Monday, May 21, 2012

Head first

A student recently found a nearly intact coyote skull near campus.  He did a nice job cleaning it up and agreed to sell it to me for teaching.  I was impressed by it's large size and it started me on a minor quest.  I needed a lab activity to look at geographic variation in a species.  Any species would do and coyotes seemed to be a as viable a candidate as any other.  They occur in 49 out of 50 US states; Hawaii being the exception.  There are no hunting restrictions and in many places they are killed as pests.  So I have made it my business to accumulate some more specimens.  It goes along with my brother's suggestion to name my blog "dead things" I suppose.

The size of the first skull struck me as unusual.  I had considered coyotes to be somewhere in the range between foxes and wolves, and I had naively considered them to be nearer the fox end of the scale.  Red foxes top out in the 15kg range.  Coyotes, I learned can be more than twice as large as the largest red fox.  There are good reasons to expect a Vermont coyote to be larger than average.  Coyotes in the northeast United States are generally considered to be the product of hybridization between western coyotes and wolves.  The hybrids colonized the northeast during the early part of the last century and have expanded their range since then.

Bergmann's rule is a reason to expect coyotes in the north in general to be larger than those in the south.  The idea is based on thermoregulation.  If an animal gets longer in one dimension, it's skin surface area gets larger by a square function of that linear dimension.  Body mass increases by a cube function of the linear dimension and so overall, larger animals have a larger surface to volume ratio.  Bergmann's logic was simple: large mammals can better thermoregulate in cold conditions and so we should expect to find the larger examples farther north.

So, are coyotes in the northeast larger than western coyotes?  Do we find the largest coyotes as we travel farther north?  These are the questions my students will answer during my spring course.  To answer questions such as this requires a large sample of skulls.  I have accumulated more than 30 specimens thus far from 14 states from Texas to Alaska and a single specimen from New Brunswick Canada (based on all logic it should the largest one; it is not...).

You may wonder how one goes about acquiring 30+ skulls?  Is there some professional network of biologists bartering skulls for insect specimens?  Perhaps a biological supply house meets the demand?  It turns out that the source is far more pedestrian......Ebay!  And I should point out that I have had skulls donated by trappers in Texas and New Mexico.