by Bob Engel, Marlboro College Professor Emeritus of Biology and Environmental Science  

This year, one of these guys, or perhaps a son, finally arrived on March 31. And what a difference a year makes: up here in Marlboro, let's call it Santa's Land, we still had more than two feet of snow on the ground at the end of March. But he showed up anyway. 

Song sparrow, (c) All rights reserved by Ed Schneider, www.edschneiderphotography.com

How does he know to sing in March, and, for that matter, why does he sing at all? Does she sing, too, or do we just have a bunch of Pavarottis out there? The "how" of this is pure physiology; the "why" has to do with ecology.

Just as with you and me, this little bird has a biological clock. And just as with us, it's a roughly a 24-hour clock. It's set every day by daybreak, and runs until it's reset by the next dawn. When the day length increases in the spring, a photosensitive portion of his clock is stimulated by light and he becomes a completely different animal. He eats more, he molts his feathers, he thinks about a long trip to his summer cabin, and he doesn't like hanging out with the guys any more.   

In birds, singing is an aggressive act.

In fact, driven by the testosterone that his newly enlarged gonads pump out, he can't stand the sight (or sound) of another male. And he just can't stop singing. If we were able to inject him with radioactively labeled testosterone, we would find it bound to special neural masses in his brain that we call song centers. The sex hormone is driving him to distraction: he sings incessantly and he zealously protects (from other song sparrows) a bit more than half an acre of land he calls home--usually where he was born or near there. And guess what? Eventually, she will come.

In birds, singing is an aggressive act, and it's a male thing. It helps procure and then proclaims ownership of a territory, and it defies other males to enter. A real virtuoso may also attract more mature females. The two guys here last year "decided" that a row of crab apples marked the boundary between their territories. Their clear, short notes with a characteristic trill started every morning at a bit after five. Only for the first week or two was there any chasing or other sparring. They just sang to each other after that. If I had recorded either song and played it back just inside the other's territory, that guy would have rushed over to see why the rules had changed. If I had recorded a third male's song and played it to either, there would have been a flurry of searching for the new guy, accompanied by lots of singing.

So why does he sing? Simple: to protect his genetic investment. You really don't want to help raise some other guy's kids. Think about that the next time you're at the opera.