Many elements of mammalian and avian thermoregulatory mechanisms are present in reptiles, and the changes involved in the transition to endothermy are more quantitative than qualitative. Drawing on our experience with reptiles and echidnas, we comment on that transition and on current theories about how it occurred. The theories divide into two categories, depending on whether selection pressures operated directly or indirectly on mechanisms producing heat. Both categories of theories focus on explaining the evolution of homeothermic endothermy but ignore heterothermy. However, noting that hibernation and torpor are almost certainly plesiomorphic (=ancestral, primitive), and that heterothermy is very common among endotherms, we propose that homeothermic endothermy evolved via heterothermy, with the earliest protoendotherms being facultatively endothermic and retaining their ectothermic capacity for "constitutional eurythermy." Thus, unlike current models for the evolution of endothermy that assume that hibernation and torpor are specialisations arising from homeothermic ancestry, and therefore irrelevant, we consider that they are central. We note the sophistication of thermoregulatory behavior and control in reptiles, including precise control over conductance, and argue that brooding endothermy seen in some otherwise ectothermic Boidae suggests an incipient capacity for facultative endothermy in reptiles. We suggest that the earliest insulation in protoendotherms may have been internal, arising from redistribution of the fat bodies that are typical of reptiles. We note that short-beaked echidnas provide a useful living model of what an (advanced) protoendotherm may have been like. Echidnas have the advantages of endothermy, including the capacity for homeothermic endothermy during incubation, but are very relaxed in their thermoregulatory precision and minimise energetic costs by using ectothermy facultatively when entering short- or long-term torpor. They also have a substantial layer of internal dorsal insulation. We favor theories about the evolution of endothermy that invoke direct selection for the benefits conferred by warmth, such as expanding daily activity into the night, higher capacities for sustained activity, higher digestion rates, climatic range expansion, and, not unrelated, control over incubation temperature and the benefits for parental care. We present an indicative, stepwise schema in which observed patterns of body temperature are a consequence of selection pressures, the underlying mechanisms, and energy optimization, and in which homeothermy results when it is energetically desirable rather than as the logical endpoint.

A bstraclA colony site occupied by grey-headed flying-foxes (Pteropus poliocephalus) from October to May on the central coast of N.S.W. was monitored over a 48 month period (1986)(1987)(1988)(1989)(1990). Faecal and spat-out material was collected for microscopic determination of contents. Comparison of food items in the droppings with the array of possible food sources present in the vicinity of the colony at the same time showed a marked preference for certain foods, in particular blossoms of the family Myrtaceae and of the genus Banksia. Cultivated orchard fruits were not a preferred food and were only taken at times when preferred food items were scarce.1035-3712/91/0100111$05.00 K. Parry-Jones and M. L. Augee Food Selection by Flying-foxes

Abstract-1. The body temperatures of five echidnas in Australia's Southern Alps were monitored by radio telemetry from February to December 1987.2. All five hibernated throughout the winter, showing very low body temperatures (4-9°C, close to ambient) when torpid, compared with 28-33°C in a typical day during the active season.3. Spontaneous arousals from hibernation occurred every 2-3 weeks, during which body temperatures rose rapidly to over 30°C for several hours before dropping to be close to ambient again.4. The identification of "classical" hibernation in a monotreme, with a similar pattern to that seen in Eutheria and in an animal as large as the largest eutherian hibernator, has important implications for current ideas about the evolution of endothermy.

Movements and numbers of grey-headed flying foxes (Pteropus poliocephalus) were recorded in and around a colony site on the central coast of New South Wales over a period of 53 months from 1986 to 1990. Daily departures from the site correlated primarily with the time of sunset. Annual occupation cycles showed wide flutuations with only one fiied period, March-May, when a mating colony of at least 20 000 bats was at the site. In most years a small nursery colony was present during October- December. Superimposed on this reproductive use of the site were highly variable patterns of occupation correlated with fluctuations in food supply. Local abundances of blossoms such as Angophorafloribunda and Eucalyptus maculata resulted in colony numbers of at least 80 000 bats.

Previous authors have reported that Pteropus poliocephalus colony sites are occupied in response to blossom availability. However, in the present study it is reported that at the Gordon site in suburban Sydney, colony numbers were negatively correlated with the occurrence of pollen in the droppings. In addition, in contrast to reported occupational patterns at other colony sites, where flying-foxes are not present at the site during winter and early spring, the Gordon site was occupied by substantial numbers of flying-foxes throughout the entire period of 62 months from 1985 to 1990. As a result of the introduction of plants native to other parts of Australia and exotics from other continents, there is a variety of foods available throughout the year in the Sydney region, in comparison with less urbanized areas. This food supply permits the occupation of the Gordon colony site during winter and spring and reduces the migratory behaviour of flying-foxes throughout the year. It is concluded that in the absence of a restrictive food supply, the occupational pattern of the Gordon colony of P. poliocephalus is the result of the reproductive requirements of the species modified by the vagaries of blossom production in the native forests outside the foraging range of the colony.