Comparison of reproductive success between parent-reared and hand-reared northern bald ibis Geronticus eremita in captivity during Proyecto Eremita
Keywords:captivity, hand-rearing, Northern Bald Ibis, parent rearing, reproduction
Modern zoos actively collaborate in the conservation of many endangered species by captive breeding for reintroduction. This paper presents the reproductive success of a captive colony of northern bald ibis Geronticus eremita (NBI) at ZooBotánico de Jerez between 1993 and 2013 (21 years). Between 2004 and 2011 was “Proyecto Eremita”, a study of the best releasing techniques for hand-reared NBI in Cadiz in order to establish a free-range, self-sustained population in the wild. During this period, first-clutch eggs were artificially incubated and chicks were hand reared until fledgling stage, allowing the pair to produce a second or replacement clutch that was parent reared. This paper compares the colony’s reproductive success between the years where one single clutch was reared by the pairs (n=13) and the years of Proyecto Eremita (n=8), with two clutches, the first hand reared and the second parent reared. The reproductive success rate was measured in 300 nests. A total of 268 fledglings reached 2 months old, the age considered here as the reproductive success. Two reproductive variables were significantly higher during the Proyecto Eremita years: mean number of fledglings per nest (1.8 versus 0.3) and overall number of fledglings recorded per year (26.5 versus 4.3). The reproductive success of hand-reared clutches was similar to parent-reared clutches. There was a significant and negative effect of colony size on the percentage of birds paired and on reproductive success. Parent-reared clutches during the Proyecto Eremita showed a higher reproductive success compared to parent-reared clutches outside this period. The data show that a remarkably high percentage of mating pairs outside of the Proyecto Eremita period failed at reproduction, probably due to density-dependent effects. The combination of hand-rearing and parent-rearing methods used in this study was a very effective tool to significantly increase the number of fledglings produced for the reintroduction programme.
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