Barn owl

Hunting in twilight or at night, the barn owl can target its prey and dive to the ground. 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. This bird hunts by flying slowly, quartering the ground and hovering over spots that may conceal prey. It has long, broad wings that enable it to manoeuvre and turn abruptly.[35] It has acute hearing, with ears placed asymmetrically, which improves detection of sound position and distance; the bird does not require sight to hunt. The facial disc helps with the bird's hearing, as is shown by the fact that, with the ruff feathers removed, the bird can still determine a sound source's direction, although without the disc it cannot determine the source's height.[36] It may perch on branches, fence posts, or other lookouts to scan its surroundings, and this is the main means of prey location in the oil palm plantations of Malaysia.[33][37]

Skull, showing the powerful beak

Rodents and other small mammals may constitute over ninety percent of the prey caught.[35][38][39] Birds are also taken, as well as lizards, amphibians, fish, spiders, and insects.[40][41] Even when they are plentiful, and other prey scarce, earthworms do not seem to be consumed. In North America and most of Europe, voles predominate in the diet, and shrews are the second most common food choice.[35] In Ireland, the accidental introduction of the bank vole in the 1950s led to a major shift in the barn owl's diet: where their ranges overlap, the vole is now by far the largest prey item.[42] Mice and rats are the main foodstuffs in the Mediterranean region, the tropics, subtropics, and Australia. Gophers, muskrats, hares, rabbits, and bats are also preyed upon.[43][44] Barn owls are usually specialist feeders in productive areas and generalists in areas where prey is scarce.[35]

On the Cape Verde Islands, geckos are the mainstay of the diet, supplemented by birds such as plovers, godwits, turnstones, weavers, and pratincoles.[45] 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).[46] On bird-rich islands, a barn owl might include birds as some fifteen to twenty percent of its diet, while in grassland it will gorge itself on swarming termites, or on Orthoptera such as Copiphorinae katydids, Jerusalem crickets (Stenopelmatidae), or true crickets (Gryllidae). Smaller prey is usually torn into chunks and eaten completely, including bones and fur, while prey larger than about 100 grams (3.5 oz)—such as baby rabbits, Cryptomys blesmols, or Otomys vlei rats—is usually dismembered and the inedible parts discarded.[28][34][47]

Compared to other owls of similar size, the barn owl has a much higher metabolic rate, requiring relatively more food. Relative to its size, barn owls consume more rodents. Studies have shown that an individual barn owl may eat one or more voles (or their equivalent) per night, equivalent to about fourteen percent of the bird's bodyweight. Excess food is often cached at roosting sites and can be used when food is scarce.[48] 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, and they can encourage barn owl habitation by providing nesting sites.[37]

Egg, Collection Museum Wiesbaden, Germany

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, such as parts of Australia, breeding may be irregular and may happen in wet periods, with the resultant temporary increase 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 Europe and 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.[49] An increase in rodent populations will usually stimulate the local barn owls to begin nesting, and, consequently, two broods are often raised in a good year, even in the cooler parts of the owl's range.[9]

Females are ready to breed at ten to eleven months of age. Barn owls are usually monogamous, sticking to one partner for life unless one of a 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 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 attract a new spouse.[50]

Clutch of eggs

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. In 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.[50]

Barn owls are cavity nesters. They choose holes in trees, fissures in cliff faces, the large nests of other birds such as the hamerkop (Scopus umbretta), and, particularly in Europe and North America, old buildings such as farm sheds and church towers. Buildings are preferred to trees in wetter climates in the British Isles and provide better protection for fledglings from inclement weather. Tree nests tend to be in open habitats rather than in the middle of woodland, and nest holes tend to be higher in North America than in Europe, because of possible predation by raccoons (Procyon lotor). No nesting material is used as such, but as the female sits incubating the eggs, she draws in the dry furry material of which her regurgitated pellets are composed, so that by the time the chicks are hatched, they are surrounded by a carpet of shredded pellets. Oftentimes, other birds such as jackdaws (Corvus monedula) nest in the same hollow tree or building and seem to live harmoniously with the owls.[51]

Brood prior to fledging, beginning to shed their nestling down

Before commencing laying, the female spends much time near the nest and is entirely provisioned by the male. Meanwhile, the male roosts nearby and may cache any prey that is surplus to their requirements. When the female has reached peak weight, the male provides a ritual presentation of food and copulation occurs at the nest. The female lays eggs on alternate days and the clutch size averages about five eggs (the range being two to nine). The eggs are chalky white, somewhat elliptical, and about the size of bantam eggs. Incubation begins as soon as the first egg is laid. While the female is sitting on the nest, the male is constantly bringing more provisions, and they may pile up beside the female. The incubation period is about thirty days, hatching takes place over a prolonged period, and the youngest chick may be several weeks younger than its oldest sibling. In years with a plentiful supply of food, there may be a hatching success rate of about 75%. The male continues to copulate with the female when he brings food, which makes the newly hatched chicks vulnerable to injury.[50]

The chicks are at first covered with greyish-white down and develop rapidly. Within a week they can hold their heads up and shuffle around in the nest. The female tears up the food brought by the male and distributes it to the chicks. Initially, the chicks make a "chittering" sound, but this soon changes into a food-demanding "snore". By two weeks old, they are already half their adult weight and look naked, as the amount of down is insufficient to cover their growing bodies. By three weeks old, quills are starting to push through the skin and the chicks stand, making snoring noises with wings raised and tail stumps waggling, begging for food items which are now given whole.[50] Atypically among birds, barn owl chicks can "negotiate" and allow weaker ones to eat first, possibly in exchange for grooming.[52] The male is the main provider of food until all the chicks are at least four weeks old, at which time the female begins to leave the nest and starts to roost elsewhere. By the sixth week, the chicks are as big as the adults, but have slimmed down somewhat by the ninth week when they are fully fledged and start leaving the nest briefly themselves. They are still dependent on the parent birds until about thirteen weeks and receive training from the female in finding, and eventually catching, prey.[50]

Feathers become abraded over time and all birds need to replace them at intervals. Barn owls are particularly dependent on their ability to fly quietly and manoeuvre efficiently. In temperate areas, the owls undergo a prolonged moult that lasts through three phases over a period of two years. The female starts to moult while incubating the eggs and brooding the chicks, a time when the male feeds her, so she does not need to fly much. The first primary feather to be shed is a central one, number 6, and it has regrown completely by the time the female resumes hunting. Feathers 4, 5, 7, and 8 are dropped at a similar time the following year and feathers 1, 2, 3, 9 and 10 in the bird's third year of adulthood. The secondary and tail feathers are lost and replaced over a similar timescale, again starting while incubation is taking place. In the case of the tail, the two outermost tail feathers are first shed, followed by the two central ones, the other tail feathers being shed the following year.[53]

The male owl moults rather later in the year than the female, at a time when there is an abundance of food, the female has recommenced hunting, and the demands of the chicks are lessening. Unmated males without family responsibilities often start losing feathers earlier in the year. Their moult follows a pattern similarly prolonged as that of the female. The first sign that the male is moulting is often when a tail feather has been dropped at the roost.[53] A consequence of moulting is the loss of thermal insulation. This is of little importance in the tropics, and barn owls there usually moult a complete complement of flight feathers annually. The hot-climate moult may still take place over a long period but is usually concentrated at a particular time of year outside the breeding season.[54]

Predators of the barn owl include large American opossums (Didelphis), the common raccoon, and similar carnivorous mammals, as well as eagles, larger hawks, and other owls. Among the latter, the great horned owl (Bubo virginianus), in the Americas, and the Eurasian eagle-owl (B. bubo) are noted predators of barn owls. Despite some sources claiming that there is little evidence of predation by great horned owls, one study from Washington found that 10.9% of the local great horned owl's diet was made up of barn owls.[55][56][57] In Africa, the principal predators of barn owls are Verreaux's eagle-owls (Bubo lacteus) and Cape eagle-owls (B. capensis).[58][59] In Europe, although less dangerous than the eagle-owls, the chief diurnal predators are the northern goshawk (Accipiter gentilis) and the common buzzard (Buteo buteo). About 12 other large diurnal raptors and owls have also been reported as predators of barn owls, ranging from the similar-sized Cooper's hawk (Accipiter cooperii) and scarcely larger tawny owl (Strix aluco) to huge bald (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos).[60] As a result of improved conservation measures, the populations of the northern goshawk and eagle-owls are increasing, thus increasing the incidence of hunting on barn owls where the species coexist.[30]

When disturbed at its roosting site, an angry barn owl lowers its head and sways it from side to side, or the head may be lowered and stretched forward and the wings outstretched and drooped while the bird emits hisses and makes snapping noises with its beak. Another defensive attitude involves lying flat on the ground or crouching with wings spread out.[17]

Barn owls are hosts to a wide range of parasites. Fleas are present at nesting sites, and externally the birds are attacked by feather lice and feather mites, which chew the barbules of the feathers and which are transferred from bird to bird by direct contact. Blood-sucking flies, such as Ornithomyia avicularia, are often present, moving about among the plumage. Internal parasites include the fluke Strigea strigis, the tapeworm Paruternia candelabraria, several species of parasitic round worm, and spiny-headed worms in the genus Centrorhynchus. These gut parasites are acquired when the birds feed on infected prey.[61] There is some indication that female birds with more and larger spots have a greater resistance to external parasites. This is correlated with smaller bursa of Fabricius, glands associated with antibody production, and a lower fecundity of the blood-sucking fly Carnus hemapterus, which attacks nestlings.[62]

Landing on a handler's gloved hand. Captive birds often live longer than wild ones.

Unusually for a medium-sized carnivorous animal, the barn owl exhibits r-selection, producing a large number of offspring with a high growth rate, which have a low probability of surviving to adulthood.[63] Its typical lifespan is around four years.[9] In Scotland, the species has been recorded living up to 18 and possibly even 34 years. A significant cause of death in temperate areas is starvation, particularly during the winter, and with significant snow cover.[64]

Collision with road vehicles is another cause of death and may result when birds forage on mown verges. Some of these birds are in poor condition and may have been less able to evade oncoming vehicles than fit individuals. In some locations, road mortality rates can be particularly high, with collision rates being influenced by higher commercial traffic, roadside verges that are grass rather than shrubs, and where small mammals are abundant.[65] Historically, many deaths were caused by the use of pesticides, and this may still be the case in some parts of the world. Collisions with power-lines kill some birds, and being shot accounts for others, especially in Mediterranean regions.[64]

Common names such as "demon owl", "death owl", "ghost owl", or "lich owl" (from lich, an old term for a corpse) show that rural populations in many places considered barn owls to be birds of evil omen. For example, the Tzeltal people in Mexico regard them as "disease givers".[81] These owls do not "hoot", instead emitting raspy screeches and hissing noises, and their white face and underbelly feathers, visible as they fly overhead, make them look "ghostly". Consequently, they were often killed by farmers who were unaware of the benefits these birds bring.[82] Negative perceptions can also be attributed to the false belief that they could eat large animals, such as chickens and cats.[83] In Thailand, people believe that when the barn owl flies over or perches on the roof of any house, the inhabitants of that house will die.[84][85] In South Africa, barn owls are often associated with witchcraft and are persecuted. In some South African cultures, these owls are used in 'muthi' (traditional medicine) and are believed to give special powers when consumed.[86][87]

In India, beliefs about the barn owl are completely different. Hindus consider the species of owl to be the mount and symbol of Lakshmi, goddess of wealth and fortune.[85]