The main cellular line of defence of the lung
consists of the free (surface) macrophages (FMs). The cells
engulf foreign agents (biological and particulate) and destroy
or sequester them. The goal of this study was to
determine whether the numbers of FMs are good indicators
of air pollution and whether birds may flourish in or prefer
less polluted areas. The numbers of FMs in the respiratory
systems in three species of birds, namely the House Sparrow
(Passer domesticus), the Cape Glossy Starling (Lamprotornis
nitens) and the Laughing Dove (Streptopelia
senegalensis), from an urban and a rural area of South
Africa were counted. Statistically significantly greater
numbers of FMs occurred in the respiratory systems of the
urban birds. For both the rural and the urban areas, the
Laughing Doves had the most body mass normalized and
total lung volume normalized FMs followed by the Cape
Glossy Starlings, with the House Sparrows having the
lowest number. The greater numbers of FMs in the urban
birds can possibly be ascribed to the high levels of air
pollution in the Johannesburg-Vaal Triangle industrial
conurbation compared to the rural, near pristine area of
Vaalwater. The differences in the number of FMs in species
from the same locality may be partly ascribed to behavioural
differences: the House Sparrows have a limited
operation range while the Cape Glossy Starlings and the
Laughing Doves have wider ranges. FMs may be good bioindicators
of air pollution. Studies of more species of birds
in different rural and urban habitats are warranted to con-
firm the observations made here.