Northern goshawk breeding ecology and nestling growth in mixed coniferous forests of west-central Idaho
Hanauska-Brown , Lauri A.
Bechard, Marc J.
Roloff, Gary J.
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This study documented the nesting chronology, productivity, and nestling growth of northern goshawks in west-central Idaho in 1998 and 1999. Egg laying began in late April, and fledging occurred in mid-July. Goshawks used >35% of historical territories and eleven new territories were discovered. Of 46 occupied territories, 80% were successful, fledging one to four young. Productivity averaged 2.1 fledglings/successful nest in 1998 and 2.0 fledglings/successful nest in 1999. Failure rates were similar between years; 17% of occupied territories failed in 1998 and 21% failed in 1999. We also measured nestling growth, a variable not previously reported for goshawks in any northwestern studies. Time for nestlings to grow from 10 to 90% of their fledging mass ranged from 16 to 35 days and their growth-rate constants, k, ranged from 0.13 to 0.27. Nestling growth rates were similar within nests, but varied among nests. The fastest mean growth at a nest was 17 days to reach 90% of fledging mass, while the slowest mean growth was 33 days to reach 90% of fledging mass. Variability in growth among nests suggested there were differences in energy intake by nestlings, potentially due to adult condition or habitat quality. Nestling growth may be a valuable indicator of habitat quality and adult breeding condition during the nestling stage. In contrast, productivity (as defined in this study) can be viewed as a more encompassing expression of habitat quality including quality of the adult winter range and breeding habitat