THE EFFECTS OF SEX, TEMPERATURE AND COMPANIONS ON LOOKING-UP AND FEEDING IN SINGLE AND MIXED SPECIES FLOCKS OF HOUSE SPARROWS (PASSER-DOMESTICUS), CHAFFINCHES (FRINGILLA-COELEBS), AND STARLINGS (STURNUS-VULGARIS)

Measurements were made during the winter peck rate, look-up rate, proportion of time in look-up and mean duration of the look-ups in small flocks. Sex differences in look-up rate and proportion of time in look-up were found in house sparrows and chaffinches, the females looking-up more than males. In male house sparrows the number of house sparrow companions has a marked effect on the measures of looking-up and peck rate. Female and male companions influence the subjects'' behaviour in different ways. In female subjects these effects are absent or very weak. Chaffinches of both sexes modify their behaviour in response to the number of chaffinch companions. For female subjects, increasing the number of female, but not male, companions has a marked influence on peck rate and proportion of time in look-up. Starlings modify their behaviour in response to the number of starling companions. Interspecific effects on behaviour were found. Female house sparrows are responsive to the number of male chaffinch companions, chaffinches of both sexes respond to the number of house sparrows, and starlings respond to the number of chaffinches. The changes in behaviour with increasing number of flock companions (both cospecific and heterospecific), support the flock vigilance hypothesis which states that birds can exploit the vigilance of their companions and can therefore reduce their own vigilance. Many of our results indicate, however, that in some circumstances this is an inadequate explanation of the behaviour seen and several other factors are discussed, particulary the role of flock members looking at each other. These factors may reinforce or contradict trends associated with the flock vigilance hypothesis, in ways that may depend on the sex of the subject and is companions. Temperature and date both influence looking-up and the peck rate. In studies of this type it is clearly important to control for these and for the sex of the subject and its flock companion.