Figure 2.

The decline of a local goshawk population in the central Netherlands associated with a decline in the relative abundance of goshawk prey. (a) During 1975–2000, populations of several principal goshawk prey species crashed simultaneously. (i) Avian biomass in spring (quadratic regression: F_2,3=40.39, p=0.007); (ii) woodpigeon breeding density (GLM on log-transformed data: F_1,12=178.65, p<0.001), and relative racing pigeon abundance (data from two plots (circles and squares); GLM on square-root transformed data: F_1,19=95.24, p<0.001); (iii) rabbit numbers (quadratic regression: F_2,23=64.89, p<0.001). (b) Decline in breeder and non-breeder fractions of the local goshawk population. (i) Number of territorial pairs (GLM on log-transformed data, 1975 excluded: F_1,23=62.13, p<0.001); (ii) number of non-territorial floaters (GLM on log-transformed data: F_1,24=31.64, p<0.001); (iii) number of pluckings found in the study area per goshawk breeding pair and hour of search effort (plot of raw data; for statistics, see text). (c) Decline in goshawk productivity. (i) Total number of fledglings produced (GLM: F_1,24=28.39, p<0.001); (ii) number of fledglings produced per pair (for statistics, see text); (iii) proportion of pairs that failed to raise young (see text).