Threats The primary threats responsible for the decline of the Oahu Elepaio are nest predation by alien black rats (Rattus rattus) and mosquito-borne diseases. Habitat loss was a problem in the past, but most areas currently inhabited by Oahu Elepaio are protected. Habitat degradation remains a problem, however, primarily due to the spread of invasive alien plants.
Conservation Rat control has proven to be an effective method of increasing Oahu Elepaio nest success and survival of breeding females, if properly implemented, and has become the cornerstone of the conservation strategy for this species. Rats have been controlled by placing traps either in a grid pattern throughout the forest in which Elepaio live, or by placing traps in each territory for more than 20 years with demonstrated success. New rat traps that reset automatically made by the Goodnature Company in New Zealand have made it easier and more efficient to control rats and protect Elepaio.
Results of Conservation Measures Trapping rats can reduce rat abundance and protect Oahu Elepaio nests. We have been trapping rats to protect Oahu Elepaio nests for over 20 years, and it works. When rats are trapped, twice as many Elepaio pairs successfully raise a chick and fewer females are eaten. But to really make a difference for the Oahu Elepaio population, we need to trap rats over a larger area and in more forested areas where they are still trying to nest. By increasing rodent control, we can increase the size of the population being protected.
Evolution of Nest Height in Oahu Elepaio Predation by non-native black rats (Rattus rattus) is the greatest threat to the Oahu Elepaio. Black rats are excellent climbers and can easily climb trees in which Elepaio nest. As part of our research on the Oahu Elepaio that we have conducted since 1996, we monitor nests to see if they produce any young, and we measure various things about each nest to try to figure out which factors might influence whether nests succeed or fail. One remarkable pattern we have discovered is that the average height of Oahu Elepaio nests increased about 50% over the past 20 years, from 7.9±1.7 meters to 12.0±1.1 meters. There are two possible explanations for this increase: either 1) individual Elepaio are learning to nest higher based on previous experience with rats, or 2) Elepaio are evolving at the population level in response to predation. It turns out there has been no consistent change in the height of sequential nests made by individual Elepaio, demonstrating they have not learned. Instead, the increase in Elepaio nest height is occurring through evolution. Nests closer to the ground (less than 3 meters high) fail more often, so birds that tend to nest lower produce fewer offspring. Elepaios that nest higher off the ground are not immune to predation, but their nests are successful more often and they produce more offspring. This is natural selection, and the selective agent is predation by rats. Oahu Elepaio nest success also has increased over time, presumably because more of them are now nesting higher, providing more hope more the long-term persistence of the species. Rat control can help to facilitate the evolution of increasing nest height by slowing the rate of population decline and allowing sufficient time for this adaptive response to spread through the population.
Contact us: Pacific Rim Conservation PO Box 61827 Honolulu, HI, 96839 firstname.lastname@example.org