The hatching and nest-exodus behaviour of mallard

Abstract

Under experimental conditions the strongest and most complete imprinting by Mallard ducklings has been found to occur at the age of 13-16 hours. This interval has been called the critical period., A study was made of the chronology of hatching and exodus from Mallard nests under natural conditions. It was found that the ducklings normally spend the critical period on the nest and that ducklings hatched in nests situated above ground (hole-nests) are older at exodus than are ducklings from an ordinary ground-nest. The hatching success, expressed as the number of unhatched eggs left in the nest, was lower in hole-nests than in ground-nests. The female Mallard can, if all eggs of her clutch fail to hatch, continue the incubation for much longer than normal. The delay did not however seem to be correlated to the presence of a small number of unhatched eggs in the nest. Observations were made on the behavior of female and ducklings in the nest. The ducklings spent periods of activity outside the female's plumage and periods of rest, usually under the female. During the periods of activity the ducklings utter 'contentment notes'' and the female 'maternal calls.' A description of the female's vocal activity is given. A comparison between the pattern of activity of the ducklings in the nest and results of laboratory experiments suggests that the ducklings under natural conditions spend enough time outside the female's plumage to make imprinting possible. The delay found in hole-nests is discussed. Contributory factors to the delay may include reduced possibilities for imprinting in hole-nests, the exodus being in response solely to auditory stimuli, and the effect of the 'visual cliff.'.