Emilio Virgós

Surveying carnivores at large spatial scales: a comparison of four broad-applied methods

Reliable methods to estimate species richness are very important to managers and conservationists because they provide key data to make the right decisions in conservation programmes. In the case of carnivore mammals, traditional methods, such as direct count censuses, are not useful since these animals are usually scarce, elusive and nocturnal. Difficulties in carnivore sampling are compounded when monitoring programmes are developed at large spatial scales, where high economic costs and field efforts are necessary to achieve reliable richness or abundance estimates. These problems have highlighted the need to find more effective carnivore survey methods, especially in regions with high rates of landscape change, such as the Mediterranean basin. The present study, performed in a typical Mediterranean area, was the first in Europe to test simultaneously the relative efficiencies of four broad-applied sampling methods to detect carnivore species at large spatial scales. Sign surveys based on scat detection, scent stations, camera-trapping and live-trapping were investigated. We compared efficiencies using biological parameters and by considering both the logistic and economic costs of each method. Overall, scent stations and sign surveys were the most efficient methods both in economic and logistic terms. In addition, the use of scent stations may be necessary to detect species rarely detected by scats. Detailed and extensive training programmes for conducting sign surveys and scent stations may overcome perceived problems thus enhancing the widespread use of both methods. Our results are applicable not only to other Mediterranean areas, but also to other habitats and regions of the world. More research into the suitability of these and other methods in relation to different landscapes, seasons and species is required.

A comparison on the response to forest fragmentation by medium-sized Iberian carnivores in central Spain

We studied the use of forest fragments by five medium-sized carnivorespecies in 280 forest fragments on the two Iberian plateaus. We looked forindirect evidence (faeces, tracks, dens) of fragment use (occurrence) by thespecies and analysed whether occurrence could be related to four groups ofvariables: local (vegetation structure and patch size), landscape (distance topossible colonisation sources), regional (fragment location on the northern orsouthern plateau) and the vegetation type of the fragments. We analysed thedifferential response of species according to their life-history and behaviouraltraits. The relationship between use by each species and the factors studied wasanalysed using stepwise logistic regressions. Results indicate that threefactors are crucial to explain fragment use: fragment size, geographic locationand vegetation type. Large fragments are used more than smaller ones, thenorthern plateau is more suitable than the southern plateau, and holm oak andbroad-leaved oak forests are more used than pine woods. The effects andmagnitude varied slightly among species, depending on habitat requirements orlife-history traits. Data indicate that conservation strategies in fragmentedenvironments must take into account elements functioning at different spatialscales, and that it is essential to consider each case within a characteristicregional context.

Relationship between small-game hunting and carnivore diversity in central Spain

Small-game hunting plays an important economic role in central Spain and some game species are key food resources for threatened predators. Small carnivores may reduce numbers of important game species. To alleviate predation pressure on game populations, management is often focused on predator control. Control methods can be non-selective, and so could potentially have a negative impact on non-target carnivore species, affecting carnivore guild composition and diversity. Using data on carnivore diversity in 70 quadrants (5xa0×xa05xa0km) in a large area of central Spain with two main land uses (small-game hunting and a mixture of big-game hunting and forestry), we assessed how game management was related to carnivore diversity. Carnivore species richness was significantly lower in those areas managed for small-game hunting than in areas where other land uses predominated. The apparently least affected species by predator control was the red fox (Vulpes vulpes), the main target species of predator control. Results suggested that low carnivore species richness was linked to small-game hunting activities, which was probably associated with non-selective predator control practices. Therefore, in order to reconcile carnivore conservation and economic goals it is imperative to develop and to evaluate selective predator control techniques.

Relative value of riparian woodlands in landscapes with different forest cover for medium-sized Iberian carnivores

This study analyses the role of riparian woodland in the conservation of five common carnivore species as compared with other non-riparian habitats according to woodland cover on the landscape scale (>60, 20–35 and <15% on 20 × 20-km surface area). I hypothesised that the importance of riparian woodlands in carnivore conservation on the regional scale would be greater in landscapes with low forest cover than in those with intermediate or high forest cover. To test this hypothesis, in each landscape type I sampled five riparian forests and 10–15 non-riparian habitats and recorded species richness and frequency of occurrence (number of sampled sites with species presence/total sampled sites) in both habitat types. The presence of (or use by) species at each particular sampling site was recorded using sign-surveys (search for scats and badger dens). The relative importance of riparian and non-riparian habitats in each landscape type was analysed by comparing species richness and frequency of occurrence for each species. Comparison of species richness and frequency of occurrence between landscape types indicate that riparian woodlands are important habitats in all landscape contexts. However, in accordance with the initial hypothesis, riparian woodlands are essential for carnivore conservation in the most deforested areas. Any agricultural or development policy should take into account the need to maintain and preserve riparian woodlands in landscapes, especially in intensively cultivated landscapes.

Patch occupancy by stone martens Martes foina in fragmented landscapes of central Spain: the role of fragment size, isolation and habitat structure

We studied the response to forest fragmentation of a generalist carnivore, the stone marten Martes foina, in highly fragmented landscapes of central Spain. Five different areas (n = 178 fragments) in central Spain were surveyed. This paper analyses the relationship between fragment use by martens (measured through scat presence) and a series of variables related to the size, isolation and vegetation structure of each fragment by means of stepwise logistic regression. Size and isolation have an important effect on stone marten presence in fragments. Our results were similar to those found for other marten species in landscapes with coarse-grain fragmentation, but they contrast with other studies conducted in landscapes with fine-grain fragmentation. These data suggested that in highly fragmented landscapes, size and isolation factors resulting from forest fragmentation were responsible for determining marten responses, irrespective of their habitat generalism. Management policies for the stone marten in highly fragmented scenarios require the maintenance of large forests near continuous forest tracts in mountains or riparian woodlands.

Are habitat generalists affected by forest fragmentation? A test with Eurasian badgers ( Meles meles ) in coarse-grained fragmented landscapes of central Spain

This study assesses the pattern of occurrence of a generalist species, the Eurasian badger Meles meles, in forest fragments located in agricultural landscapes of central Spain with a coarse-grained pattern of fragmentation (<20% forest cover in the landscape). Four forest regions (n= 139 forest fragments) were sampled. Badger presence/absence in forest fragments was studied in relation to: forest size, isolation and vegetation structure. Badgers were tested to see if, despite their habitat generalism, they were negatively affected by forest fragmentation in this type of fragmented landscape. Results indicated a strong and significant effect of fragment size on badger occurrence (presence was rare in forest fragments <100 ha) and an important effect of isolation at a local scale. The response of badgers to forest fragmentation in Spain is quite different to the response in other European landscapes. In Spain, badgers cope with a divided coarse-grained landscape where suitable habitats are embedded in a largely unsuitable matrix (cereal croplands). In contrast, in Britain or central Europe, badgers may be benefited by forest clearances in a heterogeneous but non-divided landscape where small woodlots are separated by a matrix of good quality (mainly pastures) and fragmentation produces fine-grained mosaic landscapes where food and den sites are simultaneously enhanced. Species response to forest fragmentation may strongly depend on the pattern of fragmentation and, in coarse-grained fragmented landscapes, generalist species may be affected in the same way as specialist ones.

Predator–prey relationships in a Mediterranean vertebrate system: Bonelli’s eagles, rabbits and partridges

How predators impact on prey population dynamics is still an unsolved issue for most wild predator–prey communities. When considering vertebrates, important concerns constrain a comprehensive understanding of the functioning of predator–prey relationships worldwide; e.g. studies simultaneously quantifying ‘functional’ and ‘numerical responses’ (i.e., the ‘total response’) are rare. The functional, the numerical, and the resulting total response (i.e., how the predator per capita intake, the population of predators and the total of prey eaten by the total predators vary with prey densities) are fundamental as they reveal the predator’s ability to regulate prey population dynamics. Here, we used a multi-spatio-temporal scale approach to simultaneously explore the functional and numerical responses of a territorial predator (Bonelli’s eagle Hieraaetus fasciatus) to its two main prey species (the rabbit Oryctolagus cuniculus and the red-legged partridge Alectoris rufa) during the breeding period in a Mediterranean system of south Spain. Bonelli’s eagle responded functionally, but not numerically, to rabbit/partridge density changes. Type II, non-regulatory, functional responses (typical of specialist predators) offered the best fitting models for both prey. In the absence of a numerical response, Bonelli’s eagle role as a regulating factor of rabbit and partridge populations seems to be weak in our study area. Simple (prey density-dependent) functional response models may well describe the short-term variation in a territorial predator’s consumption rate in complex ecosystems.

Badger Meles meles feeding ecology in dry Mediterranean environments of the southwest edge of its distribution range

The dietary preference of badgers Meles meles (Linnaeus, 1758) for earthworms and other food resources has been widely discussed. In the Mediterranean area, rabbits Oryctolagus cuniculus, fruits (mainly olives Olea europaea) and arthropods are the most important foods. We describe badger dietary habits in a xeric Mediterranean area, comparing use and availability of olives and rabbits. Our results indicated that olives and rabbits are the predominant resources consumed, however we did not detect any evidence of specialisation when we compared consumption versus field availability. In the case of olives we found that their consumption is reduced when juvenile rabbits or figs Ficus carica are widely available, which is evidence against any specialisation in this resource. Figs appear to be a key food item for badgers; they were consumed in large amounts when available. Badgers in this xeric area can be viewed as generalist or facultative specialists, using the most profitable resource when available but shifting its preferences to other less profitable food resources when availability of other primary food resource are reduced. Our results also indicated the high suitability of some human agricultural uses (eg fruit orchards) for this species, especially in the otherwise harsh Mediterranean environments.

How accurate are coat traits for discriminating wild and hybrid forms of Felis silvestris

Abstract Hybridisation between domestic cats, Felis catus, and wildcats, Felis silvestris, could lead to the genetic extinction of the latter; therefore, checking hybridisation rates in wild populations is of vital conservation importance. However, detecting hybridisation in the field is particularly challenging. Here, we aim to test the success of morphological-based procedures for discriminating wildcats from their hybrids and domestic cats, against genetic methods. We checked 17 putative Spanish wildcats by using two different classification systems based on coat patterns. None of the putative wildcats analysed in this study seemed to have an admixed genotype. Concordance between genetic and pelage approaches was almost total: only one coat classification produced mixed results with detection of one potential hybrid. Assignment was worse when performed in the field after a rapid examination of coat characters. We conclude that classification systems using coat traits could serve as surrogates of genetic approaches, but only after careful examination of those characters with more discriminatory power. Thus, the control of hybrid populations in the field as a management tool to preserve the genetic identity of wild forms is problematic if based on crude approaches or incomplete classification systems.

Evaluating methods for surveying the Endangered Cuvier's gazelle Gazella cuvieri in arid landscapes

The Endangered Cuviers gazelle Gazella cuvieri is an endemic ungulate of north-western Africa. Information on the species has been based primarily on non-systematic surveys, and the corresponding status estimates are of unknown quality. We evaluate the effectiveness and efficiency of two field methods for systematic surveys of populations of Cuviers gazelle in arid environments: distance sampling (based on sightings) and sampling indirect sign (tracks and scats). The work was carried out in the north-western Sahara Desert, in Morocco, where what is possibly the largest population of Cuviers gazelle persists. A logistically viable survey was conducted over a total area of c. 20.000 km² in 10 expeditions during 2011–2014. A total of 67 sites were surveyed, with 194 walking surveys (2,169 km in total). Gazelle signs were detected at 50 sites, and gazelles were sighted at 21 sites (61 individuals). We found a relationship between sightings and abundance indices based on indirect sign, which could be useful for population monitoring or ecological studies. Additionally, the data could be used in occupancy modelling. Density estimates based on distance sampling required considerable effort; however, it is possible to survey large areas during relatively short campaigns, and this proved to be the most useful approach to obtain data on the demographic structure of the population.