INNATE RELEASING MECHANISMS: NEONATAL FEEDING     page 7


SPECIES NATURAL BILL EXPERIMENTAL RELEASERS REFERENCES
Herring Gull Yellow bill with red patch Patch √
Head shape ×
Patch redness √
Head colour ×
Bill length √
Tinbergen and Perdeck, 1950
Laughing Gull Plain red bill Bill redness √
Head shape √
Shape of bill √
Head presence √
Hailman, 1962
Black Headed Gull Plain red bill Bill point √
Head shape ×
Bill length √
Weidmann, 1961
Sandwich Tern Plain black bill Bill blackness √
Weidmann, 1961
Mallard Duck Yellow bill Greenness √
(Grass?)
Oppenheim, 1966