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Terraube J.,Natural Research Ltd. | Terraube J.,Institute Investigacion en Recursos Cinegeticos | Terraube J.,French National Institute for Agricultural Research | Arroyo B.E.,Institute Investigacion en Recursos Cinegeticos | And 3 more authors.
Biodiversity and Conservation | Year: 2012

Ecological specialization can explain the declining status of many species in the face of current global changes. Amongst specialists, nomadic predators present conservation biologists with many challenges, mainly because of the difficulty of studying highly mobile individuals over time and across very large areas. For these species, the relative influence of prey abundance, habitat heterogeneity and arrival time at the breeding grounds on breeding parameters remains poorly understood. We studied the factors influencing variation in breeding numbers and performance of a declining nomadic specialist raptor, the Pallid Harrier Circus macrourus, in north-central Kazakhstan. During a 5-year period, we recorded large inter-annual variation in vole abundance in the main study area, and differences between habitats. We also recorded a strong numerical response of breeding Pallid Harriers to inter-annual changes in local vole abundance. From a 13-year dataset on breeding harriers in the same area, harrier numbers appeared to vary cyclically, with an interval between peaks of approximately 6 years. At a broader, regional scale, variations in Pallid Harrier abundance appeared asynchronous, suggesting a regional redistribution of harriers between years. Reproductive success depended on local vole abundance, but also on timing of breeding and nesting habitat. Clutch size, nest success and fledged brood size increased with vole abundance. Late breeders had smaller clutches and apparently lower hatching rates than early ones, possibly as a result of the interplay between their probable poorer body condition and habitat-specific variation in predation rates. In true nomadic specialist predators, such as Pallid Harriers, breeding success may therefore depend on a complex interplay between spatial variation in prey abundance, habitat composition and timing of breeding attempts. One of the factors influencing the start of breeding is the length of time taken to prospect between different breeding sites, which in turn may depend on the predictability of spatial and temporal variation in vole abundance. These results have important conservation implications, as changes in climate and habitat could affect spatial and temporal variations in vole abundance, with possible consequences for timing of breeding, food availability and, ultimately, the reproductive success of this declining nomadic predator. © 2012 Springer Science+Business Media B.V. Source


Katzner T.E.,West Virginia University | Katzner T.E.,U.S. Department of Agriculture | Jackson D.S.,Oberlin College | Jackson D.S.,Cornell University | And 3 more authors.
Ibis | Year: 2014

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 allocation 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, temperature 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 populations 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 manipulation 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 British Ornithologists' Union. Source


Katzner T.E.,National Aviary | Ivy J.A.R.,Purdue University | Bragin E.A.,Naurzum National Nature Reserve | Milner-Gulland E.J.,Imperial College London | Dewoody J.A.,Purdue University
Animal Conservation | Year: 2011

Estimating population size is central to species-oriented conservation and management. However, in spite of recent development in monitoring protocols, there are gaps in our ability to accurately and quickly estimate numbers of individuals present, especially for the cryptic and often non-breeding components of structured vertebrate populations. Yet knowing the size and growth trajectory of all stage classes of a population is critical for species conservation. Here we use data from 2 years of non-invasive genetic sample collection from the cryptic, non-breeding component of an endangered bird of prey population to evaluate the impact of variability in population estimates on demographic models that underpin conservation efforts. A single non-invasive sample collection in 2003 conclusively identified 47 individual non-breeding imperial eagles, 2.8 times more than were visually counted. In 2004, our comprehensive genetic and observational analyses determined that 414 imperial eagles (n=308 non-breeders+68 territory holders+38 chicks) were present. This estimate was 326% larger than the 127 birds visually observed (n=21 non-breeders+68 territory holders+38 chicks) and 265% larger than the population size predicted by demographic models with the same number of breeders (n=156±7.2;±se). Our study builds on a body of work that demonstrates that conventional visual estimation of cryptic components of structured populations may not always be effective. Furthermore, we show that reliance on those estimates can result in inaccuracies in the demographic models that are often the foundation for subsequent conservation action. © 2011 The Authors. Animal Conservation © 2011 The Zoological Society of London. Source


Terraube J.,Natural Research Ltd. | Arroyo B.E.,IREC CSIC UCLM JCCM | Mougeot F.,IREC CSIC UCLM JCCM | Katzner T.E.,National Aviary | Bragin E.A.,Naurzum National Nature Reserve
Journal of Ornithology | Year: 2010

The ecology and conservation status of Central Asian populations of Montagu's Harriers Circus pygargus are poorly known. We studied the breeding biology of this species during 3 years in the Naurzum region, north-central Kazakhstan. Most Montagu's Harriers in the study area nested in the forest-steppe transition area, in bushy areas dominated by dogrose Rosa canina, which was apparently the nesting vegetation type providing highest and densest nest cover in the study area. Laying occurred from 26 April to 7 June (average 13 May, n = 49) and, although it varied significantly between years, was earlier than in western European populations of similar latitude. Mean (±SD) clutch size was 4.44 ± 0.86 (range 2-6; n = 50), in the higher range observed for the species. There was no significant interannual variation in clutch size, despite large variations in the abundance of small mammals in the area. Diet was mainly composed of lizards (54.2%, n = 533 identified prey in all 3 years), with small mammals (17.1%), passerine birds (14.3%) and insects (13.6%) also being consumed. Mean brood size at the last visit was 2.55 ± 2.10 (range 0-6; n = 51). Failure rate was relatively high; the main identified cause of nest failure was predation. We compare the data obtained in this population breeding in natural steppes with breeding parameters from the well-studied western European populations, and discuss the implications for the conservation of this species. © 2010 Dt. Ornithologen-Gesellschaft e.V. Source

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