  In birds, the link between parental care behaviour and prolactin release
during incubation persists after hatching in altricial birds, but has never
been precisely studied during the whole rearing period in precocial species,
such as ducks. The present study aims to understand how changes in parental
care after hatching are related to circulating prolactin levels in mallard hens
rearing ducklings. Blood was sampled in hens over at least 13 post-hatching
weeks and the behaviour of the hens and the ducklings was recorded daily until
fledging. Contacts between hens and the ducklings, leadership of the ducklings
and gathering of them steadily decreased over post-hatching time. Conversely,
resting, preening and agonistic behaviour of hens towards ducklings increased.
Plasma prolactin concentrations remained at high levels after hatching and then
fell after week 6 when body mass and structural size of the young were close to
those of the hen. Parental care behaviour declined linearly with brood age,
showed a disruption of the hen-brood bond at week 6 post-hatching and was
related to prolactin concentration according to a sigmoid function. Our results
suggest that a definite threshold in circulating prolactin is necessary to
promote and/or to maintain post-hatching parental care in ducks.
