“False heat,” big testes, and the onset of natal dispersal in European pine Martens (Martes martes)

Abstract

Natal dispersal plays a central role in population biology, ecology, and evolution. Therefore, describing dispersal patterns including dispersal rate, onset, duration, and distance and investigating its main ecological and phenotype correlates are of prime importance. Dispersal data are scarce in rare and elusive carnivores such as mustelids and notably in European pine Marten Martes martes. Natal dispersal is mostly thought to occur in late winter either as a consequence of offspring eviction by adult females experiencing a “false heat” period related to the delayed implantation of embryos or as a consequence of physiological changes in offspring related to sexual maturation. Nineteen juvenile and subadult pine martens were monitored by telemetry during their first year of life to describe the dispersal pattern, in particular, to investigate the onset of natal dispersal. Only 13 out of the 19 pine martens monitored gave reliable information, and seven out of them (53.85 %) dispersed. No sex bias either in dispersal rate, distance, or duration was evidenced. As expected, all dispersers whatever their sex left their natal area in a relatively narrow period of 1 month in late winter (February 17th–March 17th). This period did not match with any body mass variation but was clearly synchronous with an increase in testis mass. Our results confirmed that this late winter period is very intense in terms of social interactions and physiological changes in the European pine marten. Last, they also pointed out that human-induced mortality of dispersers in late winter could be high so that late winter might be a focus period for management actions.