The European Starling (Sturnus vulgaris) is a common and adaptable bird species recognized for its iridescent plumage and large, murmuring flocks. Starlings generally do not mate for life. Their pair bonds are temporary and seasonal, formed exclusively for raising a single brood or a breeding season, and they rarely persist into the following year.
The Seasonal Nature of Starling Pair Bonds
Starlings primarily practice social monogamy, where a single male and female share the duties of raising their young within one breeding cycle. This arrangement is not a lifelong commitment; the bond typically dissolves once the young fledge and become independent. The breeding season, usually spanning from spring to early summer, is the full extent of the pair’s commitment.
The seasonal bond is often complicated by facultative polygyny, meaning a male may mate with and tend to multiple females concurrently. This creates a spectrum of relationships; some males remain monogamous while others attract secondary or tertiary females to different nesting sites. Despite the social bond, genetic monogamy is not guaranteed, as extra-pair copulations are common, introducing genetic diversity into the brood.
The pair bond is often short-lived, especially if the pair successfully raises a first brood. After the young leave the nest, the male may shift his attention to a new female for a second brood, or the original female may find a new male. This dynamic ensures the pair bond focuses on immediate reproductive success rather than long-term partnership.
Parental Responsibilities During the Breeding Season
Once a pair bond is established, the division of labor begins with selecting and preparing a nesting cavity. The male usually selects the site—typically a tree hollow, building crevice, or nest box—and initiates construction by filling the cavity with grass and coarse materials. The female then finalizes the nest cup, often lining it with softer materials like feathers, and may remove some of the male’s initial contributions.
The female is responsible for the majority of the incubation period, which lasts about 12 days, though the male may assist during the daytime. Once the clutch of four to six eggs hatches, both parents share the role of provisioning the nestlings. They feed the chicks a diet rich in insects and invertebrates for approximately three weeks until the young are ready to leave the nest.
Parental care often becomes unequal, particularly in polygynous situations. If a male is tending to primary and secondary nests, his attention is divided, meaning the female at the secondary nest receives less help. In these cases, the female must shoulder the bulk of the feeding and care, which can result in young from secondary nests having a lower fledging mass and a reduced chance of survival.
Factors Influencing Mating Behavior
The primary driver against lifelong pair bonds is the starling’s evolutionary pressure for high reproductive output within a short breeding window. Their ability to attempt one or two broods per season, combined with the availability of food and nesting sites, favors maximizing mating opportunities. This reproductive drive encourages males to pursue polygyny and females to prioritize a male who can secure a high-quality nest site, regardless of his long-term fidelity.
Competition for quality nesting sites also shapes their mating behavior. Since starlings are cavity-nesting birds, the best tree hollows or crevices are a limited resource, and males compete fiercely to secure and defend these locations. This competition means a female’s choice is often based on the quality of the territory and nest, not the long-term reliability of the male.
The migratory nature of many starling populations also works against lasting pair bonds. While some starlings are resident, many travel great distances between their wintering and breeding grounds. This seasonal migration often separates pairs, making a reunion the following spring unlikely and favoring the formation of new, temporary partnerships upon arrival at the breeding territory.