The Alpine chough is socially monogamous, showing high partner fidelity in summer and winter and from year to year. Nesting typically starts in early May, and is non-colonial, although in suitable habitat several pairs may nest in close proximity. The bulky nests are composed of roots, sticks and plant stems lined with grass, fine twiglets or hair, and may be constructed on ledges, in a cave or similar fissure in a cliff face, or in an abandoned building. The clutch is 3–5 glossy whitish eggs, averaging in size, which are tinged with buff, cream or light-green and marked with small brown blotches; they are incubated by the female for 14–21 days before hatching. The chicks hatch with a dense covering of natal down, in contrast to those of the red-billed chough which are almost naked, and fledge in a further 29–31 days from hatching. The young birds are fed by both parents, and may also be fed by other adults when they have fledged and joined the flock. Breeding is possible in the high mountains because chough eggs have relatively fewer pores than those of lowland species, and lose less water by evaporation at low atmospheric pressure. The embryos of bird species that breed at high altitude also have haemoglobin with a genetically determined high affinity for oxygen.