Achromatic plumage patch quality: internal organ and skeletal correlates in Aleutian cackling geese (Branta hutchinsii leucopareia)

• Main Author: Delgado, Matthew D
• Format: Text
• Language: unknown
• Published: Digital Commons @ Cal Poly Humboldt 2019
• Subjects: Humboldt; Sexual selection; Achromatic; Ornaments; Honest signal; Status signal; Honest advertisement; Behavior and Ethology; Branta hutchinsii leucopareia
• Online Access: https://digitalcommons.humboldt.edu/etd/307; https://digitalcommons.humboldt.edu/cgi/viewcontent.cgi?article=1354&context=etd

Sexual selection theory predicts unique plumage patches signaling quality or status evolve via mate-choice and competition for mates. A growing body of research supports evidence that achromatic plumage patches may act as honest indicators of quality. Irregularities in these patches are attributed to an individual’s phenotypic and genotypic quality as well as environmental wear and tear. Aleutian cackling geese (Branta hutchinsii leucopareia) display achromatic plumage patches on their heads and necks, which may signal information about an individual’s attributes. I tested the honest advertisement and status signaling hypotheses by determining whether size and irregularities in the transition between black and white edges of plumage patches (i.e., immaculateness, or smoothness of borders) were correlated to indices of individual quality. Organ mass was used as an index to indicate energy acquisition, aerobic function, and immunocompetence. More specifically, I examined the linear relationship between plumage patch morphometries and gizzard, heart, liver, and spleen mass. I also examined the linear relationship of plumage patch morphometries and the size of the processes extensors (wing spur). Smoothness in lower neck-ring borders in both sexes was positively correlated with gizzard size, supporting a prediction of the honest advertisement hypothesis. Cheek patch size was correlated with wing spur size in males, which supports the status-signaling hypothesis (e.g., fighting prowess). The distribution of lower neck-ring smoothness was unit-modal in males, indicating a strong selection via female mate choice for little variation in this attribute. Lower neck-ring smoothness was multi-modal in females, supporting a prediction of the individual identity hypothesis. Different attributes of achromatic plumage patches found on Aleutian geese may signal separate and distinct information in intra- and intersexual communication.