Pollutant effects on the reproduction of the Prairie Falcons and Merlins of the Canadian prairies

Studies of the pollution ecology of the Prairie Falcon (Falco mexicanus) and the Richardson's Merlin (Falco columbarius richardsonii) carried out by the Canadian Wildlife Service in Alberta and adjacent regions of western Canada have shown that both species have been stressed by residues of p,p'-DDE accumulated from food webs. Reproduction of the more contaminated members of both populations was significantly decreased. Changes in nest defense behavior of Merlins were significantly associated with decreasing shell-thickness index and increasing levels of DDE and possibly of PCB; more contaminated individuals were less aggressive in defending territories. DDE levels in the eggs associated with decreases in productivity were approximately 10 ppm dry weight (2 ppm wet weight) in Prairie Falcon eggs and 30 ppm dry weight (6 ppm wet weight) in Merlin eggs. Effects of current levels of PCB, dieldrin, heptachlor epoxide, and mercury on the reproduction of these populations could not be demonstrated; mean concentrations of these pollutants in eggs appeared to be below threshold levels. Pollutant levels in addled eggs and in eggs containing dead embryos were not significantly different from those in viable eggs.