The small Indian mongoose, a non-native species, was introduced to the Hawaiian Islands in 1883. This was a misguided attempt by the sugarcane industry to control rat populations damaging crops. The plan failed because rats are nocturnal while mongooses are active during the day, so they rarely encountered each other. Instead of controlling pests, mongooses became an established part of the Hawaiian ecosystem, with their diet significantly impacting it.
Primary Food Sources
The diet of Hawaiian mongooses primarily includes insects. Cockroaches alone can make up over 13.9% of their food intake, alongside other common prey like crickets, beetles, spiders, and earthworms.
Small mammals, including rodents like rats and mice, also contribute to their diet. Although introduced to control rodents, mongooses consume them when available. A significant primary food source for mongooses is the eggs and chicks of ground-nesting birds. These vulnerable prey are easily accessible, making them a regular part of their diet.
Opportunistic and Varied Diet
Mongooses are adaptable, opportunistic feeders, consuming a wide variety of items depending on availability. Beyond primary food sources, their diet includes small reptiles like geckos and lizards, amphibians such as frogs and toads, and crustaceans like crabs. This generalist nature allows them to thrive in diverse island environments.
When other food sources are scarce, mongooses also consume plant matter, including fruits, seeds, and various plant parts. They have been observed eating carrion and can even prey on domestic poultry. This broad dietary range highlights their ability to exploit nearly any available food resource.
Ecological Consequences of Their Diet
The Hawaiian mongoose’s diet has negative consequences for Hawaii’s native ecosystems. Their predation on ground-nesting bird eggs and chicks is damaging, as many Hawaiian bird species evolved without such predators and lay only one egg per year. This has led to a decline in native bird populations, including eight federally endangered species like the Hawaiian goose (nēnē), Hawaiian crow (‘alalā), and petrels. A study in Hawaiʻi Volcanoes National Park showed mongooses caused 77% of Hawaiian goose egg losses between 1978 and 1981.
The mongoose’s diet also impacts other native fauna, including endangered sea turtles whose eggs they prey upon. Their consumption of native insects, lizards, and other invertebrates disrupts ecological processes like pollination and nutrient cycling. Mongooses can also affect agricultural interests by preying on poultry and consuming crops, costing farmers. Their ongoing presence and broad diet continue to hinder reestablishment efforts for many endangered species across the islands.