How do brown rats affect native birds, reptiles, and small mammals on oceanic islands?

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black-tailed prairie dog — rodent Black-tailed prairie dog (*Cynomys ludovicianus*).

The brown rat (Rattus norvegicus) is a highly adaptable rodent and a significant invasive species that poses a severe threat to biodiversity, particularly on oceanic islands. Because they are omnivorous and aggressive, they actively hunt a wide range of prey, including native birds, reptiles, and small mammals.1

Their impact on these fragile ecosystems is profound:

Predation: Brown rats frequently consume the eggs and young of birds, which can lead to population declines or total extinction of native species.1
Competition and Destruction: By aggressively pursuing diverse prey and exploiting local resources, they disrupt the natural balance of island environments.1
Ecological Disruption: Their presence has been directly implicated in the depletion of native populations of small mammals and reptiles, as these species often lack the defensive adaptations necessary to survive the introduction of such a prolific and opportunistic predator.1

The brown rat's ability to thrive in diverse environments, combined with its high reproductive rate, makes it a persistent threat to the survival of endemic island wildlife.1