Non-breeding social behaviour as an investment in reducing future territoriality costs

Territoriality is costly, and animals should adopt strategies to cope with these costs. Seasonal territoriality for breeding - a common strategy in many groups of animals - can reduce costs during the non-breeding season but requires establishing new territories every breeding season. Many seasonal breeders also become more tolerant of conspecifics during the non-breeding season and form social groups containing many individuals. Recent evidence has suggested that these social associations are not random and can entail carry-over effects extending into the following breeding season. Here, we propose that one strategy that seasonal, territorial breeders may employ is to use non-breeding social behaviour to reduce future breeding territoriality costs, through a dear-enemy-like effect. Specifically, by being social during the non-breeding season with previous territorial neighbours, individuals can increase both their and their neighbour's survival, and jointly defend and exploit common territorial areas, ultimately reducing neighbourhood turnover. Reduced neighbourhood turnover can then facilitate re-forming prior territorial boundaries, thereby offsetting the costs of territory establishment and facilitating earlier breeding (which can significantly increase reproductive output). We review evidence supporting our hypothesis and provide predictions and future research directions to bridge current gaps in understanding the link between non-breeding social behaviours and breeding territoriality.