INVADERS ON THE ROAD: SYNANTHROPIC BIRD FORAGING ALONG HIGHWAYS

Abstract

Intercity roads potentially offer a high availability of easily accessible food and could therefore be expected to represent a preferential area for synanthropic bird foraging. As a consequence, a road-network could act as an invasion corridor for non-native urban birds. This study is a first approximation to verify such pattern of spread, by determining if foraging is actually the main activity carried out along intercity roads. With this aim, during the spring of 2011 we surveyed 200 points along the New Zealand intercity road-network, carrying out observations on four invasive synanthropic bird species (Eurasian house sparrow Passer domesticus, Eurasian blackbird Turdus merula, Eurasian starling Sturnus vulgarisand Indian myna Acridotheres tristis). For every species we also investigated: food preferences, the possibility that certain road features could affect the occurrence of feeding activity along roads, and foraging micro-habitat selection along roads. Predominant observed behaviors related to feeding activity, with differences concerning species-specific foraging strategies. Sparrows were mainly observed feeding on small-sized items (such as seeds and invertebrates), while both starlings and mynas showed more generalist feeding habits. These three species were mostly observed along the side of the lane, in contrast with blackbirds, mainly detected preying on invertebrates along the mown grassy verges of the road. Similarly to urban areas, intercity roads provide easily accessible food, available for all the study species. We propose a road-mediated invasion pattern for synanthropic birds, and encourage future studies to optimize management strategies, and targeting intercity roads as the most suitable control areas to prevent spread.