dc {birdring}

Division coefficient

Description

The function dc() calculates from the number of ringed birds per group and the number of reencountered birds per group in each destination area the estimated division coefficients per group and the estimated re-encounter probabilities per destination area as described in Kania and Busse (1987). The function bootci.dc() gives the bootstrap confidence intervals for the division coefficients and the re-encounter probabilities estimated by dc(). For details see Korner-Nievergelt et al. (2010).

Usage

dc(N, recmatrix, group.names = NA, area.names = NA, start = NA)

bootci.dc(N, recmatrix, interval = 0.95, R = 1000, 
                             group.names = NA, area.names = NA)

Arguments

N

a vector containing the number of ringed birds per group

recmatrix

a matrix containing the number of re-encountered birds per group and area. The rows of the matrix represent the bird groups; the columns represent the destination areas.

interval

proportion of the confidence interval (default = 0.95)

R

number of bootstrap replicates (default = 1000)

group.names

facultative vector of group names

area.names

facultative vector of area names

start

facultative vector of starting values for the least-square iteration for estimating the inverse of the recovery probability per destination area. The vector has the length of the number of areas and contains approximate inverse values of the recovery probabilities (default = N[1]/recmatrix[1,]/2).

Value

rec.probs

estimated re-encounter probabilities per destination area

division.coef

estimated division coefficient per group and destination area

div.coef.lower

lower limits of the confidence intervals of the estimated division coefficients

div.coef.upper

upper limits of the confidence intervals of the estimated division coefficients

Author(s)

Fraenzi Korner-Nievergelt

References

Kania W, Busse P (1987) An analysis of the recovery distribution based on finding probabilities. Acta Ornithologica 23: 121-128. Korner-Nievergelt F, Schaub M, Thorup K, Vock M, Kania W (2010) Estimation of bird distribution based on ring re-encounters: precision and bias of the division coefficient and its relation to multi-state models. Bird Study 57: 56-68.

Example data are from: Bauthian I, Gossmann F, Ferrand Y, Julliard R. (2007) Quantifying the origin of Woodcock wintering in France. Journal of Wildlife Management 71: 701-705.

Examples

N<-c(7125, 9661, 5266, 3240, 3643, 3192, 3227)

recmatrix<-matrix(c(22,25, 6, 2, 4, 1, 0, 47, 78, 49, 28, 38,27, 34), ncol=2)
colnames(recmatrix) <- c("Scandinavian", "Eastern")
rownames(recmatrix) <- c("North", "West", "Southwest",
    "Central North", "Central South", "Northeast","Southeast")

dc(N, recmatrix, group.names= c("North", "West", "Southwest",
    "Central North", "Central South", "Northeast","Southeast"),
    area.names= c("Scandinavian", "Eastern"))