Little is known about the effects of temperature extremes on natural systems. This is of increasing concern now that climate models predict dramatic increases in the intensity, duration and frequency of such extremes. Here we examine the effects of temperature extremes on behaviour and demography of vulnerable wild flying-foxes ( Pteropus spp.). On 12 January 2002 in New South Wales, Australia, temperatures exceeding 42°C killed over 3500 individuals in nine mixed-species colonies. In one colony, we recorded a predictable sequence of thermoregulatory behaviours (wing-fanning, shade-seeking, panting and saliva-spreading, respectively) and witnessed how 5–6% of bats died from hyperthermia. Mortality was greater among the tropical black flying-fox, Pteropus alecto (10–13%) than the temperate grey-headed flying-fox, Pteropus poliocephalus (less than 1%), and young and adult females were more affected than adult males (young, 23–49%; females, 10–15%; males, less than 3%). Since 1994, over 30 000 flying-foxes (including at least 24 500 P. poliocephalus ) were killed during 19 similar events. Although P. alecto was relatively less affected, it is currently expanding its range into the more variable temperature envelope of P. poliocephalus , which increases the likelihood of die-offs occurring in this species. Temperature extremes are important additional threats to Australian flying-foxes and the ecosystem services they provide, and we recommend close monitoring of colonies where temperatures exceeding 42.0°C are predicted. The effects of temperature extremes on flying-foxes highlight the complex implications of climate change for behaviour, demography and species survival.

Defeating the Cuckoo: Brood parasite-host interactions show ongoing antagonistic coevolution. What mediates rapid behavioral changes that do not reflect genetic change? Davies and Welbergen (p. 1318 ) show that reed warblers learn from their neighbors to behave aggressively toward models of the parasitic common cuckoo. Furthermore, reed warblers seem to be predisposed to learn to respond to cuckoos as enemies: Hosts that witnessed neighbors mobbing a harmless parrot model did not increase their aggression toward a cuckoo model. Thus, birds have templates for threats, and relevant antithreat behaviors can be turned on or off depending on social experience.