The effect of non-target species in presence-absence distribution surveys: A case study with hair-tubes

Detection of non-target species during distribution surveys may influence the detection of the focal species, due to bait being consumed, or trapping devices inactivated. The aim of this work was to evaluate the effect of non-target species (field mice, Apodemus sp.) on the detection and occupancy estimates of a target species (the red squirrel, Sciurus vulgaris) during hair-tubes surveys. Following a modelling approach that accounted for imperfect detection of both target and non-target species, we tested the hypothesis that detection probability of the red squirrel is affected by detection of field mice. We also investigated the level of bias that occurred in estimation of key-parameters such as probability of presence and detection probability. Our results show that detection of red squirrels and field mice using hair-tubes surveys is not independent. Detection probability of the red squirrel was higher when field mice did not visit the hair-tubes. Nevertheless, there was no bias in parameter estimates, therefore relatively accurate estimates would have been obtained despite this interference.