Table 2. Criteria and points used in calculating Oil Vulnerability Index.
Point assignment
1 3 5
Range
Breeding Large Medium Small
Migration Long Medium Short
Winter Large Medium Small
Marine orientation Coastal zone Intertidal Open water
Population
Size Large Medium Small
Productivity Large Medium Small
Habits
Roosting Shore Drift Water
Foraging Walking Flying Swimming
Escape Leave area Fly Dive
Flocking Small Medium Large
Nesting density Low Medium High
Specialization Low Medium High
Mortality
Hunted by man Low Medium High
Animal depredations Low Medium High
Non-oil pollution Low Medium High
History of oiling Low Medium High
Exposure
Spring Low Medium High
Summer Low Medium High
Fall Low Medium High
Winter Low Medium High

With these points in mind it is immediately obvious that Southeast Alaska (Table 4), which has only 9 high-score birds, offers far less potential for bird problems than does the Aleutian area (Table 5), which has 24 high-score species. The planning agency could make some immediate decisions on site priorities and research funding based on such information.

Discussion

We are convinced that the OVI principle expressed here will become a useful management tool with all sorts of possible applications. We recognize some difficulties with the present version, but believe it is timely to present the system so that a broader range of thought, improvements, and application can be applied to it.

Of prime importance is the system's simplicity. The use of four levels of value for each factor, instead of five or more, is an attempt to simplify. Ian McHarg (1969) has shown that extremely complex land-use values can be graphically compared and displayed by using three levels in a way that is useful to decision makers. The difficulty of using more levels of value was indicated by Sparrowe and Wight (1975) who used up to 10 levels, enormously complicating the problem of dealing with low-quality information, which is often all that is available. The use of scores of 0, 1, 3, 5 instead of 0, 1, 2, 3 for 20 factors enabled us to use the convenient 100 points instead of 60 points as the maximum potential total score for any species.

The 20 factors that were evaluated are admittedly arbitrary; with refinement and more detailed data they could be adjusted to show better separation between affected species. The decision to use 20 factors instead of more or less again relates to simplicity. This appears to be the minimum number that will assure species separation and that can be neatly displayed.

Table 3. Oil Vulnerability Index (OVI) for families of birds of the Northeast Pacific marine habitats, excluding rare and endangered species in the scoring.
Family Number of species Total OVI OVI per species
Average Range
Loons—Gaviidae 4 219 55 47-65
Grebes—Podicipedidae 3 148 49 44-56
Albatrosses—Diomedeidae 2 102 51 50-52
Shearwaters—Procellaridae 4 208 52 47-57
Storm-petrels—Hydrobatidae 2 130 65 63-67
Cormorants—Phalacrocoracid 4 235 59 52-63
Herons—Ardeidae 1 29 29 29
Waterfowl—Anatidae 33 1,765 53 32-78
Eagles and Hawks—Accipitridae 2 77 39 19-58
Ospreys—Pandionidae 1 37 37 37
Falcons—Falconidae 1 41 41 41
Cranes—Gruidae 1 24 24 24
Rails and Coots—Rallidae 1 33 33 33
Oystercatchers—Haematopodidae 1 65 65 65
Plovers—Charadriidae 7 287 41 26-57
Sandpipers—Scolopacidae 22 857 39 24-59
Phalaropes—Phalaropodidae 2 120 60 58-62
Jaegers and Skuas—Stercorariidae 3 123 41 39-43
Gulls and Terns—Laridae 16 730 46 32-66
Auks—Alcidae 15 1,164 78 70-88
Kingfishers—Alcedinidae 1 28 28 28
Crows—Corvidae 2 68 34 21-47
Total and Mean 128 6,490 51 19-88

The system will be much more useful when it is expanded to the subspecific level. Many Holarctic species are represented in the Northeast Pacific by a single race that would have a much higher OVI than the species as a whole. For example, the OVI for the Peale's peregrine falcon (Falco peregrinus pealei) confined to marine habitats within the Pacific region would be high; and the endangered Aleutian Canada goose (Branta canadensis leucopareia) would score 100 points instead of the 34 we show for Canada geese (B. c.). If Tables 4 and 5 showed subspecies, the differences in value would be more marked.

Tables 4 and 5 are for broad geographical areas. A comparison between smaller areas would probably show more dramatic differences.

Because the dearth of easily available, applicable information poses a problem in evaluating the various factors, our scoring was conservative. Experts on the various avian families can doubtless refine the scoring. If this system proves useful, investigators will begin to acquire the information needed for more precise evaluations. Ultimate perfection may never be achieved; however, as with the field guides, the fact of minor professional disagreement should not destroy the system's utility.

We believe re-scoring of all birds on the basis of various projects should be avoided because a standard against which individual projects can be measured is needed. If everyone did their own scoring, there would be no standard, and projects evaluated by different investigators would not be comparable. If a species list for the project area and standard point scores are used, the level of involvement for many species and perhaps for most species will be properly identified. As with any system, there will be exceptions and the assessor will need to deal with these as appropriate. The result will still be to focus attention on those species and impacting factors where it is most needed.

Table 4. Oil Vulnerability Index for 109 species of birds of Southeast Alaska (Total Points—2,678).
OVI 1-20 OVI 21-40 OVI 41-60 OVI 61-80 OVI 81-100
Marsh hawk 19 Great blue heron 29 Common loon 47 Pelagic cormorant 63 Pigeon guillemot 82
52 species, rare or occasional (one point each) 52 Canada goose 34 Arctic loon 58 Oldsquaw 66 Marbled murrelet 84
White-fronted goose 36 Red-throated loon 49 White-winged scoter 72
Snow goose 32 Red-necked grebe 44 Surf scoter 72
Mallard 36 Horned grebe 48 Black oystercatcher 65
Pintail 36 Whistling swan 50 Northern phalarope 62
Green-winged teal 34 Trumpeter swan 63 Common murre 70
American wigeon 36 Greater scaup 52
Semipalmated plover 28 Lesser scaup 52
Killdeer 26 Common goldeneye 48
Common snipe 29 Barrow's goldeneye 56
Spotted sandpiper 24 Bufflehead 52
Greater yellowlegs 30 Harlequin duck 60
Lesser yellowlegs 30 Common merganser 56
Pectoral sandpiper 32 Red-breasted merganser 56
Least sandpiper 34 Bald eagle 58
Herring gull 38 Peregrine falcon 41
Bonaparte's gull 40 Black turnstone 57
Arctic tern 32 Rock sandpiper 59
Belted kingfisher 28 Dunlin 41
Common raven 21 Short-billed dowitcher 41
Western sandpiper 47
Glaucous-winged gull 56
Thayer's gull 42
Mew gull 44
Northwestern crow 47
Totals 71 665 1,324 470 166
Table 5. Oil Vulnerability Index for 123 species of birds of the Aleutian Islands (Total Points—2,689).
OVI 1-20 OVI 21-40 OVI 41-60 OVI 61-80 OVI 81-100
80 species, rare or occasional (one point each) 80 Canada goose 34 Fulmar 57 Fork-tailed storm-petrel 67 Pigeon guillemot 82
Least sandpiper 34 Slender-billed shearwater 53 Leach's storm-petrel 63 Whiskered auklet 88
Arctic tern 32 Greater scaup 52 Pelagic cormorant 63
Common raven 21 Common goldeneye 48 Red-faced cormorant 63
Bufflehead 52 Black Brant 70
Harlequin duck 60 Emperor goose 70
Bald eagle 58 Oldsquaw 66
Peregrine falcon 41 Steller's eider 72
Ruddy turnstone 44 Common eider 68
Rock sandpiper 59 King eider 70
Western sandpiper 47 White-winged scoter 72
Red phalarope 58 Common scoter 72
Parasitic jaeger 43 Black oystercatcher 65
Glaucous-winged gull 56 Red-legged kittiwake 66
Black-legged kittiwake 49 Common murre 70
Thick-billed murre 70
Ancient murrelet 74
Parakeet auklet 80
Crested auklet 76
Least auklet 80
Horned puffin 72
Tufted puffin 72
Totals 80 121 777 1,541 170

We have used our OVI system to show the vulnerability of birds to oil, but it seems likely that the vulnerability index could be applied on a much broader scale to help make decisions in other areas of human activity and resource development. The vulnerability index system could be applied to terrestrial as well as aquatic species by adding or subtracting impacting factors, as appropriate. Indexes relating the impact of man upon each North American species could have broad uses in the field of conservation. Population explosions, as well as declines, might be predictable. Human activity could be better adjusted to favor or depress wildlife populations, as appropriate.

We believe that this vulnerability index system has promise for aiding in the decision-making processes upon which future bird conservation will depend.

References

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U.S. Forest Service and Alaska Department of Fish and Game. 1970. Birds of Southeast Alaska, a check-list. The agencies, Juneau, Alaska. 12 pp.