and the undertail is rufous, with white tips. The eye is surrounded by a thin white eye ring, and the iris is dark cinnamon or brown; the bill is dark horn-gray; the upper mandible cutting edge at the base is blue-gray, as is the entire lower mandible base. The legs are gray-brown or dark gray. The sexual dimorphism is not very marked, especially in summer when the plumage is worn, but the female's crown is less black and less sharply defined at the back, whereas the male's crown is sharply defined in glossy black Female underparts are paler and buff, while the male's are pure gray, verging to blue. The juvenile, on the other hand, is more easily distinguished, having much duller plumage and lacking the black crown; at most, the front of it is darker than the rest of the upperparts. Its russet pectoral patch is not very marked, as are the supercilium and the eyestripe. It can be distinguished from the adult female by its fresh plumage when the feathers of the latter are worn and its dark crown. Adults in their first year sometimes have some lingering brown on the feather tips of their greater coverts. Adults undergo a full post-nuptial moult (from mid-May to early September) and sometimes a partial moult before the breeding season (March), which particularly affects the chest. There is also a partial post-juvenile moult involving the middle coverts. With the front of the crown dark and the marked white supercilium, the Algerian nuthatch has cream or buff-colored underparts and lacks a large russet-brown pectoral patch. This patch is characteristic of the Krüper's nuthatch, as is the marked difference between adults and juveniles. Ecology and behavior The Krüper's nuthatch lives alone or in pairs during the breeding season, and the pair stays with their young. In autumn, it is observed in groups of two to five individuals, sometimes taking part in mixed-species foraging flocks. Vocalizations The Krüper's nuthatch is a noisy bird, and is often easily identified by its calls. The contact call is a dvui, sometimes made in a dui-dui-dui-dui series and reminiscent of the European greenfinch (Chloris chloris). When agitated, it produces a rough èèhch reminiscent of the Eurasian jay (Garrulus glandarius) or a dry puik. The song is a "tuituituituitui… nasal, alternating high and low notes", with variable rhythm. Food The Krüper's nuthatch is an active bird, and it finds