[2] In 1960, Walter R. Spofford hired Peakall as a research associate in the Department of Anatomy of the Upstate Medical Center in Syracuse, New York, where he used egg albumen protein electrophoresis to determine phylogenetic relationships in the Falconiformes.
Peakall filled blown peregrine eggs collected from the critical period with solvent and measured DDE in the extracted lipids.
In 1975, Peakall went to Ottawa to become a research scientist and Chief of the Toxic Chemicals Division in the Canadian Wildlife Service (CWS) of Environment Canada.
To the existing strengths in analytical chemistry, field biology, pesticide registration and tissue banking, he added specialists in cytogenetics, heavy metals and biochemical toxicology, and a team to focus on the problems of fish-eating birds of the Great Lakes.
Peakall's major contribution to the Great Lakes gull work was an egg swap programme between "clean" and "dirty" colonies, to isolate the effect of parental behaviour from that of embryo toxicity.
He also participated in analysing the effects on songbirds of spraying New Brunswick forests, fostered the long-term monitoring of contaminant residues in seabird eggs, and for many years was key to the success of the Research Advisory Board of the WWF-CWS Wildlife Toxicology Fund.
Peakall guided his scientific team in their collaborative investigations with CWS regional biologists on such problems as reproductive declines in falcons, effects of mercury and acid precipitation on loons and other waterfowl, and the effects of dioxins and dioxin-like compounds in pulp mill effluent on great blue heron reproduction.
From 1979 to 1985, he conducted his own extensive collaborative research program on the sub-lethal effects of oil on seabirds, working at the Mount Desert Island Biological Lab in Maine and Memorial University in Newfoundland.