Monday, September 27, 2010

Curve-billed Thrasher in Manitoba

Curve-billed Thrashers have an interesting history of wandering in fall/winter. The phenomenon of fall dispersal has made it difficult to understand the migration patterns of this species. Amazingly one showed up this weekend in Manitoba’s Whiteshell Provincial Park – a long way away from their breeding range in Arizona, New Mexico, Texas and Oklahoma.

This bird was originally reported as Bendire’s Thrasher but, as we drove up to the dumpsters where the thrasher was feeding, we quickly realized that this was a Curve-billed Thrasher, the bright orange eye and the decurved all dark bill being the most salient features. You can see this in these two photos. You will also notice how worn the plumage is…

This bird was foraging right in front of our vehicle on the gravel pull-out. It was almost as though we were observing them in a tiny patch of their preferred desert habitat! We had ample opportunity to study the features although the amount of feather wear complicated the picture.

Curve-billed Thrasher subspecific taxonomy is a little complicated but two main groups are recognised - the eastern T. c. curvirostre group (breeds in areas like Texas) and the western T. c. palmeri group (breeds in areas like Arizona). If you study the photos below you can see that this bird had fairly extensive white tail corners (outermost rectrices tipped white), visible from above (first photo) and below (second photo), despite heavy wear, but most visible when the bird flew. This made me think that this birds might be of the eastern subspecies group.



The photo above also shows the spotting on the breast, which showed a fairly pale ground colour creating contrast between the breast spots and background. This also seems consistent with an eastern bird. The wing bars were hard to gauge, this bird being in such heavily worn plumage, but certainly, although they were buffy overall, there was white tips to the outermost greater coverts and outermost median coverts (as opposed to buffy tips as expected in western birds) as you can see in the first of the two photos above (although if you compare with the very first photo of this post you will notice that the white tips on the median coversts on the bird's other side have worn away). I did not manage a good look at the undertail coverts, another useful feature, as the bird was almost always on the ground.

If you are wondering why the bird is on one leg in both of the above photos, they appeared to have an injured right foot. This and the heavily worn plumage makes me think that this bird is not likely going anywhere soon and will stick near the food supply they have found. This bird also exhbited a curious sneezing behaviour - almost as though they were trying to cough up a pellet but repeated constantly.

It is also worth studying the interesting mix of dark and light flight feathers and tail feathers. Even at a glance the birds gives a somewhat striped appearance due to the mix of light brown and dark brown feather. This suggests multiple feather generations and thus an adult bird, although at first glance the buffy "wing bars" seemed to match Sibley's illustration of a juvenile.

On a bird this worn and this far out of range, it is hard to know how to interpret such features. The bird didn't seem all that happy either, though I guess the problem with a decurved bill is that you always wear a frown!


Amazing to see this bird so far out of range!

Saturday, September 25, 2010

Some nocturnal eye-candy

As a photographer with a passion for owling (going out at night to look for nocturnal species of birds and mammals), I was very excited to learn of the publication of an extremely ambitious new book — Nightjars, Potoos, Frogmouths, Oilbird and Owlet-Nightjars of the World by Nigel Cleere. Nigel was planning to put together a photographic guide of some of the most difficult species to photograph, no easy task! Much as I find them fascinating, I have always found nightjars, potoos and frogmouths much more difficult to photograph than my favourite group, owls. Since many nightjars are so difficult to identify, a book devoted to this group seemed like an absolute must for a night birder like myself. I was therefore very keen to see what it would look like.

This book indeed features some spectacular photography — images that make me green with envy! Of course, there are some very low quality images too, in many cases these being the only images available of certain extremely rare and seldom seen species. There are also some images of birds in the hand, which I personally prefer to avoid at (nearly) all costs, but which again were probably the only images available to illustrate certain field marks. In some cases images of museum specimens are used, which make comparisons against photos of live birds difficult but again there is really no choice.

Nigel’s text is minimal to say the least. The idea is to offer the viewer the opportunity to view multiple photographs of each species side by side to compare ID features and relevant field marks. Personally, I think this is a mistake for two main reasons. Firstly, although I absolutely love looking at bird photography, when it comes to identifying birds, I prefer illustrations. The photographs in this book show too many different states (e.g. live versus dead birds), postures, and lighting effects to permit one to compare apples with apples. In other words, I believe the book’s use for identification of this extremely difficult group would be greatly enhanced with much more discussion on how to separate species X from other similar species (each species has a section on “main confusion species” but I have found this text to be too scant to be useful and not cross-referenced to the photographs). Secondly, since many of the features are so difficult to see well, one finds oneself flipping back and forward between photographs looking at a particular feature on species X and species Y. The chosen layout is just not well suited to an ID reference, or at least is far less useful as an ID reference than some succinct text and/or drawings with or without arrows pointing at the most salient ID features. In short, the choice to make this guide so photo heavy has resulted in a superbly aesthetically pleasing book, almost a coffee-table style of book, except that not all photos were selected on aesthetic grounds (they were selected to cover every species and photo quality therefore varies considerably) but has severely compromised its utility. I have therefore found my colour photocopies of the plates of Handbook of Birds of the World to be more useful than this publication.

The beauty of a newly printed edition like this is of course having a single up-to date reference on the taxonomy of a difficult group. I have always found this type of book to be an extremely useful supplement to regular field guides for trips abroad. For example, before any trip, I consult K├Ânig’s Owls of the World and make notes on taxonomy, distribution, and salient ID features including song. I tried to use Nightjars, Potoos, Frogmouths, Oilbird and Owlet-Nightjars of the World for this purpose before my latest trip to Peru and found it to be woefully lacking for this purpose because the text was so scant that I did not find any information that I had not already found in other sources (I just got back from Peru so stay tuned for some exciting blog posts). Perhaps, this book would serve better for consultation after a trip when one could compares one’s field notes or photographs to the photos in the book.

I did find this book useful for its taxonomic treatment, though here again I would have liked more text, but other information criteria were so sparse as to severely limit the utility of this book. Most troubling though were the many inaccuracies that have crept into this publication. In particular, if one is going to use such a book as a reference, detailed information on distribution of species is critical. This book contains very scant text on distribution and the range maps are sadly so full of errors as to render them unusable. Here are just a few examples: The map of the Whip-poor-will misses huge chunks of the species range, for example in Manitoba where I live the range map for this species misses out hundreds of square kilometers of some of the portions of the range where Whip-poor-wills are very common. Many other species suffer similar woeful inadequacies, especially Asian species. Worst of all however are the glaring inconsistencies within the book itself, of which it only took me a quick perusal to spot several, e.g. the three images of Bonaparte’s Nightjar were all taken in Way Kambas National Park on the island of Sumatra but according to the range map Way Kambas is outside of the range of this sedentary species. Likewise the photograph of Blyth’s Frogmouth taken at Khao Noi Chuchi in Thailand falls outside of the range as drawn in this book and the photo of Blyth’s Frogmouth from the Genting Highlands was taken at a higher elevation than the altitudinal range given.

In summary, this book falls far short of the high expectations (admittedly, perhaps unfairly high expectations) placed on it. I will be using this book as a coffee-table book, to enjoy some of the delightful photography from time to time but I won’t be consulting it as a reference book – that niche still waits to be filled! I will say though that this book is extremely ambitious in scope and that the concept of a photographic guide to nocturnal species is well worth a dedicated effort. This book was years in the making and clearly a great deal of preparation has gone into it. Perhaps a revised edition with more emphasis on accuracy and a layout that permitted slightly more text would be all that is required.

 
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