Occupancy and detectability modelling of vertebrates in northern Australia using multiple sampling methods.
Date: 27, Mar, 2019
Author(s):
Luke D. Einoder, Darren M. Southwell, Jose J. Lahoz-Monfort, Graeme R. Gillespie, Alaric Fisher, Brendan A. Wintle.
Publisher: PLoS
Understanding where species occur and how difficult they are to detect during surveys is
crucial for designing and evaluating monitoring programs, and has broader applications for
conservation planning and management. In this study, we modelled occupancy and the
effectiveness of six sampling methods at detecting vertebrates across the Top End of northern
Australia. We fitted occupancy-detection models to 136 species (83 birds, 33 reptiles,
20 mammals) of 242 recorded during surveys of 333 sites in eight conservation reserves
between 2011 and 2016. For modelled species, mean occupancy was highly variable: birds
and reptiles ranged from 0.01±0.81 and 0.01±0.49, respectively, whereas mammal occupancy
was lower, ranging from 0.02±0.30. Of the 11 environmental covariates considered
as potential predictors of occupancy, topographic ruggedness, elevation, maximum temperature,
and fire frequency were retained more readily in the top models. Using these models,
we predicted species occupancy across the Top End of northern Australia (293,017 km2)
and generated species richness maps for each species group. For mammals and reptiles,
high richness was associated with rugged terrain, while bird richness was highest in coastal
lowland woodlands. On average, detectability of diurnal birds was higher per day of surveys
(0.33 ± 0.09) compared with nocturnal birds per night of spotlighting (0.13 ± 0.06). Detectability
of reptiles was similar per day/night of pit trapping (0.30 ± 0.09) as per night of
spotlighting (0.29 ± 0.11). On average, mammals were highly detectable using motion-sensor
cameras for a week (0.36 ± 0.06), with exception of smaller-bodied species. One night of
Elliott trapping (0.20 ± 0.06) and spotlighting (0.19 ± 0.06) was more effective at detecting
mammals than cage (0.08 ± 0.03) and pit trapping (0.05 ± 0.04). Our estimates of species
occupancy and detectability will help inform decisions about how best to redesign a longrunning
vertebrate monitoring program in the Top End of northern Australia.
Occupancy and detectability modelling of vertebrates in northern Australia using multiple sampling methods.