81.4 Friday, Jan. 6 Anatomy of a shrike bite: force, speed, and pressure in relation to bill shape in loggerhead shrikes (Passeriformes: Laniidae: Lanius ludovicianus) SUSTAITA, Diego*; RUBEGA, Margaret; University of Connecticut; University of Connecticut email@example.com
Shrikes are small predatory passerines that feed on arthropods and vertebrates, and rely heavily on their beaks for catching, killing, and processing their prey prior to feeding. Given the importance of bill shape for feeding in birds in general, and the unusual nature of their bill for a passerine (e.g., a curved, hooked maxilla with tomial teeth) it stands to reason that variation in the shape of the maxilla should have important functional implications. Our previous analysis of upper bill shape in museum specimens suggested that most of the variation in shape is characterized by four main axes along which populations, subspecies, and species differentiate: hook length, maxillary depth, distal hook curvature, and dorsal culmen curvature. Here we examine the functional consequences of this intra- and interspecific variation in shape. We measured voluntary bite force, speed, and pressure of wild-caught loggerhead shrikes using force and pressure transducers coupled with high-speed digital videography, and extracted digital images of their bills for further geometric morphometric analysis. We tested for relationships among aspects of bill morphology (e.g., shape) and bite performance (e.g., force) to examine potential trade-offs in bill form and function. Certain characteristics, such as a longer bill hook, that may be favorable for seizing and processing vertebrate prey, may be disadvantageous for the production of powerful bite forces important for subduing and dispatching them (e.g., due to greater risk of fracture). Thus, predictions for morphology and performance may lead in opposite directions, resulting in complex interactions between them.