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Tolerance to disturbance by waterfowl was an individual trait. Hens occasionally deserted their clutches after the first disturbance, but in 30 instances where hens were trapped only one deserted. Hen trapping was attempted at 291 nests and 223 (80%) hens were captured. Desertion of nests after a trap was set was 6% for ring-necked ducks (Aythya collaris), 9% for American black ducks (Anas rubripes) and 26% for mallards (Anas platyrhynchos). Ten of 18 desertions occurred with a group of especially intolerant mallards on Dameas Island. Certain other mallards were more tolerant and only 16% of 49 deserted nests at other islands. Nest abandonment was not as common during the last week of incubation. Human activity on islands is detrimental to successful waterfowl production; the presence of people may discourage nesting. Chances for avian predation were increased because: (1) some potential avian predators returned to the islands sooner than did most ducks, (2) hens flushed generally left nests uncovered, (3) flushing of hens often resulted in pieces of down being left on surrounding vegetation. In certain cases dispersal of broods caused losses.