i). Non-mammalian prey, including birds, amphibians, reptiles and large insects are occasionally consumed. Prey usually are swallowed whole, although large items are sometimes torn into smaller pieces before being eaten. Indigestible bones and fur are later regurgitated in the form of an "owl pellet." The diets of barn owls can be analyzed by examining the contents of these pellets.
Habitat and Nest Sites
Barn owls inhabit open areas, including agricultural fields, grasslands and marshes. They nest in hollow trees and in buildings where there is not much human activity. Barn owls also will use artificial nest boxes. Nests typically are located on the floor of the natural tree cavity or building (Figure 2). They are made with broken-down bits of old owl pellets. Nest sites are commonly reused by the original occupants or other pairs of owls. The availability of potential nesting sites limits barn owl abundance in some areas.
Barn owls have a global distribution. They are absent only from parts of the West Indies, Indonesia, and New Zealand, and seldom occur at extreme northern latitudes. Estimates of individual home ranges, which vary greatly, have been as large as 3174 ha (12.3 sq mi) and as small as 151 ha (0.6 sq mi). This variation probably is due to differences in habitat and prey availability. For example, if food is scarce in a particular area, an owl may have to travel long distances to get the amount of food that it needs to survive. It would have to hunt over a much smaller area if food is plentiful. The home ranges of neighboring barn owls can overlap significantly.
Behavior and Sociality
These owls are strictly nocturnal predators and spend the daylight hours resting, or "roosting," in quiet protected areas. Members of a pair frequently roost together. They usually do not actively defend their foraging territories from other owls, but they will defend the area immediately around their nests. If food resources are abundant, barn owls sometimes nest in close proximity to each other. For example, at least five pairs are known to nest regularly in a single barn in south Florida. When cornered, barn owls exhibit a variety of threat displays including wing spreading, head waggling, hissing, and bill snapping.
Reproduction and Development
Barn owls usually are monogamous and often remain with the same partner for several consecutive breeding seasons. Eggs are laid between February and June, depending on locality and climate. In Florida, eggs are usually laid in February. In subtropical and tropical areas, including southern Florida, a second set of offspring are produced in the late summer or fall. The average number of eggs produced is 4–6, but extremes of more than 10 eggs in a single nest have been observed. Eggs are laid 2 or 3 days apart and hatch in that same sequence. As a result, there is always an age difference of a few days between each chick (Figure 3). This ensures that at least a few of the chicks, because they are older and stronger, will always be fed if food becomes scarce. If food is plentiful, all of the chicks will be able to eat. Chicks grow rapidly, achieving adult weight and feathering in 8–9 weeks (Figure 4). At this point they roost near the nest while learning to fly and hunt. Their parents still bring food to them for another few weeks until they become fully independent.
Barn owl populations are stable in some parts of their range, including Florida, but seven midwestern states list barn owls as threatened or endangered. Nine other states classify them as a species of concern. Population declines also have been noted in Europe. The most often cited cause of these declines has been the loss of nesting and roosting sites resulting from changing agricultural practices and urbanization. As agriculture has increased in scale and modern farming techniques implemented, many open-air barns and other farm buildings have disappeared from the landscape. Rows of trees that were once a common feature in small-scale agriculture also have been removed, further degrading barn owl habitat. Additionally, th