Cory's Shearwater     Calonectris diomedea
     Mediterranean C. d. diomedea
     Atlantic C. d. borealis
Two subspecies differ in size and subtly in plumage but are very difficult to distinguish, perhaps indistinguishable at sea. Mediterranean birds have been recorded off New York. Atlantic island breeders apparently account for the vast majority of all North American records. These two populations have been proposed as full species. The more distinctive Cape Verde Islands population C. d. edwardsii (often considered a separate species Cape Verde Shearwater C. edwardsii) is unconfirmed in North America.

Leach's Storm-Petrel     Oceanodroma leucorhoa
     White-rumped  O. l. leucorhoa
     Dark-rumped  O. l. chapmani
Variation is complex, the named subspecies are not always white- or dark-rumped as implied here. Taxonomy was revised by Ainley (1980. Auk 97:837-853). Nominate O. l. leucorhoa is widespread in the north, usually white-rumped, and individuals from the North Atlantic are indistinguishable from those in the North Pacific. The subspecies O. l. chapmani differs from leucorhoa in averaging smaller in size, in some very subtle differences in proportions, and in being mainly dark-rumped (few leucorhoa are dark-rumped), but do not differ significantly in voice. They apparently differ in foraging habitat preference, and may differ in other ways as well, but all differences are clinal with many intermediate birds off central and southern California. Two other populations nest on Guadalupe Island off Mexico and could wander to waters off California. The winter breeding population there is named O. l. cheimomnestes and the summer breeding population O. l. socorroensis.

Brown Booby     Sula leucogaster
     Atlantic S. l. leucogaster
     Eastern Pacific S. l. brewsteri
These two subspecies apparently differ only in adult male plumage, specifically in head color.

Red-footed Booby     Sula sula
     Caribbean S. s. sula
     Eastern Pacific S. s. websteri
Two subspecies differ in adult plumage, with most or all adult S. s. sula white-tailed and most or all adult websteri dark-tailed. No other differences reported, and other subspecies in Pacific and Indian oceans also vary in tail color.

Brown Pelican     Pelecanus occidentalis
     Atlantic P. o. occidentalis group
     Pacific  P. o. californicus group
Two subspecies differ slightly in size and breeding colors. Many are identifiable in the field. Interestingly, band recoveries indicate quite a bit of movement between these populations across Central America.

Double-crested Cormorant     Phalacrocorax auritus
     Eastern  P. a. auritus group
     Western P. a. cincinatus group
Subspecies differ clinally in size and in extent of white in breeding plumes but no other significant differences, any division is arbitrary.

Pelagic Cormorant     Phalacrocorax pelagicus
    Southern P. p. resplendens
    Bering Sea P. p. pelagicus
Northern birds average larger than Southern. The arbitrary division between these subspecies is around the Queen Charlotte Islands, BC, but variation is clinal with much overlap. The population in the Bering Sea  may be more distinctive.

Great Blue Heron     Ardea herodias
     Great Blue A. h. herodias group
     Great White A. h. occidentalis
Variation in this species is particularly interesting. Great White Heron was formerly considered a separate species distinguished from Great Blue by plumage color, size, and length of head plumes. Great White is known to interbreed with dark (Great Blue) birds within its range, and the intermediate "Wurdemann's" Heron (initially described as a separate species) was considered a hybrid. Now all of these southern Florida birds are considered white, intermediate, and dark morphs of a distinctive subspecies A. h. occidentalis, characterized by large size and short head plumes.

Greater Flamingo     Phoenicopterus ruber
     American   P. r. roseus
     Eurasian   P. r. ruber
Careful readers will notice that this is the only Latin subspecies name included in the book, simply because the way the page is laid out it seemed best to include the name for clarity. In fact I believe these are two distinct species with differences in plumage, bare parts colors, voice, and with no range overlap.

Tundra Swan     Cygnus columbianus
     Whistling C. c. columbianus
     Bewick's C. c. bewickii
Two subspecies distinguished by extent of yellow on bill. Sometimes considered separate species, but there is near overlap in bill pattern and no other differences known.

Greater White-fronted Goose     Anser albifrons
     Tundra  A. a. frontalis
     Taiga  A. a. gambelli
     Tule  A. a. elgasi
     Greenland A. a. flavirostris
Variation is subtle and complex, although both Greenland and Tule populations have restricted range and are fairly distinctive in size, plumage, and bill color. The variation within Tundra and Taiga populations creates extensive overlap.

Snow Goose     Chen caerulescens
     Lesser  C. c. caerulescens
     Greater  C. c. atlanticus
Two subspecies differ in size and in frequency of dark morph. Most can be identified but there is considerable overlap.

Brant     Branta bernicla
     Black  B. b. nigricans
     Intermediate B. b. unnamed?
     Pale-bellied B. b. hrota
Three subspecies in North America differ subtly in plumage. The status and identification of the recently diagnosed Intermediate population, nesting on Melville Island and wintering in Puget Sound, is poorly known. [Eurasian race B. b. bernicla could occur in North America, but would probably be indistinguishable from Intermediate birds and from Black X Pale-bellied intergrades].

Canada Goose     Branta canadensis
     Common B. c. canadensis group
     Lesser  B. c. parvipes
     Richardson's B. c. hutchinsii
     Dusky  B. c. occidentalis group
     Cackling B. c. minima
     Aleutian B. c. leucopareia
Rather arbitrarily divided here into six subspecies groups that differ in size, plumage, and voice; but all are connected by intermediate populations and identification can be difficult, even though the extremes seem like different species.

Green-winged Teal     Anas crecca
     American A. c. carolinensis
     Eurasian A. c. crecca group
Two populations sometimes considered separate species. They differ only in adult male plumage. Interbreeding occurs in the limited area where range overlaps.

Mallard     Anas platyrhynchos
     Northern  A. p. platyrhynchos group
     Mexican   A. p. diazi
Two subspecies differ in plumage, especially adult males. Identification and status in North America is complicated by the fact that virtually no pure "Mexican" Mallards occur; all show evidence of intergradation with Northern Mallards.

Common Eider     Somateria mollissima
     West Arctic S. m. v-nigra
     Hudson Bay S. m. sedentaria
     East Arctic S. m. borealis
     Atlantic S. m. dresseri
Four subspecies differ in bill structure, adult male bill color, and subtly in female color. Variation within each subspecies makes identification difficult, and most populations intergrade where ranges meet (and it is possible that other subspecies could wander to our northeastern shores from Iceland or Europe). West Arctic and Hudson Bay populations are more or less isolated. West Arctic population is the most distinctive in appearance and has been proposed for species status. More research is needed on field identification.