Hormones and Helping: How Male Red‑Winged Blackbirds Decide When to Feed

The way parents look after their young changes a lot. It can depend on whether the bird is courting, laying eggs, or feeding chicks, and it differs between males and females. Scientists wondered whether these shifts in care are linked to specific hormone levels or if the birds simply adjust their behavior while staying within a common hormonal setting. To investigate, researchers watched red‑winged blackbirds for 24 to 48 hours straight and measured several hormones in their blood, including prolactin and four steroids. The study focused on a species where females always feed the nestlings, but males vary widely—from not feeding at all to helping heavily. The first finding was clear: male birds in the courtship phase had hormone levels that were distinctly different from those of males during the nest‑feeding stage. This shows that the reproductive phase is a strong driver of hormone changes.

Next, scientists compared males and females during the nest‑feeding period. They found that the two sexes had different hormone profiles, and the way hormones related to how much they fed differed too. This means that even within the same caregiving situation, males and females use hormones in separate ways. Finally, when looking at males who did feed versus those who didn’t, the hormone profiles overlapped a lot. No single hormone could predict whether a male would feed. Instead, patterns emerged from how different hormones interacted with each other. Overall, the study suggests that a bird’s breeding stage and its sex shape hormone levels strongly. Male care decisions seem to happen within a shared hormonal backdrop rather than through distinct, separate hormone signatures for caregivers versus non‑caregivers.

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