Jesús Caro

Possible functions of alternative nests in raptors: the case of Bonelli’s Eagle

Four non-exclusive hypotheses have been proposed to explain the alternative nest-building behaviour of raptors: (1) nests as an advertising signal in territories, (2) frustration nests, (3) competition avoidance by nest-site and (4) reduction of nest ectoparasites. We report here data collected during an observational study of a population of Bonelli’s Eagle Hieraaetus fasciatus in southeastern Spain. Our data does not support the first two hypotheses based on the closeness of nests within territories, the lack of correlation between the number of nests and the distance to neighbours and the construction of secondary nests at similar frequencies after breeding failures as after successes. In contrast, the construction of alternative nests to avoid competition with other cliff-nesting raptor species breeding nearby was clearly important since 30% of the pairs obtained some direct benefit from the existence of alternative nests within their territories. We also found abundant Coleoptera (Dermestidae) and Diptera (Carnidae, Calliphoridae and Phoridae) as ectoparasites in nests, and the alternative use of nests, synergetically with the presence of greenery as mechanisms for avoiding ectoparasites, was an important factor for the breeding success of the eagle. Our data suggest that competition avoidance and, in particular, the reduction of nest ectoparasite hypotheses are the more plausible explanations for the maintenance of alternative nests in raptors.

A quantitative assessment of the release of farm-reared red-legged partridges (Alectoris rufa) for shooting in central Spain

The release of farm-reared game is considered a conflictive management tool because of its potential harmful ecological effects on wildlife and associated habitats. Estimates of the number of animals released and the area where this game management takes place could give an idea of the magnitude of their potential impacts. We aimed to quantitatively assess the release of farm-reared red-legged partridges (Alectoris rufa) in the province of Ciudad Real, central Spain, one of the main hunting areas in this country. We analysed the official permits that the regional government granted to the hunting estates to release farm-reared partridges between 2006 and 2012. Our results show that an average of 800,000 partridges were released annually in the study area. A decrease in the number of hunting estates that used this game management practice, as well as in the number of red-legged partridges officially released, was observed during the last years within the study period. This might be a consequence of the current economic crisis, rather than a change in management styles. Release intensity was spatially heterogeneous, being higher in the southeast of the study area, where historically red-legged partridge was more abundant. Most of the red-legged partridges released came from only four farms placed in northern Spain. Our results suggest that this management activity should be better monitored and that spatial regulations should also be considered.

Habitat features of settlement areas used by floaters of Bonelli's and Golden Eagles

Summary Bonelli’s Eagle Hieraaetus fasciatus and Golden Eagle Aquila chrysaetos are two declining species, in which floaters tend to be located outside of breeding territories during the dispersal period, in so-called settlement areas. We studied settlement areas for both these long-lived raptors in the southern Iberian Peninsula, to gain a better understanding of the ecological requirements of the eagles during their long pre-adult stage, a period accounting for around 80% of the species’ mortality. Eagle abundance was calculated by road censuses, and habitat characteristics of settlement and non-settlement areas compared by General Discriminant Analysis (GDA) and Logistic Regression (LR). The best model of GDA and LR incorporated the abundance of main prey for eagles (rabbits, partridges) and orchard surface area, and explained 100% of eagle presence; the best model selected by GDA also included habitat heterogeneity. Both eagles tended to share settlement areas in the southern Iberian Peninsula and, when they did not, the mean annual temperature and slope appeared to explain the segregation between the two species. Management measures for the conservation of both threatened species during the dispersal period should be focused on identifying settlement areas, maintaining high prey densities and maximum habitat heterogeneity.

The feeding ecology of Bonelli’s eagle (Aquila fasciata) floaters in southern Spain: implications for conservation

Although many studies have investigated the feeding habits of Palaearctic raptors, few have analysed non-breeding populations during dispersal. Bonelli’s eagle (Aquila fasciata), a threatened species in Western Europe, has a relatively long and critical dispersal period. We studied feeding habits, prey selection, and the influence of prey density on floater abundance in this species during its dispersal period in southern Spain. Differences were found between the diet of floaters and that of the closest breeding populations. Diet diversity was rather low for floaters, with European wild rabbits (Oryctolagus cuniculus) being the main prey and the only prey positively selected. Moreover, the number of floater Bonelli’s eagles observed in the dispersal areas was positively associated with rabbit abundance. Other prey included red-legged partridges (Alectoris rufa) and pigeons (Columba sp.). We propose measures to match suitable prey availability for floater eagles in settlement areas and the use of such areas as human hunting fields.

Improving decision-making for sustainable hunting : regulatory mechanisms of hunting pressure in red-legged partridge

AbstractKnowledge about how hunting pressure is determined, and the relative efficacy of different mechanisms to regulate harvest, can help to improve the managers’ decision-making process. We developed a general framework about the decision-making process that regulates red-legged partridge (Alectoris rufa) hunting pressure in central Spain based on information from a focus group and individual interviews with game managers. We also used available information to compare the efficiency of different tools thus improving some decision steps. We evaluated the cost-effectiveness of different population monitoring methods as a way to reduce uncertainty on partridge availability to hunters. Additionally, we investigated the relationship between annual harvest and various regulatory mechanisms of partridge hunting pressure used in the study area to identify the most potentially useful one to limit annual take-off. Game managers usually set hunting pressure after a qualitative assessment on population abundance prior to the hunting season, but this decision was frequently modified during the course of the hunting season according to variations in catch or perceived abundance at that time. Our results showed that kilometric abundance indices (counting partridges from cars along line transects) was a simple cost-efficient and reliable estimate of partridge density (estimated by Distance sampling). A variety of regulatory mechanisms were used by managers. The variables that most affected annual harvest (in addition to partridge abundance) were the number of driven-shooting days, and hunter density in walked-up hunting days, suggesting that their adjustment will be the most efficient regulatory mechanisms. We conclude that adequate monitoring on population abundance should be a critical step for managers’ decision-making, and that a better understanding of the relative value of regulatory mechanisms, combining social and ecological approaches, would help improving our understanding of any human-mediated system, thus leading to better management recommendations.

Effects of hunting management on Mediterranean farmland birds

This study was funded by the Portuguese Foundation for Science and Technology (FCT) (PRAXIS/C/AGR/11062/1998) and by the European Commission under the 7th Framework Programme for Research and Technological Development through the project HUNT(212160, FP7- ENV-2007-1), and contributes to the project CGL2009-13029 from the Spanish Ministry of Science.

Efecto de la gestión para las especies de caza menor sobre la fauna no cinegética

Arroyo, B., Delibes-Mateos, M., Caro, J., Estrada, A., Mougeot, F., Diaz-Fernandez, S., Casas, F., Vinuela, J. (2013). Effect of small game management on non-game fauna. Ecosistemas 22(2):27-32. Doi.: 10.7818/ECOS.2013.22-2.05 Hunting, as an activity implemented over wildlife, and because of its associated management, can have effects on other species. Most frequently used management tools for small game includes habitat modifications, provision of supplementary food or water, predator control or release of farm-reared animals. Information reviewed shows that maintaining appropriate habitats for game animals (a heterogeneous landscape with natural vegetation patches within the farmland matrix, vegetation along field edges) and provision of supplementary food and water frequently benefit non-game species. Predator control could be beneficial for certain non-game prey, but this effect is not observed in all studied species. In addition, this tool is associated with the use of illegal methods with very detrimental effects on protected predators. Very intensive management, particularly when based on releases of farm-reared animals, is apparently detrimental for certain species. Disturbance associated with hunting activities also appear to have negative effects on some non-game species. These results show that management combining conservation of adequate habitats, an appropriate use of feeders and water points, hunting based on wild populations (without releases of farm-reared animals), regulating hunting pressure, maintaining hunt-free reserves within the hunting estates, and sometimes the use of a legal and selective predator control, could benefit other species of conservation concern.

Exploring the views on hunting of Spanish hunters: effect of age and public vs. anonymous opinions

We explored the views held by Spanish hunters on hunting, and assessed how these views varied according to participant characteristics and whether or not the responses were made public via a hunter’s magazine. Hunters expressed many positive values in relation to hunting, but were critical of their own community as well as other stakeholders. Spanish hunters felt misunderstood and even attacked by society at large. There was also a widespread negative perception of the future of hunting. The frequency of references to different opinions varied between anonymous and public respondents and in relation to age group. Participants who expressed their opinions publicly mentioned the ecological values of hunting more frequently, were more critical towards their own community, and viewed the future of hunting more positively than anonymous participants. This may indicate an intended projected positive image; namely, Spanish hunters may publicly emphasize those views that improve their position in society.

Funciones y valoraciones de la caza y su gestión en España: estudios científicos sobre el colectivo cinegético

We summarize information provided by some recent scientific studies in relation to the opinions, views and attitudes of Spanish hunters regarding hunting and its management. In particular, we discuss the different functions (economic, ecological and social) that hunters attribute to hunting, as well as their moral judgements associated with the different motives for hunting. In addition, we explore how hunters value different game management tools (including predator control, releases of farm-reared animals and the regulation of hunting pressure), and we discuss how such valuations affect their decision-making. Finally, we assess potential future trends of hunting, as expressed by the hunters themselves.

Factors influencing mobility and survival of Eurasian Woodcock wintering in Spain

This work was partially funded by the Committee of Hunting and Continental Fishing, under the Research Project: 200430E471.