Post-hatching parental care behaviour and hormonal status in a precocial bird

TL;DR

This study investigates how parental care behaviors and prolactin hormone levels in mallard hens change over the post-hatching period, revealing a threshold prolactin level necessary for parental care maintenance in precocial birds.

Contribution

It provides the first detailed longitudinal analysis of the relationship between prolactin levels and parental care in a precocial bird species during the entire rearing period.

Findings

Parental care behaviors decline with brood age.

Prolactin levels remain high after hatching and decrease after week 6.

A prolactin threshold appears necessary for parental care maintenance.

Abstract

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.