Motion triggered camera traps are an increasingly popular tool for wildlife research and can be used to survey for multiple species simultaneously. As with all survey techniques, it is crucial to conduct camera trapping research following study designs that include adequate spatial and temporal replication, and sufficient probability of detecting species presence. The use and configuration of multiple camera traps within a single survey site are understudied considerations that could have a substantial impact on detection probability. Our objective was to test the role that camera number (one, two or three units), and spacing along a linear transect (100 m or 150 m), have on the probability of detecting a species given it is present. From January to March, 2017 we collected data on six mammal species in Maine, USA: coyote ( Canis latrans ), fisher ( Pekania pennanti ), American marten ( Martes americana ), short-tailed weasel ( Mustela erminea ), snowshoe hare ( Lepus americanus ), and American red squirrel ( Tamiasciurus hudsonicus ). We used multi-scale occupancy modelling to compare pooled detection histories of different configuration of five cameras deployed at the same survey site (n = 32), and how the configuration would influence the probability of detecting a species given it was available at the site. Across all six species, we found substantial increases in probability of detection as the number of cameras increased from one to two (22 to 400 percent increase), regardless of the spacing between cameras. For most species the magnitude of the increase was less substantial when adding a third camera (4 to 85 percent increase), with coyote and snowshoe hare showing a pronounced effect. The influence of survey station features also varied by species. We suggest that using pooled data from two or three cameras at a survey site is a cost effective approach to increase detection success over a single camera.

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.

Camera traps are a cost-effective tool for large-scale and long-term population monitoring of mammals. Either bait or lure is often used to attract animals in front of a camera; however, the relative efficiency of these two attractants, or their combination, is not well understood. Our objective was to determine the optimal attractant setup for maximizing detection probabilities of mammals in the northeast USA. We conducted a camera trapping project in northern Maine, USA, from August to November 2018, and tested three distinct attractant treatments against a control. Sampling stations were a minimum of 5 km apart, and consisted of four camera units spaced 100 m apart, and paired with one of the four setups: (1) bait plus lure (treatment), ( 2) bait (treatment), ( 3) lure (treatment), and (4) camera only (control). Detection data on 11 species of mammals were collected from 41 stations and analyzed through multi-method occupancy models. We totaled 4280 photo-trap-nights and captured 37,781 images. Results showed that the combination of bait plus lure was the most effective for increasing detection probability of carnivores. Specifically, bait plus lure proved to be particularly effective for mustelid species, while lure was particularly effective for American black bear (Ursus americanus). While attractant usage was shown to be ineffective for increasing detection probability of non-carnivores, it also did not decrease effectiveness. Based on our results, we recommend the simultaneous use of both bait and lure as attractants when conducting camera trapping work on mammals. The combination of bait and lure appears to maximize detection of carnivore species, while simultaneously having minimal effects on the detection of other taxa.

Human land use is a driving force of habitat loss and modification globally, with consequences for wildlife species. The American marten (Martes americana) and fisher (Pekania pennanti) are forest-dependent carnivores native to North America. Both species suffered population declines due to loss of forested habitat and overharvest for furs, and continued habitat modification is an ongoing threat. Furthermore, the smaller marten may be susceptible to intraguild exclusion where the larger fisher are abundant, and both habitat modification and climate change may reduce spatial refugia available to marten. A detailed understanding of co-occurrence patterns of marten and fisher in landscapes subjected to intense forest disturbance represents a key knowledge gap for wildlife ecology and management. Maine, in the northeastern United States, supports populations of both these species. It is an extensively forested state, and the vast majority is managed as commercial timberland. We designed a large-scale field study to understand the relative importance of three sets of predictions for marten and fisher occupancy patterns where commercial silviculture is widespread: (1) The intensity of forest disturbance primarily determined both marten and fisher occupancy rates, (2) fisher occupancy was limited to areas of shallower snow and marten limited by fisher presence, or (3) both species responded to the composition of tree species within forested habitat. We collected data to test these nonmutually exclusive hypotheses via camera-trap surveys, using an experimental design balanced across a gradient of forest disturbance intensity. We deployed 197 camera stations in both summer and winter over 3 years (2017)(2018)(2019)(2020). We tagged over 800,000 images and found marten at 124 (63%) and fisher at 168 (85%) of the stations. By fitting multiseason occupancy models to the data, we found that the degree of habitat disturbance negatively influenced detection, occupancy, and temporal turnover for both species. Contrary to our expectations, however, we found no evidence of interspecific competition and instead support for positive associations with detection

Weasels are small mustelid carnivores that play an important role as predators of small mammals in a wide array of ecosystems. However, their response to land use, such as forest harvest for timber products, is seldom the subject of focused research and management projects. Both the American ermine, also known as the short-tailed weasel (Mustela richardsonii), and the long-tailed weasel (Neogale frenata) are native to Maine, United States, where commercial timber harvesting is widespread. The effects of this forest disturbance on weasels are poorly understood, so to contribute toward filling this knowledge gap, we conducted a 4-year, large-scale field study: specifically, our objective was to assess the effects of forest disturbance caused by timber harvest on occupancy patterns of ermines and long-tailed weasels occupancy patterns in Maine. We collected data from 197 survey sites (three camera traps each) over 4 years and analyzed over 7,000 images of weasels using dynamic false-positive occupancy models. We found that American ermines were widely distributed across the state (naïve occupancy at 54% of sites), while long-tailed weasels were rarer (naïve occupancy at 16% of sites). Both species responded positively to forest disturbance, with higher occupancy probabilities as disturbance increased, especially at the larger scales. American ermines were more likely to occupy stands with a higher percentage of conifer trees, while no such relationship was found for long-tailed weasels. We conclude that current forest harvest practices in Maine are not detrimental to weasel populations, but that the two species warrant continued monitoring.