The effect of pulp and paper mill effluent on an insectivorous bird, the tree swallow

Abstract

Pulp mill effluent is known to affect freshwater biota in various ways. However, its effects on riparian birds that feed on insects emerging from aquatic ecosystems have not been examined. This study examined diet, circulating sex steroids, highly carboxylated porphyrins (HCPs), activity of the mixed function oxygenase enzyme 7-ethoxyresorufin-O-deethylase (EROD), the liver somatic index and reproductive performance and nestling size in tree swallows, an insectivorous bird, at sites located upstream and downstream from two pulp mills in western Canada during 1993–1996. The tree swallow diet consisted of 50–60% insects of aquatic origin. In general, physiological biomarkers in tree swallows located downstream from the pulp mill effluents did not differ from those at upstream sites, suggesting that dietary exposures to pulp mill effluents at these sites were insufficient to elicit responses. Nevertheless, it is noteworthy that 17β-oestradiol was lower in incubating females at a site downstream from one of the pulp mills in 1 of 2 years. In addition, HCPs in tree swallows downstream from the other pulp mill were elevated significantly. Reproductive performance by tree swallows did not differ significantly between upstream and downstream locations at either mill although there was a definite trend towards enhanced reproduction at downstream sites. At both pulp mills, 16 day old nestlings were significantly larger at downstream sites compared to their counterparts at upstream sites in at least 1 year. The improved reproduction and larger nestlings at downstream sites may be the result of a greater food supply, consistent with the nutrient enrichment effect often seen below pulp mills.