Comparison of the numbers of free (surface) macrophages in the respiratory systems of three species of birds in an urban and a rural area of South Africa

Abstract

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 bio-indicators of air pollution. Studies of more species of birds in different rural and urban habitats are warranted to confirm the observations made here.