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Measurements
Substantial regional variation. Most reports based on small samples that were not measured by same person. In each area males average about 2–6% larger than females (12–15% by mass ), but there is considerable overlap. Size (of breeders) decreases from west to east and from north to south. These differences, and accompanying crest characters, have not been examined comprehensively.
Linear
For all specimens combined (see Appendix 3), ranges of measurements are large: culmen, 43–63 mm; wing, 259–349 mm; tarsus, 49–74 mm. Tail is of doubtful value because often extensively worn. A discriminant function, using wing-chord and rectrix width, correctly sexed 94% of an unsorted sample of 507 breeding birds from Quebec (Bédard et al. 1995b). For wintering birds in Mississippi, Glahn and McCoy (1995) concluded that wing-chord, culmen depth, and culmen length were the most useful variables for identifying sex; mean culmen depth differed by 11%: male, 17.6 mm ± 0.1 SE (range 15.5–20, n = 160); female, 15.8 mm ± 0.2 SE (range 14–18, n = 40). This feature has rarely been reported, but might be a visible character that is useful in some field situations (see Koffijberg and Van Eerden 1995 for Great Cormorant).
Mass
Regional differences are large and no data are available from the West coast and Alaska, where largest birds occur. Mean mass of small southeastern birds is scarcely half that of northern and western birds and the extremes span almost a threefold range (1 to 3 kg). All samples collected in breeding season with the exception of those from Mississippi. From New Mexico (Watson et al. 1991): male, mean 2,453 g (range 2,200–2,750, n = 15); female 2,056 g (range 1,750–2,400, n = 17). From Quebec (Bédard et al. 1995b): male 2,089 ± 5.32 SE (n = 763); female 1,831 ± 7.17 SE (n = 375). From Florida (Owre 1967): male 1,758 (range 1,327–2079, n = 6): female 1,535 (range 1,391–1,665, n = 5). From Bahamas (Watson et al. 1991): male 1,270 (n = 1); female 1,112 (range 1,036–1,175, n = 3). From Mississippi (in winter, Glahn and McCoy 1995): male 2,498 ± 16 SD (range 2,000–3,000, n = 160); female 2,162 ± 29.8 SD (range 1,650–2,600, n = 41). For additional data, see Marshall and Erickson 1945 (Minnesota), Kury 1968 (Maine), Hartman 1961 (Florida).
Hatch, Jeremy J. and D. V. Weseloh. 1999. Double-crested Cormorant (Phalacrocorax auritus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/441
