Individual identification of Black-throated Divers (Gavia arctica)

Abstract

The potential to identify individual Black-throated Divers (Gavia arctica) on the basis of breeding plumage features was explored using 278 photos, including two paired birds followed during the years 2007–2015 at a specific breeding location. Observations were focused on: 1) white lines on the sides of neck, 2)mantle having rows of sharply contrasting white squares, and 3) small white spots on lesser andmedian coverts. In photos, the number ofwhite lines on the sides of neck varied from four to seven (mean = 5.0, n = 278), and the second line from the head was the highest in 92.1% of the photos. The number of “white square” rows on the mantle varied from 11 to 14 and the small white spots on coverts from 27 to 67. Identification of individual Black-throated Divers was potentially easiest if the plumage had some special patterns (19.4% of birds, n = 278). Plumage remained the same in the followed pair between years, as was also shown by the discriminant analysis, since the followed pair was correctly classified by sex but not by sides showing that sides are similar. To estimate whether it is possible to separate these two birds from other birds, a second discriminant analysis was accomplished. Thus, 125 other birds were added to analysis as a third group together with the followed pair (female andmale, nine years and n = 18 per sex). The linear discriminant analysis yielded a classification rate of 70.8% in original analysis and 69.6% based on the leave-one-out analysis (n = 161). These analyses were based on the relative height of the neck lines, their average relative height and standard deviation.When the number ofwhite spotswere added to this discriminant analysis, a correct classification rate of 77.4% in original analysis and 75.7% in the leave-one-out analysis was obtained (n = 115). These analyses suggest that the plumage can be used in identification, especially when following nesting pairs during their breeding seasons in different years. Presumed female andmaleBlack-throatedDiver could be distinguished based on the shape of the forehead.