grizzly: Yellowstone Grizzly Bear Population Data

In BruceKendall/PVA: Population viability analysis in R

Description

Estimated number of adult female grizzly bears in the Greater Yellowstone population, each year from 1959 to 1997

Usage

data(grizzly)

Format

A data frame with three columns:

i

Census index

yr

Census year

N

Estimated number of bears

Details

Quoting Morris and Doak (2002), p. 65:

This population is currently designated as threatened by the United States Fish and Wildlife Service, and is completely isolated from other grizzly bear populations. Each year, bear biologists count the number of unique female bears with cubs (offspring in the first year of life) in the entire Yellowstone population. Because the litters of one to three cubs remain closely associated with their mothers, females with cubs are the most conspicuous, and therefor most reliably censused, element of the population. Censuses were originally performed by observing bears at park garbage dumps, but they havbe been conducted by aerial survey since the closure of the dumps in 1970–1971. The counts of females with cubs are used to estimate the total number of adult females in the population. Specifically, the number of adult females in year t is estimated as the sum of the observed numbers of females with cubs in years t, t+1, and t+2 (Eberhardt et al. 1986). The logic underlying this estimate is that the interval between litters produced by the same mother is at least three years, so that females with cubs observed in years t+1 and t+2 could not have been the same individuals that were observed with cubs in year t. Yet, if they were observed in later years, they must have been alive in year t (although they may not have been adults in year t, which introduces some error).

Author(s)

Bruce E. Kendall ([e-mail])

Source

Morris and Doak (2002), table 3.1. Data originally from Eberhardt et al. (1986) and Haroldson (1999).

References

Eberhardt, L. L., Knight, R. R. and Blanchard, B. (1986) Monitoring grizzly bear population trends. Journal of Wildlife Management 50, 613–618.

Haroldson, M. (1999) Bear monitoring and population trend: unduplicated females. Pages 3–17 in Schwartz, C. C. and Haroldson, M. A. (eds.) Yellowstone Grizzly Bear Investigations: Annual Report of the Interagency Grizzly Bear Study Team, 1999. US Geological Survey (http://www.nrmsc.usgs.gov/research/igbst-home.htm).

Morris, W. F. and Doak D. F. (2002) Quantitative Conservation Biology: Theory and Practice of Population Viability Analysis. Sunderland: Sinauer Associates.

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