Ibis
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Научный журнал Ibis включен в БД Скопус.2024-03-29T12:32:27ZVariation in offspring sex ratio of a long-lived sexually dimorphic raptor, the Eastern Imperial Eagle Aquila heliaca
http://localhost:8080/xmlui/handle/item/532
Variation in offspring sex ratio of a long-lived sexually dimorphic raptor, the Eastern Imperial Eagle Aquila heliaca
Katzner, Todd E.; Jackson, Daniel S.; Bragin, Evgeny A.; DeWoody, Andrew
Sex ratio theory attempts to explain observed variation in offspring sex ratio at both the population and the brood levels. In the context of low-fecundity organisms producing high-investment offspring, the drivers of adaptive variation in sex ratio are incompletely understood. For raptors that display reverse sexual dimorphism (RSD), preferential alloca-tion of resources to the putatively cheaper sex (male) may be a response to environmental, social or demographic stressors. To assess the extent of skew in offspring sex ratios and to evaluate possible dietary, environmental and demographic correlates of such skew to long-lived RSD avian species, we evaluated the offspring sex ratio of 219 chicks from 119 broods in 30 territories of Eastern Imperial Eagles Aquila heliaca across 7 years and four regions at a nature reserve in Kazakhstan. Only in one region in 1 year of our study did the offspring sex ratio differ significantly from parity (10 males : 1 female in 11 territories). Whereas offspring sex ratios were independent of dietary diversity, precipitation, tempera-ture and productivity, we found that year had a moderate effect on brood sex ratio within territories. Our results provide limited evidence of brood sex manipulation in these popu-lations of Eastern Imperial Eagles, and no mechanistic insight into predictions associated with it. Stochastic variation is likely to explain much of the fluctuation we observed in sex ratios, but our observations are also consistent with the hypothesis that sex-ratio manipula-tion may occur irregularly, in concurrence with atypical environmental or demographic conditions that fluctuate at a time scale longer than that of our 7-year study.
2014-01-01T00:00:00ZDemographic consequences of nestbox use for Red-footed Falcons Falco vespertinus in Central Asia
http://localhost:8080/xmlui/handle/item/531
Demographic consequences of nestbox use for Red-footed Falcons Falco vespertinus in Central Asia
Bragin, Evgeny A.; Bragin, Alexander E.; Katzner, Todd E.
Nestbox programmes are frequently implemented for the conservation of cavity-nesting birds, but their effectiveness is rarely evaluated in comparison with birds not using nest-boxes. In the European Palaearctic, Red-footed Falcon Falco vespertinus populations are both of high conservation concern and are strongly associated with nestbox programmes in heavily managed landscapes. We used a 21-year monitoring dataset collected on 753 nesting attempts by Red-footed Falcons in unmanaged natural or semi-natural habitats to provide basic information on this poorly known species; to evaluate long-term demo-graphic trends within this population; and to evaluate response of demographic parame-ters of Red-footed Falcons to environmental factors including use of nestboxes. We observed significant differences among years in laying date, offspring loss and numbers of fledglings produced, but not in egg production. Of these four parameters, offspring loss and, to a lesser extent, number of fledglings exhibited directional trends over time. Variation in laying date and in numbers of eggs were not well explained by any one model of environmental factors, but instead by combinations of models, each with infor-mative terms for nest type. Nevertheless, laying in nestboxes occurred 2.10 0.70 days earlier than in natural nests. In contrast, variation in both offspring loss and numbers of fledglings produced were fairly well explained by a single model including terms for nest type, nest location and an interaction between the two parameters (65 and 81% model weights, respectively), with highest offspring loss in nestboxes on forest edges. Because, for other species, earlier laying dates are associated with more fit individuals, this interac-tion highlighted a possible ecological trap, whereby birds using nestboxes on forest edges lay eggs earlier but suffer greater offspring loss and produce lower numbers of fledglings than do those in other nesting settings. If nestboxes increase offspring loss for Red-footed Falcons in heavily managed landscapes where populations are at greater risk, or for the many other species of rare or endangered birds supported by nestbox programmes, these processes could have important demographic and conservation consequences.
2017-01-01T00:00:00Z