Mexican Spotted Owl

Strix occidentalis lucida

Description

The Mexican spotted owl (Strix occidentalis lucida ) is distinguished from the California (S. o. occidentalis ) and northern (S. o. caurina ) subspecies chiefly by its geographic distribution and plumage. The overall body coloration of the Mexican spotted owl is a darker brown than the other subspecies, and its plumage spots are larger, whiter, and more numerous, giving it a lighter appearance overall. Its body length is about 16 in (41 cm), and its wingspread about 42 in (107 cm). Females are larger than males.

Behavior

The Mexican spotted owl proclaims its breeding territory by a series of three to four loud hoots. They usually lay eggs in April, but as early as March. Clutch size varies from one to three eggs (rarely four), with most broods containing one or two owlets (or sometimes three). The incubation period is about 30 days. Only the female incubates; the male provides food for the female and young until the owlets are about two weeks old, after which the female also hunts. Most owlets fledge 34-36 days after hatching. Owlets are good enough at hunting to be semi-independent of their parents by late August or early September, and are fully independent by early October. The diet includes a variety of small mammals, birds, reptiles, and insects, with mammals comprising most of the diet.

Habitat

The forest habitats of the Mexican spotted owl usually have a high degree of canopy closure, high stand density, a multi-layered canopy resulting from an uneven-aged stand, and abundant downed logs, snags, and mistletoe infection that are indicative of an older-growth condition and no prior forestry management. Much of the habitat is characterized by steep slopes and canyons with rocky cliffs. Most stands are warm-temperate or cool-temperate forest, and, to a lesser extent, riparian deciduous forest. Mixed-conifer stands are most frequently used. The most abundant overstory trees in the mixed-conifer forests are white fir (Abies con-color ), Douglas fir (Pseudotsuga menziesii ), and ponderosa pine (Pinus ponderosa ).

Distribution

The range of the Mexican spotted owl extends from the southern Rocky Mountains in Colorado and the Colorado Plateau in southern Utah, southward through Arizona and New Mexico and, discontinuously, through the Sierra Madre Occidental and Oriental to the mountains at the southern end of the Mexican Plateau.

Threats

The historic range and present distribution of the Mexican spotted owl are thought to be similar. However, its overall abundance has declined due to the loss of much of the original area of its forest habitat. Surveys from 1988 to 1991 found about 1,000 birds in the southwestern United States and Mexico. The total estimated population in the early 1990s was 806 pairs and 548 singles in the southwestern United States, and a total of 2,160 owls in the overall U. S.-Mexican range. Natural threats include larger raptors, such as great horned owls (Bubo virginianus ), as well as habitat loss by wildfire.

Conservation and Recovery

The Forest Service, Bureau of Indian Affairs, National Park Service, and Bureau of Land Management are the federal land-managing agencies affecting the Mexican spotted owl. The most intensive work to estimate suitable habitat and to survey owls has been done by the Forest Service. Suitable spotted owl habitat reported by federal and state agencies in 1990 totaled about 6.82 million acres (2.76 million hectares). The Forest Service reported 4.7 million acres (69% of the total; 1.9 million hectares), the Bureau of Indian Affairs 0.88 million acres (13%; 0.36 million hectares), the Bureau of Land Management 0.71 million acres (10%; 0.29 million hectares), the National Park Service 0.24-0.44 million acres (about 5%; 0.10-0.18 million hectares), and the State of New Mexico 0.18-0.20 million acres (about 3%; 0.07 million hectares). About 5,000 acres (2,000 hectares) of suitable owl habitat occurs on private land (much less than 1% of the total). About 91% of Mexican spotted owls known at the end of 1990 occurred on national forests, 4% on Indian reservations, 4% in national parks, and 1% on Bureau of Land Management lands. In the recent past, timber harvesting on Forest Service lands accounted for the loss of about 816,000 acres (330,000 hectares) of owl habitat, and natural disturbances an additional 221,000 acres (89,000 hectares). The Forest Service estimated that 79% of those disturbed areas would require more than 50 years to return to suitable owl habitat. About 95% of the area of commercial timber managed by the Forest Service in the Southwest is planned for harvesting under the shelterwood system, which is somewhat less destructive to owl habitat than clear-cutting. Commercial forests on the Navajo Indian Reservation are being converted to shelterwood management. Other commercial forests on Indian lands in the Southwest are managed as uneven-aged stands by selective logging. Overall, a large fraction of the habitat of the Mexican spotted owl is slated for timber harvesting. It is crucial that this commercial habitat disturbance be accompanied by the monitoring of owl populations and their response to the forestry activities. If populations drop significantly, conservation of the rare owl will require that extensive areas of potentially commercial forest be withdrawn from the allowable harvest.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P. O. Box 25486
Denver, Colorado 80225
http://www.r6.fws.gov/

U. S. Fish and Wildlife Service, New Mexico Ecological Services Field Office
2105 Osuna Road N. E.
Albuquerque, New Mexico 87113-1001
Telephone: (505) 346-2525

Reference

U. S. Fish and Wildlife Service. 16 March 1993. "Endangered and Threatened Wildlife and Plants: Final Rule To List the Mexican Spotted Owl as a Threatened Species." Federal Register 58 (49): 14248-14271.