sexual dimorphism in birds

Guest Blog: Ronnie James with a little help from the Cornell Lab, and Google images, and yours truly


You might mistake this hawk for an owl

For me, the Northern harrier, formerly known as the Marsh hawk, was always the easiest hawk to identify. It forages by flying low and slow over open marshes, meadows, prairies, pastures and grasslands. If the manner in which it forages isn't a dead giveaway, wait for the moment it rocks one way or the other and you see that white rump patch. Bingo.

The northern harrier is also the only sexually dimorphic hawk I can think of. Dimorphic? Oh, please. It means the sexes don't look alike, except for matching white rump patches. In this case the male is pale gray and the female is a mottled brown. Dimorphism in birds often means that the males have multiple partners, and lo and behold, that is true of this hawk. The male may have more than one mate, possibly as many as five in a season.

Why are so many female birds drab and homely? Mostly because they need to be inconspicuous, especially if your nest is open and exposed. As you might have guessed by the female northern harrier's coloration, they nest on the ground.

So how come this hawk looks like an owl? For the same reason owls look like owls. They rely on hearing to find prey (mostly mice and other rodents) and so does this hawk. The stiff feathers of the facial disk direct sound to their ears.

 

Two baby harriers in their ground nest

SUCCESS STORY  
by
Ronnie James

In July, someone noticed a fledgling Harrier standing in a meadow eating a dead rodent held tightly in its talons. The young bird was so intent on its meal, a man walked up, grabbed it and stuffed it into a box he had with him. The man suffered a few nasty puncture wounds to his hand in the process. Then he brought it to me because he was sure there was something wrong with it since it did not fly away when he approached. 

There was absolutely nothing wrong with the bird. Harriers nest and feed on the ground and this one was a juvenile, intent on his meal, which he refused to give it up--even to a giant predator. 

I fed it for a few days, then volunteer Elly and I took it back to the meadow where it was found and released it. It stood on the ground for a long time. Just as we turned to leave, we heard a distant cry. The young hawk replied, and as we watched, it rose into the air and was last seen flying behind its mother screeching and begging for food.  It’s so rewarding when something works right. We follow rehab protocol, but never know if it really works. In my 30 years of releases, this was the first time I’ve actually witnessed a reunion.

Ronnie James,
Woodlands Wildlife
Author of Touching Wings, Touching Wild