Increase in Wedge‐tailed Shearwaters and Changes in Soil Nutrients following Removal of Alien Mammalian Predators and Nitrogen‐fixing Plants at Kaena Point, Hawaii

Abstract

A predator‐proof fence was built at Kaena Point Natural Area Reserve, Hawaii in 2010 as part of an ecosystem restoration project. All non‐native mammalian predators were removed and are now excluded. Non‐native plants are being removed and native species are being outplanted. We monitored abundance and reproduction of Puffinus pacificus (wedge‐tailed shearwaters), collected soil samples before and after fence construction, and examined the relationship between changes in shearwater numbers and soil nutrients. Shearwater numbers increased over time, from 11 young produced in 1994 to 3,274 in 2012. The average number of shearwaters produced during the 3 years before and after fence construction increased from 614 ± 249 to 2,359 ± 802 (384% increase). The average number of shearwater pairs attempting to nest also increased during the same periods, from 3,265 ± 827 to 4,726 ± 826 (45% increase). Soil samples from 2010 to 2013 showed an overall decline in concentration of ammonium (NH4+) and no change in concentration of nitrate (NO3−) or orthophosphate (PO43−). However, there was a positive relationship between changes in shearwater numbers and changes in ammonium. Examination of spatial patterns in nutrient abundance showed that the highest nutrient concentrations occurred in areas dominated by the non‐native nitrogen‐fixing plants Leucaena leucocephala and Prosopis pallida. Removal of these plants caused local nutrient declines, but increases in shearwater numbers have countered this at some points. We anticipate that shearwaters and other seabirds will replace non‐native plants as the dominant source of nitrogen and phosphorous and facilitate recovery of a native‐dominated plant assemblage.

Long‐term biodiversity trajectories for pest‐managed ecological restorations: eradication vs. suppression

“…This includes peninsula‐fenced ecosanctuaries: pest‐exclusion fencing at the peninsula neck aims to maintain low or close‐to‐zero pest abundance, despite potential reinvasion around the coastal fence ends (Maitland 2011). Biodiversity benefits within fenced peninsulas have been reported to some extent, for instance, removal of invasive mammalian predators from Hawaii’s Ka’ena Point Natural Area Reserve has increased abundance and reproduction of nesting wedge‐tailed Shearwaters ( Puffinus pacificus ; VanderWerf et al 2014).…”

Seabird population changes following mammal eradications on islands

“…To the best of our knowledge, none of the seabird colonies were established by translocation and only one, that of Monteiro's storm-petrel Hydrobates monteiro on Praia, witnessed a conservation intervention, namely provision of extra nest-boxes, that might have influenced population change after invasive eradication. With one exception, the growth of the wedgetailed shearwater Puffinus pacificus colony at Kaena Point, Oahu, Hawaii (VanderWerf et al, 2014), the data come from relatively small islands (<300 km 2 ), and not 'inland islands' protected by predator-proof fences.…”

Anti‐predator behaviour in a procellariid seabird: Wedge‐tailed shearwaters do not respond to the odour of introduced ship rats

“…In fact, the dramatic increase in some shearwaters' breeding population immediately following rat eradication (Bourgeois et al 2013;Marie et al 2014;VanderWerf et al 2014) suggested that procellariid seabirds may select their breeding sites according to direct cues. However, we hypothesized that this selection could also be at least partially driven by olfaction (avoidance of burrows 'smelling' of rats), with a predation risk assessment based upon predator chemical cues.…”