Strix occidentalisspotted owl

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Geographic Range

This species of owl is found only in western North America, from southwestern British Colombia south through the mountains of Washington, Oregon and California, the western slopes of Sierra Nevada and the southern Rockies. They are also located in Utah and central Colorado through Arizona's mountain ranges, New Mexico, extreme western Texas, and central Mexico.

Habitat

Spotted Owls are found in humid, mixed coniferous forests, wooded ravines, and canyons. They can also be located in dark forest patches in the shade of deep, hanging canyon walls. Biomes: temperate forest, low boreal mountains.

Physical Description

The average length of a Spotted Owl is 45 cm, with a wingspan of 114.3 cm. The average length of the left and right ear openings are 17.5 mm and 22 mm, respectively. Weight ranges from 518 to 760 grams. Females are generally larger than males, and have a higher pitched call. These owls are medium-sized with dark brown plumage, a round head, and large dark eyes. The head and hind neck have white spots, along with white mottling on the breast and abdomen. Depending on how thick the plumage is, the amount of coloration and white spotting varies. Birds from the humid climate of the coastal range are darkest, while those from the mountain ranges in Arizona and Mexico are the lightest with the most white spots. This difference in appearance is assumed to be an evolutionary adaptation to climate variation.

  • Average mass
    571 g
    20.12 oz
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  • Average basal metabolic rate
    2.675 W
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Reproduction

Spotted Owls roost high in the trees under the shelter of the highest canopy, shielded from direct sunlight. Summer nests are found in shady places a few degrees cooler than that of the open canopy, often closer to the cool forest floor. Nests occur in a wide variety of locations: tree cavities and stumps, potholes and cavities in sandstone cliffs, rocky ledges of caves, and deep narrow canyons. Quite often, these birds do not build their own nests. Rather, they occupy the deserted nests of hawks or ravens. If none is available, eggs are sometimes laid on bare dirt. Breeding occurs annually between nesting owl pairs; each owl is usually over the age of two years. Usually between two and three eggs are found in each clutch. The eggs are white, slightly granulated, and more oval than those of the Barred Owl.

The male's responsibility is to hunt in order to feed the young, while the female primarily incubates and cares for the eggs. She will hunt, however, if the young aren't getting enough to eat. The head of the prey is eaten by parents before feeding the remainder to their yo ung.

  • Average eggs per season
    2
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  • Average time to hatching
    30 days
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  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
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  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
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Lifespan/Longevity

Behavior

There are several distinct songs and calls of Spotted Owls. The territorial song / location call consists of three to four hesitant hoots. The contact call is composed of a series of terrifying whistles and a siren-like echo. Alarm / scolding calls resemble dog-like barks. Spotted owls are strictly nocturnal, except for an occasional hunting female during the day, under pressure to feed her young. By day, these owls hide in thick cover near a tree trunk; their coloring blends well with the surroundings.

This species is generally perceived as having a "tame, unsuspicious, cursory, or stupid" disposition; they have a reputation for being unwary around humans.

Though their amiable appearance suggests otherwise, they do have potentially formidable strength.

Spotted Owls find high air temperatures (over 27 degrees Celsius) quite unpleasant, and thus have developed certain behavioral thermoregulatory strategies to endure the heat. When faced with such conditions, they invariably retreat to the north side of mountain slopes and canyon walls in search of the cool comfort of the canopy. They position themselves around tree trunks during the course of the day to remain in the shade. While perching, they expose their legs and feet and lift up their footpads to maximize heat evaporation. They also expand their wings and dorsal feathers and flutter with a partially open beak to allow rapid evaporation.

Communication and Perception

Food Habits

Spotted Owls are carnivorous and prey on anything they are able catch. Prey consists mainly of small arboreal or semiarboreal mammals, as well as birds, several species of bat, and large insects. They are skilled hunters that rely more so on acute hearing than eyesight. Hunting takes place more often through the medium strata of the forest, rather than on the forest floor or in an open field. Catches are generally made by swooping down from a perch above and collecting the prey with sharp talons. Occasionally, smaller birds are caught on the wing in midflight.

A certain technique is applied to feeding: an ear is torn off to break the resistant skin, and the spinal column is broken by a twist of the beak. Prey is always eaten head first.

Economic Importance for Humans: Positive

The image of an owl symbolizes wisdom, which has been marketed in a number of ways to make a profit. Examples of this include the knowledgeable owl from Milne's Winnie the Pooh, as well as the cartoon owl in the Tootsie Roll Pops commercials. Owls are also extremely appealing birds to ornithologists. Areas in the west with the Spotted Owl attract a larger number of bird-watchers.

Economic Importance for Humans: Negative

The restrictions enforced on the logging industry will most likely be costly, and will potentially set back any business that relies on these resources for lumber and wood products.

Conservation Status

The status of this species of owl varies from region to region. In Washington it is endangered, in Oregon it is considered threatened, and in California, it is on the special concern list. This species receives protection under the Migratory Bird Treaty Act of 1918, and according to the Endangered Species Act of 1973 (as amended), it has been listed as a threatened species. Their habitat is being destroyed rapidly by unrestricted exploitation, clear-felling, and logging of old-climax forests; the continued existence of this owl in its realized niche is threatened. Owl habitat has been reduced by 60% since the early 1800's.

Contributors

Erica Semeyn (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

visual

uses sight to communicate

References

Walker, L.W. 1993. The Book Of Owls. University of Texas Press, Austin.

Voous, Karen H. 1989. Owls of the Northern Hemisphere. The MIT Press, Cambridge.

Burton, John A. 1973. Owls of the World. E.P. Dutton & Co, Inc., N.Y.

Thomas, J.W. 1990. A Conservation Strategy for the Northern Spotted Owl. U.S. Government Printing Office, Portland.