SEASONAL AND HABITAT DIFFERENCES IN VISIBILITY OF MOOSE PELLETS

Abstract

Counts of faecal pellet groups have been widely used to estimate population densities and trends of large ungulates like moose (Alces alces). The visibility of pellet groups affects the accuracy of estimates, decreases with time, and varies among habitat types. I investigated the impact of season and habitat type on how, over time, visibility of moose pellets decreased along a forest productivity gradient in boreal forests of northeastern Sweden. Visibility decreased at the fastest rate during the transition from spring to summer due to concealment by new vegetation. Visibility also varied significantly among habitat types and was correlated with vegetative litter production. After one winter of exposure, more than 95% of all pellet groups were visible independent of habitat type, but thereafter visibility decreased fast in more productive habitats. The results demonstrated that if study plots are cleared in late autumn after the vegetation period and then visited as soon as possible after snowmelt, pellet counts can be used to estimate population trends and habitat use of moose in winter without bias caused by differences in visibility within different habitat types. Also, the correlation with litter production suggests that if a sightability correction factor is developed, pellet counts could be used to estimate habitat use and population distribution during the vegetation period and with longer periods between plot visits.