To maintain and protect special interest species and enhance the suitability and extent of riparian habitat.

Peregrine Falcon Population Sites

Relevance - 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.
Human and Environmental Drivers - 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).

2015 Threshold Evaluation


- Considerably Better Than Target
- Considerably better than target. In the most recent year data is available (2015), four active peregrine falcon nests were observed which is 200 percent of the threshold standard. Therefore, a status of considerably better than the target is determined. Previous habitat evaluations concluded that the Tahoe Basin contains less than ideal nesting habitat (Boyce and White 1980), and prior reintroduction efforts were not successful (U.S. Forest Service 2009). As a result, peregrine falcons were not expected to nest within the Tahoe Basin and nest surveys were only conducted sporadically. In 2007, several biologists reported seeing peregrine falcons within the basin, and the U.S. Forest Service began conducting annual nest surveys in 2008. One active nest was confirmed in 2009 and 2010. From 2011 through 2013, two active nests were confirmed. In 2014 and 2015, one additional nest was discovered each year, in addition to successful breeding pairs at previously known sites (U.S. Forest Service 2015b).


- Rapid Improvement
- Rapid improvement. Since 2008, the year before the first active nest was confirmed within the Tahoe Basin, there is a significant upward trend in the number of nests (U.S. Forest Service 2015b). Since 2008, the estimated increase in more than 20 percent annually. Therefore, a trend of rapid improvement is determined. Additionally, at least 20 juveniles have fledged within the basin since 2008 (U.S. Forest Service 2015b). The trend is consistent with an increase in peregrine falcon abundance nationally and across California (Linthicum 2006).


- Moderate
- View Details Below

Population trend estimated using an exponential growth state-space (EGSS) model, that accounts for both process noise and observation error (Humbert et al. 2009). Process noise refers to differences in observed population abundance that result from environmental variability. Observation error refers to errors introduced in the data itself because monitoring may not be able to provide a perfect population census.


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. 

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. Threshold standard is the two nests, indicated by the red line. The solid blue line is the population trend estimated by exponential growth state-space (EGSS) model (Humbert et al. 2009). Dashed blue lines represent the 95 percent confidence interval for number of active nests.

Connecting Actions to Outcomes


Intermediate Results


TRPA does not permit projects that would disturb nesting peregrine falcon or their habitat within 0.25 miles of known nests. The U.S. Forest Service has initiated public outreach in collaboration with local rock climbers to limit the use of rock climbing routes near active nests. Additional measures that provide indirect benefits to peregrine falcon are found in the TRPA Goals and Polices and the Code of Ordinances, as well as other state and federal laws.
It is too early to evaluate the effectiveness of specific programs to protect peregrine falcon as they were only recently implemented after the detection of nests within the Tahoe Basin. The number of peregrine falcon nests has increased and recently attained the threshold standard, indicating that recent management activities have not resulted in major impediments to the species.
None. Threshold standard is in attainment.
None. Threshold standard is in attainment.

Applicable Standard

- Provide a minimum of two peregrine falcon population sites.
- Provide a minimum of two peregrine falcon population sites.


Biologists observe historic or potential nest sites for a minimum of four hours per month, April through August following standard U.S. Forest Service protocol. All potential nesting habitat is surveyed and incidental sighting are used to help focus monitoring efforts. 


<p>Active peregrine falcon nests in the Tahoe Basin from 2011-2015. Source: U.S. Forest Service</p>

Confidence Details

- High. The lower 95 percent confidence interval suggest that the number of nests in the region is above two, suggesting there is high confidence that the standard is in attainment.
- Moderate. The lower 95 percent confidence interval suggests that the number of active nests in the region has at least doubled in the past five years.
- Moderate. Overall confidence takes the lower of the two confidence determinations.


Consider the use of a multi-year average of population sites or the trend line estimate to assess indicator status relative to the standard, to minimize the influence of process error.

Consider a dual frame sampling design (for additional detail see Haines and Pollock 1998; U.S. Fish and Wildlife Service 2009).

Standard evaluation relies on interpretation of the term “population site” which is not defined. This evaluation follows the convention of previous threshold evaluation reports and defines a “population site” as ”active nests.” While this evaluation follows that convention it is recognized that other interpretations are possible, and are used to evaluate the term “population site” as it pertains to other avian species in this evaluation. Review and revise threshold standard to clarify target and reflect best available science.

No changes recommended.

Historic Evaluations

View Evaluation Legend