In Arizona, USA, Double-crested Cormorants (Nannopterum auritum) primarily overwinter, whereas Neotropic Cormorants (N. brasilianum) are common residents year round. Concern exists that both species ...are increasing in numbers and may have a negative impact on fish populations. We collected data during January 2017–April 2019 to characterize cormorant numbers seasonally, describe their foraging patterns, and evaluate environmental factors associated with cormorant numbers at community fishing waters. With more than 100 trained volunteers, we surveyed water bodies across the state simultaneously once each quarter of the year during January 2017–March 2018. We also visited 36 community fishing waters and other locations to document cormorant foraging activities and to explore potential associations between environmental factors and the maximum number of cormorants counted at each site. We collected stomach contents from lethally sampled cormorants to examine size and species of consumed fish. Our seasonal counts showed the greatest cormorant numbers during the winter and spring, with larger concentrations in metropolitan areas and fewer birds at higher elevations. At community fishing waters, cormorants fed primarily on fish ≤12 cm long, though they did consume larger sport fish in reservoirs and along the Colorado River. At community fishing waters, cormorant numbers were positively associated with the number of artificial structures in/near the water’s edge and with the number of large trees within 200 meters of the water. To reduce cormorant numbers and their anticipated impacts, we recommend stocking larger, stout-bodied fish and removing woody vegetation close to shorelines while adding fully submerged structures to provide security cover for fish from cormorants. This study is unique and important in that it addresses cormorant populations located in the southwestern USA, an area that has not historically been viewed as waterbird habitat, and it presents an unbiased evaluation of cormorant foraging activities in desert areas manipulated by water. It also offers reasonable, non-lethal actions to reducing potential cormorant impacts on aquatic resources.
As part of a larger study evaluating desert bighorn sheep (Ovis canadensis) habitat selection and factors influencing mortality risk, we captured and deployed global positioning system radio collars ...on four male mountain lions (Puma concolor) in west central Arizona. From January 2014 to July 2017, we investigated potential kill sites identified from global positioning system location clusters and documented mountain lion prey items. We identified burro (Equus asinus) remains at 39 of 279 investigated mountain lion kill sites. This report is the first documentation in the primary literature of mountain lion preying on burros in Arizona. Further investigations of mountain lion and burro predator-prey interactions would benefit better understanding of the potential of mountain lions to regulate burro populations as well as predation impacts on native ungulate populations due to the possibility of burros facilitating apparent competition, prey switching, and predator subsidization.
Bighorn sheep (Ovis canadensis) evolved for thousands of years in the presence of numerous predators, including mountain lions (Puma concolor). Bighorn sheep have presumably developed predator ...avoidance strategies; however, the effectiveness of these strategies in reducing risk of mountain lion predation is not well understood. These strategies are of increasing interest because mountain lion predation on bighorn sheep has been identified as a leading cause of mortality in some sheep populations. Therefore, we investigated how mountain lions affect both bighorn sheep habitat selection and risk of mortality in Arizona, USA. We used 2 approaches to investigate the predator‐prey relationship between mountain lions and bighorn sheep. We fit 103 bighorn sheep (81 females and 22 males) with global positioning system radio‐collars in 2 Arizona populations from 2013 to 2017, and used a negative binomial resource selection probability function to evaluate whether bighorn sheep selected for habitat features in accordance with presumed predator avoidance strategies, including terrain ruggedness, slope, topographic position, and horizontal obstruction, in 2 seasons (winter and summer). We then estimated how habitat features such as terrain ruggedness, slope, horizontal obstruction, and group size, influence the risk of mortality due to mountain lion predation using an Andersen‐Gill proportional hazards model. Generally, both sexes selected areas with lower horizontal obstruction and intermediate ruggedness and slope, but selection patterns differed between seasons and sexes. The use of more rugged areas and steeper slopes decreased the risk of mortality due to mountain lion predation, consistent with presumed predator avoidance strategies. Increased group size decreased risk of bighorn sheep mortality due to mountain lion predation but this effect became marginal at approximately 10 individuals/group. We did not identify a relationship between horizontal obstruction and bighorn sheep mortality risk. Our findings can be used in habitat and population management decisions such as the prioritization of habitat restoration sites or selection of translocation sites. In addition, we suggest that augmentation of low‐density bighorn sheep populations may reduce mountain lion predation risk by increasing group size, and that releasing large groups of bighorn sheep in population augmentation and reintroduction efforts may help to reduce mountain lion predation.
Bighorn sheep selected for areas with decreased horizontal obstruction and areas of intermediate slope and ruggedness. Ruggedness, steep slopes, and increased bighorn sheep group size decrease the risk of bighorn sheep mortality due to mountain lion predation. We suggest that habitat manipulations, such as prescribed fire, and translocating larger groups of bighorn sheep may increase the amount of available bighorn sheep habitat and decrease the risk of bighorn sheep mortality due to mountain lion predation, respectively.
Estimating wildlife abundance, particularly for rare and elusive species, is challenging because of time, cost, and methodological constraints. The Mexican wolf (Canis lupus baileyi), a ...federally‐listed endangered subspecies of gray wolf, is currently monitored using ground and aerial methods to obtain a minimum known population count. As the Mexican wolf population has grown and expanded, the time and cost required to monitor the subspecies has increased. We investigated the efficacy of camera trapping for estimating Mexican wolf abundance by comparing the accuracy, precision, and cost of camera trapping to those obtained with current monitoring techniques. Between 1 November 2019 and 31 July 2020, we collected 13,317 photos of wolves from 124 camera traps in Arizona where Mexican wolves were known to occur, excluding tribal lands. We used a spatial mark‐resight analysis to estimate abundance for both winter (November 2019 through February 2020) and summer (April through July 2020) seasons, with and without the assistance of global positioning system (GPS) telemetry data to identify individual wolves. Combined with GPS data, camera trapping provided a summer abundance estimate (N
ˆ $\hat{N}$ = 50, 95% CI = 37–64) that was 14% lower than the 2019 minimum known population count (N = 59), but included the minimum known population count in the 95% confidence interval. The summer no telemetry abundance estimate was 27% below the minimum known population count (N
ˆ $\hat{N}$ = 43, 95% CI = 30–56). During winter, abundance estimates obtained from camera trapping (no telemetry: N
ˆ $\hat{N}$ = 33, 95% CI = 15–52; telemetry: N
ˆ $\hat{N}$ = 45, 95% CI = 28–62), were much lower than the 2019 Mexican wolf minimum known population count (winter: N = 62), but included the minimum known population count in the 95% confidence interval for the winter telemetry dataset. A cost comparison indicated that the first‐year camera trapping equipment expenses were 1.7 times the equipment cost of the current method and that camera trapping equipment expenses in subsequent years were equivalent to the equipment cost of the current method, and required at least 1.4 times the labor hours. We provide recommendations to potentially improve Mexican wolf abundance estimates and minimize camera trapping expenses. The results of our project may help managers make appropriate decisions for their population monitoring needs, while considering budget, staffing capabilities, precision, and accuracy.
We investigated the efficacy of camera trapping with spatial mark‐resight methods for estimating Mexican wolf abundance, and compared the accuracy, precision, and cost to the estimate obtained with current survey techniques. The results of our project provide information on the cost and reliability of camera trapping methods, to help a manager make the most appropriate decision for their population monitoring needs.
