Do line-transect surveys systematically underestimate primate densities in logged forests?

Area of Science:

• Ecology
• Wildlife Biology
• Conservation Science

Background:

• Encounter rates of primate social groups in disturbed rainforests may differ from those in undisturbed areas.
• Post-logging studies show reduced raw encounter rates despite stable primate densities, suggesting potential biases.
• Biased encounter rates could lead to misleading conclusions about primate population declines in disturbed habitats.

Purpose of the Study:

• To assess systematic bias in line-transect density estimates from logged forests.
• To compare line-transect estimates with range-mapping estimates.
• To illustrate the effect of biased encounter rates on detectability functions.

Main Methods:

• Line-transect density estimates from logged forest were compared with range-mapping density estimates.
• A Fourier series detectability function was used to model responses to hypothetical bias patterns in encounter rates.

Main Results:

• Tests revealed no systematic bias in line-transect density estimates from logged forest.
• Fourier series analysis indicated that line-transect estimators can often correct for biases in raw encounter rates.
• Transformed encounter rates, such as density estimates, generally yield reliable comparative results.

Conclusions:

• Line-transect density estimates are generally reliable for comparative primate surveys in disturbed forests.
• Raw encounter rates, without transformation, are more susceptible to error and can lead to inaccurate conclusions.
• Conservation assessments should utilize transformed data like density estimates for greater accuracy.