Illegal hunting represents a major threat to the conservation of predators, but its impact remains difficult to assess as there are strong incentives to conceal this criminal activity. Attributing declines of carnivores to poaching is therefore an important conservation challenge. We present a case study of the Eurasian lynx (Lynx lynx) in the Swiss Alps (Valais) where the current distribution range is smaller than in the recent past and population density is by ≥80% lower than in the adjacent Swiss Prealps. We tested four hypotheses to explain this lower density: (1) a too low density of camera-traps deployed for lynx surveys in Valais compared to the Prealps (methodological artifact); (2) less favorable environmental conditions around the camera-trap sites; (3) lower densities of the main prey; and (4) poaching. We estimated lynx and ungulate densities and environmental conditions at trail camera sites and could clearly reject the first three hypotheses because: (1) the survey protocol was similarly effective; (2) environmental conditions around the trapping sites in Valais were even more favorable for lynx detection than in the Prealps; and (3) prey supply was even larger in Valais. Concerning hypothesis 4, we discovered a network of illegal lynx traps (neck snares) in the main immigration corridor into Valais from the thriving adjacent lynx population in the Prealps, suggesting intense local poaching. Our findings substantiate the suspicions of long-lasting lynx poaching as a threat to the establishment and survival of the Valais population. The fact that instances of poaching were publicly known since 1995 but remained unabated for at least two decades, until the first conviction occurred, questions the commitment of local authorities to address this case of wildlife crime. Our study demonstrates the need for inquiries about poaching of top predators to be carried out at the highest levels of jurisdiction to avoid any risk of collusion between law enforcement agents and poachers.

The return of top carnivores to their historical range triggers conflicts with the interests of different stakeholder groups. Anticipating such conflicts is key to appropriate conservation management, which calls for reliable spatial predictions of future carnivore occurrence. Previous models have assessed general habitat suitability for wolves, but the factors driving the settlement of dispersing individuals remain ill-understood. In particular, little attention has been paid to the role of prey availability in the recolonization process. High spatial resolution and area-wide relative densities of the wolf's main ungulate prey species (red deer, roe deer and chamois) were assessed from snow-track surveys and modelled along with wolf presence data and other environmental descriptors to identify the main drivers of habitat selection of re-establishing wolves in the Western European Alps. Prey species abundance was estimated from the minimum number of individuals recorded from snow-tracks along two hundred and eighteen 1-km transects surveyed twice a year during four successive winters (2012/2013-2015/2016). Abundance estimates per transect, corrected for species-specific detection probabilities and averaged across winters, were used to model area-wide relative prey density and biomass. Confirmed wolf observations during the same four winters were used to develop a spatially explicit habitat selection model for establishing wolves, based on our estimates of prey supply and other environmental descriptors of topography, land-use and climate. Detection-corrected ungulate prey abundances and modelled relative densities varied considerably in space (0-2.8, 1.3-4.5 and 0-6.3 per 50 ha in red deer, roe deer and chamois respectively; 1.3-11.65 pooled), while total predicted prey biomass ranged from 23 to 304 kg per 50 ha. Red deer density was the most important factor explaining wolf occurrence (31% contribution), followed by roe deer density (22%), winter precipitation (19%) and presence of game reserves (16%), showing that food supply, especially red deer as the most profitable prey in the Western Alps, was the main driver of winter habitat selection during the settlement phase. Synthesis and applications. We demonstrate the crucial importance of including accurate, fine-grained information about prey supply for predicting recolonization patterns of carnivores and thus anticipating areas with potential human-wildlife conflicts where preventive measures should be prioritized.

Le statut actuel du lynx en Valais a fait l’objet d’un suivi durant quatre hivers ( 2011–2015 ) au moyen de pieges photographiques repartis sur l’ensemble du territoire cantonal. Les resultats montrent une distribution spatiale tres heterogene du felin. La densite la plus elevee est atteinte dans la partie nord-ouest du canton – a proximite des populations sources supposees ( Prealpes vaudoises ) –, alors qu’elle est tres faible dans le reste des Alpes bernoises, et plonge litteralement dans les Alpes pennines et le Chablais, soit au Sud du Rhone. La densite parait aussi anormalement basse en comparaison de ce qui est observe ailleurs dans les Alpes suisses et a ce qui prevalait au sud du Rhone dans les annees 1980. Quatre hypotheses sont invoquees pour expliquer le statut actuel precaire du lynx en Valais. L’existence d’un braconnage rampant semble cependant le facteur le plus plausible. Sans enquetes penales serieuses et poursuite systematique des actes delictueux, l’etablissement stable du lynx en Valais parait compromis.

1. Human disturbance upon widlife is of growing conservation concern. There are few studies that have looked simultaneously at the impact of man on wild, free-ranging animals from different perspectives, i.e. using different approaches. We investigated stress, behavioural and energetic responses in free-living Black grouse, a declining emblematic species of Alpine ecosystems. 2. Radiomonitored birds were experimentally flushed from their snow burrows in the afternoon, and response to disturbance was quantified from a hormonal, behavioural and energetic viewpoint. Stress hormone metabolites (FCM) were quantified from droppings collected from igloos, as far as possible daily. Changes in activity budgets were reconstitued from the signals emitted by the activity-sensitive radiotags. Energy budgets were modelled to account for possible extra energetic costs induced by disturbance, by linking energy expenditures (data obtained from captive birds in the respirometric laboratory) with in situ collected temperature data and activity budgets. 3. There was no significant increase of stress between control and treatment when all nine experimental birds were considered, but the difference showed significantly higher FCM concentrations for treatment (i.e. after artificially elicited disturbance) when a peculiar bird with the highest initial value and a comparatively low treatment value was removed. Overall, initial stress levels showed a large interindividual variation. 4. Birds significantly prolonged foraging duration in the mornings following disturbance by, on average, 23%. In contrast, foraging duration in the afternoon did not differ between treatment and control situations. Disturbed birds were thus potentially exposed to a 12% greater risk of predation by diurnal raptors and carnivores as they did no longer benefit from the protective shelter of igloos. 5. Prolonged foraging time in the mornings following disturbance entailed extra foraging costs that amounted to about 6-9% of overall morning (00:00 to 12:00) energy expenditures (increasing with decreasing ambient temperature), or ca 1.8–3.7% of a whole daily energy budget. These figures represent very conservative minimal estimates as not all components of daily energy budgets could be accounted for, e.g. the costs of sudden escape flights, or the costs of mounting a stress response. 6. Synthesis and applications. Winter human disturbance, such as off-piste 2 skiing or snowboarding, elicits stress and behavioural compensation, which might be detrimental to wintering Black grouse. This study is a new step towards defining tolerance thresholds with regards to winter human disturbance in a vunerable wildlife species of Alpine ecosystems. Implementing conservation measures with the aim to decrease human impact below acceptable disturbance levels for Black grouse will eventually benefit the entire sympatric biocenose.