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Home Land Upland Species and Communities

Osprey

Status and Trend

Interpretation and Commentary

OSPREY


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Status: Considerably Better Than Target
Trend: Moderate Improvement
Confidence: High

 

  • Relevance - The Osprey (Pandion haliaetus) is a conspicuous large raptor that is valued for wildlife viewing. Ospreys are protected by the Migratory Bird Treaty Act, which prohibits the harming or killing of Ospreys. They are listed as a species of special concern by the California Department of Fish and Game. This provides extra protection for them when analyzing the effects of a proposed project. The number of active Osprey nests is an indicator of the viability of the Osprey population within the Tahoe Basin.
  • Adopted Standards  - Provide a minimum of 4 population sites (defined as active nests) and a 0.25 mile disturbance zone around population sites.
  • Indicator - The number of active Osprey nests detected each year.
  • Status – The Threshold Standard is in attainment. Over the past 14 years (1997-2010), the number of active Osprey nests has fluctuated between 12 and 29. The number of nests has consistently exceeded the Threshold Standard of 4 population sites, and has been 3 to 7 times the Threshold Standard. At least 29 sites are currently managed for the protection of Ospreys in the Region.
  • Trend –  A linear regression showed a significant increasing trend in the number of active Osprey nests detected over the long term (R2 = 0.48, P < 0.01). The data from the 5 years since the last evaluation (2006-2010) show no major divergence from the long term trend line, indicating no recent changes in the existence or direction of the long term trend. The increasing trend is consistent with a reported global increase in the abundance of the species (NatureServe 2011).

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  • Confidence  - There is a high degree of confidence in the status because Osprey nests are easy to observe, and qualified biologists intensively monitor them following standardized boat and land-based survey protocols. There is a high degree of confidence inthe existence and direction of thelong-term trend because there is some variation of yearly points (counts) around the regression line with the exception of high numbers of active nests in 2003 and 2004. The overall confidence in the status and trend is high.
  • Human and Environmental Drivers - Human disturbance near nesting and foraging areas can impact Osprey breeding success. Ospreys may be able to habituate to human activity depending on the timing, type, and consistency of the activity (Romsos 2000b; Ewins 1997). Osprey populations could be limited by the number of large nest trees near water and open areas, or competition with Bald Eagles or other species (Ewins 1997). However, given the limited number of Bald Eagles present during the breeding season, and the existing protections for large trees, these are not likely to be major limiting factors in Tahoe. Ospreys that breed in the Tahoe Basin likely migrate to Central or South America for the winter (Martell et al. 2001; Romsos 2000b). Ospreysbreedingin Tahoe may be affected by a variety of factors in their wintering areas or along migration routes, including contamination from organochlorines (e.g. DDT), which is still used in parts of their wintering grounds (Romsos 2000b; NatureServe 2011).
  • Monitoring Approach – A shoreline survey is conducted by boat monthly during spring and summer months following standard protocols. Additional surveys are conducted at historic and likely nest sites at other lakes and upland areas.
  • Monitoring Partners – U.S. Forest Service, California Department of Parks and Recreation, and Nevada Department of Wildlife.

Links

 
  • Monitoring Plan
  • Conceptual Model

Map

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Approximate locations of all recorded Osprey nests in the Tahoe Basin (1980 to 2010). Source: USFS and TRPA survey records.

 

Trend Charts

Chart data not available at this time.
 

Additional Info

References

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Additional Information

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  3. Conceptual Model:
  4. Monitoring Plan:
Last Updated on Tuesday, 04 September 2012 12:37