Incorporating uncertainty into analyses of red-crested pochard habitat selection

Studies describing habitat use in animal species need to take into account detectability of individuals in order to reach more robust conclusions. However, the importance of detectability in habitat selection analyses of rare and cryptic species has received little investigation, although robust methods for estimating detectability have been made recently available. Understanding habitat requirements should be an important management tool for the conservation of the red-crested pochard (Netta rufina), a rare duck species in France and Europe. Three different lake samples (82 lakes in total) were conjointly used in 2000 and 2001 to assess the species habitat requirements, using its presence, density and hatching dates as response variables. Risk of false absence was estimated using the double-observer approach at less than 0.001. A robust-design approach produced estimates of individual brood detectability (0.545, SE = 0.053). Observed red-crested pochard densities were adjusted to time dependent detectabilities, and modelled as a function of habitat variables. Habitat fragmentation and low permanent water levels negatively affected brood densities. Interestingly, these variables were not retained when modelling the unadjusted densities. This analysis showed that investigating temporal variation in brood detectability was a crucial prerequisite in the study of this rare species’ habitat requirements. More generally, it strongly suggests that integrating detection probability and its variations in habitat use analyses of cryptic species of conservation concern may be an essential methodological step to reach more valid conclusions on habitat management.