Telling Boys From Girls

In species that are sexually dimorphic, it’s pretty easy!  The Common Yellowthroat, for example.  Remember mother and baby from a previous post?
Common Yellowthroat Mommy and Baby

Now here’s dad:
Common Yellowthroat - Adult Male

In Common Yellowthroats, the boys and girls look quite different.

Now here’s a pair that is NOT dimorphic (at least not visually – from a distance):
Red-eyed Vireo Pair
Red-eyed Vireo

Can you tell the boy from the girl?  I’ll give you a hint… I’m holding the boy and Tom is holding the girl.  (What, you can’t tell my hand from his?)  OK, I’ll tell you:  The boy is on the left and the girl is on the right.  I only know this, because we examined them carefully while banding them.  The male Red-eyed Vireo is supposed to be slightly larger than the female, though they look pretty close in size here.

At a previous banding session, Tom had mentioned something about how in some species of birds, the boy will help incubate eggs.  In species that do that, the plumage of males and females is often quite similar.  The Red-eyed Vireo proved that out.  The boy had a partial brood patch.  The female’s belly was quite interesting:  She not only had a brood patch, but her belly was quite distended.  We think she was about to drop an egg!

We had a lot of birds at that net check, so I didn’t get a picture of the Vireos’ bellies.  But I did get one of a female Common Yellowthroat.  The brood patch is skin on her belly that she can put directly on the eggs when incubating.  The lack of insulation allows her body heat to transfer more effectively to the eggs:

Common Yellowthroat - Adult Female - Brood Patch

Learn more:

Another Fine Day at Bird Banding

Yesterday, I spent the morning at Allegany State Park with Tom (a.k.a. mon@rch) learning about birds and bird banding.  I had been thinking during my drive to the park that it was odd that we hadn’t caught a Red-winged Blackbird, since the habitat seems agreeable for them.  “Ask and ye shall receive.” Look who was waiting for us at the first net check:

Red-winged Blackbird Female
Red-winged Blackbird, Female

It doesn’t show terrifically well in this photo, but look closely at the top of her wing.  I had no idea when looking at these birds in the field that the female has a bit of red on her wing, too.  I thought she was all brown.  When I searched Tom’s photostream in Flickr to find a picture of the male, I found this picture of a female that he took in June 2006.  Look at all THAT red!

Red-winged Blackbird Female
Another Red-winged Blackbird Female

Maybe next time we’ll catch the male.

Common Yellowthroat Male AdultThis is a great time of year for learning about all the plumage differences in birds – male vs female, juvenile vs adult.  I borrowed the picture of the male at right from Tom (again)…  We didn’t catch a male yesterday.  But we did catch Mother and Fledgling:

Common Yellowthroat Mommy and Baby
Common Yellowthroat Mother and Child

Once again, we caught several American Redstarts.  Their changes in plumage are quite dramatic.  This fellow provided quite a lesson in feather moult and regrowth:
American Redstart Male 1a

American Redstart, Male

He was born last year.  He has mostly adult feathers, but still some first year feathers:
American Redstart Male 1b

Eventually, the feathers with yellow will be replaced with feathers like those on the left – with orange.

Here are two views of another American Redstart male – younger.  Notice that his head is still gray, not black:
American Redstart Male 2a

And his wing feathers are all yellow, no hint of orange:
American Redstart Male 2b

American Redstart, Male

There were plenty more birds, and there was plenty more learning… But I have to get ready for work now… So I’ll save them for future posts.