Bird Food Habits
W. L. McAtee made a significant contribution to ornithology by reporting on the food habits of individual bird species. From before he even graduated from the University of Indiana in 1904, he spent his entire career working for the United States Division of Biological Survey - today the Biology Resources Division of the U. S. Geological Survey.
McAtee will always be known as the most famous economic ornithologist in the world. No one will ever be able to surpass his accomplishments, because he lived at a time when he could study what birds ate by shooting them and examining their stomach contents. Consider examples of the numbers of birds he and his associates collected and examined: 928 Eastern meadowlarks, 1422 robins and 417 pine grosbeaks.
Many readers today will consider the shooting of about a half million birds a terrible way to carry out such an investigation, but they should consider three things. First, well into the 20th century the way ornithologists identified birds was "in the hand"; in other words shot. McAtee was at least collecting the birds for a purpose. (Bird droppings were also collected and examined.) Second, there are reasons for the large number of birds studied: he was able to describe food habits at different times of year and in different parts of the country. And finally, do we feel quite as bad about his studies of the diet of mice and rats in this same way?
Whether we like his methods or not, much useful information has been derived from this data. The best source for this information is a book by Martin, Zim and Nelson, American Wildlife and Plants: A Guide to Wildlife Food Habits.
Consider for example what we know from the data collected by McAtee and others about the wild turkey. Its most common animal food items are: "beetles, grasshoppers, crickets and walking sticks, ants, wasps and bees, flies (especially Marchflies), crayfish, spiders, snails, millipedes and centipedes, caterpillars and true bugs. There are a few records of salamanders being eaten." And the turkey's plant food: They are "particularly fond of nuts such as acorns and beechnuts (one crop contained 221 large acorns)" but they also consume grape and dogwood fruit in season. Corn and wheat play only a minor role in their diet.
Or consider the great blue heron: 43% of its diet is non-game fish, 25% useful species, 8% insects, 8% crayfish and other crustaceans, 5% mice and shrews and 4% snakes and amphibians. Virtually no plant food is eaten.
Among the interesting conclusions derived from this data, one relates to tree swallows. Birders know this swallow species as the first to arrive in spring. They show up a week or two before barn, rough-winged and other swallows. It is not uncommon to see tree swallows flying over our regional marshes amid late winter snowflakes. Data provided by McAtee and Frank Chapman show that all swallow species except tree swallows feed exclusively on flying insects. But tree swallows eat plant food as well. In fact, in late winter 30% of their diet is botanical. Thus they can get along on plant food before the early hatches of flying insects necessary to their swallow cousins.
It is especially interesting to examine the information about birds that we now attract to feeders for McAtee's data were collected before people thought of providing such food. The winter diet of the white-breasted nuthatch, for example, was 68% plant food, largely oak, corn and pine. But that percentage dropped off rapidly with no plant food consumed during summer when insects are readily available.
This nuthatch information relates to a question I am often asked: why do birds stop coming to my feeder in spring? McAtee's reports show that many birds turn from plant food (including those seeds you have been feeding them) to insects at nesting time, thus building up their protein resources for breeding.
Shortly before McAtee died in 1961, he contacted me about another of his ornithological contributions. Over his lifetime he had collected bird folk names and he sought to have those he found in New York published in The Kingbird, the state journal I edited at the time. I will write about those interesting names in another column.-- Gerry Rising