Pilansberg Nature Reserve Series. Description and ecology This is a family of insect and seed-eating, ground-nesting birds resembling partridges, but with featherless heads and spangled grey plumage. At least three of the species are poorly studied. Helmeted Guineafowl from Namibia. Helmeted Guineafowl from Namibia. The species for which the information is known are normally monogamous, mating for life. However, occasional bigamy has been recorded for the Helmeted Guineafowl (Madge and McGowan, p345-352). They are large birds which measure from 40-71 cm in length, and weigh 700-1600 g. The Helmeted Guineafowl has been domesticated and introduced outside its natural range, for example in southern France, the West Indies, and esp. the United States. The American Ornithologists' Union includes guineafowl (Numididae) as a subfamily of Phasianidae.