Stable hydrogen isotope (δD) values in songbird nestlings: effects of diet, temperature, and body size (original) (raw)
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Variations in stable hydrogen and oxygen isotope ratios in terrestrial animal tissues are used to reconstruct origin and movement. An underlying assumption of these applications is that tissues grown at the same site share a similar isotopic signal, representative of the location of their origin. However, large variations in tissue isotopic compositions often exist even among conspecific individuals within local populations, which complicates origin and migration inferences. Field-data and correlation analyses have provided hints about the underlying mechanisms of within-site among-individual isotopic variance, but a theory explaining the causes and magnitude of such variance has not been established. Here we develop a mechanistic modeling framework that provides explicit predictions of the magnitude, patterns, and drivers of isotopic variation among individuals living in a common but environmentally heterogeneous habitat. The model toolbox includes isoscape models of environmental isotopic variability, an agent-based model of behavior and movement, and a physiology-biochemistry model of isotopic incorporation into tissues. We compare model predictions against observed variation in hatch-year individuals of the songbird Spotted Towhee (Pipilo maculatus) in Red Butte Canyon, Utah, and evaluate the ability of the model to reproduce this variation under different sets of assumptions. Only models that account for environmental isotopic variability predict a similar magnitude of isotopic variation as observed. Within the modeling framework, behavioral rules and properties govern how animals nesting in different locations acquire resources from different habitats, and birds nesting in or near riparian habitat preferentially access isotopically lighter resources than those associated with the meadow and slope habitats, which results in more negative body water and tissue isotope values. Riparian nesters also have faster body water turnover Magozzi et al.
Canadian Journal of Fisheries and Aquatic Sciences, 2011
Recent studies suggest that stable hydrogen isotope ratios (dD) of fish can be used to track their watershed origin and the relative contributions of source material. Both applications assume that there is no metabolic or trophic effect on tissue dD. We studied the local variation of dD values in four fish species of contrasting size and feeding habits in an isotopically homogenous reservoir (Flix, Spain). Other isotopic values (d 15 N, d 13 C) and trace metal content were measured as indicators of trophic and bioaccumulation patterns. In addition, isotopic values (dD, d 15 N, d 13 C) of other food web components were measured for comparison. Muscle dD values differed greatly among fish species: European catfish, Silurus glanis (-131‰); common carp, Cyprinus carpio (-141‰); rudd, Scardinius erythrophthalmus (-158‰); and roach, Rutilus rutilus (-163‰). The influence of fish size and trophic position affected the fish dD values. Possible mechanisms that drive dD variation among fish might be a metabolic effect and (or) the compounding effect of ambient water dD on exchangeable H at each trophic stage. Our findings showed that size and feeding habits are factors that should be controlled when tracing origins of fish or their dependence on nutrient inputs using dD measurements. Résumé : Des études récentes indiquent que les rapports d'isotopes stables d'hydrogène (dD) des poissons peuvent servir à retracer leur bassin versant d'origine et les contributions relatives des matériaux sources. Ces deux utilisations présupposent qu'il n'y a pas d'effet métabolique ou trophique sur le dD des tissus. Nous avons étudié la variation locale des valeurs de dD chez quatre espèces de poissons de tailles et d'habitudes alimentaires très différentes dans un réservoir homogène par ses isotopes (Flix, Espagne). Nous avons déterminé les autres valeurs isotopiques (d 15 N, d 13 C) et les concentrations des métaux en trace comme indicateurs des patrons trophiques et des patrons de bioconcentration. Nous avons, de plus, mesuré les valeurs isotopiques (dD, d 15 N, d 13 C) des autres composantes du réseau alimentaire pour établir des comparaisons. Les valeurs de dD du muscle varient considérablement d'une espèce de poisson à une autre : le silure glane, Silurus glanis (-131 ‰), la carpe commune, Cyprinus carpio (-141 ‰), le rotengle, Scardinius erythrophthalmus (-158 ‰) et le gardon, Rutilus rutilus (-163 ‰). La taille du poisson et sa position trophique affectent les valeurs de dD du poisson. Les mécanismes explicatifs possibles de la variation de dD chez les poissons pourraient inclure un effet métabolique et (ou) l'effet cumulatif du dD de l'eau ambiante sur l'H échangeable à chaque stade trophique. Nos résultats démontrent qu'il faut tenir compte de la taille et des habitudes alimentaires pour retracer à l'aide de mesures de dD les origines des poissons ou leur dépendance des apports de nutriments. [Traduit par la Rédaction]
BACKGROUND: Tracking small migrant organisms worldwide has been hampered by technological and recovery limitations and sampling bias inherent in exogenous markers. Naturally occurring stable isotopes of H (δ(2)H) in feathers provide an alternative intrinsic marker of animal origin due to the predictable spatial linkage to underlying hydrologically driven flow of H isotopes into foodwebs. This approach can assess the likelihood that a migrant animal originated from a given location(s) within a continent but requires a robust algorithm linking H isotopes in tissues of interest to an appropriate hydrological isotopic spatio-temporal pattern, such as weighted-annual rainfall. However, a number of factors contribute to or alter expected isotopic patterns in animals. We present results of an extensive investigation into taxonomic and environmental factors influencing feather δ(2)H patterns across North America. PRINCIPAL FINDINGS: Stable isotope data were measured from 544 feathers from 40 species and 140 known locations. For δ(2)H, the most parsimonious model explaining 83% of the isotopic variance was found with amount-weighted growing-season precipitation δ(2)H, foraging substrate and migratory strategy. CONCLUSIONS/SIGNIFICANCE: This extensive H isotopic analysis of known-origin feathers of songbirds in North America and elsewhere reconfirmed the strong coupling between tissue δ(2)H and global hydrologic δ(2)H patterns, and accounting for variance associated with foraging substrate and migratory strategy, can be used in conservation and research for the purpose of assigning birds and other species to their approximate origin.
Unexpected hydrogen isotope variation in oceanic pelagic seabirds
Oecologia, 2014
Buller's shearwater (Puffinus bulleri). the similarity between muscle δD values of hatch-year hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.
2013
Northern Saw-whet Owls (Aegolius acadicus) breed throughout the boreal forest of North America, but little is known about their population trends or distribution within this region. Analysis of stable hydrogen isotopes (δ 2 H) in feathers can delineate origins of a variety of avian migrants, but raptors are reported to have high intrafeather isotopic variance and mean δ 2 H values higher than predicted from δ 2 H isoscapes specific to raptor feathers, making assignment of geographic origin sometimes difficult. We examined the applicability of δ 2 H analysis of sawwhet owl feathers to delineating origins of migrants and to assessing differences in the migratory behavior of adult and young owls by using multiple generations of feathers from owls captured during fall migration at the Delta Marsh Bird Observatory, Manitoba, 2006Manitoba, -2007 Values of δ 2 H in saw-whet owl feathers were higher than predicted from a δ 2 H isoscape specific to raptor feathers and from patterns of movements inferred from analysis of band recoveries. This effect was pronounced in adults, while values of δ 2 H in feathers of hatching-year owls fell primarily within the range predicted for the boreal forest northwest of Delta Marsh. Significant differences in δ 2 H values among feather generations suggest that physiological or behavioral differences between adults and young give rise to greater 2 H enrichment in adult feathers. These results indicate that current δ 2 H isoscapes for feathers cannot be used to track adult saw-whet owls reliably and further research into the mechanisms of 2 H enrichment in owl feathers is required.
Canadian Journal of Zoology, 2012
In North America, gradients in the ratio of stable hydrogen isotopes in amount-weighted, growing-season mean precipitation (2H:1H; depicted as δ2Hp) form a largely latitude-sensitive isoscape that can be used to estimate the geographical origin of animals. Feathers are metabolically inert following growth and δ2Hf values retain information on geographical origins. However, there are important assumptions underlying this approach that can only be tested using birds of known origin. Here, we investigated sources of variation in δ2Hf measurements from Ovenbirds ( Seiurus aurocapilla (L., 1766)) associated with year, age class, feather type, season, and habitat type in New Brunswick, Canada. The observed δ2Hf generally followed that predicted from the Global Network of Isotopes in Precipitation database. However, we found a strong year × age interaction on δ2Hf. Season, habitat type, and feather type explained only a small portion of the overall variation in δ2Hf. These results show the...