Scaling restoration to achieve quantitative enhancement of loon, seaduck, and other seabird populations

Abstract

The 1996 'North Cape' oil spill along the Rhode Island coast led to the deaths of at least 2292 birds, resulting in an estimated 6275 bird-years lost (adjusted by expected longevity and pro- ductivity). We synthesize information on bird population dynamics to develop an appropriate restor- ation strategy. Marine birds (seaducks, loons, grebes) with natural recovery periods estimated to exceed 1 yr accounted for 87% of the total bird-years lost. Marine birds (gulls, cormorants, alcids, gannets) with recovery estimated to be less than a year accounted for 10% of injuries. Common loons Gavia immer and common eiders Somateria mollissima were selected as targets for restoration because of regional concern over their population status and the magnitude of lost bird-years. Three restoration options were evaluated for loons: nest site protection; nest site enhancement; and public education/outreach. Nest site enhancement opportunities were limited and benefits from public edu- cation/outreach efforts were uncertain. Nest site protection was preferred for both loons and eiders because nest site availability and/or quality currently limit(s) productivity. This option assumes that preventing future productivity loss compensates for productivity loss that resulted from the 'North Cape' oil spill. This assumption is supported by regional productivity estimates for the 2 target spe- cies, is consistent with scientific literature, and represents the consensus of expert opinions. Based on a series of scaling calculations, protection of 25 nest sites for a 100 yr period is expected to balance the loss of 2920 loon-years. Protection of 315 eider nest sites over a 100 yr period would replace 2605 bird-years lost (remaining marine bird injury). Calculations adjust future production credit through economic discounting of 3% yr -1 . Our analysis provides a means of quantifying the level of breeding habitat protection required to restore injured populations of marine birds.