January 22, 2015
We love this guest student blog post by Connor Rosenblatt — now we know a bit more about how different species cope with the wind. Thanks Connor!
As cold weather sets in, we are all reminded of the signs of winter by the rapid drop in temperatures and the cold, biting wind. Fortunately, we have the option of putting on a heavy jacket or huddling around a warm, cozy fire. But unlike us, the birds are not so fortunate. So what do they do when the weather gets cold?
When it comes to dealing with winter, researchers Andrew S. Dolby and Thomas C. Grubb Jr. found that in small, isolated blocks of forest, birds adjust their foraging behavior to deal with these cold conditions. Specifically, these two researchers looked at isolated woodland plots that were on average about 13 acres (equivalent to slightly less than 10 football fields-just around the size of a woodland plot many residents in suburban and rural communities have behind their houses). By placing color bands on the legs of Carolina Chickadees (Poecile carolinensis), Tufted Titmice (Baeolophus bicolor), White-breasted Nuthatches (Sitta canadensis), and Downy Woodpeckers (Picoides pubescens), the researchers were able to track these birds as they moved throughout the plots, and drew some very interesting conclusions about how the foraging behavior of these birds changed with respect to weather.
On the windiest days, it was found that Carolina Chickadees and Tufted Titmice foraged significantly lower in trees than on the least windy days. This is likely to shield them from the wind and help maintain body heat. The researchers concluded that the failure to find a correlation with Downy Woodpeckers and White-breasted Nuthatches likely stems from modes of foraging. Downy Woodpeckers and White-breasted Nuthatches forage by gripping the trunk of the tree, and can easily orient themselves to the side of the trunk that is shielded from the wind, while Chickadees and Titmice cannot easily do this while foraging.
In addition, horizontal use (overall land area used by the birds) of the woodland plot was greatly reduced in all species with the exception of female Downy Woodpeckers (due to dominant male woodpeckers excluding females from the best foraging areas). On cold, windy days, birds were found further away from the windward edge, and tended to concentrate around the center of the plot, furthest away from exposed edges.
So what does this mean for the flock of birds living in the small woodlot behind your house? Because these birds have a restricted foraging area on the harshest days (the center area of a woodland plot), they can rapidly consume all available food in this particular section of the plot. In a particularly harsh winter, when the food supply in a localized area of a small woodland plot is quickly diminished, the birds are forced to move out to a new plot, and if they do not, they may die from exposure to harsh conditions by having to forage on the outskirts of the plot where food remains.
As the weather continues to harshen, pay close attention to what happens to the birds living in that small woodlot behind your house. It is possible that on the windiest days, they may retreat deep into the woods, and be relatively scarce at your feeders. If it is a particularly bad winter, you may witness a dramatic decrease in bird abundance if they are forced to move into a large area of woods. Of course, this is all saying the birds weight the costs of metabolism over the costs of snagging a delicious treat at the feeders.
Reference: Dolby, A. S., and Grubb Jr., T. C. (1999). Effects of Winter Weather on Horizontal and Vertical Use of Isolated Forest Fragments by Bark-Foraging Birds. The Condor, 101(2), 408-412. 10.2307/1370006