Determinants of homing in nest-guarding females: balancing risks while travelling through unfamiliar landscapes

Determining the context in which animals move through unfamiliar landscapes helps elucidate the risks associated with returning to known resources and the factors that outweigh those risks. For example, females that become separated from their nests can return to protect their offspring from predation, thereby increasing fitness, but also risking having the nest preyed upon or being preyed upon themselves. We predicted that after being displaced, long-tailed skinks, Eutropis longicaudata, guarding eggs would adjust their homing behaviour to minimize these risks. Nest-guarding females reduced the likelihood of encountering predators by homing at night, when lizard predators were inactive. Homing success rates decreased with increasing displacement distance (50–300 m), probably because homing took longer from further away, which may increase the chances of nest predation during the female’s absence. However, large clutches were associated with successful homing at distances over 50 m, suggesting that increased fitness benefits provided by having more eggs outweighed the risks of returning. Females were more likely to return to a nest with freshly laid eggs, possibly because fresh eggs are easier for predators to locate, and thus more susceptible to predation. Finally, when females were exposed to an egg predator prior to displacement, they homed almost 50% faster, reflecting the ability to adjust homing behaviour according to the risk of nest predation. As predicted, nest-guarding mothers adjusted their homing behaviour so that the fitness benefits of returning to protect a nest outweighed the risks associated with becoming preyed upon or returning to an empty nest.