VERTEBRATE PESTS: A Guide to Managing Crows: Part I

Most of us are familiar with crows.

Their large size, penetrating glances and familiar "caw, caw" are hard to mistake for any other bird. Crows now have much more of a presence in and around various urban areas all around the world. In fact, crows are now considered major pests in many urban communities.

Consequently, pest management professionals are being increasingly called upon to "do something" about these annoying birds. Here, we’ll examine the biology and behavior of this fascinating bird. Next month, in part II, we will discuss crow management programs.

IDENTIFICATION. Crows belong to the bird genus, Corvus, which means "harsh sound." Four species of crows occur in the United States: the American crow, Corvus brachyrhynchos; the fish crow, Corvus ossi-fragus; the northwestern crow, C. caurinus; and the Mexican crow, C. imparatus.

Ornithologists and birding enthusiasts can distinguish among the different species but it may be difficult for most other people and pest professionals. It is the American Crow however, that is the most commonly encountered crow throughout the United States. Thus, the American crow is also referred to as the common crow and the eastern crow.

The American crow is a relatively large bird (17 to 21 inches/43 to 53 cm). Male and female crows are similar in appearance. The only other bird mistaken for a crow is the raven, which is a close relative (i.e., ravens also belong to the genus Corvus). Ravens are larger and lankier than crows, have wedge-shaped tails, heavier bills and deeper voices. Ravens have a soaring, gliding flight pattern; crows have a frequent steady wing beat with little or no gliding.

BIOLOGY AND BEHAVIOR. Crows are among the most intelligent of all birds, although many exaggerations are made as to their abilities. Still, crows can count up to four, have excellent memories, can solve various puzzles and quickly learn to associate various noises and symbols with food. Crows have been recorded in parks watching people storing food inside latched coolers, waiting for the owners to walk away and then unlatching the coolers using their beaks and toes and stealing the food. Crows have also been seen dropping nuts onto residential streets and waiting for automobiles to crack the nuts.

Many other "smart crow stories" exist. On a more everyday level, most of us can attest as to the amazing ability of the crow to avoid our cars at the last second when we rapidly come upon them feeding on carrion in the road.

Crows nest in February and continue through May depending on the part of the country and the particular year. Their nests are established in trees and various types of vertical structures (e.g., telephone poles, utility towers, etc.) in both rural and urban areas. Nests are commonly established as high up as 60 to 75 feet. When necessary, crows will also nest on the ground. Crow nests are crude structures comprised of twigs, sticks and plant stems and are lined with grass, cloth, feathers and various other items the crow has scavenged in its local environment.

A CROW’S DIET. Crows are highly adaptable in what they will eat. In urban areas, crows are opportunists, feeding on a wide range of items. Crows will eat virtually anything humans eat and all the foods and food scraps people discard. Natural foods include insects, berries, nuts and a wide range of animals both alive and dead. In fact, crows are valuable natural "garbage collectors" as they consume road-killed animals and other types of carrion.

Crows, in addition to many other animals, also help to provide some balance in nature as they consume beetles, larvae, caterpillars, spiders, millipedes, snakes and a long list of invertebrates and small vertebrates they encounter. Crows also attack and eat the eggs and young of other birds. In agricultural areas, crows feed heavily from cornfields, as well as other grains such as wheat, peanuts, pecans, sorghum, etc.

The average clutch is four to six eggs that hatch in about 18 days. The American crow typically produces only one brood per year, although two broods are common in some southern areas. The young are fledged at about one month of age and learn their local territory and how to forage by remaining with and mimicking their parents throughout the summer.

In urban areas, wild crows usually live for about four to six years, although in captivity, some crows have lived for more than 20 years. Due to their intelligence and wariness, crows can avoid many predators, although raccoons, hawks and owls take nestlings and young inexperienced crows.

Families of crows tend to join together during the fall season, sometimes creating large crow flocks in urban areas. Depending on the locale, the particular season and species, sometimes the larger groups will migrate in the late fall or winter.

In some parts of the U.S., winter flocks result in millions of crows roosting. These flocks roost together at night and disperse over large areas to feed during the day. Their feeding range is typically within 6 to 12 miles (10 to 20 km) from the roost. It is often these large flocks that cause people to call the board of health, or inquire of their pest professional as to getting rid of these obnoxious birds.

Next month we’ll discuss management options for crow infestations.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@pctonline.com.