The 176 species of birds using marine habitats of the Northeast Pacific are graded on the basis of 20 factors that affect their survival. A score of 0, 1, 3, or 5, respectively, representing no, low, medium, or high significance is assigned for each factor. The total score is the Oil Vulnerability Index (OVI). The OVI's range from 1 to 100, an index of 100 indicating the greatest vulnerability. Using this system, one can rank the avifauna of different areas according to their vulnerability to environmental hazards as an aid in making management decisions.
Today's decision makers require an ever-increasing array of information and planning documents. The Federal Government's requirement for environmental impact statements under the National Environmental Protection Act of 1969 is but one example of this trend. These documents generally consider the effects of proposed actions on waterfowl and a few other species of birds, but the bulk of the avifauna is usually only listed, or sometimes ignored completely. A simple system for evaluating and presenting avian data is badly needed so that those interested in birds, whether technically trained or not, can easily grasp the implications of proposed actions. It is incumbent on biologists to devise new ways of presenting their knowledge so that it can be easily and effectively used by decision makers, who are often less informed. In short, biologists must do for the environmental impact statement assessors what Roger Tory Peterson did for the bird watchers by giving them a simple and comprehensible system.
The need for a system to evaluate relative vulnerabilities of bird populations is particularly great for birds that are being increasingly affected by marine oil pollution. The system needs to allow comparisons of potential impacts to birds resulting from various oil development projects in different locations and served by various modes of transport. The Oil Vulnerability Index (OVI) is our attempt to fulfill this informational need on the avifauna of the Northeast Pacific. Insofar as we know, this approach to assessing a wildlife management problem has been attempted only for ranking endangered species in a numeric ranking system that identified where restoration efforts could best be directed (Sparrowe and Wight 1975).
We are indebted to Gene Ruhr and Keith Schreiner for ideas generated in their work with endangered species. Frank Pitelka, James Bartonek, Kent Wohl, and Mary Lou King reviewed portions of the manuscript and offered helpful suggestions. Jack Hodges helped prepare the OVI tables.
Methods
A list of 176 species of birds using marine habitats in or near the States of Washington and Alaska and the Province of British Columbia (Table 1, left column) was compiled from checklists by the American Ornithologists' Union (AOU 1957) and Gibson (1970). Nomenclature is from AOU (1957). The scientific names of three species of shorebirds recently identified in the Aleutian Islands that were not listed by the AOU (1957) came from Peterson et al. (1967).
Each bird was scored on 20 factors that affect its survival (Table 1). Point scores for most birds were either 0, 1, 3, or 5, indicating no, low, medium, or high importance, respectively, in their biology or habits as related to Northeast Pacific oil development. Rare or accidental species were given only one point for occurrence, and endangered species 99 points for population size plus 1 point for occurrence. Thus the potential range of the OVI's is from 1 to 100.
The factors in Table are largely self-explanatory. The items under "range" apply to the entire world population of the species. "Productivity" is derived from a combination of clutch size and age at first nesting. Specialization is used in the biological sense to compare a versatile species like mallards (Anas platyrhynchos) with a less versatile species such as the trumpeter swan (Olor buccinator). Mortality under "history of oiling" is based on our knowledge that some species (e.g., alcids) have been more involved than others such as gulls. Exposure relates to the level of exposure within the Pacific area in any season.
Information on many of the factors for many species is scanty at best, and subjective appraisals were made by us when information was lacking. Opinions as to appropriate scores will vary among experts. References used, in part, in preparing Table 1 were: AOU 1957; Fay and Cade 1959; Gabrielson and Lincoln 1959; Isleib and Kessel 1973; Kortright 1942; Murie 1959; Palmer 1962; Robbins et al. 1966; Sanger 1972; and Stout et al. 1967.