Experimental Evaluation of δ2H, δ13C and δ15N Variability in Blood and Feathers of Wild and Captive Birds: Implications for Interspecific Food Web Studies

Stable-hydrogen (delta H-2), nitrogen (delta N-15), and carbon (delta C-13) isotopes are used to decipher broad movement patterns and trophic relationships among diverse species, and an improved understanding of factors controlling natural variation in tissue-isotope measurements will enhance these applications. To evaluate the rearing environment and family-related effects on the isotopic composition of tissues, we cross-fostered nestling tree swallows (Tachycineta bicolor, Vieillot 1808) and American kestrels (Falco sparverius, Linnaeus 1758) by swapping recently hatched birds (< 4 days old) among nest boxes and collecting blood and feathers prior to fledging. To assess developmental effects, we measured delta H-2 in blood and feathers of captive mallard (Anas platyrhynchos, Linnaeus 1758) ducklings challenged energetically during growth. Stable isotope composition was not strongly related to nest box type or natal nest (i.e., family of origin) effects in swallows and kestrels; tissue-isotope composition was related to rearing environment, indicative of differences in nest and parental quality or parental provisioning tactics. Blood and feather delta H-2 values in swallows were positively related to antecedent maximum ambient temperature, and unrelated to elevated energy expenditure in mallards. The average differences between delta H-2 in blood and feathers were similar for nestling swallows (27 parts per thousand, 32 parts per thousand; two sites) and mallards (26 parts per thousand, 30 parts per thousand; two age groups), and lower than in nestling kestrels (50 parts per thousand). Strong species-specific patterns in blood-feather differences were not observed for delta N-15 and delta C-13 in swallows or kestrels; divergent delta H-2 results may be related to differences in nest ambient conditions, diet composition, or physiological processes affecting hydrogen assimilation during growth and feather synthesis. In swallows, tissue-isotope values reflected parental prey selection from spatially distinct food webs during nestling development with little effect(s) of family of origin, egg composition, or early growth.

Automated summary

Stable isotopes of hydrogen, nitrogen, and carbon are used to analyze movement patterns and trophic relationships among different species. The study found that rearing environment and family-related effects can influence the isotopic composition of tissues. The isotopic composition of swallows and kestrels was affected by the rearing environment, while the isotopic composition of mallards was influenced by energy expenditure.