Conservation Lessons From The California Spotted Owl
Many animal species are threatened or endangered due to human activity, but trying to determine how fast a species’ population is declining can be a monumental task. Rare species are often widely distributed but at low densities, which makes it difficult to assess how their populations are doing. The conventional approach for measuring population trends relies on a single source of information measured over time, such as “mark, recapture, count” data or “presence-absence” data. Another more recent approach, called integrated population modeling (IPM), uses a variety of data sources to triangulate results. While IPM is promising, much of the current literature focuses on how well IPM works in theory. Few examples of its practical applications have been published.
This study fills this gap by applying IPM to the central Sierra Nevada population of the California spotted owl. This species is of particular concern for conservationists because they inhabit old growth forests, which are of great economic value to loggers. Despite this concern, the owls’ conservation status has remained uncertain for more than 20 years, in part because there has not been a way to precisely measure changes in their population. In response, the authors of this study developed an IPM to improve population change estimates, including the effect that immigration of owls from outside of the Sierra Nevada population has on that local population’s dynamics.
Using data from years 1986 to 2012, the study authors identified 45 spotted owl territories that could hold about 90 individuals. They found a steady decline in the estimated population of adults, which dropped from a peak of 88 individuals in 1990 to 42 individuals in 2012. The authors state that this dramatic drop in numbers necessitates an understanding of the exact cause for the decline. This includes determining whether current management practices are a potential cause. At the very least, the authors contend that “rigorous monitoring of this species should continue.”
For advocates, the study shows that IPM may be a promising new tool in the conservationist’s toolbox. While its accuracy still needs to be evaluated, IPM can certainly provide more precise estimates of changes in a species’ population over time. This information may offer advocates compelling arguments for increased investments in conservation resources.
The full text of this article is currently available here (PDF).