SEPTEMBER
2006

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

9-14-06

Other Animals Help Birds Find Bug Food

Food is essential to all living animals. "Eat or be eaten" is more than a catch phrase in the rough-and-tumble world of animal behavior. It is a matter of survival.

For instance, insects can be nutritious meals for some of our fine-feathered friends. Even though insects are among the most numerous of animals, rustling up bug grub can be a full-time job for birds. This is especially true if bottomless pit, open-mouthed babies are growing up in a nest.

A few species of birds sometimes enlist the help of other animals in the bug-food acquisition process. Cowbirds are examples of such behavior. However, it is not their food-finding habits that make cowbirds unusual.

Cowbirds are best known for their habit of laying eggs in nests of other bird species. Such egg-laying behavior means that cowbirds are classified biologically as parasites. By definition, parasites are plants or animals that live at the expense of other living things. In this case, the cowbird delegates the rigors of child rearing to other birds, oftentimes to the detriment of the host's real offspring, and is, therefore, a parasitic bird.

The name of the cowbird has nothing to do with its egg-laying habits. But the name cowbird does say something about feeding behavior. The name is based on the bird's habit of hanging around grazing cattle. Actually, such behavior began with the great herds of bison that roamed the North American prairies long before cattle were introduced on the continent. The movement of grass-chomping bison or cattle disturbs insects in the vegetation. The dislodged insects become easy meals for the cowbirds that saunter along among the grazing bovines.

Several species of birds also take advantage of insects flushed from hiding by other animals. For instance, shrikes feed on insects that flee advancing columns of African driver ants.

Sometimes human activity assists birds as they forage for insect prey. Nighthawks can frequently be seen zooming in and out of the aura of a pole light as they feast upon flying insects, which are attracted by the light. Other insectivorous animals have also discovered that insects accumulating around a light make easy pickings. Bats join the nighthawks in the aerial repast, while toads hang around the base of the pole light to pick off any low-flying tasty morsels.

Hay cutting and lawn mowing are human activities that create masses of flying insects. These are reasons that flocks of swallows can be seen circling and following mowing machines. The swallows are taking advantage of the situation to fill their crops with insects that have been dislodged from their plant homes.

Seagulls and cattle egrets are sometimes observed following farm equipment as fields are tilled in the heartland of the United States. These birds are gleaning soil-dwelling insects, such as grubs and wireworms, from the upturned soil. Both of these insects can be pests, so farmers are happy to have the birds stopping to feed.

Seagulls are not normally seen treading on soil destined to be cornfields of Iowa or wheat fields of Kansas. These birds are shore and ocean birds, but great flocks have been observed feeding in fields far from a lake or ocean. The vagabond seagull travelers have learned that human activity can make an insect meal accessible and are as happy to follow a plow as an ocean trawler in their search for a meal.

Cars and trucks can also provide an insect meal for birds. Vehicles moving over roadways during the summer months kill many insects. Several species of birds, including cardinals and English sparrows, have learned that stopped vehicles provide a smorgasbord of "bugs on the grill." You can frequently witness such birds picking up a meal at Interstate rest areas and mall parking lots during the summer months.

Yellow jackets feed on other insects and willingly carry away "insect road kill" from bumpers or grills of vehicles. When it comes to food procurement by insect eaters, a few species have adopted a behavior summarized by a line from the Beatles, "I'll get by with a little help from my friends."

 

Writer: Tom Turpin
Editor: Olivia Maddox