# Carbon and Nitrogen Stable Isotopic Discrimination Factors Between Diet and Feces in Wild Giant Pandas

## TL;DR

This study finds that carbon and nitrogen isotopes in panda feces can reveal their bamboo diet and seasonal changes, offering a non-invasive tool for studying their ecology.

## Contribution

The study reports the first fecal isotopic discrimination factors for wild giant pandas, revealing unique adaptations to their specialized bamboo diet.

## Key findings

- Carbon discrimination factor between diet and feces in pandas is nearly zero (0.6 ± 0.8‰).
- Nitrogen is significantly enriched in panda feces (Δ15Ndiet–feces = 2.1 ± 1.2‰).
- Panda fecal isotopes can effectively track seasonal dietary shifts.

## Abstract

This study employed carbon and nitrogen stable isotope analysis to determine the diet–feces discrimination factors (Δ) of wild giant pandas exclusively depending on bamboos. The results showed that the carbon discrimination factor between diet and feces (Δ13Cdiet–feces) was approximately zero (0.6 ± 0.8‰), while nitrogen was significantly enriched in feces (Δ15Ndiet–feces = 2.1 ± 1.2‰). These distinct values, which differ from those of typical herbivores, reflect the adaptation of the panda’s carnivore-derived digestive system to its highly specialized diet. This study demonstrated that panda fecal carbon isotopes can reliably record dietary shifts and provided crucial background data for applying stable isotope analysis to investigate the foraging ecology and conservation of this unique species.

Stable isotope analysis is very useful for studying animal nutritional ecology. Feces are the most accessible and non-invasive samples for short-term dietary reconstruction. The giant panda is a special Carnivora species with a highly specialized diet. However, no relevant research has yet explored the reliability of fecal isotopes in wild giant pandas, and the key parameter—fecal isotopic discrimination factors—remains unreported. Thus, we analyzed carbon and nitrogen isotopes of different bamboo species and parts with associated pandas’ feces collected from their foraging sites. The results showed carbon isotopes of shoots were more positive than those of leaves, and the isotopic composition of their feces can effectively reflect seasonal dietary shifts. The calculated fecal carbon discrimination factor was close to zero (Δ13Cdiet-feces = 0.6 ± 0.8‰), while the nitrogen DFs were significantly positive (Δ15Ndiet-feces = 2.1 ± 1.2‰). The typical metabolic pattern, physiological adaptations and distinctive microbiota of giant pandas contribute to the unique DFs different from those of other herbivores. These findings provide valuable short-term dietary records, key parameters for the application of fecal isotopes to interpret foraging strategies and nutritional status for an endangered species in the wild, expand the application of stable isotope methods in studies to specialized diet animals, and offer a reference for studies utilizing non-invasive materials in other mammals.