FOOD AVAILABILITY AND EGG-LAYING OF CAPTIVE EUROPEAN STARLINGS

We investigated egg-laying in captive European starlings, Sturnus vulg aris, with moderate differences in food availability. From February-Ma rch onwards, experimentally food-rationed (FR) birds got 80% of the fo od ration of an ad libitum fed control (AL-FR) group, which led to a r eduction in body mass and activity, and a redigestion of feces. FR bir ds showed less courtship behavior than AL-FR birds, and did not start laying until their food ration was increased to 90%, during the second half of the breeding season. Fewer FR than AL-FR females started layi ng. Among those that did, body mass was 6-7 g lower than that of AL-FR females throughout courtship, laying and incubation. No differences i n clutch size, egg mass and egg composition were found. Compared to th e AL-FR birds, mean laying date was 11-14 days earlier in ad libitum f ed (AL) starlings that had no visual contact with FR birds. Initiation of egg-laying in FR starlings apparently was triggered by increased f ood availability, whereas that of AL-FR starlings may have been delaye d because of the near absence of breeding activity among the FR birds with which they were in visual contact.