FIELD PRESERVATION TECHNIQUES FOR THE ANALYSIS OF STABLE-CARBON AND NITROGEN ISOTOPE RATIOS IN EGGS

Tissue preservation is a challenge faced by researchers collecting egg s in the field. Use of stable isotope analyses of eggs will undoubtedl y increase as a means to trace directly avian trophic relationships an d nutrient allocation to reproduction, and so field preservation techn iques that do not alter stable-isotope ratios are needed. We evaluated effects of several preservation techniques on stable-carbon (C-13/C-1 2) and nitrogen (N-15/N-14) isotope ratios in lipid-free yolk and albu men, and stable-carbon isotope ratios in yolk lipid. Drying, freezing, boiling then freezing eggs, and storage of egg components in 70% etha nol did not alter stable-carbon and nitrogen isotope abundance in egg components, and we recommend these preservation techniques prior to is otopic analysis. Boiling eggs prior to freezing facilitates future sep aration of albumen and yolk. Maintaining boiled eggs at 6 C for 7 d re duced C-13 abundance in lipid-free yolk, while maintenance at 6 C for 50 d increased N-15 abundance in albumen. Preservation in Formalin sho uld be avoided as it reduced C-13 abundance in lipid-free yolk and alb umen but did not affect yolk lipids.