Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean

Sympatric species are expected to differ in ecological requirements to minimize niche overlap and avoid competition. Here we assess the trophic interactions among three coexisting dolphin species from southern Brazil: the franciscana dolphin (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis), and the Lahille's bottlenose dolphin (Tursiops truncatus gephyreus). We evaluated temporal variation in carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values of bone collagen to examine potential dietary shifts resulting from increased fishing activity over the past three decades. We estimated the degree of niche overlap among these species and the contribution of potential prey sources to their diet. δ¹⁵N values were consistent among species and across years, while δ¹³C values increased for Guiana dolphins and decreased for bottlenose dolphins, suggesting changes in diet and/or foraging habitats through time. The similar δ¹³C and δ¹⁵N values and the high niche overlap between Guiana and bottlenose dolphins indicate that these species are primarily feeding on demersal prey. The franciscana diet is primarily composed of pelagic prey, resulting in a lower niche overlap in comparison with the other dolphin species. Our study provides further information about the foraging ecology of this unique dolphin community in southern Brazil with implications for its management and conservation.     

Foraging habits in a generalist predator: Sex and age influence habitat selection and resource use among bottlenose dolphins (Tursiops truncatus)

This study examines resource use (diet, habitat use, and trophic level) within and among demographic groups (males, females, and juveniles) of bottlenose dolphins (Tursiops truncatus). We analyzed the δ¹³C and δ¹⁵N values of 15 prey species constituting 84% of the species found in stomach contents. We used these data to establish a trophic enrichment factor (TEF) to inform dietary analysis using a Bayesian isotope mixing model. We document a TEF of 0‰ and 2.0‰ for δ¹³C and δ¹⁵N, respectively. The dietary results showed that all demographic groups relied heavily on low trophic level seagrass‐associated prey. Bayesian standard ellipse areas (SEA_b) were calculated to assess diversity in resource use. The SEA_b of females was nearly four times larger than that of males indicating varied resource use, likely a consequence of small home ranges and habitat specialization. Juveniles possessed an intermediate SEA_b, generally feeding at a lower trophic level compared to females, potentially an effect of natal philopatry and immature foraging skills. The small SEA_b of males reflects a high degree of specialization on seagrass associated prey. Patterns in resource use by the demographic groups are likely linked to differences in the relative importance of social and ecological factors.     

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

Teeth of odontocetes accumulate annual dentinal growth layer groups (GLGs) that record isotope ratios, which reflect the time of their synthesis. Collectively, they provide lifetime records of individual feeding patterns from which life history traits can be inferred. We subsampled the prenatal dentin and postnatal GLGs in Risso's dolphins (Grampus griseus) (n = 65) that stranded or were collected as bycatch in Taiwan (1994–2014) and analyzed them for δ¹⁵N and δ¹³C. Age‐specific δ¹⁵N and δ¹³C values were corrected for effects of calendar year, stranding site, C/N, and sex. δ¹⁵N values were higher in prenatal layers (14.94‰ ± 0.74‰) than in adult female GLGs (12.58‰ ± 0.20‰), suggesting fetal enrichment during gestation. Decreasing δ¹⁵N values in early GLGs suggested changes in dietary protein sources during transition to complete weaning. Weaning age was earlier in males (1.09 yr) than in females (1.81 yr). Significant differences in δ¹⁵N values between weaned males and females suggest potential sexual segregation in feeding habits. δ¹³C values increased from the prenatal to the 4th GLG by ~1.0‰, indicative of a diet shift from ¹³C‐depleted milk to prey items. Our results provide novel insights into the sex‐specific ontogenetic changes in feeding patterns and some life history traits of Risso's dolphins.     

The diet of great tit nestlings: Comparing observation records and stable isotope analyses

The diet of wild animals has been studied using many different strategies, approaches and methods in recent decades. In this regard, stable isotopes analysis (SIA) is becoming a widespread tool, but no study has yet, to our knowledge, compared diet estimations from SIA with direct observations of the diet of passerine nestlings. Accordingly, our aim was to test the predictive power of SIA for this purpose and identify potential confounding factors such as habitat effects. To do this, we compared isotopic signatures of δ¹³C and δ¹⁵N in the feathers of great tit (Parus major) nestlings, and the corresponding estimates of their diet based on stable isotope mixing models, with prey proportions delivered by their parents obtained through video-recordings. Between-nest differences in isotopic signatures of δ¹⁵N were larger than within-nest differences. We found that δ¹⁵N signatures of nestling feathers correlated positively with the proportion of spiders and negatively with the proportion of caterpillars in the nestlings’ diet, the most important prey types. On the other hand, between-nest and within-nest differences in δ¹³C ratios were of similar magnitude and δ¹³C ratios correlated mainly with the proportion of trees surrounding nest-boxes that were Quercus spp. Estimates of diet composition based on mixing models correlated with the observed nestling diet, yet effect sizes were quite low. Although mixing models are commonly used to ascertain diets, our data show that they can provide valuable information on the relative intake of prey types from different trophic levels; but when complex dietary patterns are recorded (e.g. due to the confounding effects of habitat and/or temporal variation) it can be difficult to draw firm conclusions about diet composition.     

Multivariate carbon and nitrogen stable isotope model for the reconstruction of prehistoric human diet

Using a sample of published archaeological data, we expand on an earlier bivariate carbon model for diet reconstruction by adding bone collagen nitrogen stable isotope values (δ(15) N), which provide information on trophic level and consumption of terrestrial vs. marine protein. The bivariate carbon model (δ(13) C(apatite) vs. δ(13) C(collagen) ) provides detailed information on the isotopic signatures of whole diet and dietary protein, but is limited in its ability to distinguish between C(4) and marine protein. Here, using cluster analysis and discriminant function analysis, we generate a multivariate diet reconstruction model that incorporates δ(13) C(apatite) , δ(13) C(collagen) , and δ(15) N holistically. Inclusion of the δ(15) N data proves useful in resolving protein-related limitations of the bivariate carbon model, and splits the sample into five distinct dietary clusters. Two significant discriminant functions account for 98.8% of the sample variance, providing a multivariate model for diet reconstruction. Both carbon variables dominate the first function, while δ(15) N most strongly influences the second. Independent support for the functions' ability to accurately classify individuals according to diet comes from a small sample of experimental rats, which cluster as expected from their diets. The new model also provides a statistical basis for distinguishing between food sources with similar isotopic signatures, as in a previously analyzed archaeological population from Saipan (see Ambrose et al.: AJPA 104(1997) 343-361). Our model suggests that the Saipan islanders' (13) C-enriched signal derives mainly from sugarcane, not seaweed. Further development and application of this model can similarly improve dietary reconstructions in archaeological, paleontological, and primatological contexts.     

Stable isotope evidence from formalin–ethanol-preserved specimens indicates dietary shifts and increasing diet overlap in Lake Victoria cichlids

Stable isotopes are increasingly being used to infer past and present trophic interactions in light of environmental changes. The Lake Victoria haplochromine cichlids have experienced severe environmental changes in the past decades that, amongst others, resulted in a dietary shift towards larger prey. We investigated how the changed environment and diet of the haplochromines influenced stable isotope values of formalin-then-ethanol-preserved cichlid specimens, and then investigated how these values differed among species before (1977–1982) and after substantial environmental changes (2005–2007). We found a small preservation effect on both δ¹³C and δ¹⁵N values, and significant differences in isotope values among haplochromine species collected before the environmental changes. In contrast, there was a remarkable similarity in δ¹³C and δ¹⁵N values among species collected from the contemporary ecosystem and two out three species showed significantly different stable isotope values compared to species of the historic ecosystem. In addition, we found a putative isotopic gradient effect along our 5-km-long research transect indicating that the studied demersal species are more stenotopic than previously thought. The environmental changes have resulted in dietary change and overlap of the haplochromines which provides insight into the trophic plasticity of these species, which are often considered trophic specialists.     

Using Bayesian stable isotope mixing models to estimate wolf diet in a multi-prey ecosystem

Stable isotope analysis (SIA) of wolf (Canis lupus) tissues can be used to estimate diet and intra-population diet variability when potential prey have distinct δ¹³C and δ¹⁵N values. We tested this technique using guard hairs collected from 44 wolves in 12 northwestern Montana packs, summer 2009. We used hierarchical Bayesian stable isotope mixing models to determine diet and scales of diet variation from δ¹³C and δ¹⁵N of wolves and potential prey, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), snowshoe hare (Lepus americanus), and other prey. As a check on SIA results, we conducted a separate diet analysis with temporally matched scats (i.e., collected in summer 2008) from 4 of the same packs. Wolves were centered on the ungulate prey in the isotope mixing space. Both methods revealed differences among pack diets and that wolves may consume moose in greater proportions than predicted by available biomass. Stable isotope analysis, and scat results were not entirely concordant; assumptions related to tissues of use in SIA, hair growth period in wolves, and scat sampling may have contributed to a mismatch between methods. Incorrect fractionation values, insufficient separation of prey in the isotope mixing space, choice of prior information in the Bayesian mixing models, and unexplained factors may have distorted diet estimates. However, the consistently high proportion of moose in pack diets suggests that increased population monitoring would benefit management of moose and wolves. Our results also support suggestions of other researchers that species-specific fractionation values should be used whenever possible, and that SIA may sometimes only provide indices of use for general groups of prey (e.g., large ungulates). © 2012 The Wildlife Society.     

Prey composition and ontogenetic shift in coastal populations of longnose gar Lepisosteus osseus

Longnose gar Lepisosteus osseus were collected from May 2012 to July 2013 in the Charleston Harbor and Winyah Bay estuaries (SC, U.S.A.). This study examined trends in stomach fullness, described major prey components and their importance in the diet of L. osseus, compared stomach content‐based trophic level estimates with the stable‐isotope‐based proxy: δ¹⁵N and tested for the occurrence of an ontogenetic diet shift using stomach content analysis and stable C and N isotopes (δ¹³C and δ¹⁵N). Dominant prey families were Clupeidae, Sciaenidae, Penaeidae, Fundulidae and Mugilidae, with the highest consumption rates in autumn. Trophic levels calculated using stomach contents did not correspond to δ¹⁵N (P > 0·05). Stomach contents and stable‐isotope signatures indicate ontogenetic prey composition shifts from low trophic level benthic prey (fundulids) to higher trophic level pelagic prey (clupeids) as the fish grow between 400 and 600 mm in standard length. Due to their biomass, abundance and top predator status, L. osseus play a significant ecological role in the estuarine community composition, although this effect has often been overlooked by past researchers and should be considered in future estuarine community studies.     

Combined gut‐content and stable isotope trophic analysis of the pelagic stingray Pteroplaytrygon violacea (Bonaparte, 1832) diet from the western North Atlantic Ocean

The understanding of trophic relationships is vital for correctly modeling ecosystems and ecosystem effects of fisheries removals. The pelagic stingray is found in epipelagic sub‐tropical and tropical waters worldwide and is a common bycatch in pelagic longline fisheries. Between August 2008 and November 2011, 156 specimens (81 males; 75 females) were collected during pelagic longline fishing operations in the US South Atlantic Bight and Gulf of Mexico. Stomach content analyses found that the major prey items were cephalopod molluscs (59.18%), followed by actinopterygiian fishes (37.75%), and decapod crustaceans (35.71%). These concentrations of prey items found in the stomachs coincide with previous studies done in the Pacific Ocean. In contrast to previous studies that found high percentages of empty stomachs (63%), the current percentage of empty stomachs was much lower (25.6%), likely due to shorter times between collection and inspection. Stable isotope analysis (δ¹³C and δ¹⁵N) was performed on white muscle in order to correlate the trophic position with gut‐content analysis. The δ¹³C values ranged from ‐18.81‰ to ‐16.70‰, while the δ¹⁵N ranged from 6.11‰ to 11.88‰. Modeling of stable isotope data suggest that while squid are occasionally an important part of the pelagic stingray diet, prey usually consist of shrimp and other pelagic crustaceans. Pelagic stingrays fed within two trophic levels, but their prey appeared to feed on different carbon sources than those found in other pelagic elasmobranchs. A deeper understanding of the pelagic stingray diet sources can help fisheries management as it begins to transition into ecosystem‐based management.     

Stable isotopes differentiate bottlenose dolphins off west-central Florida

Distinguishing discrete population units among continuously distributed coastal small cetaceans is challenging and crucial to conservation. We evaluated the utility of stable isotopes in assessing group membership in bottlenose dolphins (Tursiops truncatus) off west-central Florida by analyzing carbon, nitrogen, and sulfur isotope values (δ¹³C, δ¹⁵N, and δ³⁴S) of tooth collagen from stranded dolphins. Individuals derived from three putative general population units: Sarasota Bay (SB), nearshore Gulf of Mexico (GULF), and offshore waters (OFF). Animals of known history (SB) served to ground truth the approach against animals of unknown history from the Gulf of Mexico (GULF, OFF). Dolphin groups differed significantly for each isotope. Average δ¹³C values from SB dolphins (−10.6‰) utilizing sea grass ecosystems differed from those of GULF (−11.9‰) and OFF (−11.9‰). Average δ¹⁵N values of GULF (12.7‰) and OFF (13.2‰) were higher than those of SB dolphins (11.9‰), consistent with differences in prey trophic levels. δ³⁴S values showed definitive differences among SB (7.1‰), GULF (11.3‰), and OFF (16.5‰) dolphins. This is the first application of isotopes to population assignment of bottlenose dolphins in the Gulf of Mexico and results suggest that isotopes may provide a powerful tool in the conservation of small cetaceans.     

The influence of climate and habitat on stable isotope signatures and the isotopic niche of nestling White‐headed Woodpeckers (Dryobates albolarvatus)

The majority of landbird species feed their nestlings arthropods and variation in arthropod populations can impact reproductive outcomes in these species. Arthropod populations in turn are influenced by climate because temperature affects survival and reproduction, and larval development. Thus, climate factors have the potential to influence many bird species during their reproductive phases. In this study, we assessed climate factors that impact the diet of nestling White‐headed Woodpecker (Dryobates albolarvatus), an at‐risk keystone species in much of its range in western North America. To do this, we measured stable isotope signatures (δ¹³C and δ¹⁵N) in 152 nestlings across six years and linked variation in isotopic values to winter (December–February) and spring (June) precipitation and temperature using mixed effects models. We also explored habitat factors that may impact δ¹³C and δ¹⁵N and the relationship between δ¹⁵N and nest productivity. Last, we estimated isotopic niche width for nestlings in different watersheds and years using Bayesian standard ellipses, which allowed us to compare dietary niche width and overlap. We found that colder winter temperatures were associated with an increase in δ¹⁵N and δ¹⁵N levels had a weak positive relationship with nest productivity. We also found that sites with a more diverse tree community were associated with a broader isotopic niche width in nestlings. Our findings suggest that nestling diet is affected by climate, and under future warming climate scenarios, White‐headed Woodpecker nestling diet may shift in favor of lower trophic level prey (prey with lower δ¹⁵N levels). The impact of such changes on woodpecker populations merits further study.     

Changes in diets of individual Baltic ringed seals (Phoca hispida botnica) during their breeding season inferred from stable isotope analysis of multiple tissues

The stable isotope ratios (δ¹³C and δ¹⁵N) of three tissues with different metabolic rates (plasma, liver, and muscle) were used to investigate temporal variation in diet among nine individual Baltic ringed seals (Phoca hispida botnica Gmelin) from the Bothnian Bay, northeast Baltic Sea. The isotope values from plasma should reflect the most recent diet, values from liver the diet of the past weeks prior to sampling, and values from muscle should integrate diet over almost the entire breeding season of the ringed seals. In general, δ¹³C values of liver were more enriched in ¹³C than were those of either muscle or plasma, suggesting that the diet of the seals may have included a higher proportion of ¹³C‐enriched benthic prey in April. Females showed more variable δ¹³C values than males, suggesting possible gender differences in diet or in foraging locations. The differences that were apparent between females possibly reflect individual variation in the onset and duration of parturition and lactation, both of which likely restrict female foraging. Previous data from parasite infections and from alimentary tract contents of the same seals were linked to the isotope data to assist in drawing inferences about changes in the diets of individual seals.     

Diet of common dolphins (Delphinus delphis) off the south-east coast of southern Africa: opportunism or specialization?

A total of 297 common dolphin (Delphinus delphis) stomachs was used for these diet analyses. All originated from common dolphins incidentally captured in Natal, where their occurrence is strongly associated with an annual, northward fish migration, the sardine run, along the east coast. Thirty-six fish and four cephalopod prey species were identified. Though 86.9% by weight of the diet was made up of only five prey species, common dolphins appear to feed opportunistically, their diet reflecting local prey abundance and availability. Prey were primarily small, easily-caught, pelagic shoaling species, with the main prey being South African pilchard (Sardinops ocellatus). Although pilchard dominated the diet between 1974 and 1992, there were marked annual and seasonal fluctuations in dietary composition, reflecting changes in prey availability and abundance. There were clear differences in the contribution of particular prey species to the diet of different sex and size groups, with strong evidence for resource partitioning between groups. The influence of the annual 'sardine run', and the fish predators associated with it, on the diet, feeding biology and distribution of common dolphins is discussed.     

Trophic interaction between striped marlin and swordfish using different timescales in waters around Baja California Sur,Mexico

Isotopic niche and resource partitioning were examined between striped marlin (Kajikia audax) and swordfish (Xiphias gladius) using stable isotope ratios from spine bone and muscle samples. The δ¹³C (¹³C/¹²C) and δ¹⁵N (¹⁵N/¹⁴N) values were measured in annual growth bands from fin spines and muscle collected from striped marlin and swordfish off Baja California Sur to evaluate the trophic interaction between these two species, the relative contribution of the main prey and the isotopic niche within two different timescales. Mean trophic level (TL) values were different when tissues were compared with the highest value found in muscle samples from K. audax. When TL was analysed in all growth bands for both species, no changes were detected throughout time, suggesting only minor differences in feeding habits between these species. We determined that Dosidicus gigas, Sthenoteuthis oualaniensis, and Ancistrocheirus lesueurii were the most important prey for both species, but the relative contribution of each of them to the diet differed. There is likely no trophic overlap between K. audax and X. gladius off Baja California Sur, as K. audax occupied a larger isotopic niche with more diverse prey than X. gladius.     

Stable isotope analysis indicates a lack of inter- and intra-specific dietary redundancy among ecologically important coral reef fishes

Parrotfish are critical consumers on coral reefs, mediating the balance between algae and corals, and are often categorised into three functional groups based on adult morphology and feeding behaviour. We used stable isotope analysis (δ¹³C, δ¹⁵N) to investigate size-related ontogenetic dietary changes in multiple species of parrotfish on coral reefs around Zanzibar. We compared signatures among species and functional groups (scrapers, excavators and browsers) as well as ontogenetic stages (immature, initial and terminal phase) within species. Stable isotope analysis suggests that ontogenetic dietary shifts occurred in seven of the nine species examined; larger individuals had enriched δ¹³C values, with no relationship between size and δ¹⁵N. The relationship between fish length and δ¹³C signature was maintained when species were categorised as scrapers and excavators, but was more pronounced for scrapers than excavators, indicating stronger ontogenetic changes. Isotopic mixing models classified the initial phase of both the most abundant excavator (Chlorurus sordidus) as a scraper and the immature stage of the scraper Scarus ghobban (the largest species) as an excavator, indicating that diet relates to size rather than taxonomy. The results indicate that parrotfish may show similar intra-group changes in diet with length, but that their trophic ecology is more complex than suggested by morphology alone. Stable isotope analyses indicate that feeding ecology may differ among species within functional groups, and according to ontogenetic stage within a species.     

Feeding ecology of pelagic fish larvae and juveniles in slope waters of the Gulf of Mexico

Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were used to investigate feeding patterns of larval and early juvenile pelagic fishes in slope waters of the Gulf of Mexico. Contribution of organic matter supplied to fishes and trophic position within this pelagic food web was estimated in 2007 and 2008 by comparing dietary signatures of the two main producers in this ecosystem: phytoplankton [based on particulate organic matter (POM)] and Sargassum spp. Stable isotope ratios of POM and pelagic Sargassum spp. were significantly different from one another with δ¹³C values of POM depleted by 3–6‰ and δ¹⁵N values enriched by 2 relative to Sargassum spp. Stable isotope ratios were significantly different among the five pelagic fishes examined: blue marlin Makaira nigricans, dolphinfish Coryphaena hippurus, pompano dolphinfish Coryphaena equiselis, sailfish Istiophorus platypterus and swordfish Xiphias gladius. Mean δ¹³C values ranged almost 2 among fishes and were most depleted in I. platypterus. In addition, mean δ¹⁵N values ranged 4–5 with highest mean values found for both C. hippurus and C. equiselis and the lowest mean value for M. nigricans during both years. Increasing δ¹³C or δ¹⁵N with standard length suggested that shifts in trophic position and diet occurred during early life for several species examined. Results of a two‐source mixing model suggest approximately an equal contribution of organic matter by both sources (POM = 55%; pelagic Sargassum spp. = 45%) to the early life stages of pelagic fishes examined. Contribution of organic matter, however, varied among species, and sensitivity analyses indicated that organic source estimates changed from 2 to 13% for a δ¹³C fractionation change of ±0·25‰ or a δ¹⁵N fractionation change of ± 1·0‰ relative to original fractionation values.     

THE DIETS OF MODERN AND HISTORIC BOTTLENOSE DOLPHIN POPULATIONS REFLECTED THROUGH STABLE ISOTOPES

The δ¹³C and δ¹⁵N compositions of teeth used in combination with existing data provide dietary information for different populations of western North Atlantic bottlenose dolphins (Tursiops truncatus). The dental isotopic signatures of bottlenose dolphins collected during the 1980s significantly differ for coastal and offshore ecotypes and are consistent with reports that coastal forms feed primarily on fish whereas offshore individuals consume more squid. In a second study, the isotopic compositions of teeth from bottlenose dolphins that span a 100-yr period and data from published stomach content analyses as well as field observations made during the past 100 yr provide evidence that coastal bottlenose dolphins from the 1880s, 1920s, and 1980s had similar diets.     

Dietary heterogeneity among Western industrialized countries reflected in the stable isotope ratios of human hair

Although the globalization of food production is often assumed to result in a homogenization of consumption patterns with a convergence towards a Western style diet, the resources used to make global food products may still be locally produced (glocalization). Stable isotope ratios of human hair can quantify the extent to which residents of industrialized nations have converged on a standardized diet or whether there is persistent heterogeneity and glocalization among countries as a result of different dietary patterns and the use of local food products. Here we report isotopic differences among carbon, nitrogen and sulfur isotope ratios of human hair collected in thirteen Western European countries and in the USA. European hair samples had significantly lower δ(13)C values (-22.7 to -18.3‰), and significantly higher δ(15)N (7.8 to 10.3‰) and δ(34)S (4.8 to 8.3‰) values than samples from the USA (δ(13)C: -21.9 to -15.0‰, δ(15)N: 6.7 to 9.9‰, δ(34)S: -1.2 to 9.9‰). Within Europe, we detected differences in hair δ(13)C and δ(34)S values among countries and covariation of isotope ratios with latitude and longitude. This geographic structuring of isotopic data suggests heterogeneity in the food resources used by citizens of industrialized nations and supports the presence of different dietary patterns within Western Europe despite globalization trends. Here we showed the potential of stable isotope analysis as a population-wide tool for dietary screening, particularly as a complement of dietary surveys, that can provide additional information on assimilated macronutrients and independent verification of data obtained by those self-reporting instruments.     

Shared dietary niche between sexes in Magellanic Penguins

Prey use by male and female Magellanic Penguins (Spheniscus magellanicus) was quantified during chick rearing in northern Golfo San Jorge, Argentina and the dietary niches and diet composition of each sex were assessed and compared. A total of 67 males and 45 females were flushed during the chick stages of 2011 and 2012. Argentine Anchovy (Engraulis anchoita) was the main prey in terms of importance by mass in males and females in all stages and years (52.4–86.6% and 83.8–88.7%, respectively), except during the old chick stage in 2011 when the main prey in males and females was the Shortfin Squid (Illex argentinus) (63.1% and 44.4%, respectively). Analyses of similarity showed that diet composition in terms of contribution by mass of the main prey species was similar between sexes. Based on the isotopic values of δ¹³C and δ¹⁵N corresponding to 38 males and 21 females, the Bayesian mixing model outputs showed that Argentine Anchovy was also the main prey. In both years and chick stages, the isotopic niche of males and females was similar. The similarity in the dietary niche between male and female Magellanic Penguins raising chicks may be due to the high availability of Argentine Anchovy during the study period and the consequent dominance of this forage species in the diet of both sexes.     

Carry‐over effects of winter habitat vary with age and sex in yellow warblers Setophaga petechia

We use stable isotope data to investigate the role of winter habitat use in altering the breeding phenology of yellow warblers Setophaga petechia. We first confirm that δ¹³C and δ¹⁵N isotopic signatures vary with winter habitat use in this species. We then examine the relationship between winter habitat use, breeding phenology and productivity within four age‐sex‐classes, since life history theory would predict that carry‐over effects should vary with age and gender. The δ¹³C signatures of yellow warblers using riparian habitats over winter were more depleted than the signatures of those using agricultural or scrub habitat. Individuals on the Pacific coast of Mexico were also more δ¹⁵N enriched than those on the southern Gulf of Mexico. δ¹³C and δ¹⁵N signatures were only correlated with earlier clutch initiation and subsequent higher productivity in first‐breeding‐season females. We estimate that shifts in δ¹³C equivalent to a shift from scrub to riparian winter habitat would be associated with the production of 0.8 more fledglings by yearling females. Pre‐breeding events that influence the timing of breeding could also influence the reproductive performance of older males and females, but we found little evidence that winter habitat use influenced breeding season phenology in these birds.