The American barn owl (Tyto furcata) is usually considered a subspecies group and together with the western barn owl group, the eastern barn owl group, and sometimes the Andaman masked owl, make up the barn owl, cosmopolitan in range. The barn owl is recognized by most taxonomic authorities. A few (including the International Ornithologists' Union) separate them into distinct species, as is done here. The American barn owl is native to North and South America, and has been introduced to Hawaii.
The ashy-faced owl (T. glaucops) was for some time included in T. alba, and by some authors its populations from the Lesser Antilles still are. Based on DNA evidence, König, Weick & Becking (2009) recognised the American barn owl (T. furcata) and the Curaçao barn owl (T. bargei) as separate species, though the latter is now considered a subspecies of the American barn owl (T. furcata bargei; see #Subspecies, below).
Description The American barn owl is a medium-sized, pale-coloured owl with long wings and a short, squarish tail. However, the largest-bodied race of barn owl, T. f. furcata from Cuba and Jamaica, is also an island race, albeit being found on more sizeable islands with larger prey and few larger owls competing for dietary resources.Owls of the World: A Photographic Guide by Mikkola, H. Firefly Books (2012), The shape of the tail is a means of distinguishing the barn owl from typical owls when seen in the air. Other distinguishing features are the undulating flight pattern and the dangling, feathered legs. The pale face with its heart shape and black eyes give the flying bird a distinctive appearance, like a flat mask with oversized, oblique black eye-slits, the ridge of feathers above the beak somewhat resembling a nose.Bruce (1999) pp 34–75, Svensson et al. (1999) pp. 212–213
The bird's head and upper body typically vary between pale brown and some shade of grey (especially on the forehead and back) in most subspecies. Some are purer, richer brown instead, and all have fine black-and-white speckles except on the remiges and rectrices (main wing feathers), which are light brown with darker bands. The heart-shaped face is usually bright white, but in some subspecies it is brown. The underparts, including the tarsometatarsal (lower leg) feathers, vary from white to reddish buff among the subspecies and are either mostly unpatterned or bear a varying number of tiny blackish-brown speckles. It has been found that at least in the continental European populations, females with more spotting are healthier than plainer birds. This does not hold true for European males by contrast, where the spotting varies according to subspecies. The beak varies from pale horn to dark buff, corresponding to the general plumage hue, and the iris is blackish brown. The talons, like the beak, vary in color, ranging from pink to dark pinkish-grey and the talons are black.
On average within any one population, males tend to have fewer spots on the underside and are paler in color than females. The latter is also larger with a strong female T. alba of a large subspecies weighing over , while males are typically about 10% lighter. Nestlings are covered in white down, but the heart-shaped facial disk becomes visible soon after hatching.
In the United States, dispersal is typically over distances of , with the most travelled individuals ending up some from the point of origin. The barn owl has been successfully introduced into the Hawaiian island of Kauai in an attempt to control rodents; however, it has been found to also feed on native birds.
Behaviour and ecology
Like most owls, it is nocturnal, relying on its acute sense of hearing when hunting in complete darkness. It often becomes active shortly before dusk and can sometimes be seen during the day when relocating from one roosting site to another. Barn owls are not particularly territorial but have a home range inside which they forage. Female home ranges largely coincide with that of their mates. Outside the breeding season, males and females usually roost separately, each one having about three favoured sites in which to conceal themselves by day, and which are also visited for short periods during the night. Roosting sites include holes in trees, fissures in cliffs, disused buildings, chimneys and haysheds and are often small in comparison to nesting sites. As the breeding season approaches, the birds move back to the vicinity of the chosen nest to roost.
It is a bird of open country such as farmland or grassland with some interspersed woodland, usually at altitudes below but occasionally as high as in the tropics. This owl prefers to hunt along the edges of woods or in rough grass strips adjoining pasture. It has an effortless wavering flight as it quarters the ground, alert to the sounds made by potential prey. Like most owls, the barn owl flies silently; tiny serrations on the leading edges of its flight feathers and a hairlike fringe to the trailing edges help to break up the flow of air over the wings, thereby reducing turbulence and the noise that accompanies it. Hairlike extensions to the barbules of its feathers, which give the plumage a soft feel, also minimise noise produced during wingbeats.
Diet and feeding
The diet of the barn owl has been much studied; the items consumed can be ascertained from identifying the prey fragments in the pellets of indigestible matter that the bird regurgitates. Studies of diet have been made in most parts of the bird's range, and in moist temperate areas over 90% of the prey tends to be small mammals, whereas in hot, dry, unproductive areas, the proportion is lower, and a great variety of other creatures are eaten depending on local abundance. Most prey is terrestrial but bats and birds are also taken, as well as lizards, amphibians and insects. Even when they are plentiful and other prey scarce, earthworms do not seem to be consumed.
In North America, voles predominate in the diet and shrews are the second most common food choice. On a rocky islet off the coast of California, a clutch of four young were being reared on a diet of Leach's storm petrel (Oceanodroma leucorhoa). Locally superabundant rodent species in the weight class of several grams per individual usually make up the single largest proportion of prey. In the United States, rodents and other small mammals usually make up ninety-five percent of the diet and worldwide, over ninety percent of the prey caught.
The barn owl hunts by flying slowly, quartering the ground and hovering over spots that may conceal prey. It may also use branches, fence posts or other lookouts to scan its surroundings. The bird has long, broad wings, enabling it to maneuver and turn abruptly. Its legs and toes are long and slender which improves its ability to forage among dense foliage or beneath the snow and gives it a wide spread of talons when attacking prey. Studies have shown that an individual barn owl may eat one or more voles (or their equivalent) per night, equivalent to about twenty-three percent of the bird's bodyweight. Excess food is often cached at roosting sites and can be used when food is scarce.
Small prey is usually torn into chunks and eaten completely including bones and fur, while prey larger than about 100 g (4 oz), such as baby rabbits, Cryptomys blesmols, or Otomys vlei rats, is usually dismembered and the inedible parts discarded. Contrary to what is sometimes assumed, the barn owl does not eat domestic animals on any sort of regular basis. Regionally, non-rodent foods are used as per availability. On bird-rich islands, a barn owl might include some fifteen to twenty percent of birds in its diet, while in grassland it will gorge itself on swarming termites, or on Orthoptera such as Copiphorinae katydids, or true crickets (Gryllidae). Bats and even frogs, lizards and snakes may make a minor but significant contribution to the diet.
It has acute hearing, with ears placed asymmetrically. This improves detection of sound position and distance and the bird does not require sight to hunt. The facial disc plays a part in this process, as is shown by the fact that with the ruff feathers removed, the bird can still locate the source in azimuth but fails to do so in elevation. Hunting nocturnally or crepuscularly, this bird can target its prey and dive to the ground, penetrating its talons through snow, grass or brush to seize small creatures with deadly accuracy. Compared to other owls of similar size, it has a much higher metabolic rate, requiring relatively more food. Weight for weight, they consume more rodents—often regarded as pests by humans—than possibly any other creature. This makes the barn owl one of the most economically valuable wildlife animals for agriculture. Farmers often find these owls more effective than poison in keeping down rodent pests.
Breeding Barn owls living in tropical regions can breed at any time of year, but some seasonality in nesting is still evident. Where there are distinct wet and dry seasons, egg-laying usually takes place during the dry season, with increased rodent prey becoming available to the birds as the vegetation dies off. In arid regions, breeding may be irregular and may happen in wet periods, triggered by temporary increases in the populations of small mammals. In temperate climates, nesting seasons become more distinct and there are some seasons of the year when no egg-laying takes place. In North America, most nesting takes place between March and June when temperatures are increasing. The actual dates of egg-laying vary by year and by location, being correlated with the amount of prey-rich foraging habitat around the nest site and often with the phase of the rodent abundance cycle.
Females are ready to breed at 10 to 11 months of age although males sometimes wait till the following year. Barn owls are usually monogamous, sticking to one partner for life unless one of the pair dies. During the non-breeding season they may roost separately, but as the breeding season approaches they return to their established nesting site, showing considerable site fidelity. In colder climates, in harsh weather and where winter food supplies may be scarce, they may roost in farm buildings and in barns between hay bales, but they then run the risk that their selected nesting hole may be taken over by some other, earlier-nesting species. Single males may establish feeding territories, patrolling the hunting areas, occasionally stopping to hover, and perching on lofty eminences where they screech to attract a mate. Where a female has lost her mate but maintained her breeding site, she usually seems to manage to attract a new spouse.Shawyer (1994) pp. 67–87
Once a pair-bond has been formed, the male will make short flights at dusk around the nesting and roosting sites and then longer circuits to establish a home range. When he is later joined by the female, there is much chasing, turning and twisting in flight, and frequent screeches, the male's being high-pitched and tremulous and the female's lower and harsher. At later stages of courtship, the male emerges at dusk, climbs high into the sky and then swoops back to the vicinity of the female at speed. He then sets off to forage. The female meanwhile sits in an eminent position and preens, returning to the nest a minute or two before the male arrives with food for her. Such feeding behaviour of the female by the male is common, helps build the pair-bond and increases the female's fitness before egg-laying commences.