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Rats Eradicated, Petrel Breeding Soars on NZ Island
2 Oct
Summary
- Rat removal dramatically increased seabird breeding success.
- Cats' earlier removal paradoxically increased rat predation.
- High-altitude petrels were more vulnerable to rat predation.
The eradication of introduced Pacific rats from New Zealand's Little Barrier Island has resulted in a remarkable recovery for the native Cook's petrel seabird. Prior to the rat removal in 2004, these seabirds faced severe predation of their eggs and chicks, with nesting success rates often dropping to as low as 5% in high-altitude colonies.
Following the successful rat eradication campaign, monitoring revealed a significant upturn. By 2005, breeding success had surged to approximately 53%, a stark contrast to the pre-eradication levels. This ecological intervention also offered insights into predator dynamics; the earlier removal of cats in 1980 had, unexpectedly, intensified the predation pressure from the remaining rats, a phenomenon known as mesopredator release.
This ecological shift underscores the complex interactions within island ecosystems. While lower-altitude petrel colonies showed less dramatic changes, the high-altitude populations demonstrated a clear vulnerability to rat predation. Little Barrier Island, now largely free of introduced mammals, serves as a vital refuge for the largest population of Cook's petrels globally.
