Tuesday, 21 February 2012

Rosy Finches - Third Time's the Charm

One of my target birds for 2012 was the Gray-crowned Rosy Finch.  These little songbirds spend the summer nesting in cliffs or rock piles in high alpine or arctic tundra, such as at Sunshine Meadows near Banff.  However, rather than spending July hunting out nesting pairs while dangling from cliffs and dodging grizzly bears, a simpler option is to look for them in the winter when large flocks descend to valley floors to feed and to spend the cold season in more sheltered conditions.  Having struck out twice in recent months I was not holding my breath as my daughter and I drove over to Exshaw early on Sunday morning to check the feeders along Barrier Mountain Drive.  However, this time the supposed "sure thing" did materialize and, as you can see from these photographs, we had great views of a large flock along with a few dozen Pine Siskins and a couple of Mountain Chickadees.
I really needed my wider angle lens - less than a fifth of one flock of Gray-crowned Rosy Finches, Leucosticte tephrocotis
The particularly neat thing about this sighting is that the flock contained both of the two main subspecies (out of 6+) of this type of Rosy-finch.  The littoralis subspecies ("Hepburn's Rosy-Finch") and the nominate tephrocotis subspecies are both fairly migratory and since western Alberta is close to the overlap of their ranges it's not surprising to see them together.  Why are there so many subspecies?  The most likely explanation is their breeding habitat, which puts small populations in relatively isolated alpine and island locales.  This reduces gene flow between the groups, particularly the four less widespread subspecies.  Drawing meaningful taxonomic lines is challenging and some scientists consider the whole Rosy-finch complex (3 North American and 1 Asian species) to be a single species.  This conclusion is supported to some extent by the extensive hybridization observed and by DNA sequencing.  In any case it's an interesting example of the complexities of avian genetics.  Here are a few pictures from Exshaw showing the key differences (click to enlarge as usual).
Leucosticte tephrocotis tephrocotis - note the gray crown which stops at the eyeline
Leucosticte tephrocotis littoralis - aka. "Hepburn's Rosy-Finch", note the completely gray head
On reviewing my pictures later in the day, I realized that by pure luck I had both subspecies in the same frame on one shot
Hope you enjoyed these finches as much as I did!

Information for this post taken from Dunn and Alderfer's Field Guide to the Birds of North America, 6th ed. (great subspecies maps!) and Kaufman's Lives of North American Birds.

1 comment:

  1. Good to see these little guys. I use to look forward to observing them at my feeders back in the 80's when they would descend, numbering in the 30's or more. For the last twenty years I have only seen them on a few occasions and even then just single birds.