Diel variation in anti-predation behavior of a ground squirrel and relationships between vigilance and escape

Abstract

Predation risk is among the most fundamental selection pressures, making anti-predation behavior a highly adaptive trait. Vigilance and escape are two important aspects of anti-predation behavior and have received considerable attention for decades. However, the relationship between them remains largely unexplored, and our knowledge on the diel patterns of these behaviors is also limited. In the present study, we measured various types of vigilance and escape behavior in Daurian ground squirrel (Spermophilus dauricus), to assess the function of vigilance in promoting detection and escape. We also explored the diel patterns of these anti-predation behaviors using comparisons among three periods within a day (morning, noon and evening). Total duration of vigilance was not closely associated with flight initiation distance, alert distance or buffer distance. However, duration of quadrupedal vigilance was negatively related to flight initiation distance, while positively related to alert distance and buffer distance. Alert distance was also negatively associated with duration of standing scan. These suggested that more vigilant individuals did not flee sooner as usually expected, and highlighted the necessity of separately considering the anti-predation function of various components of vigilance. A significant diel pattern was detected, with ground squirrels spending more time on energetically expensive vigilance (standing scan) and fleeing sooner (with longer flight initiation distance) at noon. Such a temporal pattern was more likely to be driven by the temporal changes in energetic status and balance between energy intake and safety thereof, rather than temporal changes in predation risk, competitors or detection ability.

Significance statement

Although vigilance and escape behavior have been frequently studied for decades, their relationship is rarely explored and it remains unclear whether a more vigilant individual would also flee sooner. In this study, we explored the relationship between individual vigilance level and flight initiation distance in a ground squirrel. We found that duration of quadrupedal vigilance, rather than total duration of vigilance, is significantly related to flight initiation distance. Contrary to expectations, individuals spending more time on quadrupedal vigilance tended to flee later, although they generally detected predators earlier. We also found that compared to the morning and evening, squirrels were more vigilant and fled sooner at noon, possibly due the temporal change in individual energetic status. Our results suggest that the anti-predation function of vigilance deserves reconsideration, and emphasize the importance of splitting vigilance into multiple components.