Climate change and urbanisation are among the most pervasive and rapidly growing threats
to biodiversity worldwide. However, their impacts are usually considered in isolation,
and interactions are rarely examined. Predicting species' responses to the combined
effects of climate change and urbanisation, therefore, represents a pressing challenge
in global change biology. Birds are important model taxa for exploring the impacts
of both climate change and urbanisation, and their behaviour and physiology have been
well studied in urban and non-urban systems. This understanding should allow interactive
effects of rising temperatures and urbanisation to be inferred, yet considerations
of these interactions are almost entirely lacking from empirical research. Here, we
synthesise our current understanding of the potential mechanisms that could affect
how species respond to the combined effects of rising temperatures and urbanisation,
with a focus on avian taxa. We discuss potential interactive effects to motivate future
in-depth research on this critically important, yet overlooked, aspect of global change
biology. Increased temperatures are a pronounced consequence of both urbanisation
(through the urban heat island effect) and climate change. The biological impact of
this warming in urban and non-urban systems will likely differ in magnitude and direction
when interacting with other factors that typically vary between these habitats, such
as resource availability (e.g. water, food and microsites) and pollution levels. Furthermore,
the nature of such interactions may differ for cities situated in different climate
types, for example, tropical, arid, temperate, continental and polar. Within this
article, we highlight the potential for interactive effects of climate and urban drivers
on the mechanistic responses of birds, identify knowledge gaps and propose promising
future research avenues. A deeper understanding of the behavioural and physiological
mechanisms mediating species' responses to urbanisation and rising temperatures will
provide novel insights into ecology and evolution under global change and may help
better predict future population responses.
