Guided by the light: Roost choice and behaviour of urban Rainbow Lorikeets (Trichoglossus haematodus)

Abstract

1. The formation of large communal roosts is a conspicuous phenomenon associated with a wide range of bird species successfully exploiting urban environments. In many Australian cities, the abundance of the Rainbow Lorikeet (Trichoglossus haematodus), a native parrot, has increased markedly in recent decades, with the species roosting in very large numbers within suburban sites. These roosting locations are noisy and cause significant fouling of the land beneath, resulting in conflict with humans. 2. We investigated the selection of roosting sites in this species in Brisbane, Australia, by comparing characteristics of both the general sites of these roosts as well as individual trees used within roosting sites and trees that were avoided. 3. Lorikeets used a wide variety of tree types for roosting but demonstrated a clear preference for clumped trees within sparsely treed areas that received significantly more artificial light at night than otherwise suitable sites and trees nearby. 4. These features of roosting sites may enhance the detection of nocturnal predators by Rainbow Lorikeets, suggesting a potential positive impact of anthropogenic lighting. Our findings provide valuable insights into the management of roost-related conflicts in urban areas. We encourage further investigations into the possible benefits of artificial light.