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Abstract In the first comprehensive assessment of the reproductive rates of critically endangered California Condors (Gymnogyps californianus) recovering from complete extirpation in the wild, we analyzed 20 years (1999–2018) of data from condor flocks in southern and central California. We found that several anthropogenic threats affected reproductive rates: (1) coastal space use by female condors was associated with lower hatch probability, presumably due to foraging on marine mammals and associated DDE exposure; (2) trash ingestion by chicks decreased fledging probability prior to implementation of trash management in 2007; and (3) all parent deaths during rearing resulted in chick or early fledgling deaths, and most parental deaths were due to lead poisoning. We also detected several effects on reproductive rates from the complex individual-based management of condors, which involves ongoing releases of captive-bred individuals and health interventions including treatment of lead poisoning. Recruitment rates were lower for new release sites, which we attribute to a lack of individual- and flock-level experience. In addition, the number of free-flying days in the wild in the year before first breeding and in the 8 weeks before subsequent breeding was positively associated with female and male recruitment and with female rebreeding probabilities, respectively, indicating that removing individuals from the wild may reduce their breeding success. Finally, probabilities of recruitment, rebreeding, and fledging all increased with age, and given the age distribution skew of the recovering flocks toward younger individuals, overall reproductive success was lower than would be expected at the stable age distribution. Thus, reproductive rates should increase over time as the mean age of California Condors increases if current and emerging threats to reproduction, including the loss of breeders due to lead poisoning, can be addressed.
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Postnatal dispersal and drivers of successful recruitment in resident Poecile gambeli (Mountain Chickadee)
Abstract Many animals disperse from their natal sites as juveniles to settle in new locations where they may eventually breed. Estimating distances of such postnatal dispersal within and across populations, as well as identifying factors affecting recruitment success, is important for understanding the evolutionary consequences of dispersal. We investigated patterns of postnatal dispersal and identified predictors of successful recruitment in highly resident Poecile gambeli (Mountain Chickadee) using data on 326 recruits of 5,226 total fledglings detected at winter feeders (recruitment into winter flocks) and nest boxes (recruitment into the breeding population) over 12 years at 2 elevational sites in the northern Sierra Nevada, USA. Like most Parids, chickadees dispersed close to their natal sites (median distance: 644 m). Dispersal distance was not associated with fledgling mass, but females dispersed significantly longer distances than males. When only considering dispersal distances based on recaptures at nest boxes, birds that fledged earlier dispersed significantly shorter distances. Successful recruitment both into winter flocks and into the breeding population was associated with higher fledgling mass and earlier fledging. Over the study period, only 13 birds were detected dispersing from one elevational site to the other, and 12 of these birds hatched at low elevation and dispersed to the high-elevation site. Our results suggest that earlier fledging timing and higher fledgling mass are both critical for successful recruitment in P. gambeli and confirm that fledgling mass is a key measure of individual quality in which even small differences in mass (~2%–3%) may have important implications for recruitment and, therefore, fitness.
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- Award ID(s):
- 2119824
- PAR ID:
- 10629601
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Ornithology
- Volume:
- 142
- Issue:
- 3
- ISSN:
- 0004-8038
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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