Raptors - San Diego County [ds171]

Point data on raptor species locations were collected to provide an initial baseline of information on many of the breeding and wintering raptors within the MSCP and environs. These data will serve to identify appropriate long-term raptor monitoring locations, develop a scientifically based monitoring program (including survey locations and protocols), test the monitoring methods, and identify opportunities for population enhancements. For more information on project objectives, methods, and outcomes see The Wildlife Research Institute's final report. DATA ASSUMPTIONS AND LIMITATIONS: These points represent a summary of WRI's raptor surveying activity for the period of January 1, 2001 through December 31, 2003, focusing on the breeding and wintering seasons. This work did not, officially, include the Burrowing Owl. Therefore, with few exceptions, surveys were not conducted during what would normally have been the most productive time for this species (i.e., early morning and early evening). Fieldwork was conducted during the daylight hours to maximize chances for seeing the diurnal raptors that were the focus of the contracted scope. Although nocturnal owls can be expected to nest and winter in many of the study sites, they would be expected to often escape observation under this temporal survey regime. However, the methods required documenting any raptor, regardless of whether or not it was a target species and, when a Burrowing Owl or any other owl was observed, it was noted. KNOWN CAVEATS OF THE DATA: A natural phenomenon created a situation that could be considered a constraint. This was the extreme drought that the region experienced for several years (1999-2004). Therefore, 2001 through 2003 may not have been the best of raptor breeding years. Drought clearly plays a significant factor in the density and reproductive success of raptors. This study was conducted during the worst drought for San Diego in over 160 years. This fact should be noted for future researchers and resource managers/planners. This kind of extreme drought has the potential effect of reducing the available prey biomass, which, in turn, can have at least two effects. First, it likely reduces the "attractiveness" of a habitat complex, partly because of low prey densities, and may encourage raptors and other predators to look elsewhere. Second, for those individuals that choose to stay in a less-than-ideal environment, the lack of prey often results in lowered reproductive success or even total nest failure. If a nest site is not successful, the birds are more likely to disperse, which leaves the historically active territories apparently, or actually, vacant. The unnatural type of constraints came in the form of restricted access. Although we did not experience any access restriction to city-owned property, we were partially restricted to one site (Navy Satellite Surveillance Station), which is juxtaposed to a city study site (Brown Field) and, because of delays in processing our request for access to a military site (North Island), we were only able to survey that site a limited number of times as part of a related NCCP study.

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