Tuesday, March 5, 2013

Where Do Birds Go During Blizzards?

Cold, barren, bird-less...
As plumes of snow stream down from the heavens and bury me indoors, I wonder again about the lives of avifauna around me. Why are forests so lifeless, so silent, when snowstorms come through? Why are prairies so desolate? Why are wetlands populated by nothing more than wind and snow? It certainly enhances the mystique of the blizzard, but in the end it comes down to the survival of creatures that don't have the propensity to shelter that we do.

Before we take pity on the birds, we must remember that millions of years of adaptation have morphed these creatures into a form wherein they are highly able to eek out a living in the winter. But what does this mean? In nature, any adaptation is always a compromise, a balance, between the new and the old, as the new develops from the old. For most songbirds, the old behavior is to cover larger areas in search of every morsel of food in every nook and cranny to reap the greatest benefits from their territory. For example, Baltimore Oriole pairs maintain a territory around the size of a football field during the breeding season. While doing this, they must defend their territory from intruders and themselves from predators. But this old way of behavior must change entirely for the winter, and especially during a snowstorm.

Our first factor in winter survival is that food is far less evenly distributed, with some areas being supplied with super-abundant food, while others have no available food at all. With food sources fewer and farther in between, songbirds have to find these isolated food sources to supply their daily energy needs. This breaks down the  breeding season concept of territory. Now that resident songbirds no longer have to defend territory containing nests, they can roam more freely in search of reliable food sources. Once they find them, the bird is more likely to stay there because constantly searching for food requires much more energy in the cold, which is the second factor in adapting to survival in the winter. With more energy used to stay warm, it makes more sense to stop wandering and stay put in areas that will reliably provide food for a sustained period of time, e.g. feeders or large areas packed fruiting plants. That's where the initial adaptation is.

European winter feeding flock
This all results in a more social element in winter songbirds. So whereas you will find birds like American Robins, Red-winged Blackbirds, American Goldfinches, and various sparrows to be isolated in the breeding season, when snow comes through, you find them in sometimes unbelievably huge roosts and feeding flocks. Birds that were once evenly distributed around given areas like their food sources are forced to cluster unevenly around their unevenly clustered food sources.  Remember too that flocks, though often forming simply because more birds have to pack around reliable food sources, also allow birds to use less energy searching for predators and more energy collecting food. This reconciles even more for energy lost remaining warm. In the winter, it becomes an advantage to be social at these isolated food sources, where other songbirds are invariably going to group. This is the initial adaptation--staying put around isolated and reliable food sources--taken to the next level; I'll call it the "resulting adaptation": social behavior. I like thinking of it as an equation, or better yet a conditional statement: If cold weather + isolated food sources -> birds stay put at food sources. If more birds stay put stay put at food sources -> social behavior develops. If you're still following, ultimately, this would mean that cold weather + isolated food sources = larger, social feeding flocks. Cool!!

The breeding season could be said to tear birds apart, and then the challenge of surviving winter, especially snowstorms, brings them back together. It would be accurate to summarize this process by saying that once the territorial boundaries of breeding songbirds break down, and food sources become more difficult to find, songbirds adapt their behavior to cluster together in social feeding flocks, and remain tight around food rich areas. That's all it is: an adaptation of behavior to survive in the winter.

With more birds clustered tightly in specific areas, this leaves greater areas of perfectly desirable habitat, well, bird-less because they lack reliable food sources. And voila!! The perfect recipe for making it seem like resident songbirds "disappear" in a snowstorm, and the winter overall.

Winter is a perfect time to see this strategy in survival--how staying alive requires an exact formula that results from millions of years of adaptation in similar conditions. That's not to say that songbirds are never found alone in the winter, because they are. That's not to that songbirds don't die in the winter, because they do, but the majority survive in an average winter, and there's a reason for that.

Stunning winter Cardinal by Daniel Behm
So as you're watching sadly as a cloud of snow descends upon your neighborhood, dreaming nostalgically of the Cardinal that sang outside your window just yesterday (birding blues), know that to find him, and many others like him, all you have to do is find the food sources. And with these food sources, you will find so many birds, and maybe a few rare ones too!


  1. Another impressive piece, Nick. And now my mind is connecting to behaviors seen at winter bird feeders. Hmmm...

    1. Awesome. Glad I could catalyze some more connections, Mr. Yellowparts!