Feeding Behavior of the American Merganser in Captivity

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Abstract
In 1962, two American mergansers (Mergus merganser americanus) and in 1963, six were held in captivity for 49-69 days to study feeding behavior. In both years and for all birds, the amount of fish consumed per bird per day equaled 17.9-26.8 percent of the mean weight of the birds. However, all except three of these captive mergansers continually lost weight. Three birds maintained their body weight for 49-51 days on a daily ration of 6.02 to 6.62 ounces of fish--18.3 to 19.6 percent of mean bird weight. Three different series of tests were made on size of trout selected in feeding the mergansers. When presented with live trout 4-8 inches long, the mergansers showed a preference for the smaller trout over the larger ones. Two series of tests were made to determine the upper limit in size of trout that mergansers can eat. Girth rather than length of trout seemed critical. The largest merganser (60 ounces) was able to consume a trout with a girth of 6.2 inches, while the smallest merganser (33 ounces) could swallow trout with girth of up to only 4.9 inches. In 1963, equal numbers of mottled sculpins (Cottus bairdi), creek chubs (Semotilus atromaculatus), and brook trout (Salvelinus fontinalis) of approximately the same size were presented to four mergansers to determine if there was selection of a particular species for consumption. The mergansers consumed about equal numbers of creek chubs and brook trout but a few less of mottled sculpins.

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