Rob,
I am not a professional ornithologist, but for what it's worth, here is my
understanding. In the old days, the production of fertile(NB) hybrid
offspring would immediately establish that two taxa are races,not distinct
species. But more modern thinking prefers to look at the frequency of events
rather than the yes/no dimension. Consider it this way. 0 is a small
number, and 1 is closer to 0 than it is to 100. So if you had an area of
sympatry, in which two taxa occurred together, and 99 out of every 100
pairings were between the same taxon, with the other 1 between the two
taxa,even if the offspring of that 1 pairing were fertile, modern thinking
would say that the two taxa had effectively developed reproductive isolating
mechanisms and should be considered distinct species.
An excellent example is the Black-eared Miner, which is being genetically
swamped by the Yellow-throated Miner. Since the Y-t M can hybridize with
B-e M and the offspring are fertile, it used to be argued that the B-e M
must be only a race of Y-t M. But Les Christidis (I think it was him)
established that B-e M. is genetically closer to Common Miner than to Y-t
Miner, and thus is a good species. What has happened here is that the key
isolating mechanism was habitat, and with the destruction of the mallee
habitat, the two species can interbreed. But they would not have done so
had the habitat been intact.
I hope this is accurate and that it helps.
At 16:52 23/06/97 +1000, you wrote:
>Hi all.
>I noticed in the new Pizzey and Knight guide (thanks to that person for
>the tip on Big W) that the Grey Teal hybridizes with the PBD and
>Chestnut Teal. When I mentioned this to a friend he said that the 3
>birds must be the same species.
>We talked about the definition for species but couldn't come to an
>agreement.
>
>What definition for species is used in the taxonomy of birds?
>
>Are the offspring of such matings mules or are they viable?
>
>If they are not mules, how can the three birds be considered separate
>species?
>
>I hope someone can help me here as I have virtually no knowledge in this
>area..
>
>Please note, this is just to satisfy my curiosity and confusion.
>
>TIA.
>--
>Rob Quinan
>
>Email:
>
>
>
Associate Professor John M. Penhallurick<>
Canberra, Australia
Phone BH( 61 6) 201 2346 AH (61 6 2585428)
FAX (61 6) 258 0426
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