How did invertebrates respond to eradication of rats from Kapiti Island, New Zealand?

Kapiti Island is an important wildlife sanctuary off the west coast of the North Island, New Zealand. Restoration of the island after human occupation has included a 60-year programme of eradication of 10 pest mammals, ending with the removal of Norway and Pacific rats in 1996 using brodifacoum rodenticide bait. We monitored the impact of rat removal on invertebrate communities using pitfall traps. Three years after rat eradication we detected a significant decrease in invertebrate catch frequency and diversity, most obvious in the Carabidae and Amphipoda. Site and season accounted for most of the variation in the data. A four-fold increase in the conspicuousness and condition of some insectivorous birds, and fluctuations between El Nino and La Nina weather patterns may have affected the "recovery" of the island invertebrates.