Abstract
Research into the terrestrial locomotion of birds is often based upon laboratory treadmill experiments. However, it is unclear how transposable these results are for birds moving in the wild. Here, using video recordings, we compared the kinematics of locomotion (stride frequency, stride length, stance phase, swing phase, duty factor) and speed range of Svalbard rock ptarmigan (Lagopus muta hyperborea) under field and laboratory treadmill conditions. Our findings indicate that the kinematics of walking and aerial running are conserved when moving on the treadmill and in the field. Differences, however, were found when grounded running under the two conditions, linked to substrate. Substrate effects were confirmed by analysing trials only moving over very hard snow. In line with laboratory treadmill energetic predictions, wild ptarmigan have a preferred speed during walking and to a lesser extent when aerial running but not when moving with a grounded running gait. The birds were also capable of a higher top speed in the field than that observed during treadmill studies. Our findings demonstrate that laboratory treadmill research provides meaningful information relevant to wild birds while highlighting the importance of understanding the substrate the animals are moving over.
Highlights
Research into the terrestrial locomotion of birds is often based upon laboratory treadmill experiments
Svalbard ptarmigan were selected for these studies as they are one of the few avian species where a comprehensive laboratory treadmill dataset exists on the kinematics and energetics of their locomotion[7]
Our findings show that the kinematics of locomotion in the Svalbard ptarmigan when walking and aerial running are conserved across laboratory treadmill and field datasets where the birds were moving over snow
Summary
Research into the terrestrial locomotion of birds is often based upon laboratory treadmill experiments. Our findings demonstrate that laboratory treadmill research provides meaningful information relevant to wild birds while highlighting the importance of understanding the substrate the animals are moving over. While treadmill studies have facilitated great insight into animal locomotion, they are conducted under idealised conditions[14,15] These basic tenants of experimental research allow specific parameters of interest to be manipulated without additional factor(s) confounding results. Preliminary attempts to analyse substrate effects on Svalbard ptarmigan locomotion[40] focused only on grass rather than the natural snowy substrate the birds move over in the wild and did not distinguish between the sexes Aside from these studies, comparative real-world data from birds moving over natural substrates are lacking. These data are important because without them it is impossible to determine, for example, what the potential impact might be of environmental change
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