Tuesday, September 8, 2015

Vultures - talking the stork!

Turkey Vulture - Luke Tiller

During the summer I was lucky enough to go spend a few hours at an incredible bird and raptor spot just a stone’s throw across the Kern County line from Los Angeles, CA. Here a number of California Condors spend their summer months loafing around a piece of private property that is almost the size of the five boroughs of New York! It’s amazing to see these birds back from the brink, and worth remembering that without the work of many different organizations they wouldn’t be.

It’s not like the California Condors are the only attraction here, we also ran into a Peregrine Falcon that was out hunting the fields (hopefully not for the cute Burrowing Owls we saw along the fence line), soaring adult Golden Eagles with a recently fledged juvenile, a myriad of dark and light calarus Red-tailed Hawks and light Swanson’s Hawk (a localized breeder in the region). Even with the other raptor goodies, I have to say that getting incredible perched and flight views of these magnificent vultures is pretty much enough in and of itself.

Anyway the reason I bring my weekend up, apart from birding bragging, is that I again found myself hearing that old chestnut that New World Vultures are less closely related to hawks and eagles, than they are to storks. It’s one of those stories that has an appeal as it allows the teller to discuss things like convergent evolution and, thanks to their obvious physical differences, to also get an amazed response from the person you’ve told it to. Unfortunately it’s also essentially a story that hasn’t been believed by most ornithologists for at least five years now.

If you’ve spent time though at a hawkwatch I’m betting it’s a story you have both heard and perhaps even told yourself. Essentially historically there have been three trains of thought with New World Vultures (Cathartidae): that they should be included in the order Ciconiiformes along with storks, that they should be included in the Accipitriformes with hawks and eagles or that they should be in an order all of their own.

Basically what happened is that an early DNA study (unfortunately based on erroneous data) seemed to suggest that vultures were more closely linked to storks than hawks and eagles. This was also backed up by some behavioral, morphological and karyotype similarities. Recent multi-locus DNA studies, however, now seem to suggest that the vultures are more closely related to hawks and eagles. As of current writing if you check the American Ornithologists’ Union Check-list of North American Birds you will find them sat among the Accipitriformes which includes kites, harriers, eagles and hawks among others. This decision to put them in this new order was made in the 51st supplement which is based on committee deliberations between January 2009 and March 2010 and published in the summer of 2010.

Interestingly the same supplement announced another big change for raptor aficionados by the AOU. I had been hearing rumors from scientists I knew, for a few years, that there was little to suggest that hawks and falcons were closely related and it was in this supplement that the AOU decided that DNA comparisons showed that these birds (which had previously been lumped in the Order Falconiformes) are not closely related. The hawks, eagles etc were split out into the new order Accipitriformes (which also included the New World Vultures ), while the Falconiformes held on to just falcons, forest falcons and caracaras. These birds were agreed to be much more closely related to parrots and passerines than they were to hawks.

Though the relationship between vultures and hawks is still somewhat in flux highlighted by the South American Classification Committee decision to place the birds into their own order: Cathartiformes, rather than putting them back into an order with hawks, eagles, kites, harriers etc, there is no longer much evidence to suggest that they are that closely related to storks or that they are more related to storks than they are to hawks.

So latest studies seem to suggest that we don’t need to worry about the validity of counting vultures at our hawkwatches, but what to do about those pesky falcons?!?

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