Hihi (Notiomystis cincta) were reintroduced to Mokoia Island, Lake Rotorua, New Zealand, in September 1994, and two years later there was an aerial drop of brodifacoum cereal pellets aimed to eradicate mice (Mus musculus). Using Program MARK, we analyzed data from resighting surveys to assess whether hihi had lower than normal survival in the 6-week interval following the drop. The resighting data were collected on a regular basis over a 3-year period, from 1994-97, allowing us to control for yearly and seasonal variation in resighting and survival probabilities.
Several recent studies have used "roll calls"—searches for individually-marked birds—to assess impacts of aerial poison operations on non-target species. Roll calls have advantages over methods such as 5-minute bird counts, call counts, and dead body counts, but roll calls are based on the assumption that detection rates are 100%, or that detection rates are constant over time and space. They also require more than one group of birds, at a poisoned and unpoisoned site for example, for valid statistical comparisons.
Many endemic species on islands are vulnerable to predation and local extinction by introduced rats (Rattus spp.). As a result, the reintroduction of species to predator-free sanctuaries is a successful conservation strategy, especially in New Zealand. Nevertheless, reintroduced populations, even those that reach high densities, are still vulnerable to predation in the event of a rat reinvasion, and may also be susceptible to non-target poisoning during a subsequent eradication operation.