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Mellone U.,University of Alicante | Liminana R.,University of Alicante | Liminana R.,Institute Of Investigacion En Recursos Cinegeticos | Mallia E.,Parco Gallipoli Cognato Piccole Dolomiti Lucane | Urios V.,University of Alicante
Journal of Avian Biology | Year: 2011

We tagged two juvenile short-toed eagles in southern Italian peninsula with GPS satellite transmitters. According to previous visual observations, two different migratory routes for Italian short-toed eagles to reach Africa in autumn have been proposed: via Sicily and via Gibraltar. These routes include different over-water distances to cross the Mediterranean Sea, and thus different proportions of flight modes (soaring-gliding vs flapping-gliding) with resulting different transport costs. Considering different scenarios of energy cost of transport, with flapping-gliding flight over water being more costly than flying over land using soaring-gliding flight, we predicted a maximum optimal detour of 1218 km. Both individuals reached Africa using the longest, detoured, route, avoiding the longest water crossing. To achieve this they began migrating northwards, keeping for ca 700 km a direction opposite to that followed by any other migrating bird from the Northern hemisphere in autumn. The comparison of optimal detour predictions with observed migratory tracks suggests that this migratory strategy prioritizes not only energy minimization, but also safety, given the mortality risk associated with the sea crossing. Finally, it is unlike that these inexperienced individuals followed such a complex route relying only on endogenous information and we therefore suggest, also on the basis of field observations, that social interactions (adult guidance) allow these individuals to learn the detoured route. © 2011 The Authors.

Lopez-Bao J.V.,CSIC - Doñana Biological Station | Palomares F.,CSIC - Doñana Biological Station | Rodriguez A.,CSIC - Doñana Biological Station | Ferreras P.,Institute Of Investigacion En Recursos Cinegeticos
Oikos | Year: 2011

Resource clumping (prey hotspots) and intraspecific competition may interact to influence predator foraging behaviour. Optimal foraging theory suggests that predators should concentrate most of their foraging activity on prey hotspots, but this prediction has received limited empirical support. On the other hand, if prey concentration at hotspots is high enough to allow its use by several individuals, increased competition may impose constraints on foraging decisions of conspecifics, resulting in a temporal segregation in the use of shared resources. We investigated how artificial prey hotspots influence foraging behaviour in the Iberian lynx Lynx pardinus, and examined variations in the use of prey hotspots by individuals with different competitive abilities. All lynx, irrespective of their position in the competitive hierarchy, focused their activity on prey hotspots. Supplemented lynx concentrated higher proportions of active time on 100 m circular areas around hotspots than non-supplemented lynx did on any area of the same size. However, we found evidence for a dynamic temporal segregation, where inferior competitors may actively avoid the use of prey hotspots when dominants were present. Dynamic temporal segregation may operate in solitary and territorial predators as a mechanism to facilitate coexistence of conspecifics in the absence of opportunities for spatial segregation when they use extremely clumped resources. © 2011 The Authors.

Terraube J.,Natural Research Ltd | Terraube J.,Institute Of Investigacion En Recursos Cinegeticos | Arroyo B.,Natural Research Ltd | Arroyo B.,Institute Of Investigacion En Recursos Cinegeticos | And 3 more authors.
Oikos | Year: 2011

Specialist species, using a narrow range of resources, are predicted to be more efficient when foraging on their preferred food than generalist species consuming a wider range of foods. We tested whether the foraging efficiency of the pallid harrier Circus macrourus, a vole specialist, and of sympatric Montagu's harriers C. pygargus, a closely related generalist, differed in relation to inter-annual variations in vole abundance over five years (including two peak- one intermediate and two low vole abundance years). We show that the hunting parameters of pallid harriers strongly varied with vole abundance (higher encounter rates, capture rates and proportion of successful strikes in high than intermediate and low vole abundance years, respectively), whereas Montagu's harriers showed stable capture rates and hunting success (proportion of strikes that were successful), irrespective of vole abundance. Encounter rates and capture rates were higher for pallid than for Montagu's harriers when voles were abundant, but lower when voles were scarce. The hunting success of pallid harriers was also lower than that of Montagu's harriers when voles were scarce, and when they had to target alternative preys, in particular birds. Overall, estimated biomass intake rate was 40% higher for pallid harriers than for Montagu's harriers when voles were abundant, but 50% lower when voles were scarce. Our results indicate that specialists predators, like pallid harriers, which evolve specific adaptations or breeding strategies, do better when their preferred prey is abundant, but may face a cost of specialisation, being not efficient enough when their preferred prey is scarce. These results have broader implications for understanding why specialist predators are, in general, more vulnerable than generalists, and for predicting how specialists can cope with rapid environmental changes affecting the abundance or predictability of their preferred resources. © 2011 The Authors.

Carpio A.J.,University of Cordoba, Spain | Guerrero-Casado J.,University of Cordoba, Spain | Ruiz-Aizpurua L.,University of Cordoba, Spain | Vicente J.,Institute Of Investigacion En Recursos Cinegeticos | Tortosa F.S.,University of Cordoba, Spain
Wildlife Biology | Year: 2014

The landscape in southern Iberia has, over the last four decades, altered as a result of the land abandonment, while the abundance of wild boar Sus scrofa and red deer Cervus elaphus has simultaneously increased, and some key prey species such as the European rabbit Oryctolagus cuniculus have declined. In this work we explore: 1) the relationships between big game species (red deer and wild boar) and rabbit abundance, and 2) whether these relationships could have effects on food quality (total nitrogen available in the pasture and percentage of leguminosae) and food availability of (herbaceous cover). We therefore selected nine big game estates with a range of abundance as regards ungulates and similar Mediterranean habitat. Wild boar abundance was statistically negative in relation to rabbit abundance, while no significant statistical relationships between rabbit abundance and habitat structure and forage quality were evidenced. However, wild boar abundance, but not that of red deer, was negatively associated with leguminosae cover, and the percentage of surface rooted by wild boar was negatively associated with the percentage of herbaceous cover. Overall, our results suggest that the abundance of wild boar is negatively related to that of rabbits, and could have a negative effects on rabbit abundances by food competition as a result of: 1) a decrease in herbaceous coverage and leguminosae in the pasture and 2) an increase in the total percentage of soil disturbed as a result of rooting. © 2014 The Authors. This is an Open Access article.

Barrio I.C.,University of Alberta | Barrio I.C.,Institute Of Investigacion En Recursos Cinegeticos | Hik D.S.,University of Alberta | Hik D.S.,Institute Of Investigacion En Recursos Cinegeticos | And 4 more authors.
Oikos | Year: 2013

The role of positive interactions has become widely accepted as a mechanism shaping community dynamics. Most empirical evidence comes from plant communities and sessile marine organisms. However, evidence for the relative role of positive interactions in organizing terrestrial animal communities is more limited, and a general framework that includes positive interactions among animals is lacking. The 'stress gradient hypothesis' (SGH) developed by plant ecologists predicts that the balance between positive and negative interactions will vary along gradients of biotic and abiotic stress, with positive interactions being more important in stressful environments. Paralleling the SGH, stress gradients for terrestrial herbivores could be equated to inverse primary productivity gradients, so we would expect positive interactions to prevail in more stressful, low productivity environments. However, this contradicts the typical view of terrestrial animal ecology that low primary productivity systems will foster intense competition for resources among consumers. Here we use alpine herbivores as a case study to test one of the predictions of the SGH in animal communities, namely the prevalence of positive interactions in low productivity environments. We identify potential mechanisms of facilitation and review the limited number of examples of interspecific interactions among alpine herbivores to assess the role of positive and negative interactions in structuring their communities. A meta-analysis showed no clear trend in the strength and direction of interactions among alpine herbivores. Although studies were biased towards reporting significant negative inter actions, we found no evidence of competition dominating in harsh environments. Thus, our results only partially support the SGH, but directly challenge the dominant view among animal ecologists. Clearly, a sound theoretical framework is needed to include competition, positive and neutral interactions as potential mechanisms determining the structure of animal communities under differing environmental conditions, and the stress-gradient hypothesis can provide a solid starting point. © 2012 The Authors. Oikos © 2012 Nordic Society Oikos.

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