Density surface and excursion sets modeling as an approach to estimating population densities

Effective species management and conservation require knowledge of distribution status. We used point-transect distance sampling surveys the endangered palila (Loxioides bailleui), a honeycreeper currently found only on Island Hawai'i, USA, to generate robust estimates total abundance simultaneously model distribution, abundance, spatial correlation as density surface (DSM). Point-transect is widely applied method estimate bird densities accounting for imperfect detection probability. For DSM we generalized additive framework soap film smoothers control effects boundary features. This modeling approach allowed us account propagate probability uncertainty. compared uncertainty in using standard from DSM. The DSM, both distance-sampling-derived variance variance, did not improve population estimator precision; however, it provided insight into species' density, also excursion sets analysis objectively identify areas where occurs high densities. 2017 global <2,000 individuals was limited an area 1,500 ha. Our findings can help regulatory agencies by mapping improving survey protocols, providing information important conservation.