Toward reliable population density estimates of partially marked populations using spatially explicit mark-resight...

Area of Science:

• Wildlife ecology
• Conservation biology
• Population dynamics

Background:

• Camera traps are increasingly used for estimating population density of elusive species.
• Standard practice involves placing cameras on roads, trails, and paths for efficiency, but reliability for density estimation is debated.
• Understanding spatial arrangement effects on density estimates is crucial for conservation and wildlife management.

Purpose of the Study:

• To evaluate the effect of camera-trap placement (on- vs. off-track) on population density estimates for red foxes (Vulpes vulpes).
• To assess how resighting rates of marked individuals influence density estimates using spatially explicit mark-resight models.
• To determine the reliability of track-based camera surveys for density estimation.

Main Methods:

• Conducted a two-year camera-trap survey in a semi-arid conservation reserve in south-eastern Australia.
• Employed several survey designs with varying camera placements (on-track and off-track).
• Utilized GPS collars to track individuals and assess resighting rates for mark-resight analysis with maximum likelihood spatially explicit models.

Main Results:

• Fox detection rates were significantly higher for cameras placed on tracks compared to off-track.
• Camera placement had minimal effect on the point estimates of red fox density.
• The precision of density estimates varied considerably, influenced by the number of marked foxes detected, resighting frequency, and unmarked fox detections.

Conclusions:

• The precision of population density estimates using spatially explicit mark-resight models is sensitive to the resighting rates of identifiable individuals.
• Both on-track and off-track camera surveys can yield reliable population density estimates when using spatially explicit mark-resight models.
• Incorporating species' spatial behavior into survey planning is essential for robust camera-trap studies.