Data for: Improving population size estimation at Western Capercaillie leks: lek counts vs. genetic methods

The Western Capercaillie (Tetrao urogallus), hereafter capercaillie, is
the largest galliform bird present in the boreal and montane forests of
the Western Palearctic. Precise and accurate methods for estimating the
number of individuals and/or their densities are crucial for the proper
management of its free-ranging populations. However, obtaining reliable
estimates of the abundance of populations of wild species and,
particularly, of birds is not a simple task. In the case of lek-mating
birds such as capercaillie, surveys are traditionally based on lek counts,
that is, counts of calling males present in their mating areas: the leks.
This study was carried out on the Pyrenees at six capercaillie leks where
two different lek counting approaches were performed: hide-based and
walk-based. The results were compared with those obtained from an estimate
of minimum population size (MPE) derived from genotyping all faeces
samples found in the lek area, and with a population size estimate derived
from a genetic mark-recapture model (N ̂) of each capercaillie lek. The
results of N ̂ were used to estimate the detection rate (D) of both lek
count approaches. Our results show that traditional lek counts do not
detect all male capercaillies since the detection rate was 0.34 (95% CI:
0.26-0.43) for hide- and 0.56 (95% CI: 0.43-0.68) for walk-based lek
counts. Our results suggest that the walk-based lek counts were more
efficient than the hide-based ones, providing more accurate results
compared to the N ̂ estimate. The combination of non-invasive sampling
with the genetic mark-recapture model was found to be the most reliable
method for obtaining the N ̂ of leks given that traditional lek counts
underestimate the number of capercaillies and, furthermore, can cause
disturbance to the species at these sites.