Monday, December 28, 2015

Black Squirrels

While spending Christmas with our daughter, her husband and extended family members in Melrose, Massachusetts we were surprised by the appearance of a melanistic Gray Squirrel.  It was in the company of typical gray morph individuals foraging for acorns under a backyard oak tree. Now I have been aware of the existence of melanistic populations in other parts of the country, such as in several mid-western states, since having studied genetics during my long-ago college years, but until this sighting I had never seen one in the flesh.

As many birders have experienced, including myself, once a long sought after "lifer" species is seen, it afterwards seems to pop up everywhere with little to no effort.   And so, I may be experiencing this phenomenon once again except now with black Gray Squirrels.  This past Sunday, now back in Vermont and running errands, I saw another black squirrel feeding under a local bird feeder. What's with that: two black squirrel sightings in different states within a day of one another?

Melanism, a genetic condition whereby tissues (skin, hair, feathers) produce excessive amounts of the dark-colored pigment melanin, occurs widely in the animal kingdom at both individual and population levels.  Among birds, several raptor species exhibit dark plumage morphs, including Short-tailed, Swainson's, Red-tailed, Ferruginous and Rough-legged hawks, and the Gyrfalcon. Unlike amelanism (the absence of melanin) and albinism, melanism appears to be a genetic adaptation to a particular environment increasing a species fitness for survival.  Adaptive melanism may allow animals to better absorb solar heat and more efficiently maintain body warmth in cold environs; or others to blend in with their habitat enabling either dark-morph hunting predators to evade detection by prey species or, vice versa, allow dark-morph prey to hide from predators.

Dark-morph Red-tailed Hawk, Catron County, New Mexico

So what is the adaptive advantage to a black squirrel inhabiting an urban or suburban environment? It seems doubtful that such individuals are better camouflaged from predators, such as hawks and free-ranging house cats.  Easily the gray-coated squirrel in the photo below blends in better with the setting than if it was black.  On the other hand, melanism seems to be an effective survival strategy as long as the squirrel is not out in the open but takes advantage of deep shade produced by thick vegetation and forest canopy (bottom photo).  

Here are a couple links to web sites discussing specifically melanism in Gray Squirrel populations: Wikipedia and a more technical treatise in the Journal of Heredity.

Thursday, December 3, 2015

December 2015

As 2015 winds down birders' attentions may be catching the few remaining lingering fall migrants or enjoying some early winter arrivals, or many of us look forward to taking part in one or more annual Christmas Bird Counts. The holiday season also calls on many to indulge in more family-centric activities.  In addition to all of these activities I find this is a good time to reflect on the many birding experiences encountered over the year, such as my attending a family reunion in central Missouri and finding a little time to steal away for first time birding in that state; the spring and fall trips we made to New Mexico; and here in Vermont a personal first: birding in all 14 counties.  The following photos are a small sample of ones taken last May during a visit to Bosque del Apache National Wildlife Refuge, one of the premier birding destinations in New Mexico.

Yellow-headed Blackbird, male, and Brewer's Blackbird, female

Blue-winged Teal, male

Cliff Swallow constructing mud nest

A completed nest

Cinnamon Teal, male

Greater Roadrunner

Northern Shoveler, male

Snow Goose, a straggler

White-faced Ibis