# Gouldian Finches (Chloebia gouldiae) Increase the Frequency of Head Movements with Increasing Risk at Water-holes but Prolong Interscan Intervals While Drinking: Two Different Strategies?

## TL;DR

Gouldian finches adjust their vigilance behaviors at waterholes by increasing head movements when perceiving higher risk and changing how long they drink before scanning again.

## Contribution

The study reveals two distinct vigilance strategies in Gouldian finches based on perceived risk and environmental factors.

## Key findings

- Head movement frequency increases at small waterholes and when birds are on the ground, indicating higher perceived risk.
- Interscan intervals vary with waterhole size and group size, showing adaptive vigilance behaviors.
- Frequency of head movements correlates with longer drinking bouts, suggesting different scanning strategies.

## Abstract

Animals scan their environment to detect predators. However, being vigilant is costly as animals must interrupt other activities. Here, we investigated vigilance at waterholes, which are dangerous sites as they attract predators. We assessed vigilance during drinking by measuring the frequency of head movements when the birds raised their head above the water surface and also measured the time taking-in water (interscan interval). The frequency of head movements was lower when the birds sat in trees when compared to being on the ground, indicating that the birds felt more vulnerable as they moved closer to the ground. While drinking, the frequency of head movements was highest at small waterholes when compared to larger waterholes, showing that small waterholes are perceived as more dangerous. This is concerning as droughts are predicted to increase. Furthermore, interscan interval was affected by waterhole size and group size in a complicating manner, showing that birds adjust their vigilance levels in response to specific situations. Finally, frequency of head movements and interscan interval were correlated. Individuals with a high frequency of head movements (high vigilance) had longer drinking bouts, whereas individuals with a lower frequency of head movements (lower vigilance) raised their head after shorter drinking intervals, possibly adjusting for the lower frequency of head movements.

Animals scan their environment to detect threats. Such vigilance behaviour is costly, and animals adjust their vigilance to prevailing threats. Waterholes are dangerous places that attract predators, and require heightened vigilance. We investigated how Gouldian finches adjust their vigilance at waterholes by measuring the frequency of head movements and interscan interval while drinking. The frequency of head movements increased with increasing risk perception (a) from perching in the tree to being on the ground and (b) while drinking, with a higher frequency of movements recorded at small waterholes compared to medium and large ones. The latter adds to recent findings that small waterholes are perceived as more dangerous and require further investigation. With a predicted increase in droughts, birds will rely on small waterholes for longer during the dry season which might cause stress. Furthermore, interscan interval varied in terms of interaction with waterhole size and group size, indicating adjustments linked to perceived threat and social effects. Finally, frequency of head movements and interscan intervals were positively correlated. This might reflect different strategies to check the environment, with either a high frequency of head movements when scanning accompanied by long drinking bouts or looking in one direction for a longer time (lower vigilance) but repeating this behaviour at shorter intervals.