4. CLIMPSES OF THE NARINA TROGON

Bertram, B. C. R. &; Burger, A. E. 1981. Aspects of incubation in Ostriches. Ostrich 52:36-43.

We studied incubation in domesticated Ostriches Struthio camelus in South Africa and wild Ostriches in Kenya. Although the eggs were large, with relatively high thermal capacities, unattended eggs exposed to the sun reached dangerously high temperatures (40,5°C). Experimental exposure of fresh eggs to the sun for seven days prior to incubation greatly reduced the percentage of embryos which developed, and no embryos survived 15 days of exposure. In the wild. Ostriches frequently shade their eggs in the pre-incubation period to prevent overheating.

During natural incubation, temperatures in the eggs (range 30,8-33,8°C) and of nest-air (31,9-34,6°C) were remarkably constant, despite the daily ambient fluctuations of air temperatures (17,8-38,9°C). Similarly the humidity of the nest-air (39–52%) was lower and less variable than the ambient air (39–72%). Water loss during 42 days of incubation was 11–12% of initial egg weight and, in addition, early laid eggs lost 3–4% during the 2½-3 week pre-incubation period. The water vapour conductivity and the daily water loss of Ostrich eggs were similar to those of other birds, in proportion to epg size, despite the arid environment inhabited by Ostriches. Some of the constraints on the feeding and breeding behaviour of Ostriches imposed by the physical requirements of their eggs are discussed.