Rebecca Wheatley, Amanda C. Niehaus, Diana O. Fisher, Robbie S. Wilson

Animals move through their environments to complete essential activities like foraging for food, locating mates, and evading predators. Despite this, relatively little is known about how animals choose the speeds they use in nature. Faster movement speeds reduce accuracy and agility, often use more energy, and can decrease the probability of detecting food and predators. Therefore, we expect animals to choose speeds depending on the priorities of the particular activity they are undertaking. Escaping animals need to run fast enough to avoid being caught, but not so fast that they trip or fall. Meanwhile, foraging animals should avoid the costs associated with moving at high speeds.

Buff-footed antechinus (Amanda Niehaus)
Buff-footed antechinus (Amanda Niehaus)

To test these predictions, we examined speed choice in a small branch-running marsupial, the buff-footed antechinus (Antechinus mysticus), during escape or foraging behaviours. We also examined whether the probability of slipping affected foraging site selection. Antechinus were either chased along wide or narrow branches (escape) or were left undisturbed to use the same branches to access feeding stations (foraging).

We found that antechinus ran 8x faster when escaping (~1.21 ms-1) than when foraging (~0.15 ms-1), and slipped more often during escapes. Despite this, foraging antechinus still slipped frequently on narrow branches, despite running far more slowly than they did on wide branches. Antechinus also slipped at much lower speeds when foraging than they did when escaping, which suggests they may be distracted when searching for food.

Antechinus preferred to forage on a wide branch, even when feeding stations were 33–67% farther away than on narrow branches. This suggests that distance to safety is less important than the possibility of costly mistakes to these animals.

Our study demonstrates that animals choose both where and how fast to move based on the risk of mistakes, and that the cost of mistakes is likely to depend on the ecological activity being performed. This study takes an important step towards understanding how animals select speeds in nature.

Image caption: Buff-footed antechinus (Amanda Niehaus)

Read the paper in full here.