When it comes to late winter on Cape Cod, and the knowledge that beach weather is still four months away, it’s the little signs of better things to come that keep you going. If you are paying attention to the birds around you every day, you should be brimming with hope, because they clearly are, too.
Even though the bird bath is still frozen every morning, species like Northern Cardinals, Song Sparrows, Carolina Wrens, and House Finches have been belting out lusty, full throated versions of their territorial songs. Even species we don’t exactly think of as songsters, like titmice, chickadees, and woodpeckers, have been “singing” their versions of male territorial songs a lot more frequently the last couple of weeks. So what is it on these frozen mornings that gives these birds the seemingly irrational exuberance to sing like it’s mid-May? It’s obviously not temperature. The answer is something that has deep evolutionary roots across all kinds of organisms, including humans, and it’s called photoperiod.
Photoperiod is the ratio of dark to light hours in any given day, so it’s basically day length, but you sound way smarter if you call it “photoperiod”. And it’s absolutely fundamental to some of the most important aspects of plant and animal physiology. It regulates everything from leaf fall in deciduous trees to flowering of certain garden plants to migration of birds, and reproductive hormones in many animals.
The mechanism is different in different organisms, but basically everything has some kind of photoreceptors that transmit information about light and dark periods to the brain or directly to the endocrine system, which then produces hormones that create physical and behavioral changes. Even we humans are not immune to photoperiod. Information about light travels through our eye and eventually reaches the pineal gland, which produces melatonin, the hormone that tells us whether to be sleepy or not. But if you’re sleepy right now, it’s more likely because this bird report has gotten a little too technical. But stay with me.
In birds, photoperiod regulates both singing and reproduction, but in different ways. Song frequency is regulated by melatonin, oddly enough, which causes song control structures in their brains to develop. So that extra loud performance by your local Carolina Wren this week is a direct result of structural changes in the brain. Day length also directly affects birds’ reproductive organs, which shrink each fall and develop anew each spring. This means many birds technically go through puberty every year. I don’t know how they do it – I barely survived it once.
If the extra singing isn’t enough to get you through late winter, there are new birds arriving back from their wintering grounds already. The hardiest of the hardy migrant songbirds are on the move in the form of Red-winged Blackbirds and Common Grackles, and Turkey Vultures are also beginning to trickle back. Plus, many of our locally breeding American Woodcocks are already back and displaying in the last week.
So as we slow-roll towards spring, look to the birds for signs of hope. Maybe you’ll even be moved to belt out a cheerful, forward-looking tune from your back deck one of these mornings. Just ignore the “For Sale” signs that go up in your neighbor’s yards as a result – they obviously don’t understand photoperiod.