Using proxies to elucidate environmental threats to endangered species

The Blue Swallow, Hirundo atrocaerulea, is one of Southern Africas most threatened bird species. The species is unique among terrestrial birds as it has a plumage almost as water repellent as water birds, an adaptation to foraging on the wing in dense fog. We show that strong detergents are formed by reactions between air pollutants at the Blue Swallow Natural Heritage Site, and argue that these are a threat to the survival of the species. We cannot do experiments with the species itself and have to rely on the vegetation in the area as proxy to elucidate threats to the species