Variation drives response to urbanisation: Evolutionary ecology of two introduced birds within anthropogenic environments : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Anthropogenic change causes landscape alteration and fragmentation, which leads to novel challenges for wildlife. Wildlife colonising anthropogenic habitats confront new conditions, such as air and noise pollution, limited space and food resources, higher levels of competition and predator pressures. Such colonists should display a wide spectrum of behavioural, phenotypic, physiological and genetic modifications. Adaptively responding to novel stimuli is a major challenge for urban and rural wildlife and is linked with their fitness. These responses will likely differ between urban and rural habitats as well. Populations will show behavioural and morphological variation along an urban-rural gradient in response to accompanying environmental changes. Certain behaviours, risk-taking, aggression and exploratory behaviour, will increase opportunities for populations to establish and maintain themselves in novel environments. I examined behavioural and morphological traits that allow blackbirds (Turdus merula merula Linnaeus, 1758) and thrushes (Turdus philomelos C. L. Brehm, 1831) to thrive in New Zealand anthropogenic landscapes. Urban blackbirds and thrushes were bolder, more aggressive and more exploratory compared to rural and peri-urban riverside individuals. I assessed the extent to which urban birds showed trends toward using more aggressive behaviour, increased flight duration around a speaker (rather than a signalling response), and decreased duration of singing over the speaker compared to the peri-urban river and rural individuals. The probability of responding with signalling behaviours toward conspecific songs increased in rural and peri-urban river birds. I identified variation in exploratory behaviour and approach response in the presence of a novel object to gather information. Urban birds approached closer to a novel object and had a higher rate of approach at the second attempt. There were inter-specific differences in exploratory behaviour between blackbirds and song thrushes. Blackbirds showed a faster approach response to a novel object compared to song thrushes. However, song thrushes approached closer to the novel object than blackbirds. Morphological traits changed in response to urban-rural landscapes, including increased body mass in rural blackbirds compared to urban individuals. There were morphological variations in response to different regions, including increased tail length for song thrushes and longer bill length for blackbirds in the Canterbury region compared to the Wellington region. Sex-specific traits, such as wing and tail length, varied between male and female blackbirds. There were also differences between the New Zealand populations, isolated for over a century, and their source English populations in tarsus and tail length. My findings can be used for future investigations into urban wildlife behaviours including risk-taking, aggression and novel avoidance behaviours and morphological variation between individuals. Before conducting conservation and reintroduction programs, we need to understand the behavioural variation between environmental sites and how birds cope with anthropogenic changes and perceive the human presence and potential predators in native and exotic populations. It also shows that morphological and behavioural variation in response to habitat change can occur in spatially adjacent areas, even for highly mobile species.