Splitting Red-tailed Hawks?

Red-tailed Hawk_CanonCity-CO_LAH_8371.nef

If you’ve been birding for any length of time, you know that species come and species go. The birds don’t change, but our perception of which variations are actually different species is constantly undergoing review. We have lumpers, who combine disparate species into one, and splitters, who separate subspecies into two or more different species. Add in the (relatively) new ability to examine DNA, and you have a recipe for constant change.

Currently, it seems the splitters prevail. Just in the past few years we’ve acquired a new Red Crossbill by splitting off the Cassia Crossbill from the rest of the pack (2017), and we’ve gained an “armchair lifer” from the 2016 division the Western Scrub Jay into California and Woodhouse’s Scrub Jays (which are themselves divided between the Sumichrast’s Scrub Jay subspecies of southern Mexico and the type species of the interior western USA).

Now I hear that the Harlan’s Hawk is being considered for elevation to species status, splitting off from the Red-tailed Hawk. Most of the AOS proposals for 2019 are concerned with reordering the phylogenetic order of various species, punctuation nuances (eliminating apostrophes, for example), or refer to birds most of us never see anyway. (The only other species currently being considered for division is the White-winged Scoter—our North American bird would be separated from its relatives in the eastern hemisphere.)

Harlan’s Hawks, while fairly rare, are seen on a regular basis, at least here in Colorado. Splitting them would give most of us birders another check mark on our life lists. Of course we approve.

They are typically dark, as you can see from my photo at the top of this page, although there are light morphs, and Red-tailed Hawks (I show their typical plumage here) can have dark morphs. The variations in Buteo plumage can make identification very tricky!

William S. (Bill) Clark, of the Global Raptor Impact Network, has created a PowerPoint listing ways in which Harlan’s Hawks differ from Red-tailed Hawks:

  1. Frequency of color morphs;
  2. Adult plumage by color morph, especially in tail pattern and color;
  3. Harlan’s adult and juvenile plumages are almost alike; whereas those of Red-tails differ.
  4. Extent of bare area on the tarsus.
  5. Some behaviors.

He then gets a bit technical, offering wing measurements, the frequency of specific color morphs, and other carefully researched details. In addition, he includes a zillion photos. Clark makes a strong case for splitting the two. If a DNA analysis is done, it will be interesting to see what else we can learn.

Harlan’s and Red-tailed Hawks have been both split and lumped in the past. It’s nice to believe that this time we’ll reach a decisive conclusion, then carry on knowing that our understanding is accurate. However, science is rarely so neat and tidy, and I wouldn’t be surprised to again see the matter on the list of proposals in the years ahead. In the meantime, I’m counting on yet another armchair lifer!

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