Scaling up ideals to freedom: are densities of red knots across western Europe consistent with ideal free distribution?

Local studies have shown that the distribution of red knots Calidris canutus across intertidal mudflats is consistent with the predictions of an ideal distribution, but not a free distribution. Here, we scale up the study of feeding distributions to their entire wintering area in western Europe. Densities of red knots were compared among seven wintering sites in The Netherlands, UK and France, where the available mollusc food stocks were also measured and from where diets were known. We tested between three different distribution models that respectively assumed (i) a uniform distribution of red knots over all areas, (ii) a uniform distribution across all suitable habitat (based on threshold densities of harvestable mollusc prey), and (iii) an ideal and free distribution (IFD) across all suitable habitats. Red knots were not homogeneously distributed across the different European wintering areas, also not when considering suitable habitats only. Their distribution was best explained by the IFD model, suggesting that the birds are exposed to interference and have good knowledge about their resource landscape at the spatial scale of NW Europe, and that the costs of movement between estuaries, at least when averaged over a whole winter, are negligible.

Rock hyrax (Procavia capensis) den site selection: preference for artificial sites

Context Objective assessments of habitat requirements for endangered species are often lacking when planning management strategies, and inappropriate landscape manipulation can sometimes turn an endangered species into a pest. Recent expansive population growth of the rock hyrax Procavia capensis in northern Israel has been attributed largely to the proliferation of man-made boulder piles on the fringes of new residential developments. Aims The hyrax is a protected species, but when in proximity to residential areas it can be a garden pest and is medically important as a reservoir of cutaneous leishmaniasis. Management should thus consider preservation of hyrax populations in combination with minimising pest potential. We examined the hypothesis that hyraxes prefer artificial boulder piles to natural outcrop crevices as den sites. Methods We surveyed all 57 potential den sites in a 1 × 1 km area around a village in northern Israel, and conducted logistic regression to examine the correlation of hyrax presence with site type (pile or crevice), size, distance from the village, distance from other den sites and network centrality within the den site network. We used the Aikaike information criterion (AIC) to compare logistic models. Key results Occupancy was well predicted by site type, site size, and distance from other sites, explaining 59% of the variation in the logistic regression. These three predictors were selected both by considering the combination of predictors that gave the lowest AIC value, and also by the stepwise logistic algorithm. Conclusions and implications Hyrax den site preference, and in particular preference for boulder piles over natural crevices, should be integrated into managing this species simultaneously for conservation and pest control in the face of continuing residential encroachment on natural areas.

Habitat Choices of Nubian Ibex (Capra Nubiana) Evaluated with A habitat Suitability Modeling and Isodar Analysis

The value of a habitat for a forager may be affected by habitat characteristics related to food availability, energetic costs of foraging, predation costs, and the foraging opportunities available in other habitats. Nubian ibex (Capra nubiana) are stout, sure-footed social wild goats that inhabit arid landscapes with steep terrain. We investigated their habitat selection behavior using indicators to (1) develop a habitat suitability index (HSI) model that would account for the variation in the activity densities of Nubian ibex across habitat types and seasons, (2) apply the isodar technique to look for density-dependent habitat selection behavior in Nubian ibex, and (3) investigate the proximate environmental factors that correlate to relative activity densities of Nubian ibex. We determined relative densities of the ibex by recording sightings of animals along standard walking transects. We incorporated the habitat variables that had greatest influence on the densities of Nubian ibex into habitat suitability index models for both spring and summer seasons.

The HSI models revealed that Nubian ibex most preferred open cliff face habitat offering safety during the spring season, but their habitat preference shifted towards an area with watered gardens ("grave area habitat") during the summer season. Significant isodars were only obtained for the summer season comparisons between grave area versus cliff face, and between grave area versus plateau habitats. The slopes of the isodars suggest that the grave area habitat is 10.5 and 7.6 times more productive than the plateau and the cliff face habitats, respectively. Our results suggest that the relative abundances and habitat preferences of Nubian ibex varied with the seasonal availability of habitat resources, extent of predation risks, and human nuisance disturbances across the landscape. We recommend that wildlife managers dealing with the conservation and protection of the endangered Nubian ibex should focus on the various ecological and anthropogenic factors governing the habitat selection and preferences.