THE EFFECT OF PULP AND PAPER-MILL EFFLUENT ON AN INSECTIVOROUS BIRD, THE TREE SWALLOW

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 d iet, circulating sex steroids, highly carboxylated porphyrins (HCPs), activity of the mixed function oxygenase enzyme 7-ethoxyresorufin-O-de ethylase (EROD), the liver somatic index and reproductive performance and nestling size in tree swallows, an insectivorous bird, at sites lo cated upstream and downstream from two pulp mills in western Canada du ring 1993-1996. The tree swallow diet consisted of 50-60% insects of a quatic origin. In general, physiological biomarkers in tree swallows l ocated downstream from the pulp mill effluents did not differ from tho se at upstream sites, suggesting that dietary exposures to pulp mill e ffluents at these sites were insufficient to elicit responses. Neverth eless, it is noteworthy that 17 beta-oestradiol was lower in incubatin g females at a site downstream from one of the pulp mills in 1 of 2 ye ars. In addition, HCPs in tree swallows downstream from the other pulp mill were elevated significantly. Reproductive performance by tree sw allows did not differ significantly between upstream and downstream lo cations at either mill although there was a definite trend towards enh anced reproduction at downstream sites, At both pulp mills, 16 day old nestlings were significantly larger at downstream sites compared to t heir counterparts at upstream sites in at least 1 year. The improved r eproduction and larger nestlings at downstream sites may be the result of a greater food supply, consistent,with the nutrient enrichment eff ect often seen below pulp mills.