Homebodies

What a beautiful day!  I went for a run late this morning and the sun was out, a nice spring breeze was blowing and the dogwoods in Freedom Park are full of giant, gorgeous blossoms!  Fantastic stuff.   I stopped a few times on the run to get some nice views of all those flowers.  On one of those stops, right at East Blvd, near the tennis courts, there is a greenway entrance surrounded by big dogwoods and rows of hedges.  And there in the hedges were a bunch of little ground foraging birds.  Well, in the grass under the dogwoods were some American Robins.  They’re everywhere in the open grass.  Right at the hedgeline was a pair of Brown Thrashers.  It’s almost unfair to call them ‘brown’.  It’s such a rich, reddish brown color- much more striking than the dull, dusty browns of the thrashers out west (though they do have those cool, curved bills going for them).

The other birds that I found in the hedges- and they were really doing their foraging in the hedges completely- were some Chipping Sparrows.  I’m actually kind of a weird fan of Chipping Sparrows.  They’re smaller than the typical ones (Song and White-throated and Juncos).  They’ve also got a very simple, mechanical kind of song- fascinating in just how simple it is.  As I wrapped up my run, though, I started thinking about these little birds.  I’ve seen them here, in Missouri when I worked there and in California.  They do seem to get around, but I don’t actually know anything about their real distribution, so I came home to start looking things up about them and found out a couple interesting things:

1.  Not many people do work on Chipping Sparrows.

2.  They have a wide distribution, but individuals don’t move very far. The interesting part about that fact is that it didn’t come from following individuals over the course of their lives, but from looking at mitochondrial DNA sequences.  Mitochondria are small organelles found inside cells that have their own DNA.  All the mitochondria (and therefore all the mitochondrial DNA) inside an individual are passed down from the mother (as opposed to nuclear DNA, which comes from mom and dad).   By looking at these mitochondrial DNA sequences, researchers can figure out patterns of relationships between individuals and across populations.

Well, one group of researchers studied these patterns in Chipping Sparrows and found a couple of very interesting things:

Yes…the numbering starts over, here.

1.  There are no major geographical differences in Chipping Sparrows.  I mean, there are variations, certainly, but those differences are just a function of distance.  There are no clear-cut regional variants.  What does this mean?  Well, it means that individuals don’t tend to stay clumped in a particular area.  The only way to avoid getting regionally specific genetic variants is by moving around.  In contrast, though, read on…

2.  By looking at mitochondrial DNA sequences, they were able to estimate that dispersal of offspring averages about 5.4km.  That means your kids would, on average, only move about 3 miles away before establishing their own nest.  That’s not a lot of movement.  I suppose it makes it easier to go home and do laundry.

Zink, R.M. and D.L. Dittman.  1993.  Population structure and gene flow in the Chipping Sparrow and a hypothesis for evolution in the genus Spizella. Wilson Bulletin 105:  399-413

So these birds aren’t moving much, but they keep on moving.  They stay close to relatives, but not too close.

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About thomasbiology

I'm an Associate Professor of Biology at Queens University of Charlotte with a background in animal behavior with an emphasis in bird song. I've got two secret goals with this blog (well, since I'm sharing them, they're not so secret): 1. To encourage people to look at the natural world around them- not just as a hiking destination, but to notice all the little things moving around them all the time; and 2. To show some of the science that relates to these little things moving around. There's some really fascinating research out there that so few people get to see.
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