The insect- and seed-eating, ground-nesting birds of this family resemble partridges, but with featherless heads, though both members of the genus Guttera have a distinctive black crest, and the vulturine guineafowl has a downy brown patch on the nape. Most species of guineafowl have a dark grey or blackish plumage with dense white spots, but both members of the genus Agelastes lack the spots. While several species are relatively well known, the plumed guineafowl and the two members of the genus Agelastes remain relatively poorly known. These large birds measure 40–71 cm (15+1⁄2–28 in) in length, and weigh 700–1,600 g (1 lb 9 oz – 3 lb 8 oz). Guinea hens weigh more than guinea cocks, possibly because of the larger reproductive organs in the female compared to the male guinea fowl. Also, the presence of relatively larger egg clusters in the dual-purpose guinea hens may be a factor that contributes to the higher body weight of the guinea hens.