. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Martin, de Solla, Ewins, and Barker: Osprey Nesting 61 C > ^ O Q- o. V .' Stump nests Artificial nests b \ >â \ v. â â '» \ » .'" i i i â ⢠i â Low nests High nests \ . Age at beginning of interval (years) Age at beginning of interval (years) Figure 3. Proportion of nests surviving any given year in a) Stump and Artificial nests and b) High and Low nests. during the first three years of their use (Gehan's Wil- coxon, P = ), whereas after this age, Stump nests tended
. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Martin, de Solla, Ewins, and Barker: Osprey Nesting 61 C > ^ O Q- o. V .' Stump nests Artificial nests b \ >â \ v. â â '» \ » .'" i i i â ⢠i â Low nests High nests \ . Age at beginning of interval (years) Age at beginning of interval (years) Figure 3. Proportion of nests surviving any given year in a) Stump and Artificial nests and b) High and Low nests. during the first three years of their use (Gehan's Wil- coxon, P = ), whereas after this age, Stump nests tended to have reduced survivorship compared to Artificial nests (Cox's F-test, F[44 U] = , P = ; Figure 3a). Cox's F-test (also known as log-rank) and Gehan's Wilcoxon test emphasize the weight of later vs. earlier censored data, respectively (Fleming et al. 1987). Both Stump and Artificial nests surviving for 6 years appeared to have relatively high survivorship after that point, although the sample size was small for these older nests. The comparison of longevity of High versus Low nests indicated that High nests had a greater longevity (Gehan's Wilcoxon Test, P = ). The survivorship of High nests was largely independent of age, where- as Low nests, which were primarily Stump nests, tend- ed to have reduced survivorship after three to five years (Figure 3b). Overall, High nests had greater survivorship than Low nests for all age classes. Discussion Ospreys breeding in the Kawartha Lakes region of south-central Ontario were found to nest successfully on low overwater flooded stumps. We found that, where stumps constituted the primary natural nest substrate, natural nests were more productive than nests built on artificial substrates. This contrasts with the findings of most other comparisons of natural and man-made Osprey nesting substrates. Ewins et al. (1995) found that natural nests, typically trees, were more likely to collapse and had lower productivity
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