Burrowing Owl

The burrowing owl (Athene cunicularia) is a small, long-legged, primarily terrestrial—though not flightless—species of owl native to the open landscapes of North and South America. They are typically found in grasslands, rangelands, agricultural areas, deserts, or any other open, dry area with low vegetation. They nest and roost in burrows, and, despite their common name, do not often construct these dwellings themselves, rather repurposing disused burrows or tunnels previously excavated and inhabited by other species, such as American badgers (Taxidea taxus), foxes (Vulpes sp.), ground squirrels or prairie dogs (Cynomys spp.), among others.

Unlike most owls, burrowing owls are often active during the day, although they tend to avoid the heat of midday. But, similar to many other species of owls, they are mostly crepuscular hunters, as they can utilize their night vision and attuned hearing to maximum potential during sunrise and sunset. Having evolved to live on open grasslands and prairie habitat (as well as badlands, chaparral and desert ecosystems), as opposed to dense forest, the burrowing owl has developed longer legs than other owls, a trait which enables it to sprint when pursuing its prey, not dissimilarly to the greater roadrunner, as well as providing momentum when taking flight; however, burrowing owls typically only become airborne for short bursts, such as when fleeing threats, and typically do not fly very high off of the ground.

Taxonomy

The burrowing owl was formally described by Spanish naturalist Juan Ignacio Molina in 1782 under the binomial name Strix cunicularia from a specimen collected in Chile. The specific epithet is from the Latin cunicularius, meaning "burrower" or "miner". The burrowing owl is now placed in the genus Athene which was introduced by German zoologist Friedrich Boie in 1822.

The burrowing owl is sometimes classified in the monotypic genus Speotyto (based on an overall unique morphology and karyotype). Osteology and DNA sequence data, though, suggests that the burrowing owl is a terrestrial member of the little owls genus (Athene), thus it is placed in that group today by most authorities.

A considerable number of subspecies have been described, though they differ little in appearance; the taxonomic validity of several is still up for debate. Most subspecies are found in or near the Andes and within the Antilles of the Caribbean Sea. Although distinct from each other, the relationship of the Florida subspecies, for instance, to (and its distinctness from) the Caribbean owls, is not quite clear.

The 18 recognised subspecies, of which two are now extinct, are:

†A. c. amaura (Lawrence, 1878): Antiguan burrowing owl – formerly Antigua and Saint Kitts and Nevis; extinct (circa 1905)

A. c. boliviana (L. Kelso, 1939): Bolivian burrowing owl – the Bolivian altiplano

A. c. brachyptera (Richmond, 1896): Margarita Island burrowing owl – Margarita Island (may include A. c. apurensis)

A. c. carrikeri (Stone, 1922): East Colombian burrowing owl – Eastern Colombia; doubtfully distinct from A. c. tolimae

A. c. cunicularia (Molina, 1782):- southern burrowing owl – lowlands of southern Bolivia and southern Brazil south to Tierra del Fuego

A. c. floridana (Ridgway, 1874): Florida burrowing owl – Florida and the Bahamas; listed as Vulnerable

A. c. grallaria (Temminck, 1822): Brazilian burrowing owl – Central and eastern Brazil

†A. c. guadeloupensis (Ridgway, 1874): Guadeloupe burrowing owl – formerly Guadeloupe and Marie-Galante islands; extinct (circa 1890)

A. c. guantanamensis (Garrido, 2001): Cuban burrowing owl – Cuba and Isla de la Juventud

A. c. hypugaea (Bonaparte, 1825): western burrowing owl – Southern Canada through the Great Plains, south to Central America; listed as Apparently Secure

A. c. juninensis (Berlepsch & Stolzmann, 1902): south Andean burrowing owl – Andes Mountains and foothills from central Perú to northwestern Argentina (may include A. c. punensis)

A. c. minor (Cory, 1918): Guyanese burrowing owl – southern Guyana and Roraima state (Brazil)

A. c. nanodes (Berlepsch & Stolzmann, 1892): Southwest Peruvian burrowing owl – southwestern Perú (may include A. c. intermedia)

A. c. pichinchae (Boetticher, 1929): West Ecuadorean burrowing owl – western Ecuador

A. c. rostrata (C. H. Townsend, 1890): Revillagigedo burrowing owl – Clarion and Revillagigedo Islands

A. c. tolimae (Stone, 1899): West Colombian burrowing owl – Western Colombia (may include A. c. carrikeri)

A. c. troglodytes (Wetmore & Swales, 1931): Hispaniolan burrowing owl – Hispaniola (Haiti and the Dominican Republic) and surrounding islands (Gonâve, Beata Island)

A. c. partridgei (Olrog, 1976): Corrientes burrowing owl – Corrientes Province, Argentina (probably not distinct from A. c. cunicularia)

A paleosubspecies, A. c. providentiae, has been described from fossil remains from the Pleistocene of the Bahamas. How these birds relate to the extant A. c. floridana – that is, whether they were among the ancestors of that subspecies, or whether they represented a more distant lineage that completely disappeared later – is unknown.

In addition, prehistoric fossils of similar owls have been recovered from many islands in the Caribbean (Barbuda, the Cayman Islands, Jamaica, Mona Island and Puerto Rico). These birds became extinct towards the end of the Pleistocene, probably because of ecological and sea-level changes at the end of the last ice age rather than human activity. These fossil owls differed in size from present-day burrowing owls, and their relationship to the modern taxa has not been resolved.

Description

Burrowing owls have bright eyes; their beaks can be dark yellow or gray depending on the subspecies. They lack ear tufts and have a flattened facial disc. The owls have prominent white eyebrows and a white "chin" patch which they expand and display during certain behaviors, such as a bobbing of the head when agitated.

Adults have brown heads and wings with white spotting. Their chests and abdomens are white with variable brown spotting or barring, also depending on the subspecies. Juvenile owls are similar in appearance, but they lack most of the white spotting above and brown barring below. The juveniles have a buff bar across their upper wings and their breasts may be buff-colored rather than white. Burrowing owls of all ages have grayish legs longer than those of other owls.

Males and females are similar in size and appearance, so display little sexual dimorphism. Females tend to be heavier, but males tend to have longer linear measurements (wing length, tail length, etc.). Adult males appear lighter in color than females because they spend more time outside the burrow during daylight, and their feathers become "sun-bleached". The burrowing owl measures 19–28 cm (7–11 in) long and spans 50.8–61 cm (20–24 in) across the wings, and weighs 140–240 g (5–8 oz). As a size comparison, an average adult is slightly larger than an American robin (Turdus migratorius).

Distribution and habitat

Before European colonization, burrowing owls probably inhabited every suitable area of the New World, but in North America, they have experienced some restrictions in distribution since then. In parts of South America, they are expanding their range due to deforestation. The western burrowing owls (A. c. hypugaea) are most common in the Rocky Mountain Arsenal National Wildlife Refuge, as well as in most of the western states. Known resident populations inhabit areas of Colorado, Arizona, New Mexico, Texas and California, where their population is reportedly threatened by human encroachment and construction.

Burrowing owls range from the southern portions of the western Canadian provinces (British Columbia, Alberta, Saskatchewan, Manitoba) and all the way through Mexico to western Panamá. They are also found across the state of Florida, as well as some Caribbean islands. In South America, they are fairly common, and are known to inhabit every country on the continent, with the exception of the dense Amazon rainforest interior and the highest ranges of the Andes Mountains. Their preference is for the cooler, possibly sub-tropical coastal and temperate regions. South of the Amazon, their population seems to again rebound, as they are widely distributed from southern Brazil and the Pantanal down to Patagonia and Tierra del Fuego.

Burrowing owls are year-round residents in most of their range. Birds that breed in Canada and the northern U.S. usually migrate south to Mexico and the southern U.S. during winter months.

Behaviour and ecology

This species can live for at least 9 years in the wild and over 10 years in captivity. They are often killed by vehicles when crossing roads, and have many natural enemies, including badgers, coyotes, and snakes. They are also killed by both feral and domestic cats and dogs. Two birds studied in the Parque Nacional de La Macarena of Colombia were free of blood parasites.

Burrowing owls often nest and roost in the burrows made by ground squirrels, a strategy also used by rattlesnakes. When threatened, the owl retreats to the burrow and produces rattling and hissing sounds similar to those of a rattlesnake. The behavior is suggested to be an example of acoustic Batesian mimicry and has been observed to be an effective strategy against animals that are familiar with the dangers posed by rattlesnakes.

Breeding

The nesting season begins in late March or April in North America. Burrowing owls usually only have one mate but occasionally a male will have two mates. Pairs of owls will sometimes nest in loose colonies. Their typical breeding habitat is open grassland or prairie, but they can occasionally adapt to other open areas like airports, golf courses, and agricultural fields. Burrowing owls are slightly tolerant of human presence, often nesting near roads, farms, homes, and regularly maintained irrigation canals.

The owls nest in a burrow, hence the name burrowing owl. If burrows are unavailable and the soil is not hard or rocky, the owls may excavate their own. Burrowing owls will also nest in shallow, underground, man-made structures that have easy access to the surface.

During the nesting season, burrowing owls will collect a wide variety of materials to line their nest, some of which are left around the entrance to the burrow. The most common material is mammal dung, usually from cattle. At one time it was thought that the dung helped to mask the scent of the juvenile owls, but researchers now believe the dung helps to control the microclimate inside the burrow and to attract insects, which the owls may eat.

The female lays an egg every one or two days until she has completed a clutch, which can consist of four to 12 eggs (usually 9). She then incubates the eggs for 3–4 weeks while the male brings her food. After the eggs hatch, both parents feed the chicks. Four weeks after hatching, the chicks can make short flights and begin leaving the nest burrow. The parents still help feed the chicks for 1–3 months.

Site fidelity rates appear to vary among populations. In some locations, owls will frequently reuse a nest several years in a row. Owls in migratory northern populations are less likely to return to the same burrow every year. Also, as with many other birds, the female owls are more likely to disperse to a different site than are male owls.

Food and feeding