With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14‐week period (17 August–24 November of 2019). We sampled wildlife at 1,509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian’s eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the United States. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban–wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot‐usa, as will future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species‐specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication.

Intrinsic and environmental stressors, such as age and seasonality, may influence social behavior and endocrine levels in gregarious foragers, but little is known about how season and age affect both behavioral and physiological responses. We evaluated seasonal/age variation of aggression and vigilance, and seasonal/age variation of endocrine levels (fecal cortisol and testosterone metabolites), in a gregarious herbivore, the Apennine chamois Rupicapra pyrenaica ornata. We examined a period of decreasing resource abundance and maternal care from July to October, a key period for nursing, weaning, and early growth of offspring. Aggression rate, vigilance, and cortisol levels decreased throughout July-October, while aggression intensity showed the reverse. Aggression intensity peaked when chamois were on the most nutritious vegetation patches. Dominance increased with age, and prime-aged females (4-8 years old) showed higher cortisol and testosterone levels and were involved in aggressive interactions more often than subadult or older females. Our findings suggest that, in early summer, when nursing effort is the greatest, selection of nutritious food patches leads to frequent encounters between female chamois, enhancing aggression rate, vigilance, and endogenous stress response. The progressive decrease in food abundance throughout July-October triggers competition for scarce resources and increased intensity of aggression. Most likely, the energetic demands of lactation and offspring guarding were key determinants of behavioral and physiological stress of female chamois. Our results suggest a multi-factorial compromise between reproductive state and stress levels, in a group-living species. Significance statementThe cost of motherhood: in female chamois, aggression, vigilance, and stress peak during lactation, despite abundant food resources. In females, aggression and dominance increase with age. A multi-factorial compromise between reproductive stage and stress may be necessary in a group-living animal. We suggest that motherhood is a stressful event for female chamois.

Evolutionary theory suggests two alternative ways in which competitive interactions could vary in response to different levels of food abundance. Competition theory suggests that aggression should be greater when resource availability is lower, as an evolutionary stable strategy to access food. Alternatively, energy allocated to aggressive interactions should increase when the available spectrum of food resources is wider, in turn allowing a greater selec-tion. We tested these hypotheses on a group-living herbivore, the Apennine chamois, Rupicapra pyrenaica ornata. We compared social, aggressive and vigilance behaviour and relevant endocrine correlates across three areas: two 'poorer' areas, i.e. with a lower availability of nutritious pasture, and a 'richer' one. In the richer area, we observed: (1) the largest group size/greatest proportion of young individuals in groups; (2) the lowest rate/intensity of aggression between individuals, at feeding; (3) the lowest duration of vigilance and proportion of 'costly' vigilance, i.e. postures performed without chewing food; and (4) the lowest levels of testosterone and cortisol metabolites, suggesting a lower endogenous aggressiveness/stress response. Our findings agree with the competition theory, suggesting a role of food depletion in increasing aggression between foraging individuals, as an evolutionary stable strategy, with cascading effects on group phenology, vigilance and stress.

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