Food-sharing signals among socially foraging Cliff Swallows
Colonially nesting cliff swallows, Hirundo pyrrhonota, in southwestern Nebraska use a vocal signal, termed the squeak call, which alerts conspecifics that food has been found. Birds were recruited to playbacks of this call, and the frequency of calling increased when insect swarms were provided to the swallows. Squeak calls were used mostly while birds were foraging in loose groups away from their colonies. Calling occurred primarily on days when temperatures were less than 17°C, solar radiation was less than 500 W/m2, and wind speed was less than 26 km/h, conditions under which foraging success was presumably poor. Weather conditions appropriate for calling occurred regularly, with an average 24·5% of days in each breeding season suitable for use of the squeak call. Calling probably improves the caller's own foraging efficiency. By recruiting other foragers to a discovered food source, the caller may increase the chances that the insects' movements will be tracked and thus that the caller itself will be able to exploit the insect swarm for a longer time.