THE REPRODUCTIVE SUCCESS OF TREE SWALLOWS NESTING NEAR EXPERIMENTALLYACIDIFIED LAKES IN NORTHWESTERN ONTARIO

We examined a number of reproductive parameters of tree swallows (Tach ycineta bicolor) breeding near experimentally acidified lakes in north western Ontario. We found that near acidified lakes, eggs were smaller in certain dimensions, hatching success was lower (and by definition fewer nestlings fledged per nest box), certain nestling body character s were smaller 4 days posthatch, nestling wing length was shorter near time of fledging, and growth functions were different from those near unmanipulated reference lakes. These results are consistent with earl ier findings that calcium-rich food items needed for egg production by laying females and growth of nestlings are more scarce at acidified l akes than at nonacidic reference lakes, and that potentially toxic met als accumulate to higher concentrations both in the chironomids that s wallows consume and in nestling swallows at acidified lakes. Our resul ts clearly show that even nonaquatic organisms are affected by acidifi cation of freshwater ecosystems.