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Eagle Population (eagle + population)
Selected AbstractsThe regulation of brood reduction in Booted Eagles Hieraaetus pennatus through habitat heterogeneityIBIS, Issue 4 2008EVA CASADO Brood reduction, the death of one or more chicks through siblicide or starvation, can occur through density-dependence in fecundity. Brood reduction may arise in territorial breeding systems either as a response to a high level of territorial interference in a situation of high density or as a result of habitat heterogeneity. To test the predictions of the two main hypotheses that attempt to explain how density-dependent fecundity is generated, the Habitat Heterogeneity Hypothesis (HHH) and the Individual Adjustment Hypothesis (IAH), we analysed the relationship between density and fecundity in an expanding population of Booted Eagles in Doñana National Park, Spain, using an 18-year data series. We also studied the occurrence and frequency of brood reduction in the same Booted Eagle population to appreciate further its effects and the factors that influence its occurrence and frequency. Our results support the HHH in the present situation of high density, as fecundity in the better territories (older and more frequently occupied) was higher than in low quality territories and was not affected by population density in high density periods. Nevertheless, the fecundity of high quality territories was affected (although not significantly) by population density in periods of low density, suggesting that the IAH was supported when only high quality territories were occupied. Older territories were used more frequently and chicks in these areas hatched earlier and suffered lower mortality than in new territories. We found a significant negative relationship between mean fecundity and its skewness, a finding that also supports HHH. During years of food shortage, less frequently occupied territories suffered higher rates of brood reduction. Brood reduction in this Booted Eagle population was a consequence of the heterogeneous structure of the habitat, with some territories having a higher probability of brood reduction than others. Parental nutritional condition did not affect brood reduction. The effect of brood reduction on nestling quality and population dynamics is also discussed. [source] Breeding performance, age effects and territory occupancy in a Bonelli's Eagle Hieraaetus fasciatus populationIBIS, Issue 2 2008JOSÉ A. MARTÍNEZ Bonelli's Eagle Hieraaetus fasciatus is one of the most endangered birds of prey in Europe. Despite mounting interest and research, several questions regarding the conservation implications of territory occupancy and site-dependent population regulation remain insufficiently explored for this species. Here, we report on a 12-year study of the territorial structure of a Bonelli's Eagle population in southeastern Spain. No signals of population decline were found in the breeding population, as mean annual productivity was stable and the presence of mixed-age pairs in the population decreased with the years. However, the average proportion of subadults occupying territories was larger than that observed in other Spanish populations. Contrary to the predictions of a despotic distribution model, we found no significant relationship between occupancy rates and breeding parameters. Our results showed significant variations in productivity attributable to differences in the quality of individuals (i.e. mixed versus adult pairs), but no variability among territories per se (i.e. caused by habitat heterogeneity). Moreover, coexistence with intraguild species did not have any significant effect on productivity, although the proximity of Eagle Owls Bubo bubo affected the occupation rate of territories. Finally, our population does not appear to experience site-dependent population regulation, as a positive relation between mean annual productivity and density was found. The threat posed by changes in land use in the study area leads us to suggest that strict protection of current territories is necessary to ensure population persistence, and we suggest that a significant population increase is only likely if new or deserted territories become available. [source] Non-independence of demographic parameters: positive density-dependent fecundity in eaglesJOURNAL OF APPLIED ECOLOGY, Issue 5 2008Miguel Ferrer Summary 1Using information on the Doñana population of Spanish imperial eagles Aquila adalberti from 1959 to 2004, we present strong empirical support to theoretical models on the regulation of population trajectories by the relationships between breeder mortality and floater availability. 2During the study period, the eagle population showed three distinct phases: (i) a population increase with negative density-dependent fecundity; (ii) a period of stability without any relationship between density and fecundity; and (iii) a population decrease with a positive relationship between density and fecundity. 3A dramatic increase in annual adult mortality due to an increase in poisoning in hunting areas surrounding the Doñana National Park was recorded. The use of poison against generalist predators accounted for more than 54% of the total number of breeding eagles found dead since 1990, increasing annual adult mortality from 6·07 to 12·01%. 4This high mortality reduced the population annually by 6% during the 1992,2004 period. Also, the population changed from a negative to a positive relationship between density and fecundity (Allee effect). These trends made the population approach extinction due to the double effect of increasing breeder mortality and low availability of floaters. 5A supplementary feeding programme established in 1990 did not increase fecundity because it was a consequence of high adult mortality rather than low food availability. The high mortality of adults increased the risk of breeding failure and also decreased the availability of floaters, decreasing the likelihood of mate substitution. 6Synthesis and applications. The main target in species conservation management plans is often a single demographic parameter (typically, fecundity in raptor populations). Our research demonstrates, however, that demographic parameters must not be considered as independent variables when formulating management programmes. The essential relationship between adult mortality and the availability of floaters must be better understood to avoid the risk of implementing inefficient management strategies. Although fecundity was low in this eagle population, it was a result of high adult mortality rates. Consequently, management must aim to correct the unusual mortality and recover the floater population. [source] Population fragmentation leads to spatial and temporal genetic structure in the endangered Spanish imperial eagleMOLECULAR ECOLOGY, Issue 3 2007B. MARTÍNEZ-CRUZ Abstract The fragmentation of a population may have important consequences for population genetic diversity and structure due to the effects of genetic drift and reduced gene flow. We studied the genetic consequences of the fragmentation of the Spanish imperial eagle (Aquila adalberti) population into small patches through a temporal analysis. Thirty-four museum individuals representing the population predating the fragmentation were analysed for a 345-bp segment of the mitochondrial control region and a set of 10 nuclear microsatellite loci. Data from a previous study on the current population (N = 79) were re-analysed for this subset of 10 microsatellite markers and results compared to those obtained from the historical sample. Three shared mitochondrial haplotypes were found in both populations, although fluctuations in haplotype frequencies and the occurrence of a fourth haplotype in the historical population resulted in lower current levels of haplotype and nucleotide diversity. However, microsatellite markers revealed undiminished levels of nuclear diversity. No evidence for genetic structure was observed for the historical Spanish imperial eagle population, suggesting that the current pattern of structure is the direct consequence of population fragmentation. Temporal fluctuations in mitochondrial and microsatellite allelic frequencies were found between the historical and the current population as well as for each pairwise comparison between historical and current Centro and historical and current Parque Nacional de Doñana nuclei. Our results indicate an ancestral panmictic situation for the species that management policies should aim to restore. A historical analysis like the one taken here provides the baseline upon which the relative role of recent drift in shaping current genetic patterns in endangered species can be evaluated and this knowledge is used to guide conservation actions. [source] Widespread hybridization between the Greater Spotted Eagle Aquila clanga and the Lesser Spotted Eagle Aquila pomarina (Aves: Accipitriformes) in EuropeBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010ÜLO VÄLI Hybridization is a significant threat for endangered species and could potentially even lead to their extinction. This concern applies to the globally vulnerable Greater Spotted Eagle Aquila clanga, a species that co-occurs, and potentially interbreeds, with the more common Lesser Spotted Eagle Aquila pomarina in a vast area of Eastern Europe. We applied single nucleotide polymorphism (SNP) and microsatellite markers in order to study hybridization and introgression in 14 European spotted eagle populations. We detected hybridization and/or introgression in all studied sympatric populations. In most regions, hybridization took place prevalently between A. pomarina males and A. clanga females, with introgression to the more common A. pomarina. However, such a pattern was not as obvious in regions where A. clanga is still numerous. In the course of 16 years of genetic monitoring of a mixed population in Estonia, we observed the abandonment of A. clanga breeding territories and the replacement of A. clanga pairs by A. pomarina, whereby on several occasions hybridization was an intermediate step before the disappearance of A. clanga. Although the total number of Estonian A. clanga × A. pomarina pairs was twice as high as that of A. clanga pairs, the number of pairs recorded yearly were approximately equal, which suggests a higher turnover rate in interbreeding pairs. This study shows that interspecific introgressive hybridization occurs rather frequently in a hybrid zone at least 1700-km wide: it poses an additional threat for the vulnerable A. clanga, and may contribute to the extinction of its populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 725,736. [source] | ||||||||||