Age-specific differences in settlement rates of saddlebacks (Philesturnus carunculatus) reintroduced to a fenced mainland sanctuary

Mortality and/or dispersal immediately after release can cause translocated populations to fail over both the short and long term, particularly at mainland sanctuaries. However, post-release mortality and dispersal can be limited by releasing individuals with an increased probability of survival and site attachment. We monitored a South Island saddleback (tieke; Philesturnus carunculatus carunculatus) population, translocated to a mainland sanctuary, for one year after release to understand the combined influence of post-release mortality and dispersal on initial establishment. We related settlement propensity to three individual characteristics (sex, age class, and previous pairing history) that are known to play a role in the success of reintroductions of other species. Observations of 38 individually marked birds within the sanctuary declined sharply immediately after release, similar to a pattern of post-release mortality observed after a saddleback translocation onto an offshore island. Thereafter, observations declined more gradually until after the start of the first breeding season (5 months after release), likely due to dispersal out of the sanctuary. By the middle of the first breeding season, significantly more subadults than adults survived and remained at the release site, which we attribute to differences in territorial status prior to translocation. Although only 18% of the released birds survived and settled inside the sanctuary at one year after release, our results suggest that, for saddlebacks, releasing a greater proportion of subadults than adults could have a positive effect on reintroduction outcomes at mainland sites where dispersal is of concern.