Scientists looking for environmental contaminants in the eggs of herring gulls from the Great Lakes have stumbled on something they didn't expect: trans-fats.
These fatty acids do not occur in nature; they are an ingredient in processed foods. Yet trans-fats started appearing in herring gull diets almost 15 years ago and have been increasing ever since, according to a recent study published in the journal Ecology.
The source, of course, is garbage, but experts say the herring gulls likely are not raiding the refuse bin by choice. Ring-billed gulls, a common smaller species, are the ones more likely to be seen begging morsels from beach picnics and flying around landfills.
Most herring gulls prefer to eat fish, but the gulls prey on the same fish as stocked salmon, and the salmon have been beating the birds to the table. As a result, herring gulls are in decline across the Great Lakes, and "the one factor that definitely seems to be universally important is the introduction of these stocked [salmon]," said Craig Hebert, research scientist with Environment Canada and the study's lead author.
The gulls' unexpected foraging is just one example of the unintended consequences of human intervention in the Great Lakes, which has radically changed the ecosystem. Fish stocking programs have pumped more than three quarters of a billion non-native fish into the lakes since 1965.
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