The Response of Chicks of the Franklin's Gull to Parental Bill-Color

Abstract

THE adult Franklin's Gull (Larus pipixcan) in the breeding season has a black head and a bright red bill with a vague dusky spot near the tip. The downy young may be fed by regurgitation of food from the mouth of the parent. The young may peck at the bill of the parent when the latter arrives at the nest and stands next to the young with bill lowered. The purpose of our study was to see whether the red color of the parental bill helped stimulate the feeding responses of the downy young to the parent, as is suggested by their pecking at the bill of the parent. Tinbergen and Perdeck (Behaviour, 3: 1-39, 1950) have reported experiments with models from which they concluded that the feeding responses of downy Herring Gull chicks are stimulated by sight of the red spot on the lower mandible of the yellow bill of the parent. This work was responsible for the initiation of our own studies. However, instead of using presentation of hand-held models as did these authors, we have attempted to make our experimental procedure somewhat more objective by not touching the models and by usually not touching the chicks during the course of an experimental test. We also used simultaneous presentation of models of heads, each with a differently colored bill, instead of successive presentation as was done by Tinbergen and his colleagues. Method and materials.-Each gull chick to be tested was placed in a cardboard box on one end of which there were two flat models of adult heads of the Franklin's Gull, placed so as to face each other with the bills pointing downward at an angle of about 600 and with the tips of the two bills about Y inch apart (Figure 1). The bill of one head was red; the bill of the other head was either green or white. Each bill was attached to a plain black head, devoid of eyes and pasted on a piece of brown paper, which in turn was fastened to a firm cardboard backing. Each bill actually was a complex affair, consisting in the first place of a hole, cut in the shape of the bill, through the cardboard backing and brown paper on which the black heads of the models were fastened. The purpose of each bill-shaped hole was to enable us to shine a light through from behind, illuminating the bill. An ordinary goosenecked lamp was used for this purpose and was centered behind at an equal distance from each of the two bills.