Assessing the effect of feather wear on carbon and nitrogen stable isotope ratios, and the use of stable isotopes to determine predator diets in the Namibian Islands marine protected area

• Main Author: Johnson, Laurie
• Other Authors: Ryan, Peter, Connan, Maëlle
• Format: Master Thesis
• Language: English
• Published: Faculty of Science 2019
• Subjects: science; Rockhopper penguin
• Online Access: http://hdl.handle.net/11427/31248; https://open.uct.ac.za/bitstream/11427/31248/1/thesis_sci_2019_johnson_laurie.pdf

The stable isotope (SI) approach is widely used in ecological research to tackle problems such as delineating food web structure or tracing the migratory origins of various organisms. This thesis first tested the widely accepted assumption that SI ratios are fixed in an inert tissue, and then used the SI approach to infer the food web structure, from a marine top predator point of view, of a profoundly impacted marine ecosystem off southern Namibia. In bird research, it is assumed that SI ratios are fixed in feathers once they have completed their growth during moult. This assumption is crucial in determining where birds moult, and has been used to infer changes in the environment over time, as well as changes in the trophic levels of individuals. Recent comparisons of feathers collected from several penguin species during their annual moult have shown systematic differences between newly moulted and old feather SI ratios. I thus tested whether a change in SI ratios occurs as feathers age by comparing the carbon and nitrogen SI ratios of black and white feathers collected from captive, individually known African (Spheniscus demersus) and northern rockhopper (Eudyptes moseleyi) penguins at three occasions over a year. I found a clear trend for the rockhopper penguin feathers with new and old black feathers differing in their δ13C and δ15N values; this trend was not as clear for the African penguins. I then tested factors related to feather wear as a possible mechanism for differences in SI ratios between new and old feathers; these factors were feather reflectance and microstructure. In both penguin species, old black feathers reflected more light, and had a larger proportion of their barbs without barbules near their tips compared to new feathers. Feather wear may result in melanin leakage, which may explain the observed trends in the SI ratios between new and old pigmented penguin feathers. Differences in SI values were observed between species and may be a result of facility at which the penguins were housed, ...