Monday, August 16, 2010
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Answer by Tony Leukering
All respondents got this week's quiz birds to the right genus, but none got the correct answer; somewhat disappointing. Our birds were obviously Plegadis ibis and those dark eyes and dark legs are key characters pointing to Glossy Ibis, which was the species promulgated by the majority of respondents. However, those characters also match White-faced Ibis, at least at some times.
Both of the birds sport anomalous patches of white on the neck and/or head, a feature at odds with both submitted IDs. At least, of identification of birds older than a few months. Yes, the oddly-patterned bills and the white patches on the necks support the contention by many respondents that these are juvenile ibis. Adding more certainty to that age assumption are the fresh, unworn, and even-aged flight feathers. Even though multiple folks noted this feature in our quiz, the age of our quiz birds seemed not to cause much in the way of caution in respondents. There was something of a geographic bias in responses, with all easterners (those living east of the Mississippi River) going for Glossy Ibis and the only votes for White-faced coming from westerners. Interesting to me, multiple respondents provided both species in their answers.
As noted in most (if not all) field guides to "North American" birds, juvenile dark ibis are indistinguishable. While there may be some characters that may suggest one or the other of the two species, as far as I'm aware (and I've looked at a LOT of juvenile ibis), there are no certain separators of the two, thus the correct answer, and one that I hope would be practiced in the field, is "Plegadis sp."
I took this picture of two juvenile dark ibis in July in some U.S. state in which I've lived at that time of year. Of course, that is a considerable number of places, and includes the following states (listed alphabetically): CA, CO, CT, GA, MI, NH, NJ, NY, and OH. White-faced Ibis breeds in two of those, Glossy in four (CT?), and neither in three. One can see the dilemna. If I took this picture in Michigan or Ohio, where both species are rarities, how would I back up any specific ID to the state's records committee? As I have seen breeding-season individuals of one species in two states in which the other species breeds, but which the first is not known to breed and in which the non-breeding species is a rarity, again, how do I back up any ID? Do I let them go in CO and NJ as simply the locally-breeding species, when I have no solid evidence of such, other than location? Why do that? Finally, how do I rule out the possibility of a hybrid, of which I've seen a fair few in CO, a state just south of Wyoming in which both species have bred or do breed?
Birding is more than simply slapping a label onto any given target. At least, I want it to be. That name should not be the end-all, be-all of birding, but simply a way to organize the chaos that is inherent in all biology. It is incumbent upon all of us, I think, to refrain from identifying something definitively, if there is no reason for that definitiveness. We can learn so much more, if our minds remain open to new things, novel theses, rather than simply slapping a name on an unidentifiable bird and moving on to the next. We should not be afraid to let a bird go unidentified.
Okay, I'm done with the philosophizing, let's check out the next quiz!
Incorrect species provided as answers:
Glossy Ibis - 13
White-faced Ibis - 4
All 14 answers submitted were considered incorrect.
Answer: Plegadis sp.