Accounting for central place foraging constraints in habitat selection studies

Habitat selection studies contrast the actual space use with the expected use under the null hypothesis of no preference (hereafter neutral use). Neutral use is most often assimilated to the relative abundance of the different habitat types. This generates a considerable bias when studying habitat selection by foragers that perform numerous back and forth to a central place (CP). Indeed, the increased space use close to the CP with respect to distant places reflects a mechanical effect rather than a true preference for the closest habitats. Yet, correctly estimating habitat selection by CP foragers is of paramount importance for a better understanding of their ecology and efficiency of conservation actions. We show that (1) including the distance to the CP as a covariate in unconditional Resource Selection Functions (RSFs), as did in several studies, is quite inefficient to correct for the bias. Bias can be eliminated only by contrasting the actual use distribution to an appropriate neutral distribution that takes the CP forager behavior into account. (2) The need to specify such an appropriate neutral use distribution can be bypassed by relying on a conditional RSF, where the neutral use is assessed locally without reference to the CP.