Nocturnal and diurnal territorial activity in the Leon Springs pupfish, Cyprinodon bovinus

Territorial behaviour is exhibited by a wide variety of species for reasons such as resource control, mate acquisition, or protection of offspring. Most studies of short-term territorial activity focus on diurnal behaviours. Here, we present evidence of male nocturnal territorial behaviour by a subset of the Leon Springs pupfish population. Approximately half of the males behaved cathemerally, defending their territories during the daytime and continuing to do so through the nighttime hours (Cathemeral Defenders). In contrast, other males did not defend nor spend significant time within their territories at night (Day Defenders). None of the defensive variables examined (male patrols, chasing behaviours, or frequency of conspecific and heterospecific intruders) predicted which male pupfish would exhibit cathemeral territorial behaviour. The absolute number of spawns observed during the day also were not predictive of which males continued to hold nighttime territories, but there appeared to be an inverse relationship with diurnal mating success: males that did not spawn during daytime observations were more likely to maintain nighttime territories. These results indicate that further investigation into cathemeral behaviour is required to understand the optimal expression of territorial behaviour.