7 January 2013 Science Briefs

SNAMP PUB #9: Evaluating the efficacy of protected habitat areas for the California spotted owl using long-term monitoring data

Article Title: Evaluating the efficacy of protected habitat areas for the California spotted owl using long-term monitoring data.

Authors: William J. Berigan, R. J. GutiƩrrez, and Douglas J. Tempel.

Research Highlights:


  • We compared the spatial overlap of California spotted owl core use areas (defined below) and Protected Activity Centers (PACs; defined below) on the Eldorado Density Study Area (EDSA).

  • We found that PACs have been effective at providing core habitat that spotted owls used frequently over a 25-year period.

Background:

A central, but untested, premise of the 1992 California Spotted Owl Technical Assessment (CASPO) was that the best available 300 acres of contiguous habitat around owl territory centers represented the core area of a spotted owl pair. Thus, CASPO recommended to the U. S. Forest Service that Protected Activity Centers (PACs) of this size be established at all known spotted owl sites. No stand-altering activities, except light underburning, would be allowed within PACs. Although PACs were intended to be an interim conservation strategy, the Forest Service has continued using PACs to the present day. To our knowledge, no one had quantitatively evaluated whether PACs represent the core habitat areas actually used by owls. Therefore, we used long-term monitoring data to examine whether PACs delineated by the Forest Service in the early 1990s encompass the core habitat used by owls.

Results:


  • The average size of 95% owl core use areas (334.7 acres), as defined by locations of nests and roosts found over long periods of time, was similar to the average PAC size (287.5 acres).

  • The spatial overlap between owl core use areas and PACs was high. The average proportions of each core area that overlapped a PAC were 0.84, 0.70, and 0.61 for the 50, 90, and 95% usage distributions, respectively.

Conclusions:


  1. PACs encompassed areas used by owls over very long periods of time and, hence, can be considered core habitat areas for roosting and nesting territorial pairs.

  2. We recommend that PACs should remain an integral feature of owl management in the Sierra Nevada because owls consistently use these areas over long time periods.

  3. Because long-term monitoring data are routinely collected for rare and endangered species, such data present an opportunity to define key areas for protection or special management for the species being monitored.
  4. Full Reference: Berigan, GutiƩrrez, and Tempel. 2012. Evaluating the efficacy of protected habitat areas for the California spotted owl using long-term monitoring data. Journal of Forestry 110: 299-303.

    The full paper is available here.

    For more information about the SNAMP project and the owl team, please see: here.

    Definitions:

    Core use area: Area of concentrated use around a spotted owl territory center. We used owl nest and roost locations from 1986-2009 to estimate the size and spatial location of core areas frequently used by owls over a long period of time.

    Protected Activity Center (PAC): Special management areas delineated by the U. S. Forest Service around spotted owl nest or roost sites and designed to protect critical spotted owl habitat.

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