Bait consumption by Sooty Terns: implications for island eradication programmes

Abstract

SummaryRat Rattus spp. predation is widely recognised as a major threat to insular seabird populations. Rodent eradication programmes have advanced over the last two decades with purported benefits to ecosystems and seabird conservation. However, the danger of non-target poisoning to seabirds has rarely been examined, despite hundreds of insular eradication efforts. We initiated research to assess the risk of rodenticide bait to nesting Sooty Terns Sterna fuscata on Wake Atoll Complex. Placebo bait with a fluorescing dye was used in a control treatment design to track exposure and ingestion. Camera-based observations and faecal samples, post-mortem inspections and live chick observations suggested that bait exposure and consumption occurred, but that it was infrequent. Results indicated that poison bait eradication should occur outside the chick rearing phase to minimise risks to nesting seabirds. Our study also documents previously unreported environmental fluorescence, which may increase false positive results in pre-eradication assessments of bait palatability, bait uptake rates, and bait application methods that use inactive fluorescing test baits. We recommend that future conservation efforts begin with an evaluation of environmentally-based fluorescence before formal biomarker studies.