Oaks ‘n’ Folks – Volume 6, Issue 3 – December 1991
The northern spotted owl (Strix occidentalis caurina) is an extremely controversial issue throughout the timber areas in northern California and the Pacific Northwest. Listed as Threatened in 1991, the subspecies was granted protection under the Endangered Species Act because of concern over the loss of habitat. A secretive animal, the northern spotted owl is found from Northern California, throughout western Oregon and Washington, and over much of western Canada. The northern subspecies favors mature stands of timber with a multi-layered understory. The bird is nocturnal and feeds primarily on rodents. With continued field studies biologists will be able to determine the habitat requirements necessary to maintain viable owl populations.
The northern spotted owl is one of three recognized subspecies of spotted owls and at the present time the only one afforded protection under the Endangered Species Act. The California spotted owl (S. o. occidentalis), is currently being evaluated for possible listing. The other subspecies, the Mexican spotted owl (S. o. lucida), is found in northern Arizona, southeastern Utah, central Colorado, western Texas, and in some parts of Mexico. The Mexican spotted owl is not considered Endangered at this time.
The California subspecies is widely distributed throughout California. It is found throughout the Sierra-Nevada ranges, the coast ranges, and the forested areas of southern California. Nesting pairs of California spotted owls have been found in oak woodland habitat. In addition, the California subspecies is also found as a seasonal resident in valley foothills, breeding in upland mixed conifer forests of the west slope of the Sierra Nevada, then migrating into foothill hardwood-conifer forests in the winter months.
All of the subspecies of spotted owl are secondary cavity nesters, preferring to nest in trees or in the tops of broken trees. They prefer nests that are 30 to 50 feet from the ground in areas that have large trees, typically with some understory that affords much shade.
Very little was known about any of the subspecies prior to 1975. Since then, data have been gathered on some aspects of the owl’s biology, with the greatest emphasis being placed on the northern subspecies. Only recently has an effort been made to gather natural history data on the California subspecies. A great deal of data is still needed on the California spotted owl regarding genetics, physiology, behavior, and population demographics.
In the July 1990 issue of Fremontia (Native Plant Society Publication, pp. 72-76), Block, Morrison, and Verner summarized the extent of information known at that time about the California owl and its habitat. They wrote, “… We have found California spotted owls in canyon live oak stands of the Tehachapi Mountains. Studies by Cameron Barrows and William Lahaye also found California spotted owls in similar habitats in other southern California mountain ranges. Recent studies by Donald Neal and George Steger have found California spotted owls breeding in blue oak-grey pine (Pinus sabiniana) woodlands of the foothills of the central Sierra Nevada.”
The owl’s habitat needs are at the center of much of the present controversy. In the past, forest management practices and urbanization have altered hundreds of thousands of acres of owl habitat. Current management objectives are focusing on ensuring the needed amount of acreage for the owl to nest, forage and roost.
Unlike the northern subspecies, the California subspecies is found over much of its range in hardwood forests. Since hardwood rangelands are an important component within the range of this subspecies, its possible listing would have major impacts on hardwood range management activities.
When a species becomes “listed” it is the responsibility of the landowner or manager to ensure that no “take” of the species occurs. The meaning of “take” in the Endangered Species Act prohibits any management decisions that would impact the species directly or indirectly through the loss of habitat. In this case, “take” could mean the loss of habitat through hardwood harvesting, residential developments, and land conversion to intensive agriculture.
A California spotted owl steering committee, jointly chaired by the Resources Agency of the state, and Region V of the USDA Forest Service has been established to gather and analyze information on the current condition of the California spotted owl population, and to suggest conservation strategies to ensure the sustainability of the subspecies.
As information on the California spotted owl is developed, especially in regards to its habitat requirements on hardwood rangelands, additional articles will appear in future issues of Oaks ‘n Folks.
prepared and edited by John M. Harper, Richard B. Standiford, and John W. LeBlanc
Gregory A. Giusti, U.C. Integrated Hardwood Range Management Program