Svalbard ptarmigan on the cover

Vocalizing rock Svalbard ptarmigan (Lagopus muta hyperborea) in winter plumage, illustrating key points of Wild Clock research. This high Arctic herbivore's circadian and seasonal time-keeping accommodates overwintering under extreme environmental conditions. Its flexible circadian system allows partial break-down of daily rhythmicity in Arctic midsummer and midwinter. A strong seasonal clock system times moult to anticipate snow cover; the birds alternate between brown summer and white winter camouflage, but rigid timing makes them vulnerable to altered seasonality. Ptarmigan also illustrate sexual selection on timing. Males maintain their conspicuous winter plumage longer than females, but reduce the heightened predation risk by soiling it when females can no longer be fertilized. Image © Stig Br√łndbo, UiT - The Arctic University of Norway.

This is the cover of the recently published theme issue ‘Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals’ in

Review article: Timing as a sexually selected trait: the right mate at the right moment
Michaela Hau, Davide Dominoni, Stefania Casagrande, C. Loren Buck, Gabriela Wagner, David Hazlerigg, Timothy Greives, Roelof A. Hut
Phil. Trans. R. Soc. B 2017 372 20160249; DOI: 10.1098/rstb.2016.0249. Published 9 October 2017