After wintering in the South, doves often concentrate into large flocks in late winter and early spring. In March and April these flocks break up and many birds move north, where they remain for the nesting season. During the summer breeding season, doves occupy all of the lower 48 states, portions of southern Canada, and much of Mexico (Figure 3). Doves begin to leave northern states after the first cold weather in late August or early September. The doves that remain in the South have a longer nesting season and make more nests than those in northern states. During nesting, the movements of parents are confined to a small area around the nest. After nesting, local parents and young birds use a home range of about 10 square miles and travel up to three miles between feeding sites in fields and roosts. Favored roosts are in tall pines. During the summer, the local population increases with the regular addition of young birds from the nests. When dove season opens in the Southeast, it is mainly local birds found in dove fields. After a few days of shooting, the birds may change their habits. Some will disperse from grain fields where there is shooting and move to feed in unhunted areas or the suburbs of nearby cities.
Nesting declines in September and ends in October. Some doves winter in northern states but the majority head south after the first cold weather in late August or early September. They fly south at an average of 10 miles a day. Contrary to popular stories, doves rarely fly faster than 35 miles an hour but they are capable of brief spurts of slightly more than 50 mph. Migrant doves provide an increasing percentage of the harvest in the late fall and early winter dove hunting seasons.
Population dynamics is the study of the increases and decreases in a population, and the factors that cause them. How can doves keep their numbers up in the face of heavy losses caused by hunting, nest losses, a short life span and a clutch size of only two eggs? Doves are not adaptable to a wide variety of habitats. Yet doves are more numerous than quail, turkeys and other birds that lay far more eggs. How can this be so?
Dove populations are near their peak in early September. At this time daily mortality averages four to five percent. As young birds get more experience the survivors increase their chances of living long enough to nest. Doves have a survivorship of about 50 percent. Banding studies show that about 53 percent of adults and 44 percent of young will survive for another year, and about 40 percent of nests produce at least one fledgling. Hunters shoot about 50 million birds a year, out of a population of perhaps 500 million. Some doves are lost to diseases, such as trichomoniasis (an infection of the crop), and predators.
One reason for the abundance of mourning doves is that they are adapted to agricultural land. Land that is frequently broken, tilled, planted, even abused or eroded is beneficial to doves. Annual plants that invade cleared lands benefit doves, because these plants bear far more seed than perennials do.
A second reason for high numbers of doves is that they feed at the bottom of the food chain where there is more food available. The food chain starts with plants, which are eaten by vegetarians, which are in turn eaten by predators. Doves need only plant food to survive, and plants are the most abundant food source in any ecosystem. Most birds, even grain eaters, cannot exist on plant food alone. They need at least a portion of their diet in the form of high-protein insects or other animal matter. Doves, on the other hand, can be healthy on a year-round diet composed exclusively of seeds, and they eat a wide variety of seeds, as compared to some animals that eat a limited variety.
Doves are not territorial, so they can tolerate nesting close to one another, unlike robins or mockingbirds, which are intolerant of close neighbors. Doves can live in social flocks and travel long distances to concentrated food sources.
Doves become independent from their parents at an early age. Even if the nest is successful the parents do not linger with the young or quit reproducing for the year. Quail, turkeys and wood ducks do not normally produce another nest that season if their young remain alive, but doves, if they are well nourished, will renest within a few days of their young leaving the nest.
Doves are numerous because they have habits different from those that caused the extinction of their larger relative the passenger pigeon. The passenger pigeon nested in dense colonies, so it was easy for people to overexploit them. Mourning doves nest individually over a wide area, so their nests are not easy for people to find and destroy. Passenger pigeons used old oak and chestnut forests for nesting but the mourning dove could use the farmland created by the destruction of these forests. The passenger pigeon needed concentrations of food, and the mourning dove benefits from concentrated food sources such as grainfields, but can also thrive on sparse scattered food sources.
Wildlife biologists cannot claim credit for restoring and increasing dove populations the way they can for increasing other popular species such as deer, turkey and wood ducks. High dove populations are an accident of land use in the Southeast. Doves can rebound after almost any amount of hunting pressure. As a result, we can expect to have healthy dove populations in the future.