How the Egg Rolls: A Morphological Analysis of Egg Shape in the Context of Displacement Dynamics

• Main Author: Hays, Ian R.
• Format: Thesis
• Language: English
• Published: CUNY Academic Works 2018
• Subjects: Morphology; Egg Movement; Egg Shape; Nesting; Avian Eggs; Uria aalge; Auk; Shore Birds; Animal Studies; Behavior and Ethology; Integrative Biology; uria
• Online Access: https://academicworks.cuny.edu/hc_sas_etds/252; https://academicworks.cuny.edu/cgi/viewcontent.cgi?article=1281&context=hc_sas_etds

Very little is known about how morphology effects the motion, stability and the resulting viability of avian eggs. The limited research that exists focuses on the pyriform or ‘pointed’ egg shapes found in the Alcidea family. This unusual shell form is thought to suppress displacement and prevents egg loss on the cliffside nesting habitat of the Uria genera. Unfortunately, these studies never isolated or quantify the specific morphological features (elongation, asymmetry and conicality) of these pyriform eggs, which limits their applicability to other taxa and hampers a robust proof of concept. We isolated each feature as a variable, produced models with incremental expressions of a single variable, and then all three variables simultaneously. Motion trials were conducted to test the individual and combinatorial effects of each morphological characteristic on displacement, on a range of inclines representative of the conditions found in nesting habitats. Increasing elongation (width over length) and asymmetry (distance of the apical width of the egg to the blunt end over length) significantly increased displacement, while conicality (pointed end of the egg geometrically mimicking a cone) decreased displacement in the single variable egg-models. In the multi-variable egg models, only conicality constantly suppressed displacement, while lower levels of asymmetry significantly increases displacement. Our findings broadly support previous studies' assertions of the adaptive value of the pyriform eggs, while providing data for future analysis of interactions between nesting habitat, behavior and egg shape beyond the confines of the model species.