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

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.

💡 Research Summary

This study provides the first comprehensive longitudinal investigation of post‑hatching parental care and its hormonal regulation in a precocial bird, the mallard (Anas platyrhynchos). Twelve adult females were monitored from the day of hatching until 13 weeks later. Each week, blood samples were collected to measure plasma prolactin concentrations using ELISA, and daily video recordings captured eight behavioral parameters for both the hens and their ducklings. The behavioral repertoire included hen‑duckling physical contact, duckling leadership (following the hen), brood cohesion, hen resting, preening, agonistic interactions, foraging, and the degree of duckling independence.

During the first two weeks after hatching, hens displayed intense parental involvement: contact frequency, leadership events, and brood cohesion were at their maximum, while hens spent little time resting or preening. As the ducklings grew, these metrics declined gradually, with a marked inflection at week 6. At that point, physical contact and leadership dropped sharply, hen resting and preening increased, and a modest rise in agonistic behavior was observed. Concurrently, ducklings reached a body mass (~1.2 kg) and structural size comparable to the hen, indicating a transition toward independence.

Plasma prolactin remained high (≈45 ng mL⁻¹) during weeks 1–5, then fell precipitously to ≈22 ng mL⁻¹ at week 6 and stabilized below 15 ng mL⁻¹ for the remainder of the study. Correlation analyses revealed a strong positive relationship between prolactin levels and parental‑care metrics (contact, leadership). Importantly, the relationship was best described by a sigmoidal function rather than a linear trend. The authors fitted the model

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