Howland, Baker and Jarvis Islands 25 years after cat eradication: the recovery of seabirds in a biogeographical context

Feral cats (Felis catus) were eradicated from Howland, Baker and Jarvis Islands, all U.S. National Wildlife Refuges in the equatorial Central Pacific Ocean, by the 1980s. The cats were introduced during the 1930s to control rodents, and succeeded in extirpating Norway rats (Rattus norvegicus) and Pacific rats (R. exulans), but not mice (Mus musculus). The cats also extirpated small species of seabirds including grey-backed terns (Onychoprion lunata), blue noddies (Procelsterna cerulea), brown noddies (Anous stolidus), Christmas (Puffinus nativitatis) and Tropical (Puffinus bailloni dichrous) shearwaters and Polynesian storm-petrels (Nesofregetta fuliginosa), and ate chicks and adults of larger Pelecaniformes such as boobies and frigatebirds. With cats eradicated, the extirpated seabirds began to recolonise these islands. Grey-backed terns recolonised Jarvis Island within four years and 20 years later Polynesian storm-petrels were also thought to be breeding there. On Baker and Howland Islands, which are separated by less than 40 miles, military occupations, invasive plants, and pests, apparently made some species of birds move between the islands. However, by 1996, the seabird diversity and population levels were returning to historically recorded levels. The position of these three islands near the Equator and in the flow path of the Equatorial Undercurrent (EUC), a cold, nutrient-rich subsurface current, has enhanced the recovery of seabirds. Regional and local upwelling provides nutrients which fuels high productivity of zooplankton, the primary food of blue noddies. On occasions, severe climate-driven fluctuations can impede upwelling and deprive marine ecosystems of nutrients that in turn affects seabird productivity. The strongest El Nino on record occurred during the 1982 cat eradication effort on Jarvis Island, suppressing seabird populations and thereby helping to limit cat numbers.