Data from: Interspecific signalling between mutualists: food-thieving drongos use a cooperative sentinel call to manipulate foraging partners

Interspecific communication is common in nature, particularly between
mutualists. However, whether signals evolved for communication with other
species, or are in fact conspecific signals eavesdropped upon by partners,
is often unclear. Fork-tailed drongos (Dicrurus adsimilis) associate with
mixed-species groups and often produce true alarms at predators, whereupon
associating species flee to cover, but also false alarms to steal
associating species' food (kleptoparasitism). Despite such deception,
associating species respond to drongo non-alarm calls by increasing their
foraging and decreasing vigilance. Yet, whether these calls represent
interspecific sentinel signals remains unknown. We show that drongos
produced a specific sentinel call when foraging with a common associate,
the sociable weaver (Philetairus socius), but not when alone. Weavers
increased their foraging and decreased vigilance when naturally
associating with drongos, and in response to sentinel call playback.
Further, drongos sentinel-called more often when weavers were moving, and
weavers approached sentinel calls, suggesting a recruitment function.
Finally, drongos sentinel-called when weavers fled following false alarms,
thereby reducing disruption to weaver foraging time. Results therefore
provide evidence of an ‘all clear’ signal that mitigates the cost of
inaccurate communication. Our results suggest that drongos enhance
exploitation of a foraging mutualist through coevolution of interspecific
sentinel signals.