For the Birds Radio Program: Fruit-eating birds in winter
Like humans, birds need a balanced diet to grow healthy body tissue and fuel their activities. Birds are much more mobile than we are, moving about when food resources disappear. Every winter birds migrate from North America to Central and South America. Some, like most warblers, require insects year-round, and when supplies grow limited or completely disappear in the north, they can still find plenty of bugs in the tropics.
Insects lack some nutrients that many birds need, so many species achieve a balanced diet not every day but over a year’s time. Some birds switch from insects in summer to fruits in fall and/or winter. Eastern Kingbirds, nicknamed “bee birds” because they’re so effective at capturing bees without being stung, specialize on flying insects all summer, and then retreat to the tropics to feed almost exclusively on fruits. Tanagers and orioles take some fruits during the breeding season but strongly prefer insects, which provide protein for producing baby birds. During fall and winter they continue eating insects, but on balance take far more fruit.
Even birds who do not retreat to the tropics sometimes switch to a fruit diet in winter. American Robins, Townsend’s Solitaires, Varied Thrushes, and Cedar and Bohemian Waxwings all eat fruit almost exclusively in winter. Some seed eaters, such as Pine Grosbeaks, also take a lot of fruit in the winter.
Fruit has a patchy distribution. It may be abundant on a few trees scattered out over a large area, with absolutely none anywhere else in that area. So fruit-eaters are usually gregarious, flocking species. Their many eyes help locate fruit trees as they move along, and as they feast, their many eyes help detect predators. Waxwings pass a single fruit from bird to bird before one finally swallows it. The many mouths soften the waxy coating, making the fruit more digestible. When I was rehabbing, I once fed a Bohemian Waxwing the same mountain ash berries that birds outside were eating, and ten or fifteen minutes after swallowing one, the berry came out the other end completely intact. Rolling the berries between my fingers for a few minutes softened and broke up the outer coating enough that the bird could digest them.
Mountain ash and apple trees are very popular with birds in the north in winter. Unfortunately, so is buckthorn, and so birds are the ones who spread this invasive, exotic weed. Buckthorn crowds out native shrubs, including ones that provide fruits during different windows of time, meaning it actually reduces the food available during an annual cycle. Buckthorn sprouts up beneath branches that birds perch on. In my yard it grows right within my lilac bushes, so every year we have to chop it out again. If you have fruit trees, scan them periodically every day, or you’ll miss birds that come and go. Fruit eaters are chatty, and they recognize calls not only of their own species but of other fruit eaters, so flocks are often mixed. A Pine Grosbeak or a rare Townsend’s Solitaire might be chowing down in the midst of a waxwing or a robin flock. So when you do spy birds in your fruit trees, try to check out every individual.
“You are what you eat” seems to be spot-on with reference to birds with a sweet diet. They feed side by side, sometimes even sharing their food from bird to bird, and appear to have genuinely sweet natures. In the harshness of winter, when we are hungriest for evidence of peace on earth and good will toward one another, robins, waxwings, and other fruit-eating birds are not just a visual treat; they also warm our hearts.