Eastick et al 2019.pdf (1.74 MB)
Cassowary casques act as thermal windows
journal contributionposted on 2021-08-25, 01:27 authored by Danielle EastickDanielle Eastick, Glenn J Tattersall, Simon J Watson, John LeskuJohn Lesku, Kylie RobertKylie Robert
Many ideas have been put forward for the adaptive value of the cassowary casque; and yet, its purpose remains speculative. Homeothermic animals elevate body temperature through metabolic heat production. Heat gain must be offset by heat loss to maintain internal temperatures within a range for optimal performance. Living in a tropical climate, cassowaries, being large bodied, dark feathered birds, are under thermal pressure to offload heat. We tested the original hypothesis that the casque acts as a thermal window. With infrared thermographic analyses of living cassowaries over an expansive range of ambient temperatures, we provide evidence that the casque acts as a thermal radiator, offloading heat at high temperatures and restricting heat loss at low temperatures. Interestingly, at intermediate temperatures, the casque appears thermally heterogeneous, with the posterior of the casque heating up before the front half. These findings might have implications for the function of similar structures in avian and non-avian dinosaurs.
This research was supported by several Zoological Parks that gave us access to their cassowaries: Australia Zoo, Birdworld Kuranda, Cairns Tropical Zoo, Currumbin Wildlife Sanctuary, David Fleay Wildlife Park, Halls Gap Zoo, Hartley's Crocodile Adventures, Healesville Sanctuary, Melbourne Zoo, Rainforestation Wildlife Park and Wildlife Habitat. M. Symonds kindly provided advice, B. Eastick sketched the cassowary heads accompanying Fig. 4. The Peter Rawlinson award and the Richard Zann Bursary to D.E. and internal funding from La Trobe University Department of Ecology, Environment and Evolution to D.E., and K.R. and J.L. funded the project.
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