Fig. 1
From: Examining the accuracy of trackways for predicting gait selection and speed of locomotion
Trackways of the Svalbard Rock Ptarmigan. a length (FL), Stride length (lstride) and Hip Height (h) are used to estimate speed. h is the distance to the top of the hip perpendicular to ground. This measurement however, is entirely dependent on accurate joint angles of the leg bones. As illustrated, a small alteration in joint angle results in different hip height measurements (h < h’). It has been suggested that four times FL can be used as a proxy of effective hip height however this method is also prone to error when applied to extinct animals where there is no information on the joint angles. Digits are numbered 1–4 for analysis as indicated. b Speed (U) predictions from stride length (lstride) using the ptarmigan species-specific model. The stars represent the data determined from video recordings and the filled circles represent the predicted value for a given lstride for 50 birds calculated from trackways that corresponded to the video recordings. Red, green and blue represent walking, grounded running and aerial running gaits, respectively. The coloured area delimited by the dashed lines represents the predictive interval for the lines of best fit (corresponding to the filled circles) described by the following equations: U = 3.20 lstride – 0.23 (walking), U = 2.34 lstride + 0.34 (grounded running) and for aerial running is U = 4.29 lstride – 0.03 (aerial running)