The European Starling (Sturnus vulgaris) is recognized globally for its iridescent plumage and large, often overwhelming flocks. Originating in Eurasia, the species was intentionally introduced to North America in the late nineteenth century, notably in New York City’s Central Park in the 1890s. The population has since proliferated to an estimated 93 million across the continent. Starlings are highly adaptable and thrive in human-modified environments, though their aggressive, non-native status often earns them a complicated reputation.
Resident vs. Migratory Populations
Starling migration is not a uniform behavior across the species, leading to their classification as partial migrants. Whether an individual bird undertakes a seasonal journey or remains resident is primarily dictated by the climate of its breeding location. Populations that occupy milder latitudes, such as those in the southern United States or the British Isles, often remain in the same area year-round. These resident birds have access to sufficient food and shelter throughout the winter months, eliminating the need for long-distance travel.
Conversely, starlings breeding in harsher, more northern climates, such as Scandinavia or the northern reaches of North America, are the ones that migrate. These northern-nesting birds must move south to escape the deep snow and freezing conditions that severely limit their food supply. This means that a starling observed during the winter in a moderate climate may be a permanent resident or a new arrival from a colder region farther north.
The Timing of Seasonal Movement
Starling migration involves two distinct phases: the southward movement in autumn and the return journey in spring. Autumn migration, when northern birds vacate their breeding grounds, generally begins in late September and continues through November. This period sees a gradual wave of birds moving toward warmer, more resource-rich areas.
The timing is not fixed, varying based on the specific latitude of the breeding site and the severity of the year’s weather. Birds nesting further north will initiate their departure earlier than those in slightly milder regions. Following the winter, the spring return migration typically occurs between February and April, driven by increasing daylight hours and the need to secure nesting territories.
In North America, this often results in a short-distance movement where northern populations simply shift to the southern half of the continent. For European populations, the movement can be more dramatic, with birds traveling from countries like Russia and Poland to overwinter in Western Europe.
Migration Routes and Environmental Triggers
The primary driver for starling migration is a predictable scarcity of food, not just cold temperatures alone. As winter sets in, the ground freezes, making it impossible for the birds to probe for their preferred diet of soil-dwelling invertebrates and insects. They must relocate to regions where fruit and insect life remain accessible.
The biological signal that initiates the migratory drive is the decreasing duration of daylight, known as photoperiodism. This consistent change in day length acts as an internal cue, preparing the birds for movement well before the first hard freeze arrives. Sudden drops in temperature or early snowfalls can serve as secondary, immediate triggers, prompting a quickened pace of southward movement.
In North America, migratory starlings often follow broad geographical features, such as river valleys or coastal plains. This short-distance migration strategy allows them to efficiently reach wintering grounds in the milder southern states. The choice of route maximizes flight efficiency and provides familiar foraging opportunities along the way.
Pre-Migration Behavior: The Phenomenon of Murmurations
A highly visible behavior associated with the migratory period is the formation of murmurations, which are massive, synchronized aerial displays. These displays occur primarily at dusk, just before the birds settle into a communal roost for the night. The flocks can swell to tens of thousands of individuals, creating dark, shape-shifting clouds in the sky.
The main function of the murmuration is believed to be a defense mechanism against predators, particularly raptors like peregrine falcons. The chaotic, unified movement of the group makes it nearly impossible for a predator to successfully target a single bird. This “safety in numbers” effect is a collective strategy for survival.
Murmurations also serve a social purpose, allowing birds to exchange information about the location of feeding sites. The behavior is most prominent during late autumn and winter when the local starling population is augmented by the arrival of northern migratory birds. Afterward, the entire flock descends simultaneously into a sheltered area, such as a reed bed or urban structure, where they spend the night.