Wildebeest
Both species of wildebeest are even-toed, horned, greyish-brown ungulates resembling cattle. Males are larger than females and both have heavy forequarters compared to their hindquarters. They have broad muzzles, Roman noses, and shaggy manes and tails. The most striking morphological differences between the black and blue wildebeest are the orientation and curvature of their horns and the color of their coats. The blue wildebeest is the bigger of the two species. In males, blue wildebeest stand 150 cm tall at the shoulder and weigh around 250 kg, while the black wildebeest stands 111 to 120 cm tall and weighs about 180 kg. In females, blue wildebeest have a shoulder height of 135 cm and weigh 180 kg while black wildebeest females stand 108 cm at the shoulder and weigh 155 kg. The horns of blue wildebeest protrude to the side, then curve downwards before curving up back towards the skull, while the horns of the black wildebeest curve forward then downward before curving upwards at the tips. Blue wildebeest tend to be a dark grey color with stripes, but may have a bluish sheen. The black wildebeest has brown-coloured hair, with a mane that ranges in color from cream to black, and a cream-coloured tail. The blue wildebeest lives in a wide variety of habitats, including woodlands and grasslands, while the black wildebeest tends to reside exclusively in open grassland areas. In some areas, the blue wildebeest migrates over long distances in the winter, whereas the black wildebeest does not. The milk of the female black wildebeest contains a higher protein, lower fat, and lower lactose content than the milk of the blue wildebeest. Wildebeest can live more than 40 years, though their average lifespan is around 20 years.
Blackburnian warbler
Blackburnian warblers are small passerines and average-sized wood-warblers. They measure around long, with a wingspan, and weigh . The average mass of an adult bird is , although is slightly higher in fall due to fat reserves, averaging . Among standard measurements, the wing chord is , the tail is , the bill is and the tarsus is . In summer, male Blackburnian warblers display dark gray backs and double white wing bars, with yellowish rumps and dark brown crowns. The underparts of these birds are white, and are tinged with yellow and streaked black. The head is strongly patterned in yellow and black, with a flaming-orange throat. It is the only North American warbler with this striking plumage. Other plumages, including the fall male and adult female, are washed-out versions of the summer male, and in particular lack the bright colors and strong head pattern. The Blackburnian warbler is practically unmistakable if seen well, even the female due her dull-yellow supercilium, contrasting with greyish cheeks and yellow throat contrasting with the dark streaky sides and back. The only other wood-warbler with an orange throat is the flame-throated warbler of Central America and is very distinctive, lacking the contrasting blackish streaking about the head and whitish underside of a male Blackburnian. Basic plumages show weaker yellows and gray in place of black in the breeding male. Blackburnian warblers' songs are a simple series of high "swi" notes, which often ascend in pitch. Transliterations have included "zip zip zip zip zip zip zip zip", "titititi tseeeeee" or "teetsa teetsa teetsa teetsa". Their call is a high "sip". Genetic research has shown that their closed living relative is the bay-breasted warbler, the latter species perhaps specialized to forage in the same coniferous trees at lower levels. Hybridization in the wild has been recorded once each with a bay-breasted warbler (in West Virginia, with a black-and-white warbler (in Pennsylvania) and possibly a wintering hybrid with a Kirtland's warbler (in Hispaniola).