Tissue Discrimination Factors Research Articles

Diet–tissue discrimination factors and turnover rates of carbon and nitrogen stable isotopes in the mottled skate Beringraja pulchra based on diet-switching experiments

Stable isotope analysis is robust tool to elucidate the diet, trophic position, and migration of typically large, highly mobile marine predators such as elasmobranchs. However, it is necessary to understand the diet–tissue discrimination factors and isotopic turnover rates of target animals. In this study, diet-switching experiments were conducted on the mottled skate (Beringraja pulchra (Liu, 1932)), caught off Sarufutsu, Hokkaido, Japan, to elucidate the diet–tissue discrimination factors and isotopic turnover rates for carbon and nitrogen stable isotopes. Ninety juvenile skates were fed Euphausia superba (C:N ratio = 3.9 ± 0.06, δ15N = 3.7±0.26‰ and δ13C = –25.9±0.15‰) to satiation at intervals of 2–3 days, and their muscle and liver tissues were serially sampled during 400 experimental days and used for stable isotope analysis. Both carbon and nitrogen stable isotopes reached steady state within the experimental days, and the estimated diet–tissue discrimination factors based on the fitting models were Δ13C = 1.5‰ and Δ15N = 2.3‰ for liver tissues and Δ13C = 3.4‰ and Δ15N = 3.5‰ for muscle tissues. The estimated turnover rates were 0.034 day–1 for δ13C and 0.039 day–1 for δ15N for liver tissues and were higher than those for muscle tissues (0.021 day–1 for δ13C and 0.019 day–1 for δ15N). In addition, the growth-based isotopic turnover rate model comprising juvenile skates revealed that the contribution of growth rate to the isotopic turnover rate was low.

Terrestrial Diet Dependence in an Unprotected Nile Crocodile (Crocodylus niloticus) Population

Nile Crocodile (Crocodylus niloticus) populations that exist outside of protected areas are under threat in South Africa. They are believed to predominantly feed on fish, but they also take prey from the terrestrial system, which brings them into conflict with humans and hampers their management. Here, we use stable light isotope analysis to explore the diet of an unprotected Nile Crocodile population in the Olifants River, Mpumalanga and Limpopo Provinces. Nitrogen stable isotope ratios were obtained from fish and crocodile populations along the length (±430 km) of the river. The catchment is severely polluted with elevated d15N values at nutrient hotspots, which provides a basis for tracking the trophic response of crocodiles to the longitudinal profile of fish d15N values. Crocodiles did not respond to changes in the d15N values of fish populations and dietary predictions based on size-specific diet to tissue discrimination factors suggests a nonaquatic food base. These results suggest terrestrial diet dependence in one of the few viable Nile Crocodile populations from outside protected areas, posing unique challenges to their conservation.

Turnover Rates and Diet-Tissue Discrimination Factors of Nitrogen and Carbon Stable Isotopes in Seahorse Hippocampus reidi Juveniles Following a Laboratory Diet Shift.

Simple SummaryThe main aim of the present study was to ascertain the effect of two feeding schedules (including copepods and Artemia nauplii) on the early development and physiology of seahorse Hippocampus reidi juveniles. For that, we analyzed seahorse performance (growth and survival) and trophic patterns by means of stable isotopes. Our results highlight that the welfare and condition of juveniles were enhanced by extending the period of feeding on copepods up to day 10 after the male’s pouch release. The analysis of turnover rates for δ13C and δ15N revealed that switching copepods to Artemia nauplii at earlier developmental stages would reduce prey assimilation resulting in lower growth rates and survivals. The present study also provides for the diet–tissue discrimination factors for δ13C and δ15N in seahorse juveniles for the first time.The initial development of seahorse juveniles is characterized by low digestion capabilities. Stable isotope analysis is an effective tool in studies of trophic food webs and animal feeding patterns. The present study provides new insights for the understanding of growth and food assimilation in early developing seahorses following a laboratory diet switch. The study was performed in the early life stages of the seahorse Hippocampus reidi by assessing the influence of diet shift on changes and turnovers in carbon (δ13C) and nitrogen (δ15N) stable isotope in juveniles. Newborn seahorses were fed for 60 days following two feeding schedules (A6 and A11) based initially on copepods Acartia tonsa and subsequently on Artemia nauplii (since days 6 and 11, respectively). After the prey shift, we determined δ13C and δ15N turnover rates as functions of change in either body mass (fitting model G) and days of development (fitting model D), contributions of metabolism and growth to those turnover rates, and diet–tissue discrimination factors. Survival, final dry weight, and final standard length for diet A11 were higher compared to diet A6. The shift from copepods to Artemia led to fast initial enrichments in δ13C and δ15N. Afterwards, the enrichment was gradually reduced until the isotopic equilibrium with the diet was reached. In most cases, both fitting models performed similarly. The isotopic analysis revealed that 100% of tissue turnover was attributed to growth in diet A11, whereas 19–25% was linked to metabolism in diet A6. Diet–tissue discrimination factors were estimated for the first time in seahorse juveniles, resulting in higher estimates for diet A11 (2.9 ± 0.7‰ for δ13C; 2.5 ± 0.2‰ for δ15N) than in diet A6 (1.8 ± 0.1‰ for δ13C; 1.9 ± 0.1‰ for δ15N). This study highlights the relevance of feeding on copepods and their effect on isotopic patterns and discrimination factors in seahorse juveniles after a dietary shift. Regarding the application of the results achieved in relation to the feeding schedules in the rearing of H. reidi, a long period of feeding on copepods during the first days of development is highly recommended.

African wild dogs (Lycaon pictus) show differences in diet composition across landscape types in Kruger National Park, South Africa

Abstract The Kruger National Park (KNP) is home to the last genetically viable, minimally managed population of African wild dogs (Lycaon pictus, wild dogs) in South Africa. Until 2004, this population remained stable, but since has been declining. In this study, we aimed to improve our understanding of the ecology of KNP wild dogs by estimating the relative contribution of different prey types to their diet across landscape types. Based on a Bayesian mixing model, we assessed wild dog diet and foraging preferences using stable isotope analysis. We sampled 73 individuals from 40 packs found in six different landscape types. In thickets, packs predominantly prey on small browsing and mixed-feeding species (accounting for ~73% of their diet), but occasionally hunt large grazers (~24%) and large browsers (~3%). In open landscape types where lions (Panthera leo) are more or less absent, such as in the Lowveld sour bushveld, wild dogs prey on large browsers and large grazers (~67%). Our results demonstrate that KNP wild dogs occupy a broader ecological niche than previously thought, with small browsers forming an integral part of their diet. We also present the first data describing differences in wild dog diet–tissue discrimination factors for tail hair and whiskers compared to respective stable nitrogen (δ15N) and carbon (δ13C) values obtained from feces of captive wild dogs, as well as from those of South Africa’s broader managed metapopulation. While these data should be considered preliminary, we suggest that until wild dog diet–tissue discrimination factors are calculated through a controlled feeding study, the discrimination factors calculated for the gray wolf (Canis lupus) should be used for wild dog-related isotope studies, rather than the often cited values for red foxes (Vulpes vulpes).

Diet‐tissue discrimination and turnover of δ13C and δ15N in muscle tissue of a penaeid prawn

RationaleStable isotopes are used to study trophic and movement ecology in aquatic systems, as they provide spatially distinct, time‐integrated signatures of diet. Stable isotope ecology has been used to quantify species‐habitat relationships in many important fisheries species (e.g., penaeid prawns), with approaches that typically assume constant values for diet‐tissue discrimination and diet‐tissue steady state, but these can be highly variable. Here we provide the first report of these processes in Metapenaeus macleayi (eastern school prawn).MethodsHere we explicitly measure and model carbon (δ13C) and nitrogen (δ15N) diet‐tissue discrimination and turnover in eastern school prawn muscle tissue as a function of experimental time following a change in diet to an isotopically distinct food source.ResultsDiet‐tissue discrimination factors were 5 and 0.6‰ for δ13C and δ15N, respectively. Prawn muscle tissue reached an approximate steady state after approximately 50 and 30 days for δ13C and δ15N. Half‐lives indicated faster turnover of δ15N (~8 days) than δ13C (~14 days).ConclusionsOur diet‐tissue discrimination factors deviate from ‘typical’ values with larger values for carbon than nitrogen isotopes, but are generally similar to those measured in other crustaceans. Similarly, our estimates of isotopic turnover align with those in other penaeid species. These findings confirm muscle tissue as a reliable indicator of long‐term diet and movement patterns in eastern school prawn.

Telemetry‐validated nitrogen stable isotope clocks identify ocean‐to‐estuarine habitat shifts in mobile organisms

Abstract Throughout their life history, many animals transition among heterogeneous environments to facilitate behaviours such as reproduction, foraging and predator avoidance. The dynamic environmental and biological conditions experienced by mobile species are integrated in the chemical composition of their tissues, providing retrospective insight into movement. Here, we present a unique application of nitrogen stable isotope clocks (‘isotopic clocks’), which integrate tissue turnover rates, consumer stable isotope ratios and habitat‐specific isotope baselines to predict time‐since‐immigration and the timing of habitat shifts in a migratory species. Nitrogen stable isotope values of blood plasma collected from juvenile sand tiger sharks Carcharias taurus, a species known to undertake seasonal movements between ocean and estuarine environments, were used to derive estimates of time‐since‐immigration and the timing of seasonal habitat shifts undertaken by this species. Nitrogen isotopic clocks estimated for 65 juvenile sand tiger sharks sampled across 6 years indicated that individual sharks predominantly arrived to estuarine habitats between June and July, with some individuals arriving as early as mid‐May. These estimates were validated by comparing isotope‐derived estuarine arrival times with those from acoustically tracked individuals. The median estuarine arrival day estimates from our isotopic approach aligned with estimates from acoustic telemetry for each sampling population. Sensitivity analyses indicated that isotopically inferred time‐since‐immigration and estuarine arrival estimates were robust to variation in isotopic turnover rate and diet tissue discrimination factors under multiple modelling scenarios. This suggests that parameterization of the nitrogen isotopic clock provides reliable estimates of time‐since‐immigration and day of arrival into new habitats if isotopic variation exists between origin and new locations. Our study presents a unique application of telemetry‐validated isotope clocks to derive retrospective estimates of time‐since‐immigration and timing of habitat shifts for animals that seasonally traverse heterogeneous environments. This approach can be readily applied across many temporal and spatial scales, and to other species and ecosystems, to facilitate rapid assessment of changes in animal habitat use and broader ecosystem structure.

From diet to hair and blood: empirical estimation of discrimination factors for C and N stable isotopes in five terrestrial mammals

AbstractCarbon and nitrogen stable isotope ratios are used widely to describe wildlife animal diet composition and trophic interactions. To reconstruct consumer diet, the isotopic differences between consumers and their diet items—called the trophic discrimination factor (TDF)—must be known. Proxies of diet composition are sensitive to the accuracy of TDFs. However, specific TDFs are still missing for many species and tissues because only a few controlled studies have been carried out on captive animals. The aim of this study was to estimate TDFs for hair and blood for carbon and nitrogen stable isotopes for caribou, moose, white-tailed deer, eastern coyote, and black bear. We obtained stable isotope ratios for diet items, hair, and blood samples, of 21 captive adult mammals. Diet–tissue discrimination factors for carbon in hair (∆ 13CLE) ranged from 0.96‰ to 3.72‰ for cervids, 3.01‰ to 3.76‰ for coyote, and 5.15‰ to 6.35‰ for black bear, while nitrogen discrimination factors (∆ 15N) ranged from 2.58‰ to 5.95‰ for cervids, 2.90‰ to 3.13‰ for coyote, and 4.48‰ to 5.44‰ for black bear. The ∆ 13CLE values in coyote blood components ranged from 2.20‰ to 2.69‰ while ∆ 15N ranged from 3.30‰ to 4.41‰. In caribou serum, ∆ 13CLE reached 3.34 ± 1.28‰ while ∆ 15N reached 5.02 ± 0.07‰. The TDFs calculated in this study will allow the evaluation of diet composition and trophic relationships between these five mammal species and will have important implications for the study of endangered caribou populations for which the use of noninvasive tissue sampling is highly relevant.

Diet to tissue discrimination factors for the blood and feathers of the monk parakeet (Myiopsitta monachus) and the ring–necked parakeet (Psittacula krameri)

Stable isotope analyses (SIAs) have been widely used in recent years to infer the diet of many species. This isotopic approach requires using diet to tissue discrimination factors (DTDFs) for each prey type and predator tissue, i.e., to determine the difference between the isotopic composition of the predator tissues and the different prey that conform its diet. Information on DTDF values in Psittaciformes is scarce. The aim of this study was to assess DTDF values for the carbon and nitrogen isotopes of the monk parakeet (Myiopsitta monachus) and the ring–necked parakeet (Psittacula krameri), two invasive alien species of concern. We fed captive birds of the two parakeet species on a single–species diet based on sunflower seeds to establish the DTDFs for the blood and feathers. In the monk parakeet (N = 9) DTDFs were Δδ13C 2.14 ‰ ± 0.90 and Δδ15N 3.21 ‰ ± 0.75 for the blood, and Δδ13C 3.97 ‰ ± 0.90 and Δδ15N 3.67 ‰ ± 0.74 for the feathers. In the ring–necked parakeet (N = 9), the DTDFs were Δδ13C (‰) 2.58 ± 0.90 and Δδ15N (‰) 2.35 ± 0.78 for the blood, and Δδ13C 3.64 ‰ ± 0.98 and Δδ15N 4.10 ‰ ± 1.84 for the feathers. DTDF values for the ring–necked parakeet blood were significantly higher than those for the monk parakeet blood. No difference was found between the two species in the DTDF for feathers. Our findings provide the first values of DTDFs for blood and feathers in these parakeets, factors that are key to infer the diet of these species based on SIA.

Use of epidermal mucus in elasmobranch stable isotope studies: a pilot study using the giant manta ray (Manta birostris)

Stable isotope analysis of tissues with different turnover rates allows for a broader temporal view of a species’ feeding habits. Epidermal mucus is a rapid to medium turnover ‘tissue’ in teleost fish, but its use in elasmobranch dietary studies is unknown. In the present study, we conducted stable isotope analysis on mucus and muscle from the giant manta ray Manta birostris. Mucus δ13C values were depleted and closer to surface zooplankton δ13C values compared with muscle, whereas there was no significant difference in δ15N values between these two tissue types. Using diet tissue discrimination factors from the literature, there was no significant difference in the expected prey profile between muscle and epidermal mucus. However, a broader range in δ13C values of expected prey was shown for mucus compared with muscle. The results suggest that if M. birostris mucus is indicative of recent dietary intake, resource use during aggregative behaviour off Ecuador is broader, but with no obvious resource switching. The present study is the first example of using bulk stable isotope analysis to evaluate mucus to investigate feeding ecology in elasmobranchs. However, the time course for the change in mucus isotope signature still needs to be determined through controlled feeding studies in an aquarium setting.

Multi‐tissue stable‐isotope analyses can identify dietary specialization

Summary Individual specialization along one or more niche axes is now recognized as an integral and ubiquitous aspect of populations. A major challenge, however, is quantifying the level of specialization using robust metrics that are applicable across species and ecosystems. Measuring stable‐isotope values in multiple tissues with different isotopic turnover rates could be one mechanism for quantifying specialization. We used simulation studies of stable‐isotope values to investigate how the recently proposed relative index of specialization varies in relation to variance in prey isotope values, diet–tissue discrimination factors, specialist group size and tissue half‐life, and applied specialization metrics to two systems – Australian freshwater fish and marine birds in the Canadian Arctic. In all simulations, populations comprised entirely of generalists were easily separated from those with even small amounts (5%) of individual specialization. In some cases, however, specialization measured using isotope values with bimodal distributions may appear similar to those with univariate distributions, but this can be detected by examining the original data. All fish and bird species examined showed varying degrees of individual specialization. Analysing stable isotopes in multiple tissues can provide a useful index of the degree of specialization within a population that can be compared to the same metric measured in other groups or species.

From the pool to the sea: Applicable isotope turnover rates and diet to skin discrimination factors for bottlenose dolphins (Tursiops truncatus)

One of the most common applications in isotopic ecology is the assessment of animal's assimilated diet through mass-balance mixing models. Its applicability relies on the use of accurate diet to tissue discrimination factors and turnover rates, which are known to vary as a function of several factors including taxon or tissue type. To date, few studies have assessed isotopic discrimination factors and turnover rates in cetacean species under controlled conditions. Previous experimental studies focused on blood, a difficult sample to obtain in the wild, or on a more appropriate tissue, the skin, but assessed in short experimental trials without arriving to the isotopic equilibrium. We carried out the longest controlled feeding experiment available (350days) in bottlenose dolphins (Tursiops truncatus) in order to assess discrimination factors and turnover rates in skin. Animals' isotopic composition was first stabilized by maintaining individuals under an isotopically constant diet during 172days. Afterwards, diet was shifted and maintained during 178days to calculate isotopic discrimination and turnover rates. Estimates for isotopic discrimination factors were 1.01±0.37‰ (mean±sd) for δ13C and 1.57±0.52‰ for δ15N. Half-life turnover rates were estimated to be 24.16±8.19days for carbon and 47.63±19days for nitrogen. This is the first time that applicable values are available to assess the diet of free ranging small cetaceans through stable isotope mixing model analysis.

Carbon and nitrogen discrimination factors of wolves and accuracy of diet inferences using stable isotope analysis

Dietary inferences using stable isotope analysis rely on comparing stable carbon and nitrogen isotope content of consumer to prey tissues by modeling discrimination between these tissues. Diet–tissue discrimination factors applied in these models for wild populations must be obtained from controlled feeding studies where consumer diets are known. Species-specific discrimination factors are lacking for wolves (Canis lupus), and most researchers assessing the diet of free-ranging wolves have used discrimination factors derived from red foxes (Vulpes vulpes) fed a commercial pellet diet. We calculated diet–tissue discrimination factors for various tissues from captive wolves fed a controlled diet of horse (Equus caballus) meat and also assessed the feasibility of seasonal delineation of diet through the partitioning of metabolically inactive tissues such as guard hairs and whiskers. Stable carbon isotopic discrimination in wolves was highest in whiskers (4.31‰), followed by guard hair (4.25‰), and lowest in serum (2.21‰) and red blood cells (2.16‰). Stable nitrogen isotopic discrimination was highest in serum (4.54‰), guard hair (3.09‰), and whiskers (3.05‰), and lowest in red blood cells (2.99‰). Using these values, we demonstrated the sensitivity of estimated wolf diet proportions to choice of discrimination factors. We also documented a decrease in growth rate of hair and whiskers from summer through autumn, which cautions estimating temporally explicit diet of mammals based on stable isotope analysis of discrete sections of hair and whiskers. We conclude that species-specific discrimination estimates should be used in dietary assessments based on stable isotope analyses to limit inaccuracies in diet interpretation of wild populations. © 2015 The Wildlife Society.

Biokinetics and discrimination factors for δ13C and δ15N in the omnivorous freshwater crustacean, Cherax destructor

Knowledge and understanding of biokinetics and discrimination factors for carbon-13 (δ13C) and nitrogen-15 (δ15N) are important when using stable isotopes for food-web studies. Therefore, we performed a controlled laboratory diet-switch experiment to examine diet–tissue and diet–faeces discrimination factors as well as the biokinetics of stable-isotope assimilation in the omnivorous freshwater crustacean, Cherax destructor. The biokinetics of δ13C could not be established; however, the δ15N value of C. destructor tissue reached equilibrium after 80 ± 35 days, with an estimated biological half-time for 15N of 19 ± 5 days. Metabolic activity contributed to the turnover of 15N by nearly an order of magnitude more than growth. The diet–tissue discrimination factors at the end of the exposure were estimated as –1.1 ± 0.5‰ for δ13C and +1.5 ± 1.0‰ for δ15N, indicating that a δ15N diet–tissue discrimination factor different from the typically assumed +3.4‰ may be required for freshwater macroinvertebrates such as C. destructor. The diet–faeces discrimination factor for δ15N after 120 days was estimated as +0.9 ± 0.5‰. The present study provides an increased understanding of the biokinetics and discrimination factors for a keystone freshwater macroinvertebrate that will be valuable for future food-web studies in freshwater ecosystems.

Diet–tissue discrimination factors of carbon and nitrogen stable isotopes in blood of Snowy Owl (Bubo scandiacus)

Analysis of carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios (hereafter δ13C and δ15N, respectively) in animal tissues is a powerful tool in food-web studies. However, isotopic ratios of prey are not transmitted directly to a consumer, as a diet–tissue discrimination factor (denoted Δ) occurs between sources and consumer’s tissues. An accurate assessment of the diet of a consumer with stable isotopes thus requires that the Δ13C and Δ15N of the studied species are known. Our aim was to establish Δ13C and Δ15N values in the Snowy Owl ( Bubo scandiacus (L., 1758)). Moreover, we assessed the potential effect of ethanol preservation of blood samples on δ13C and δ15N values. We kept four captive adult Snowy Owls on a pure diet of mice for ≥6 weeks. We then collected mouse muscle and blood samples from the owls and analyzed their δ13C and δ15N values. Δ13C and Δ15N values (mean ± SE) for owl blood were +0.3‰ ± 0.2‰ and +1.9‰ ± 0.1‰, respectively. These values are the first discrimination factors ever reported in Strigiformes and are lower, for Δ15N, than those obtained in terrestrial carnivores and other bird species, including falcons. Preservation in ethanol did not significantly affect δ13C and δ15N values.

δ15N and δ13C diet–tissue discrimination factors for large sharks under semi-controlled conditions

Stable isotopes ( δ 15N and δ 13C) are being widely applied in ecological research but there has been a call for ecologists to determine species- and tissue-specific diet discrimination factors (∆ 13C and ∆ 15N) for their study animals. For large sharks stable isotopes may provide an important tool to elucidate aspects of their ecological roles in marine systems, but laboratory based controlled feeding experiments are impractical. By utilizing commercial aquaria, we estimated ∆ 15N and ∆ 13C of muscle, liver, vertebral cartilage and a number of organs of three large sand tiger ( Carcharias taurus) and one large lemon shark ( Negaprion brevirostris) under a controlled feeding regime. For all sharks mean ± SD for ∆ 15N and ∆ 13C in lipid extracted muscle using lipid extracted prey data were 2.29‰ ± 0.22 and 0.90‰ ± 0.33, respectively. The use of non-lipid extracted muscle and prey resulted in very similar ∆ 15N and ∆ 13C values but mixing of lipid and non-lipid extracted data produced variable estimates. Values of ∆ 15N and ∆ 13C in lipid extracted liver and prey were 1.50‰ ± 0.54 and 0.22‰ ± 1.18, respectively. Non-lipid extracted diet discrimination factors in liver were highly influenced by lipid content and studies that examine stable isotopes in shark liver, and likely any high lipid tissue, should strive to remove lipid effects through standardising C:N ratios, prior to isotope analysis. Mean vertebral cartilage ∆ 15N and ∆ 13C values were 1.45‰ ± 0.61 and 3.75‰ ± 0.44, respectively. Organ ∆ 15N and ∆ 13C values were more variable among individual sharks but heart tissue was consistently enriched by ~ 1–2.5‰. Minimal variability in muscle and liver δ 15N and δ 13C sampled at different intervals along the length of individual sharks and between liver lobes suggests that stable isotope values are consistent within tissues of individual animals. To our knowledge, these are the first reported diet–tissue discrimination factors for large sharks under semi-controlled conditions, and are lower than those reported for teleost fish.

Tissue-specific isotopic discrimination factors in gentoo penguin ( Pygoscelis papua) egg components: Implications for dietary reconstruction using stable isotopes

Stable isotope analysis ( δ 13C and δ 15N) is a useful tool when examining animal diets due to a general enrichment in heavier isotopes from prey tissues to the tissues of the predators consuming them. However, the amount of this enrichment, or discrimination, can vary among taxa and tissue type, limiting the use of stable isotope analysis when estimating diet composition. In this study we calculate the dietary isotopic discrimination factors of specific Pygoscelis penguin egg tissues, including eggshell, shell membrane, albumen and yolk, using a captive population of gentoo penguins fed known diets. We found that discrimination factors varied by isotope, tissue, and whether factors were calculated from whole fish or fish muscle. The observed variation in discrimination factors across tissues likely reflects differences in biochemical and metabolic processes during tissue synthesis. We validated the use of tissue discrimination factors derived in this study by independently reconstructing the diet composition of wild gentoo penguins at Cape Sherriff, Livingston Island, Antarctica using the δ 15N values of eggshell organics and shell membrane. While eggshell organics and shell membrane from the same egg differed in raw δ 15N values, modeling confirmed that these differences were due to tissue-specific isotopic discrimination. Furthermore, our results suggest that in 2006, female gentoo penguins at Cape Sherriff consumed a higher percentage of krill than fish during the egg-laying period.

Stable carbon and nitrogen isotopic discrimination in whole blood of red-throated ant tanagers Habia fuscicauda

Analysis of stable isotope ratios is increasingly used to reconstruct diets in passerine birds, but studies of diet–tissue isotopic discrimination for this avian group are scarce. We determined 15N and 13C diet–tissue discrimination factors on whole blood in the red-throated ant tanager (Habia fuscicauda), an insectivorous–frugivorous passerine. Birds were fed an isotopically uniform, semi-synthetic diet of dog puppy dry food, soy protein isolate, wheat germ, and other ingredients, during 92 days. Average (± SD) diet–tissue discrimination was 2.6 ± 0.2‰ for N and 2.2 ± 0.1‰ for C. Nitrogen diet-tissue discrimination was similar to the values found previously in other passerines fed animal protein and it can probably be used to accurately reconstruct protein dietary origin in passerines feeding on animal protein (e.g., insects). In the case of C, diet reconstruction might be affected by metabolic routing of dietary nutrients.