Energetics and body temperature regulation in two convergent dove species from extreme habitats

The small Australian Diamond Dove Geopelia cuneata (38 g) and African Namaq ua Dove Oena capensis (36 g) live in desert and semi-desert habitats. They can be regarded as ecological counterparts on the two continents. They are both diurnal and active even throughout the hottest part of the day. Theref ore, they regularly encounter extremely high temperatures (up to 60-70 degr ees C), especially when feeding on the hot ground. Metabolic rates (MR) of both species are 20-50% below expected values. This has been described for other desert pigeons before, while species from temperate regions have MR i n the expected range of all birds. Both species tolerate elevated body temp eratures (T-b; up to 44.8 degrees C) under high external heat load. Additio nally, they show effective heat loss mechanisms (panting, gular flutter) so that metabolic heat is dissipated as fast as it is produced by the organis m without a further rise in body temperature. These physiological character istics enable them to be active and forage on the ground throughout the day even when temperatures are highest. The two dove species are opportunistic breeders in adaptation to the unpredictable climatic conditions in their h abitat. This can be seen from their fast pre- and postnatal development: Th e nestling time and total energy investment per juvenile are only 50% of th e values expected for tropical birds. Thus, several broods can be raised un der favourable conditions, especially when rainfall occurs.