Study of the microstructure and mechanical properties of hummingbird wing-bones

Abstract

A study of the microstructural and mechanical properties of wing bones of an Anna's hummingbird (Calypte Anna) and a tree swallow (Tachycineta bicolor) was conducted to determine whether the hummingbird bones exhibited unique features due to the high wing loading of the bird. It was hypothesized that the hummingbird's ability to hover, flapping its wings at an incredible rate, would create higher principal stresses that would require an internal bone structure notably different from that of the swallow. Micro-computed tomography, scanning electron microscopy, and nano-indentation experiments were conducted to determine if such anomalies existed. Additional macroscale measurements were taken to compare relative proportions of each of the bones of interest, which included the humerus, radius, and ulna. Upon examining the images produced via micro-computed tomography and scanning electron microscopy, it was found that trabecular bone was present, suggesting the mechanical advantages of the trabeculae were required. Nano-indentation results proved to be relatively inconclusive, but generally provided results reasonably close to expected literature values. Further experimentation would be required to determine if the deviation from expected values were meaningful.