Isotope (δ¹³C, δ¹⁵N, δ²H) diet–tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

ABSTRACT

Diet–tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ¹³C, δ¹⁵N, and non-exchangeable δ²H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet–feather Δ¹³C and Δ¹⁵N discrimination values were +3.8 ± 0.3 ‰ and +6.3 ± 0.7 ‰ respectively; significantly greater than expected. Non-exchangeable δ²H feather values (−62.4 ± 6.4 ‰) were more negative than water (−26.1 ± 2.5 ‰) offered during feather growth. There was no positive relationship between the δ¹³C and δ¹⁵N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ²H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.

KEYWORDS:

• Africa
• birds
• carbon-13
• diet
• diet–tissue discrimination
• feathers
• forensic application
• hydrogen-2
• isotope ecology
• nitrogen-15
• parrots
• wild population

Acknowledgements

Mr Chris Boshoff (parrot owner) is thanked for access to captive birds to conduct the experiments. Amanda Greer is thanked for comments on an early draft of this manuscript. This study was conducted under animal ethics clearance (2014/21/B) from the Animal Ethics Screening Committee (AESC) of the University of the Witwatersrand, Johannesburg. Dr Grant Hall is thanked for the carbon and nitrogen isotope analyses. Two anonymous reviewers are thanked for a thorough critical assessment in helping improve this paper.

Disclosure statement

No potential conflict of interest was reported by the authors.