Saturday, April 3, 2010

Which sub-species of Fox Sparrow do you have?

Posted by Kirk

The fox sparrows showing up this week got me thinking about these fascinating birds again. Did you know that there is a lot of disagreement over this chunky sparrow? Is it one kind of bird or many different closely related species? The AOU currently recognizes 18 sub species.

Minnesota's own Robert M. Zink at the Bell Museum of Natural History has taken a very close look at these migrants that show up each spring. He wrote the page turner, The Geography of Mitochondrial DNA Variation, Population Structure, Hybridization, and Species Limits in the Fox Sparrow (Passerella iliaca). If you subscribe to JSTOR or happen to have issue Volume 48 issue 1 of the Journal Evolution from 1994 sitting around then you too can read all about subtle differences in the DNA of Fox Sparrows from around the country. More recently he published The recent Evolutionary History of the Fox Sparrows which was published in the AUK in 2003. Wonderfully, you can download this as a pdf for free from the Field Museum. I learned that according to analysis of DNA, Spizella arborea or the American Tree Sparrow is the closest relative of the fox sparrow. Makes sense. Back to the fox sparrows...

I look forward to seeing Fox Sparrows each spring and I love their foraging behavior of scratching at the ground with little backwards jumps. I took this quick and dirty video of the first fox sparrow to show up under the feeders at work.

As I hinted at before, there's some disagreement it seems about which species of bird is in the video above. "Officially," meaning according to the AOU, there is only one kind of Fox Sparrow. The scientific name is Passerella iliaca. There are four generally accepted sub-species however. Now depending on whether you are a splitter or a lumper this will either excite you or make you say, "Here we go again."

The four major sub-species of Fox Sparrow are:

• The Red Fox Sparrow (P. i. iliaca ) Generally central and east coast. This is the brightest red thus the name.
• Slate-colored Fox Sparrow (P. i. schistacea) Found in the Rocky Mountains. It has a tiny bill with a gray head and mantle, brown wings, brown breast streaks, and a russet tail.
• Sooty Fox Sparrow (P. i. unalaschcensis) Found on the west coast. It is generally browner than the Red Fox Sparrow.
• Thick-billed Fox Sparrow (P. i. megarhyncha) Found in the Sierra Nevadas. It has a particularly thick bill, thus the name.

So clearly what we have here in Minnesota is a Red Fox Sparrow right? Well, kind of. Research such as that done by Zink reveals that the "Red Fox Sparrow" is actually made up of even smaller groups. There are actually two distinct groups, the Eastern Fox Sparrow (Passerella iliaca iliaca) and the Yukon Fox Sparrow (Passerella iliaca zaboria). What's the difference? The Yukon has a browner malar stripe and a grayer head. That's in general. It can be very hard to distinguish them in the field. Range is probably the best way for the general observer to tell them apart.

So, which do we have in Minnesota? We're close to the divide but in general it seems the birds in Minnesota and to the west are Yukon Fox Sparrows while birds in Wisconsin all the way to the east coast are Eastern Fox Sparrows.

If you're a life lister, be sure to note fox sparrows you see in other parts of the country. They may some day be split into separate species.



lefseforever said...

Saw a fox sparrow at my feeder this morning here in Burnsville!