Sexes alike. Breeding adult: black plumage with metallic blue-green sheen; white facial skin and throat; bright yellow gular pouch and white thigh patches; silky white plumes on head and neck. Non-breeding adult: no white thigh patches; gular pouch less bright. First year young: dull brown above, white below. Aquatic. Not a gregarious species outside breeding season; usually one or two birds feeding close by; dives underwater in search of fish.