The European Starling, Sturnus vulgaris, is a medium-sized songbird introduced to North America in the late 19th century. This species has successfully adapted to a wide range of environments, but its presence is frequently associated with conflict. Conservationists are concerned over the starling’s high level of aggression toward native avian populations. This behavior is primarily focused on securing limited shelter during the reproductive season, significantly impacting the nesting success of other birds.
Aggressive Competition for Nesting Sites
The starling’s aggression stems from fierce competition for nesting cavities, a resource often in short supply. Starlings are obligate cavity nesters, utilizing pre-existing holes in trees, utility poles, or human-made nest boxes. They begin nesting early in the spring, often establishing a claim before many migratory native birds arrive. This earlier start gives them a distinct advantage in securing the best available locations.
The aggressive nature of the starling allows it to physically displace other species from occupied nesting sites. Their tendency to flock also contributes to their success, as native birds are often overwhelmed by multiple starlings working in concert. This competitive behavior results from their ability to thrive near human development, where traditional nesting sites are limited but nest boxes are common. Starlings have been known to evict native species as large as Wood Ducks from their nests.
The conflict is intense because both starlings and native species rely on the same finite, enclosed spaces for raising their young. Once a starling pair decides on a cavity, they defend it vigorously against any perceived threat. This defense often involves direct, physical confrontation that can be lethal to the competing bird. The aggression is motivated by resource control and the immediate acquisition of a ready-made home.
Specific Targets and Destructive Methods
The victims of starling aggression are native cavity-nesting birds that utilize similar hole sizes for reproduction. Species such as the Eastern Bluebird, Tree Swallow, Ash-throated Flycatcher, and various woodpeckers are frequently targeted. These native birds have not evolved defenses against this sustained, lethal competition, leading to declines in local populations.
Starlings employ specific, destructive methods to force the turnover of a desirable nest site. The most common tactic involves using their long, pointed bill to puncture the eggs of an occupied nest. This action destroys the clutch, making the site immediately available for the starling pair to begin building their nest. They have also been observed removing the eggs or nestlings entirely from the cavity, dropping them to the ground.
In documented instances, starlings directly attack and fatally injure adult birds to ensure the swift takeover of the cavity. Once the resident pair is removed, starlings often construct their nest right on top of the remnants of the previous one. This immediate destruction of a rival’s reproductive efforts highlights the starling’s focus on monopolizing the limited nesting resource.
Protecting Native Birds From Starling Aggression
Homeowners and conservationists can implement design and monitoring strategies to protect native cavity-nesting species from starling usurpation. The most effective passive measure is the use of starling-resistant nest boxes, which exclude starlings based on their physical size. A starling requires an entrance hole of at least 1.5 inches to enter a box comfortably.
By contrast, many smaller native birds can utilize entrance holes sized between 1.125 and 1.5 inches in diameter. Using a precisely sized hole restrictor plate on existing nest boxes prevents starling entry while still allowing smaller target species to pass through. For larger native birds like flickers, specialized boxes may include a plexiglass shield near the entrance to deter a starling’s direct flight path.
Active management involves closely monitoring nest boxes and removing any starling nesting material immediately upon discovery. Because starlings are not protected under the Migratory Bird Treaty Act, their nests, eggs, and young can be legally removed. Another technique involves replacing starling eggs with painted wooden replicas, causing the adults to continue incubating the non-viable eggs and preventing a new destructive nesting cycle.
Adjusting feeding practices can reduce the attraction of starlings, as they are opportunistic feeders. Avoiding seed mixes that contain cracked corn or millet, which starlings prefer, and instead offering only safflower or nyjer seed discourages their presence. The consistent application of these strategies helps native bird populations successfully reproduce despite the aggressive competition.