Locomotor development in the Svalbard rock ptarmigan (Lagopus muta hyperborea)

Juvenile animals often suffer from high levels of predation. Development of an effective and efficient locomotor system is therefore likely to be crucial towards ensuring their survival. However, our understanding of locomotor efficiency, at least in terms of energetic cost in young animals is poor. We performed this study as Svalbard rock ptarmigan, Lagopus muta hyperborea must rapidly develop the ability to locomote prior to the onset of their first winter, during which conditions are extreme. To aid survival, adult ptarmigan deposit large winter fat stores, whilst at the same time males exhibit a reduced metabolic cost of locomotion. Sub-adult males, however, are unable to fully acquire fat stores during their first winter and the maturity of their locomotor systems is unknown. Here, we investigate the energetics and kinematics of terrestrial locomotion in sub-adult male birds using flow-through respirometry and high-speed video recordings, respectively. We demonstrate that in terms of running speed and metabolic cost, sub-adult ptarmigan develop a mature functioning locomotor system prior to the onset of winter. This research indicates that achieving a mature locomotor system allows young males to emerge from the winter with the ability to compete for territories and mates during the breeding season.