UC San Diego

Although the Brown Pelican wields one of the largest bills of any bird, it is distinguished by the deployable throat pouch of extensible tissue used to ‘net’ prey. Researchers have primarily focused on the bending mechanics that pelican bills demonstrate during feeding. While the mandible’s ability to endure hydrodynamic loading during plunge-diving has been reported on, little has been published on the pouch itself in the form of gular sac tissue characterization.

This thesis reports on mechanical testing and optical characterization of the pouch material, similar in scope and methods to recent studies at UCSD involving pig and rabbit skin. The data suggests a higher extensibility of the pelican skin to the pig using a limited comparison of fibril curvatures. TEM imaging provides microstructural evidence of the directionality of the collagen fibers. This, paired with the corrugated nature of the pouch material in the circumferential or expansive direction, elicits the anisotropic response observed in tensile testing. TEM also showed the dimensions of collagen fibrils to be similar in size to those in rabbits and pigs—suggesting the fibrils themselves are likely not the main reason for the enhanced extensibility observed beyond other skin types. Material characterization efforts focused on the impact of the following parameters: relative bird age, location on the pouch, and constant strain rate. Anteroposterior location and strain rate were not yet determined major influencers on exhibited strengths and extensibilities. However, bird age and dorsoventral location were found to affect the pouch material’s mechanical response significantly.