Action: Control mammalian predators on islands for rails
Two before-and-after studies from Australia and the Galapagos Islands found increases in survival or population density of rails on islands following the removal of feral pigs Sus scrofa.
Rails have been especially badly affected by introduced predators and other human impacts, with an estimated 800 species becoming extinct in the Pacific alone (Steadman 1995). They have diversified on islands across the world, with many species losing the ability to fly, thus rendering them extremely vulnerable to invasive predators.
The effectiveness assessment of the control of mammalian predators on islands was carried out across all bird species groups.
Steadman, D.W. (1995) Prehistoric extinctions of Pacific island birds: biodiversity meets zooarchaeology. Science, 267, 1123–1131.
Supporting evidence from individual studies
A before-and-after study in 1979-84 on Lord Howe Island (56 km2), Australia (Miller & Mullette 1985), found that the Lord Howe Island woodhen Tricholimnas sylvestris population increased after feral pigs Sus scrofa were controlled and a captive breeding programme was launched. Before pig control, the woodhen population was a maximum of ten breeding pairs, with adult mortality higher than juvenile recruitment. Following pig control, 56 released, captive-bred birds were found to survive for up to two years and 19 young were successfully raised between 1982 and 1984. Additionally, woodhens have started to expand their range from the unfavourable territories they were previously confined to, to more favourable, previously pig-infested regions. A total of 186 were destroyed between 1979 and 1981. This study is also discussed in ‘Release captive-bred individuals’ and ‘Use captive breeding to increase or maintain populations’.
A controlled before-and-after study on Santiago Island (585 km2), Galapagos, Ecuador (Donlan et al. 2007) found that densities of Galapagos rails Laterallus spilonotus increased following the eradication of feral mammals between 1998 and 2006 (279 rails found at 8.5-17.9 rails/ha in 2004-5 vs. 18 rails at 0-1.4 rails/ha in 1986-7). Over the same period, there was a smaller increase in rails detected on Ferdandina Island, which has remained free from invasive mammals (no rails detected during surveys in 1986-7 although some were heard outside survey times, 11 rails detected in 2004-5) and a decrease on Isabella Island, which retains feral goats, pigs and donkeys (13 rails in 247 survey plots at eight sites in 2004-5 vs. 24 rails in 60 survey plots in 1986-7). Donkeys Equus asinus, 17,000 pigs Sus scrofa and 70,000 goats Capra hircus were removed.
- Miller B. & Mullette K.J. (1985) Rehabilitation of an endangered Australian bird: the Lord Howe Island woodhen Tricholimnas sylvestris (Sclater). Biological Conservation, 34, 55-95
- Donlan C.J., Campbell K., Cabrera W., Lavoie C., Carrion V. & Cruz F. (2007) Recovery of the Galapagos rail (Laterallus spilonotus) following the removal of invasive mammals. Biological Conservation, 138, 520-524