal singing.
"Right," said Norman, "Now try him with the Tamborine song." Immediately
the bird stopped calling and very shortly afterwards was up near us and
calling to challenge the intruder.
But there was a sequel. I was running automatic recording gear studying
that bird's vocal behaviour, and a fortnight later I visited to change the
tape. I tried the Mistake Range song again and the bird reacted
immediately. Clearly he had noted the song the first time, and noted that
the same "bird" also gave the Tamborine song and therefore was a lyrebird.
In a paper in Emu (V. 96, p. 260) Norman Robinson points out that Superb
Lyrebirds in Blue Gorge and Red Rock Gorge (Sundown NP) have distinctive
songs though they are only 5 km apart. In nearby Black Jack Creek, two
males used the Blue Gorge song, but added the Red Rock Gorge song to it when
confronting each other.
But maybe not all birds are as intelligent as lyrebirds.
The existence of a population with a distinctive vocal repertoire may be an
argument, or a supporting argument for conservation of that population. But
that's another matter.
Syd
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