Date of Award


Degree Type


Degree Name

Honors Thesis



First Advisor

Shelley Etnier


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 mechanism 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, I looked at the angular changes of the toes as well as the distance between opposing toes, both when the foot is flexed and extended. My results support the hypothesis that the perching mechanism includes both passive and active elements. The foot visibly closed as the leg was flexed and the changes in the angles and distances were significantly different. Thus, there is undoubtedly part of the mechanism that is passive. However, it is possible that active mechanisms, such as muscular contractions, would make the closing of the foot more pronounced.