Birds and the urban environment: the value of green walls

The simplest form of a ‘green wall’ is where self-adhering climbing plants colonise vertical surfaces, an approach that has been used on buildings for millennia (Koehler 2008). Green walls in urban areas are now well-known for their insulation and air cleaning capacities, but little is known of their value as habitats for wildlife. This paper presents preliminary findings of their value for urban birds. The abundance of birds, on 27 green walls and within the area enclosed by a semi-circle of 10 m radius immediately surrounding them, was compared with 27 walls without vegetation (bare walls) and similar surroundings. The study was carried out during the summer and winter of 2010–11 in north Staffordshire (UK). Birds exploited the green walls for various reasons (including nesting, food and shelter) but were never found on bare control walls. The roofs of buildings and the surrounding vegetation were used by birds in both regimes, but birds were more abundant in areas with green walls. The use of green walls by birds depended on the time of day, the season and whether the vegetation was evergreen or deciduous. The birds’ activity was always restricted to the upper half of the wall vegetation. Green walls and the immediate surroundings were used by some species of conservation concern in Great Britain (e.g. Passer domesticus and Sturnus vulgaris). Therefore, encouraging householders and businesses to grow vegetation up walls may be an effective way of providing a range of resources for birds in urban areas without the need for expensive additional land-take.