Variation in the effect of repeated intrusions on calling behavior in a territorial toadlet

Abstract

Territorial animals must optimize their investment toward exploiting their territory and defending it from competitors. However, the manner in which territorial investment changes in response to repeated interactions with a rival remains unclear. We experimentally exposed nest-defending terrestrial toadlets (Pseudophryne bibronii) to playback that simulated an intruder that called and retreated 6 times. We measured the change in a resident’s investment toward calls that function to advertise their presence to mates (territory exploitation) or threaten competitors (territory defense) over successive interactions. We found significant independent effects of repeated interactions on each call type, but no trade-off between them. Aggressive call response was initially high, decreasing significantly after the first bout. In contrast, advertisement calls increased linearly over successive bouts. However, the magnitude and direction of changes over time were not consistent among individuals. Instead, individuals appeared to change their calling behavior according to their initial response. Furthermore, there was a decrease in the variability of responses over successive interactions. Together, these results suggest that residents independently optimize their exploitative and defensive behaviors in response to intruders as they gain information over successive interactions. This process will be important to consider when there is variation in the number of times a given intruder will be encountered. Key words: anuran calling, familiarity hypothesis, learning, relative threat hypothesis, repeat intruders, territoriality. [Behav Ecol]