The Passive Perching Mechanism in Passeriformes Birds

Indianapolis, IN

Passeriformes, or perching birds and songbirds, are an order of birds that includes crows, jays, starlings, wrens, cardinals, finches and many other species. It has been suggested that these birds are able to passively perch due to a tendon locking mechanism. This allows them to rest for hours in trees without falling. When the bird's foot is placed on a perch, the weight of the bird causes the tendons to pull, thus closing the toes around the perch. However, there is currently much debate about whether the mechanism is entirely passive. Recent studies argue that the mechanism must be coupled with the active contraction of muscles. This study seeks to determine whether or not the perching mechanism in Passeriformes is passive through the analysis of morphological parameters of window-strike birds. Specifically, we looked at the angular changes of the toes as well as the distance between opposing toes, both when the foot is flexed and extended. Preliminary analysis of our results indicate decrease in many of the measured angles and distances as the foot changes from the extended to flexed position. Since this data was collected on dead birds, this suggests that the perching mechanism is in fact passive.