PROXIMAL COSTS AND BENEFITS OF HETEROSPECIFIC SOCIAL FORAGING IN THE GREAT TIT, PARUS-MAJOR

The, feeding and vigilance schedules of Great Tits (Parus major) at artificial feeders were studied in winter. We compared the behaviour of birds that foraged in pairs (mono- or hetero-specific) and solitarily. The percentage of time spent foraging was higher when a Great Tit was with an individual belonging to a subordinate species rather than with another Great Tit or a member of the dominant species. When a bird was solitary, time spent foraging was less than when it was with an individual belonging to a subordinate species, and greater than when it was with one belonging to the dominant species. The proportion of time spent vigilant did not differ between Great Tits that foraged with an individual from a dominant species or a subordinate species or with a conspecific, but was higher for solitary birds. Vigilance time of solitary Great Tits, Nuthatches, and three other Parus species was not negatively correlated with interspecific dominance status. In these small passerines, vigilance does not seem to be directed towards the detection of a competitor species. Surveillance for predators and detection of competitor species may be synchronous, nonexclusive tasks. Scanning rate (number of scans per minute of feeding) was the same for Great Tits that fed either solitarily or in pairs, but mean scan duration was significantly shorter for individuals in groups than when solitary. Individual Great Tits benefited from the presence of Coal, Blue, and Crested tits (subordinate Parus species), by a lengthening of the time spent at feeding patches and by conversion of vigilance time into feeding time.