Assessing Avian Diets Using Stable Isotopes I: Turnover of¹³C in Tissues

TLDR

Stable‑isotope studies in birds require estimates of how quickly tissue isotopes are replaced, yet turnover rates are poorly understood. The study proposes using stable‑isotope analysis to quantify endogenous versus exogenous nutrient contributions to feather growth and egg production in captive and wild birds. The authors measured 13C turnover in Japanese quail tissues by switching from a wheat‑based (C3) to a corn‑based (C4) diet over 212 days, and performed a similar diet‑switch experiment on American crow feathers. Exponential models showed that 13C turnover rates varied across tissues, with liver > blood > muscle > bone collagen and half‑lives from 2.6 days in liver to 173.3 days in bone collagen, while crow feather isotope values tracked diet during feather growth.

Abstract

Studies of birds that use stable isotopes as dietary tracers require estimates of how quickly stable isotopes in tissues are replaced by isotopes derived from the diet. However, isotopic turnover rates in animals in general, and birds in particular, are poorly understood. We established the turnover rates of 13C in tissues of grown Japanese Quail (Coturnix japonica) by switching the diet of an experimental group from a wheat-based (C3) diet to a corn-based (C4) diet and sampled tissues periodically for 212 days. An exponential model described patterns of isotopic turnover in all tissues. Turnover rates for quail tissues were ranked liver > blood > muscle > bone collagen with the half life of carbon ranging from 2.6 days in liver to 173.3 days in bone collagen. A similar diet-switch experiment was conducted on captive American Crows (Corvus brachyrhynchos) and feather samples were assayed isotopically. Stable isotope values of crow feathers reflected diet during periods of growth. We suggest that stable isotope analysis could be used to determine relative contributions of endogenous and exogenous nutrient sources for feather growth and egg production in captive and wild birds.