Occupancy and detectability modelling of vertebrates in northern Australia using multiple sampling methods.

Area of Science:

• Ecology
• Conservation Biology
• Wildlife Management

Background:

• Understanding species distribution and detectability is vital for effective wildlife monitoring and conservation planning.
• Designing efficient surveys requires knowledge of where species occur and how sampling methods influence detection rates.
• Previous research highlights the need for robust data to inform conservation decisions in dynamic ecosystems.

Purpose of the Study:

• To model vertebrate species occupancy and detectability across the Top End of northern Australia.
• To evaluate the effectiveness of six different sampling methods for detecting various vertebrate groups (birds, reptiles, mammals).
• To inform the redesign of long-term vertebrate monitoring programs through occupancy and detectability estimates.

Main Methods:

• Fitted occupancy-detection models to data from 136 species surveyed across 333 sites between 2011 and 2016.
• Incorporated 11 environmental covariates (e.g., topography, temperature, fire frequency) to predict occupancy patterns.
• Assessed the detectability of birds, reptiles, and mammals using various methods including spotlighting, pit trapping, and motion-sensor cameras.

Main Results:

• Species occupancy varied significantly, with birds and reptiles showing higher ranges than mammals.
• Topographic ruggedness, elevation, maximum temperature, and fire frequency were key predictors of occupancy.
• Mammal and reptile richness concentrated in rugged areas; bird richness was highest in coastal lowland woodlands.
• Motion-sensor cameras were highly effective for mammals, while spotlighting and Elliott trapping showed better mammal detection than cage or pit trapping.
• Diurnal birds were more detectable per survey day than nocturnal birds per night.

Conclusions:

• Species occupancy and detectability are influenced by environmental factors and vary across taxonomic groups and sampling methods.
• Habitat characteristics, such as ruggedness and vegetation type, are strong drivers of species richness for different vertebrate groups.
• The study provides crucial data to optimize the design and efficiency of vertebrate monitoring programs in northern Australia.