References
- ACOCKS, J. P. H. 1975. Veld types of South Africa. Mem. bor. Surv. S. Afr. 40: 1–128.
- BAKER, J. R. 1938. The evolution of breeding seasons. In Evolution, essays on aspects of evolu tionary biology presented to G. B. Goodrich, ed. G. R. de Beer: 161–177. Oxford.
- BROEKHUYSEN, G. J. 1959. The biology of the Cape sugarbird, Promerops cafer L. Ostrich, Suppl. 3: 180–221.
- CALDER, W. A. 1971. Temperature relationships and nesting of the Calliope hummingbird. Condor, 73: 314–321.
- CALDER, W. A. 1973a. Microhabitat selection during nesting of hummingbirds in the Rocky Mountains. Ecology, 54 : 127–134.
- CALDER, W. A. 1973b. An estimate of the heat balance of a nesting hummingbird in a chilling climate. Comp. Biochem. Physiol. 46: 291–300.
- DRENT, R. H. 1973. The natural history of incubation. In Breeding biology of birds, ed. D. S. Famer : 262–311. Washington, D.C.: Nat. Acad. Sciences.
- DRENT, R. H. & STONEHOUSE, B. 1971. The thermoregulatory responses of the Peruvian penguin, Spheniscus humboldti. Comp. Biochem. Physiol. 40: 689–710.
- FUGGIE, R. F. 1970. A computer programme to determine the direct shortwave income on slopes. dim. Bull. McGill Univ. 7: 8–16.
- GEIGER, R. 1965. The climate near the ground. Cambridge: Harvard Press.
- HILDEN, O. 1965. Habitat selection in birds. Ann. Zool. Fenn. 2: 53–75.
- KENDEIGH, S. C. 1970. Energy requirements for existence in relation to size of bird. Condor, 72: 60–65.
- LOWRY, W. P. 1969. Weather and life. New York: Academic Press.
- MCLACHLAN, G. R. & LIVERSIDGE, R. 1970. Roberts birds of South Africa, 3rd ed. Johannesburg: C.N.A.
- MITCHELL, B. L. 1966. Orientation of nests of the white-browed sparrow weaver. Pau, 4: 167–170.
- MONTEITH, J. c. 1973. Principles of environmentalphysics. London: Arnold.
- ORIANS, G. H. 1971. Ecological aspects of behaviour. In Avian biology, eds. D. S. Famer & J. R. King, 1: 513–546. New York: Academic Press.
- PORTER, W. P. & GATES, D. M. 1969. Thermodynamic equilibria of animals with environment. Ecol. Monogr. 39: 227–244.
- PRESTON, F. W. 1946. Nesting heights of birds building in shrubs. Ecology, 27: 87–91.
- PRESTON, F. W. & NORIUS, R. T. 1947. Nesting heights of breeding birds. Ecology 28: 241–273.
- RICKLEFS, R. E. & HAINSWORTH, F. R. 1969. Temperature regulation in nesting cactus wrens: the nest environment. Condor, 71: 32–37.
- SOKAL, R. R. & ROBLE, F. J. 1969. Biometry, the principles and practice of statistics in biological research. San Francisco: Freeman & Co.
- STURMAN, W. A. 1968. Description and analysis of breeding habitats of the chickadees, Parus atricapellus and P. rufescens. Ecology, 49: 418–43].
- WINTERBOTTOM, J. M. 1962. Breeding season of the long-tailed sugarbird Promerops cafer. Ostrich, 33: 77.