Occupancy and detectability of Snowy Plovers in western Utah: an application to a low density population

摘要

Occupancy modeling can be used to identify habitat characteristics associated with species occurrence. Additionally, occupancy sampling can provide measures of detection probability, increasing confidence in monitoring efforts. Little is known about the distribution and habitat preferences of a small population of Snowy Plovers (Charadrius nivosus) in western Utah. We conducted a study to estimate occupancy and detection probability of Snowy Plovers in western Utah during 2011 and 2012. We made repeated visits to randomly selected survey plots during the breeding period, sampling 84 64-ha plots in 2011 and 100 64-ha plots in 2012 and recording the number of adults and habitat characteristics in each plot. We then modeled the relationship between detection, occupancy, and covariates that included distance to water, distance to roads, land cover types, and characteristics of the vegetation. We also included covariates for observer, Julian date, temperature, cloud cover, and wind speed when modeling detection probability. Detection probability was high (0.74, 95 CI = 0.57-0.86) and positively influenced by temperature. Occupancy of 64-ha plots was low (0.27, 95 CI = 0.18-0.39) and did not vary by year. Occupancy of Snowy Plovers was negatively associated with distance to water ( = -0.62 0.31, 95 CI = -1.23 to -0.01) and percent shrub cover ( = -0.28 0.02, 95 CI = -0.58 to -0.01). Land cover types also influenced plot occupancy. Management actions that conserve shallow water and adjacent habitats or minimize disturbance in these areas are likely to have conservation benefits for Snowy Plovers where water is scarce. Because our detection probabilities were high, investigators involved in future monitoring efforts can achieve reasonable precision with limited revisits to sample plots.