Effects of insecticide use on breeding birds in Christmas tree plantations in Quebec

: This research, which was carried out in the spring of 1989 and 1990 in seven balsam fir (Abies balsamea) plantations in southeastern Quebec, examines potential deleterious effects of three insecticides (i.e. dimethoate, diazinon and insecticidal soap) on breeding American Robins (Turdus migratorius) (n=87 nests) and Song Sparrows (Melospizsa melodia) (n=41 nests). Through analyses of blood serum cholinesterases (AChE and BChE) activity both prior to and the second day following applications of the two organophosphorus insecticides, we showed that adult American Robins, Song Sparrows and Chipping Sparrows (Spizella passerina) breeding in the treated plantations were exposed to diazinon and dimethoate (p<0.05). Signs of exposure to diazinon (p<0.05) were also found in young American Robins. However, despite sharp reductions in blood ChE (and, in some cases, marked inhibition confirmed by 2-PAM reactivation), no cases of adult mortality were recorded following the treatments. Cases of complete or partial mortality were recorded in American Robin and Song Sparrow nests, even among control birds (non-exposed birds). No mortality was recorded for broods exposed to the insecticidal soap. Abandonment of nests and egg infertility were ruled out as possible causes of mortality. The cases of total mortality observed in American Robin and Song Sparrow broods exposed to dimethoate were similar to those recorded for control nests (18 and 25% compared to 14 and 21%, respectively). However, among American Robin and Song Sparrow nestlings exposed to diazinon, essentially twice as many cases of total mortality (31 and 38%, respectively) were recorded as for the control nests. It appears that American Robin eggs are sensitive to diazinon and dimethoate, particularly when spraying is carried out early in the incubation stage. In the case of the Song Sparrow, it is mainly the nestlings that succumb after diazinon is sprayed on them or when dimethoate applications are made during the egg stage.