This indicator measures the number of active peregrine falcon nests in the Tahoe Region. Peregrine falcon (Falco peregrinus anatum) populations declined precipitously across the country in the mid-1900s. Peregrine falcons were recorded in the Tahoe Region in the early 1900s, but were not observed naturally occurring in the Region between 1960 and 2007. Their recovery is a result of banning DDT and similar chemical contaminants, and active species reintroductions. In the Tahoe Region, recreation such as climbing and hiking near nests is one of the threats to the species. Programs to reduce these recreation impacts aim to protect peregrine falcons. Peregrine falcons are monitored across the Region by TRPA and other partners. 

Status

Total number of active peregrine falcon nests recorded in the Tahoe Basin during years when formal surveys were conducted relative to the threshold standard of two population sites. Surveys were conducted four times between 1994 and 2008 but no confirmed nests were observed until 2009. The trendline shown was estimated using a linear regression model.

Data provided by the California Department of State Parks, California Tahoe Conservancy, Tahoe Institute for Natural Sciences, Nevada Division of Wildlife, Sierra Ecotone Solutions, USFS-Lake Tahoe Basin Management Unit. Access detailed datasets on Tahoe Open Data, including: Peregrine Falcon nest locations with buffer and Annual Data.

2023 Evaluation
See how thresholds are evaluated
Status
Considerably Better Than Target
Trend
Rapid Improvement
Confidence
Moderate
Applicable Standard
W6: Provide a minimum of 2 Peregrine population sites. W13: Provide disturbance zones and influence zones for Peregrine.
Key Points
  • Peregrine falcons have made a remarkable recovery in the Tahoe Region since they first reappeared in 2009.
  • Number of active nests varies annually but remains stable. 
  • Years of monitoring at the Castle Rock nesting site have revealed that hiker disturbances have led to nest failures. In response, multiple partners from the Environmental Improvement Program collaborated to educate and discourage hiking and climbing near the nest site during the nesting season. Due to this effort, the Castle Rock nest has been sucessful since 2019.
  • The disturbance zone standard for Peregrine falcons has been implemented by TRPA and other partner agencies.
Evaluation Map
Description

Active peregrine falcon nest sites within the Tahoe Basin from 2015 to 2023. Not all known nest locations are active every year. 

About the Threshold
Peregrine falcon (Falco peregrinus anatum) populations declined precipitously across the country in the mid-1900s (USFWS 2003). Peregrine falcons were recorded in the Tahoe Basin in the early 1900s (Orr and Moffitt 1971), but were not observed naturally occurring in the basin between 1960 and 2007 (J.S. Romsos, Schlesinger, and Manley 2000; Zanetti 2015; California Department of Fish and Wildlife 2007). In the mid-1980s, several juveniles were re-introduced, but left the basin the same year (U.S. Forest Service 2009). The species was federally listed as endangered under the Endangered Species Act until it was removed in 1999 due to an overall increase in the population. They were, however, considered endangered by the State of California until 2009. Their recovery is a result of banning DDT and similar chemical contaminants, and active re-introductions (USFWS 2003). They are still protected by the Migratory Bird Treaty Act, which prevents harming peregrine falcons or their nests.
In some areas peregrine falcons have shown reduced reproductive success when nesting cliffs are used by rock climbers (Mearns and Newton 1988; Cade, Enderson, and Linthicum 1996). Within the Tahoe Basin, some of the cliffs with nests are used by rock climbers, which could affect nesting success. However, at the two sites in the basin with rock climbing activity, the species has successfully reproduced every year since 2011, suggesting that these birds are not disturbed by the current rock climbing activity (U.S. Forest Service 2015b). An evaluation of potential peregrine falcon habitat in the basin concluded that potential nesting habitat exists, but it is of marginal quality, which may limit the total number of active nests the Region can support (Boyce and White 1980). Some peregrine falcons nesting in the basin may migrate to Central or South America for the winter, where they could be affected by contamination from organochlorine pesticides (e.g. DDT) (USFWS 2003).
Delivering and Measuring Success

EIP Action Priorities

Example EIP Projects

Monitoring Programs

Rationale Details
Considerably Better Than Target. Current status is determined by the number of active nests in the most recent monitoring year. In 2023, there were four active nests, which is 200% of the standard. Therefore, the current status is considerably better than target.
Rapid Improvement. Population trend was estimated using an EGPN (exponential growth process noise) model (Humbert et al. 2009). Process noise refers to differences in observed population abundance that result from environmental variability. From 1997-2023, there has been an annual 10.4% growth in the peregrine falcon population. Therefore, the trend is determined to be rapid improvement.

Similar results are found using simple linear regression to estimate trend. The results for this analysis show annual growth of 0.3 active peregrine falcon nests per year. The EGPN model was chosen for the trend determination because it is a more conservative model and incorporates environmental and observation errors associated with wildlife monitoring on a landscape scale. The threshold attainment results are the same with both analyses.
Confidence Details
High. Standardized protocols were utilized over many monitoring periods.
Moderate. The estimated growth is likely positive, but the 95% confidence interval includes the possibility of population decline. Using the EGPN trend analysis the number of active peregrine falcon nests is estimated to be growing at 10% annually. The confidence intervals for the estimated annual rate of change range from a decline of 0.95%/year to an increase of 23.8 %/year. Therefore, the confidence in trend is determined to be moderate. The results for the linear regression analysis show an annual growth of 0.3 active peregrine falcon nests per year with a 95% confidence interval of 0.22-0.4.
Moderate. If one confidence rating is high and the other is moderate, the overall confidence rating is the lower confidence rating.
Additional Figures and Resources

No photos available.


Peregrine Falcon Population Model Output
Uploaded On
8/30/2024
File Type
Excel (XLSX)
Description
Peregrine Falcon EGPN (exponential growth process noise) model output.