Wild birds in urban gardens : opportunity or constraint?

This thesis examines whether urban residential areas, where small private gardens are
the main wildlife resource, offer wild birds ecological opportunities as habitat or impose
ecological constraints on them. Ecological opportunities should facilitate the
establishment of an avifauna that does not depend on immigration, is similar in
composition and structure to those in less-urbanised gardens and comprises individuals
within normal ranges of biometrics, behaviour and condition. Ecological constraints
may compromise the sustainability of this avifauna and restrict successful exploitation
of the habitat to birds of particular characteristics.
The analyses presented first investigate which bird species urbanise and why, and
secondly which species use gardens and how. Patterns and trends in the use of gardens
by British birds are examined, in general and in urban areas. A case study builds on
these two themes, linking urban and garden ornithology by investigating an avifauna
that uses gardens as its primary habitat but within a highly-urbanised context. Field
studies of the breeding avifauna and some aspects of its ecology are presented, together
with data from a ringing study on the use of feeding stations and the mobility and
persistence of individual birds.
More bird species urbanise than might be expected and urbanisation is not restricted to
species with high behavioural flexibility. Gardens are an extension of natural habitat for
many species, but in urban gardens utilisation rates are declining more than in gardens
elsewhere, raising concerns for urban conservation policy. Small gardens in a highlyurbanised
area support a breeding avifauna that is of low density but appears sustainable
and of stable composition with individual birds maintaining normal territoriality and
persisting over time. The spatial distribution of breeding territories is related to all-year
artificial feeding but not to cat activity, and the mechanisms of birds' adaptation to
urban life show interesting variation between species.