Potential prey make excellent ornithologists:: adaptive, flexible responses towards avian predation threat by Arabian Babblers Turdoides squamiceps living at a migratory hotspot

During spring raptor migration, resident, group-living, Arabian Babblers Turdoides squamiceps in Israel are exposed to many avian predators that differ in the level of predation threat that they pose. Accurate information about immediate safety while foraging may be provided by the sentinel, a high-perched non-foraging Babbler that actively scans and warns for predators. We tested whether, at this migratory hotspot, the bewildering number and diversity of potential avian predators (perhaps more than anywhere else in the world) may be more than a reliable sentinel could handle. We monitored ten Babbler groups regularly for a number of hours per day throughout the migration season, and scored whether the Babblers gave alarm calls when different bird species were in sight. Analyses showed that Babblers are very skilled in distinguishing between species of high and low predation threat (interspecific threat-sensitivity). In addition, Babblers distinguished accurately between encounters with dangerous vs. harmless individuals from predator species of potentially high predation threat (intraspecific threat-sensitivity). Overall, Babblers cautiously overestimated predation threat, probably because errors involving alarms for harmless predators have a lower fitness cost than errors involving attacks by dangerous predators that are ignored. However, fewer warnings were given for the more common predators of lower threat, which suggests that Babblers initially overestimated the risk of predation, but subsequently learned to assess the level of threat more accurately as soon as more information was available. Overall, our findings agree closely with theoretical predictions regarding adaptive and sophisticated anti-predation behaviour in a variable world.