| Summary: | Ecologically, arid regions can be classified as temperate and hot,and arid or semiarid. The avifaunas of temperate arid and semiarid zones are subjected to seasonally-extreme temperature fluctuations, that necessitate (a) seasonal breeding and (b) a high incidence of migration. Such zones occur at high latitudes and high altitudes. Seasonal breeding is also a feature of birds inhabiting hot hyperarid regions such as the Namib and Atacama Deserts, where environmental cues other than photoperiod are largely absent and therefore irrelevant. Birds of hot deserts, although subject to erratic rainfall regimes,are usually able to capitalise on precipitation as a cue for breeding activity at any time of the year,although retaining an innate response to photoperiod under conditions of abundant food supply. The hot deserts of the northern hemisphere are nevertheless more seasonally variable than those of the southern hemisphere. Northern avifaunas therefore show characteristics that are more similar to those of temperate-desert avifaunas than to those of the southern hemisphere.
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