Distant neighbours: friends or foes? Eurasian beavers show context-dependent responses to simulated intruders

Abstract

Neighbour-stranger discrimination is widespread in territorial animals, and depending on the relative threat posed by neighbours and strangers, residents commonly exhibit either the “dear enemy phenomenon” or the “nasty neighbour effect”. Different members of the same group may represent different threat levels, and the response of residents can be modified depending on, e.g. the sex and dominance status of the intruder. Neighbour-stranger discrimination is primarily investigated in neighbours with shared borders, and whether residents recognize their more distant neighbours remains unexplored. Here, using experimental scent marks, we investigated whether Eurasian beavers (Castor fiber) discriminate between distant neighbours (i.e. two territories away) and strangers (i.e. further away than the known dispersal distance). We tested the hypotheses that Eurasian beavers can discriminate between distant neighbours and strangers and that social status (i.e. sub-dominant or dominant) and sex of the intruder affect the responses of resident beavers. We predicted that resident beavers show the “dear enemy phenomenon” in response towards dominant distant neighbours due to their territory ownership and the “nasty neighbour effect” in response towards sub-dominants due to their likelihood to disperse. Sex of residents and social status of intruders were important in explaining territorial responses, with males exhibiting stronger responses to sub-dominant distant neighbours, especially males, than sub-dominant strangers. No such discrimination was found by females or between dominant distant neighbours and strangers. We suggest that the “nasty neighbour” response by male resident beavers towards sub-dominant distant neighbours relates to the relative threat levels due to repeated intrusions during dispersal attempts. Territorial animals discriminate between neighbours and strangers to allocate aggressive behaviour to conspecific intruders. This neighbour-stranger discrimination has primarily been investigated between adjacent neighbours, but extraterritorial movements of residents into distant territories occur. Whether residents can discriminate between distant neighbours and strangers has only been studied in skylarks (Alauda arvensis), based on acoustic communication. Yet, it is unknown whether distant neighbours are perceived as neighbours or strangers based on olfactory recognition. Here we investigated whether Eurasian beavers (C. fiber) can discriminate between distant neighbours (i.e. two territories away) and strangers, based on olfactory scent samples including information on social status (i.e. dominant or sub-dominant) and sex of the intruder. Our results show that male residents showed a “nasty neighbour” response towards sub-dominant distant neighbours. These findings highlight the sensitivity of territorial mammals to the familiarity and social status of intruders.