Cooperative harassment strategy by the European Starling to usurp cavities and reproductive cost for the neotropical Green-barred Woodpecker

Abstract

The European Starling (Sturnus vulgaris) is a cavity-nesting bird with great invasive potential. As a result of human intervention, this bird is now distributed across all continents (except Antarctica) and its distribution range is increasing at an alarming rate. The European Starling was introduced to Argentina in 1983 and is currently distributed across almost the entire country. It is considered one of the hundred most damaging invasive species in the world and constitutes a serious competitive threat to native cavity-nesting birds. Interactions between European Starlings and cavity-nesting birds generally have negative consequences on native bird populations, although there are still few reports in the literature that account for the degree of damage. In this study, we report for the first time details of the harassment strategy and subsequent cavity usurpation by European Starlings on a breeding pair of Green-barred Woodpeckers (Colaptes melanochloros) in an urban area of central-eastern Argentina. Over one breeding season, the woodpeckers excavated seven cavities, none of which were successful. In six of these reproductive attempts (86%) we recorded interactions with European Starlings and in five (71%) the cavity was usurped. On three occasions we recorded a cooperative harassment strategy by a group of European Starlings causing the woodpeckers to abandon the cavity. Our report is especially relevant if we consider the invasive potential of the European Starling worldwide and the frequently limited cavity supply in bird breeding habitats. Therefore, we encourage governmental authorities and environmental NGOs to take measures to control the populations of this aggressive invasive species.