Friday, May 16, 2008

Tasmanian & Brown Thornbills

I've been setting up a pbase site of bird photographs, during a recent bout of illness. While doing so, I happened to find a few similar shots, taken in similar lighting conditions, comparing two of what appears to be, among the more difficult Tasmanian birds to separate. I say appears to be, as I've noted a spat of reported sightings of Tasmanian Thornbills in areas and habitat that are not "usual"--no names, no pack drill! While I'd not like to say that they could never occur at these sites, they appear to be recorded by visitors to this state, which makes me 'uneasy'! I'm not setting myself up as an expert, merely hoping that the accompanying images will help separate two similar species. Tasmanians on the left, Browns on the right.
There appear to be a few obvious differences--easy when you have images and not looking at birds in the canopy or against the light. The Browns are much better marked on the breast, and they have noticeably larger bills. The undertail coverts are light brown in the Brown, and white in the Tasmanian--t
his has been one of my diagnostic points to look for, often very noticeable in the Tasmanian, as they are often seen 'fluffed ' out. I would be disinclined to use any colour differences you may note, as the vagaries of my image editing, and the differences of screen colour settings, will influence this.
So if you're looking at 'brown' thornbills in Tasmania, I suggest you go for a couple of the diagnostic points, to satisfy yourself of the species. In the main, the endemic Tasmanian Thornbill will be in wetter, more heavily forested areas, especially in the South East.
The Tasmanian Thornbill images were shot in the Wielangta Forest, and the Browns in the Peter Murrell Reserve.

NB.If you're interested in looking at the Tasmanian Bird images that I'm currently inputting, you may find them at www.pbase.com/tassiebirds , I will eventually put a link in. The site is still under construction.

4 comments:

John Tongue said...

Hi Alan,
Nice comparison shots! We generally find the 'white fluffy underpants' one of the easiest features to pick up in the Tas. Thornbills, as you note. Another is the comparatively longer tail. The proportions of the colour bands in the tail are also different, but usually pretty hard to distinguish positively, without the two different species together for comparison (which they almost never are!) I've also heard others say the Tas. Thornbills tend to end their song phrases with a "Wit, wit,wit", but I find the song of both of them so variable, that this is not really a satisfactory identifier. The bill lengths are clear in your shots, but they usually bounce around so actively, I find that hard to pick out with certainty. Mostly, we go on habitat likelihood, then 'underpants' and tail length. Both Thornbills are great little birds!

BirdingTas said...

Hi John,
Thanks for commenting. I wrote the piece mainly to caution observers to be more vigilant in distinguishing these 2 birds. Habitat is a strong first stage guide, which field guides don't seem to highlight. I've never found tail length useful, and my banding data indicates that there is considerable overlap, so beware. I didn't go into the area of juvenile birds either, but at the time they're about, habitat would be a good indicator. Both species are great vocal mimics, mainly in their sub song, and I too, have never found that I'm sufficiently confident to separate them on call.

Murray Lord said...

A topic I know we have corresponded on before! I have a number of recordings of Brown and Tasmanian Thornbills that Dave Stewart kindly provided to me and I have been trying to find the time to sit down and play round with them on the computer. The calls are quite different - the challenge is to describe how they are different. As far as plumages are concerned, I think the field guides don't adequately highlight that Tasmanians when perched show quite a rufous panel in the primaries, which Brown does not, as shown in your photos. Recently when writing an article on Colonel Legge I discovered that the description in the Pizzey Field Guide of the Tasmanian's call is actually a misquote of an article Legge wrote in the 1880s - the words used were actually his description of a Brown Thornbill call.

BirdingTas said...

Hi Murray,
Yes, the dreaded Tas v Brown again! I still recall my early attempts to tell them apart, and I have to own up to fudging them all too often, based on habitat! Not actually a bad ploy. The calls are quite different as you mention, but they don't always oblige by singing. I think the most obvious distinguisher, is the wit, wit, wit, part of the call (as mentioned ny John) by the Tasmanian, which has a more strident and melodious call than the Brown. I think, perhaps, what bugs me, is people (make that visitors!), all too often are 'ticking' the 'Tasmanian' off, without actually seeing one, often in habitat not usually associated with them, and in so doing, encourage others to do the same thing, however unwittingly. There's not really much excuse, as in the right habitat, Tasmanian Thornbills are common enough.