Monitoring distributions using call surveys: estimating site occupancy, detection probabilities and inferring absence

Abstract

Monitoring programs serve to track changes in the distribution and abundance of species. A major problem with most monitoring programs is that species detection is imperfect and some populations are inevitably missed. Therefore, in most monitoring programs the true distribution of a species will be underestimated. Here, we report a field test of the reliability and performance of a commonly used method to monitor the distribution of amphibians (anuran call surveys). We surveyed the distribution of four anuran species in western Switzerland, and estimated detection probabilities to account for imperfect species detection and used these estimates to adjust our estimate of site occupancy (i.e., distribution). Next, we assessed how detection probabilities were affected by weather and how site occupancy was affected by site specific covariates. For one species (Hyla arborea), call surveys proved efficient in determining the regional distribution with only few site visits because detection probabilities were relatively high. The call surveys apparently missed many populations of another common species (Bufo calamita) because detection probabilities were lower. Two other species (Bombina variegata and Alytes obstetricans) were uncommon and strong inference from the analysis is not possible. Thus, multispecies surveys may be inefficient for rare species. Estimates of detection probabilities were used to calculate how many site visits are necessary to infer the absence of a species with some predetermined statistical certainty. The implications of ''false absences'' are important in ecology as they are known to bias usual habitat suitability models and overestimate extinction/colonization events in metapopulations. Large-scale monitoring programs would benefit from the application of an estimation-based approach to monitoring the distribution of species.

Habitat-use model for the New Zealand endemic frog Leiopelma hochstetteri

“…We used the approach of Pellet & Schmidt (2005) to calculate the minimum number of visits necessary to be 95% certain that Leiopelma hochstetteri would be absent from a stream section in the Waitakere Ranges.…”

“…Nevertheless, it should be noted that the detection probabilities of some amphibian species (e.g. Ambystoma tigrinum) may vary among years (MacKenzie et al 2003); consequently, the number of searches neces- (Pellet & Schmidt 2005).…”

Improving herpetological surveys in eastern North America using the environmental DNA method

“…To increase detection probability with practical efforts, surveys and monitoring programs are generally limited to a time window maximizing species detection (Erb et al 2015; Massachusetts Cooperative Fish and Wildlife Research Unit and the Northeast Wood Turtle Working Group 2013; Petitot et al 2014). Additionally, the time window optimizing species detection differs from one species to another, therefore, limiting the ability of developing simultaneous monitoring programs for the different species (Bailey et al 2004b;de Solla et al 2005;Pellet and Schmidt 2005). Improving distribution data for every species or for the entire range of a species within a jurisdiction territory using non-invasive methods is thus particularly challenging for large-scale herpetological management purposes.…”

Habitat characterization, occupancy and detection probability of the Endangered and endemic Junín giant frog Telmatobius macrostomus

“…Additionally, we used the estimate of detection probability to determine the number of surveys necessary to establish whether a species is truly absent from a site (Kéry 2002). We used the approach of Pellet & Schmidt (2005) to calculate the minimum number of surveys necessary to be 95% certain that the Junín giant frog would be absent from a stream transect in the study area.…”

“…This information, along with the information on documenting the various threats to T. macrostomus, will likely prove invaluable to conservation and management plans in and around the various protected areas where the Junín giant frog occurs. For example, if a mining lease is re quested in the buffer zone of a protected area, the developers should provide evidence of T. macrostomus absence, and we suggest that such evidence must be backed with statistical analyses before development activities are approved and initiated (Pellet & Schmidt 2005, Nájera-Hillman el al. 2009).…”