A query about an odd thornbill in the mulga scrub at Bowra, SW
Thornbills. The eye was dark, and there was some scalloping on mottling
on the forehead, whilst the underparts were whitish with fine dark
streaks on the chin and throat, this being a confusing feature. Rump
chestnut etc. Do immature Slaty-backs have fine
On the face of it, this would seem to fit Broad-tailed (Inland, whatever)
rather than Slaty-backed. Some forms of Broad-tailed have very inconspicuous
streaking below, and in some populations, the streaking can be quite hard to
see in the field. This could well be so at Bowra. The description of
scalloping on the forehead sounds exactly right for Broad-tailed, and
nothing else you say would seem to rule that species out. The comparison
points you make re Chestnut-tailed would also make sense for Broad-tailed
(greyer back, more solitary). If you are used to Broad-tails in other areas
where they look more like Brown Thronbills, then these paler, less-streaky
birds can look very unfamiliar. I seem to remember the name Whitlock
Thornbill might have once been applied to such birds.
Probably irrelevant in the current context, but on the subject of
eye-colour, it is worth noting that the white iris of Chestnut-tailed (and
other birds) may be invisible in low light, due to the iris opening up. Thus
the eye can look dark, and basically appear the same as the red iris of
related species. I experienced this with Chestnut-tails in the predawn out
west of Windorah, where I was hoping I might have Slaty-backs. But as the
sun got higher, the eyes got whiter! When I finally got to see Slaty-backs,
I realised they are very different-looking birds - even if the streaking on
the crown can be hard to see.
Cheers, Chris.
Chris Corben
www.hoarybat.com
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