Birds of a feather winter together: migratory connectivity in the Reed Warbler Acrocephalus scirpaceus

To investigate migratory connectivity in the Reed Warbler Acrocephalus scirpaceus, we analysed (1) all available sub-Saharan ringing recoveries and (2) stable isotopes in feathers grown in Africa sampled at 17 European breeding sites across a migratory divide. A cluster analysis of ringing recoveries showed remarkable connectivity between breeding and non-breeding grounds. Two main clusters represented populations taking the two main migratory routes [southwesterly (SW) and southeasterly (SE)]. Stable isotope analysis confirmed the separation of wintering areas of SW- and SE-migrating populations. Higher δ¹⁵N values in feathers of SE-migrating birds indicated that they occupied more xeric biome types. Values of δ¹³C that did not differ significantly among populations were higher than those from feathers of known European origin and indicated a C4 biome. Three populations with an unknown migratory direction were assigned to the SE-migrating populations on the basis of δ¹⁵N values.     

Philopatry of winter moult area in migratory Great Reed Warblers Acrocephalus arundinaceus demonstrated by stable isotope profiles

Stable carbon- (δ¹³C), nitrogen- (δ¹⁵N) and hydrogen (δD) isotope profiles in feathers of migratory Great Reed Warblers Acrocephalus arundinaceus recaptured for 2 or more years in 6 successive years were examined to test whether the isotope profiles of individual warblers appeared to be consistent between years. Similar isotopic signatures in successive years suggested that individual birds tended to return and grow their feathers in Afro-tropical wintering habitats that generate similar δ¹³C, δ¹⁵N and δD signatures. Previous studies have shown that Great Reed Warblers exhibit strong natal and breeding philopatry, with most of the surviving birds returning to the breeding site. The present study of feather δ¹³C, δ¹⁵N and δD isotopic values demonstrate the year-to-year fidelity might also include the African moulting sites in this migratory species.     

Migratory connectivity in a declining bird species: using feather isotopes to inform demographic modelling

Aim Conservation programmes for endangered migratory species or populations require locating and evaluating breeding, stopover and wintering areas. We used multiple stable isotopes in two endangered European populations of wrynecks, Jynx torquilla L., to locate wintering regions and assess the degree of migratory connectivity between breeding and wintering populations. Location Switzerland and Germany. Methods We analysed stable nitrogen (δ¹⁵N), carbon (δ¹³C) and hydrogen (δD) isotopes from wing feathers from two populations of wrynecks to infer their wintering origins and to assess the strength of migratory connectivity. We tested whether variation in feather isotopic values within the Swiss population was affected by bird age and collection year and then considered differences in isotopic values between the two breeding populations. We used isotopic values of summer‐ and winter‐grown feathers to estimate seasonal distributions. Finally, we calculated a species‐specific δD discrimination factor between feathers and mean annual δD values to assign winter‐grown feathers to origin. Results Bird age and collection year caused substantial isotopic variation in winter‐grown feathers, which may be because of annually variable weather conditions, movements of birds among wintering sites and/or reflect asynchronous moulting or selection pressure. The large isotopic variance in winter‐grown feathers nevertheless suggested low migratory connectivity for each breeding population, with partially overlapping wintering regions for the two populations. Main conclusions Isotopic variance in winter‐grown feathers of two breeding populations of wrynecks and their geographical assignment point to defined, albeit overlapping, wintering areas, suggesting both leapfrog migration and low migratory connectivity. On this basis, integrative demographic models can be built looking at seasonal survival patterns with links to local environmental conditions on both breeding and wintering grounds, which may elucidate causes of declines in migratory bird species.     

Comparison of trace element and stable isotope approaches to the study of migratory connectivity: an example using two hirundine species breeding in Europe and wintering in Africa

Analyses of stable isotopes and trace elements in feathers may provide important information about location and habitat use during molt, thereby enabling the investigation of migratory connectivity and its ecological consequences in bird species that breed and winter in different areas. We have compared the conclusions arrived at based on the use of these two methods on the same samples of feathers from two migratory birds, the Sand Martin Riparia riparia and the Barn Swallow Hirundo rustica. We investigated the effects of location, age and sex on stable isotope (δ¹³C, δ¹⁵N, δD) and trace element profiles (As, Cd, Mg, Mn, Mo, Se, Sr, Co, Fe, Zn, Li, P, Ti, V, Ag, Cr, Ba, Hg, Pb, S, Ni and Cu). The feathers of adults at the breeding grounds were removed, forcing in birds to grow new feathers at the breeding grounds; this enabled a comparison of composition of feathers grown in Europe and Africa by the same individual. Stable isotope and trace element profiles varied geographically, even at micro-geographic scales, and also among age classes. The results of both methods suggest that food composition and/or source differs between adults and nestlings in the breeding area and that food and/or molting location changes with the age of individuals in Africa. In an attempt to determine the usefulness of data obtained from composition of feathers, we performed discriminant function analyses on information obtained on stable isotopes and trace elements in order to assess the correctness of the classification of group membership. When feathers molted in Africa were compared to those molted in Europe, trace element profiles of the 22 elements generally had a much greater resolution than the stable isotope profiles based on three stable isotopes. The proportion of correctly classified samples was also greater for analyses based on trace elements than for those based on stable isotopes.     

A test of geographic assignment using isotope tracers in feathers of known origin

We used feathers of known origin collected from across the breeding range of a migratory shorebird to test the use of isotope tracers for assigning breeding origins. We analyzed δD, δ¹³C, and δ¹⁵N in feathers from 75 mountain plover (Charadrius montanus) chicks sampled in 2001 and from 119 chicks sampled in 2002. We estimated parameters for continuous-response inverse regression models and for discrete-response Bayesian probability models from data for each year independently. We evaluated model predictions with both the training data and by using the alternate year as an independent test dataset. Our results provide weak support for modeling latitude and isotope values as monotonic functions of one another, especially when data are pooled over known sources of variation such as sample year or location. We were unable to make even qualitative statements, such as north versus south, about the likely origin of birds using both δD and δ¹³C in inverse regression models; results were no better than random assignment. Probability models provided better results and a more natural framework for the problem. Correct assignment rates were highest when considering all three isotopes in the probability framework, but the use of even a single isotope was better than random assignment. The method appears relatively robust to temporal effects and is most sensitive to the isotope discrimination gradients over which samples are taken. We offer that the problem of using isotope tracers to infer geographic origin is best framed as one of assignment, rather than prediction.     

Linking breeding and wintering grounds of neotropical migrant songbirds using stable hydrogen isotopic analysis of feathers

 Recent studies have shown that stable hydrogen isotope ratios (δD) in the tissues of animals often correlate with δD of local precipitation. Here we examined the relationship between δD in feathers and growing season precipitation for neotropical migrant songbirds breeding over a continent-wide isotopic gradient. δD values were determined on feathers of 140 individuals of 6 species of wild insectivorous forest songbirds (Setophaga ruticilla, Empidonax minimus, Vermivora peregrinus, Catharus ustulatus, Seiurus aurocapillus, Hylocichla mustelina) taken from 14 breeding locations across North America. The δD of feathers was strongly correlated with the δD of growing season precipitation at breeding sites across North America. As feather hydrogen is metabolically inert after growth, this relationship was then used to assess the breeding origins of wintering migrants. Deuterium values of feathers from 64 individuals representing 5 species of migrants (Helmitheros vermivorus, Wilsonia citrina, Hylocichla mustelina, Dumetella carolinensis, Seirus aurocapillus) at a wintering site in Guatemala were consistent with those predicted from the known breeding ranges of these species. This study demonstrates hydrogen isotopes may become a powerful tool for linking breeding and wintering grounds of neotropical migrant songbirds, as well as other migratory species moving between isotopically distinct regions. Received: 25 August 1995 / Accepted: 28 May 1996     

Using stable-isotope analysis of feathers to distinguish moulting and breeding origins of seabirds

To determine whether stable isotope measurements of bird feathers can be used to identify moulting (interbreeding) foraging areas of adult seabirds, we examined the stable-carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic composition of feathers of chicks and adults of black-browed albatrosses (Diomedea melanophrys) from Kerguelen Islands, southern Indian Ocean. Albatross chicks are fed primarily fish (75% by mass), the diet being dominated by various species of the family Nototheniidae and Channichthyidae which commonly occur in the shelf waters in the vicinity of the colony. δ¹³C and δ¹⁵N values in chick feathers, which are grown in summer in the breeding area, were lower than values in adult feathers, which are grown in winter (δ¹³C: –19.6‰ versus –17.6‰ and δ¹⁵N: 12.4‰ versus 15.7‰, respectively). No differences in δ¹³C and δ¹⁵N values were found in adult wing feathers moulted in 1993 and 1994 and in adult feathers formed at the beginning, middle and end of the 1994 moulting period. These data are consistent with adults moulting in the same area and feeding at the same trophic level from one year to the next and with no major changes in foraging ecology within a given moulting season; they suggest that foraging grounds were different in summer and winter and that these differed in their stable-isotope signature. Changes in both feather δ¹³C and δ¹⁵N values indicated feeding south of the Subtropical Front (STF) during chick rearing, which is in agreement with the known foraging ecology at this time and feeding north of the STF during moult. This, together with band recoveries from adult birds, indicates that black-browed albatrosses from Kerguelen Islands wintered in subtropical waters off southern Australia. The stable-isotope markers in feathers, therefore, have the potential for locating moulting areas of migratory seabird species moving between isotopically distinct regions and for investigating seabirds’ foraging ecology during the poorly known interbreeding period. Such information is needed for studies of year-round ecology of seabirds as well as for their conservation and the long-term monitoring of the pelagic environment. Received: 28 June 1999 / Accepted: 14 September 1999     

Linking isotopic and migratory patterns in a pelagic seabird

The value of stable isotope analysis in tracking animal migrations in marine environments is poorly understood, mainly due to insufficient knowledge of isotopic integration into animal tissues within distinct water masses. We investigated isotopic and moult patterns in Cory’s shearwaters to assess the integration of different stable isotopes into feathers in relation to the birds’ transoceanic movements. Specimens of Mediterranean Cory’s shearwater Calonectris diomedea diomedea caught accidentally by Catalan longliners were collected and the signatures of stable isotopes of C (δ¹³C), N (δ¹⁵N) and S (δ³⁴S) were analysed in 11 wing and two tail feathers from 20 birds, and in some breast feathers. Based on isotopic signatures and moult patterns, the feathers segregated into two groups (breeding and wintering), corresponding to those grown in the Mediterranean or Atlantic regions, respectively. In addition, feathers grown during winter, i.e. moulted in Atlantic waters, were grouped into two isotopically distinct profiles, presumably corresponding to the two main wintering areas previously identified for Mediterranean Cory’s shearwater in tracking studies. N signatures mainly indicated the Mediterranean-to-Atlantic migration, whereas C and S signatures differed according to the Atlantic wintering area. Our results indicate that isotopic signatures from distant oceanic regions can integrate the feathers of a given bird and can indicate the region in which each feather was grown. This study thus underscores how stable isotope analysis can link marine animals to specific breeding and wintering areas, and thereby shed new light on studies involving assignment, migratory connectivity and carry-over effects in the marine environment. Xavier Ruiz deceased 27 April 2008.     

The influence of breeding colony and sex on mercury,selenium and lead levels and carbon and nitrogen stable isotope signatures in summer and winter feathers of <Emphasis Type="Italic">Calonectris</Emphasis> shearwaters

Contamination in marine foodwebs is nowadays of great environmental concern owing to the increasing levels of pollution in marine ecosystems from different anthropogenic sources. Seabirds can be used as indicators of regional contaminant patterns across large temporal and spatial scales. We analysed Hg, Se and Pb levels as well as stable isotope ratios of C (¹³C/¹²C, δ¹³C) and N (¹⁵N/¹⁴N, δ¹⁵N) in breeding- and winter-season feathers on males and females of two related shearwater species, providing information on spatiotemporal patterns of contaminants as well as the influence of the trophic ecology of these seabirds on contaminant levels. During the breeding season, Se and Pb concentrations were highest at the Cape Verde archipelago, showing no differences among the other colonies or between the sexes. However, Hg levels varied among colonies, being highest in the Mediterranean, probably resulting from the larger emissions and fallout of this pollutant in Europe. Feathers grown during breeding also showed sexual differences in Hg concentrations and δ¹³C. Differences in Hg concentration between sexes are mainly due to egg-laying decontamination in females. In contrast, differences in Hg among colonies are probably related to differences in trophic ecology, as indicated by δ¹³C and δ¹⁵N measurements. Contaminant concentrations in winter-grown feathers did not show any relationship with stable isotope values but were affected by contaminant loads associated with the breeding season. These findings suggest that the interpretation of contaminant levels of migratory species from feathers moulted out of the breeding season should be made with caution because those values could reflect exposures to contaminants acquired during the breeding season. We conclude that factors other than feeding ecology may play an important role in the interpretation of contaminant levels and their annual dynamics at several spatial scales. Consideration of the relevant temporal context provided by isotopic signatures and contaminant concentrations is important in deciphering contaminant information based on various tissues. Xavier Ruiz: deceased 27 April 2008.     

Range‐wide patterns of migratory connectivity in the western sandpiper Calidris mauri

Understanding the population dynamics of migratory animals and predicting the consequences of environmental change requires knowing how populations are spatially connected between different periods of the annual cycle. We used stable isotopes to examine patterns of migratory connectivity across the range of the western sandpiper Calidris mauri. First, we developed a winter isotope basemap from stable‐hydrogen (δD), ‐carbon (δ¹³C), and ‐nitrogen (δ¹⁵N) isotopes of feathers grown in wintering areas. δD and δ¹⁵N values from wintering individuals varied with the latitude and longitude of capture location, while δ¹³C varied with longitude only. We then tested the ability of the basemap to assign known‐origin individuals. Sixty percent of wintering individuals were correctly assigned to their region of origin out of seven possible regions. Finally, we estimated the winter origins of breeding and migrant individuals and compared the resulting empirical distribution against the distribution that would be expected based on patterns of winter relative abundance. For breeding birds, the distribution of winter origins differed from expected only among males in the Yukon‐Kuskokwim (Y‐K) Delta and Nome, Alaska. Males in the Y‐K Delta originated overwhelmingly from western Mexico, while in Nome, there were fewer males from western North America and more from the Baja Peninsula than expected. An unexpectedly high proportion of migrants captured at a stopover site in the interior United States originated from eastern and southern wintering areas, while none originated from western North America. In general, we document substantial mixing between the breeding and wintering populations of both sexes, which will buffer the global population of western sandpipers from the effects of local habitat loss on both breeding and wintering grounds.     

Hydrogen isotopic variation in migratory bird tissues of known origin: implications for geographic assignment

Continent-wide variation in hydrogen isotopic composition of precipitation is incorporated into animal diets, providing an intrinsic marker of geographic location at the time of tissue growth. Feathers from migratory birds are now frequently analyzed for stable-hydrogen isotopes (δD) to estimate the location of individuals during a preceding molt. Using known-origin birds, we tested several assumptions associated with this emerging technique. We examined hydrogen isotopic variation as a function of age, sex, feather type and the timing of molt in a marked population of American redstarts (Setophaga ruticilla) breeding in southeastern Ontario. We measured δD in feathers and blood from individuals that bred or hatched at our study site during the year in which those tissues were grown. Juvenile tissues from 5- to 10-day-old birds had more negative δD values than those from adults, which most likely reflected age-related differences in diet. Within adults, primary feathers had more negative δD values than contour feathers. The mean δD value in adult primary feathers was relatively consistent among years and with the value expected for our study population. However, among-individual variation in δD corresponded to an estimated latitudinal range of 6–8° (650–900 km). We conclude that feathers sampled from recently hatched juveniles may not provide a reliable estimate of expected local isotopic signatures for comparison with adult feathers of unknown origin. Furthermore, we urge researchers to use caution when using δD values in feathers to infer geographic origin, and suggest that the best approach is to assign individuals to broad geographic zones within a species’ potential molting range.     

Stable isotopes (δD and δ13C) are geographic indicators of natal origins of monarch butterflies in eastern North America

Wing membranes of laboratory and field-reared monarch butterflies (Danaus plexippus) were analyzed for their stable-hydrogen (δD) and carbon (δ¹³C) isotope ratios to determine whether this technique could be used to identify their natal origins. We hypothesized that the hydrogen isotopic composition of monarch butterfly wing keratin would reflect the hydrogen isotope patterns of rainfall in areas of natal origin where wings were formed. Monarchs were reared in the laboratory on milkweed plants (Asclepias sp.) grown with water of known deuterium content, and, with the assistance of volunteers, on native milkweeds throughout eastern North America. The results show that the stable hydrogen isotopic composition of monarch butterflies is highly correlated with the isotopic composition of the milkweed host plants, which in turn corresponds closely with the long-term geographic patterns of deuterium in rainfall. Stable-carbon isotope values in milkweed host plants were similarly correlated with those values in monarch butterflies and showed a general pattern of enrichment along a southwest to northeast gradient bisecting the Great Lakes. These findings indicate that natal origins of migratory and wintering monarchs in Mexico can be inferred from the combined δD and δ¹³C isotopic signatures in their wings. This relationship establishes that analysis of hydrogen and carbon isotopes can be used to answer questions concerning the biology of migratory monarch butterflies and provides a new approach to tracking similar migratory movements of other organisms. Received: 1 July 1998 / Accepted: 11 November 1998     

Foraging areas of Wilson’s storm-petrel Oceanites oceanicus in the breeding and inter-breeding period determined by stable isotope analysis

To understand the year-round ecology of seabirds it is necessary not only to study the birds in their breeding grounds, but also to gain information about their movements during the inter-breeding period. Especially for the smaller procellariiform species, such studies are still scarce, mainly due to methodological problems. The recovery rates of banded birds are low and satellite tracking devices still far too heavy to equip these small birds. Here, we present data on foraging areas of Wilson’s storm-petrel Oceanites oceanicus inferred from stable isotope analysis. We compared ratios of δ¹³C and δ¹⁵N between different life-history stages and between the breeding and inter-breeding period. Samples of adult and chick feathers, chick down and egg-white were taken between 1996 and 2005 on King-George-Island, South Shetland Islands. δ¹³C values can be clearly distinguished between the breeding and inter-breeding period. During the inter-breeding period, most pre-breeders foraged in the same area as breeders, but four pre-breeders were found to forage in latitudes north of the Subtropical Front. In the 2002 inter-breeding period adult birds wintered further north than in 2003, which is in line with the different locations of food rich frontal systems in these years. We show that isotope ratios of both δ¹³C and δ¹⁵N increase from egg white, over chick down to chick feathers. We suggest that this isotopic change, due to a change in both foraging location and diet between egg production and chick feeding, may be used to trace the shift from the use of maternal resources from the egg to the uptake of nutrients from the diet.     

Tracing origins and migration of wildlife using stable isotopes: a review

To understand the ecology of migratory animals it is important to link geographic regions used by individuals including breeding, wintering, and intermediate stopover sites. Previous conventional approaches used to track animal movements have relied on extrinsic markers and typically the subsequent recovery of individuals. This approach has generally been inappropriate for most small, or non-game animals. The use of intrinsic markers such as fatty acid profiles, molecular DNA analyses, and the measurement of naturally occurring stable isotopes in animal tissues offer alternative approaches. This paper reviews the use of stable isotope analyses (primarily δ¹³C, δ¹⁵N, δ³⁴S, δD, δ⁸⁷Sr) to trace nutritional origin and migration in animals. This approach relies on the fact that foodweb isotopic signatures are reflected in the tissues of organisms and that such signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs can carry with them information on the location of previous feeding. Such an approach has been used to track animal use of inshore versus offshore, marine versus freshwater, terrestrial C₃ versus marine, terrestrial mesic versus xeric, and C₃ versus C₄ or Crassulacean acid metabolism foodwebs. More recently, the use of stable hydrogen isotope analyses (δD) to link organisms to broad geographic origin in North America is based on large-scale isotopic contours of growing-season average δD values in precipitation. This technique, especially when combined with the assay of other stable isotopes, will be extremely useful in helping to track migration and movement of a wide range of animals from insects to birds and mammals. Future research to refine our understanding of natural and anthropogenic-induced isotopic gradients in nature, and to explore the use of stable isotopes of other elements, is recommended. Received: 1 July 1998 / Accepted: 9 December 1998     

Stable isotope and band-encounter analyses delineate migratory patterns and catchment areas of white-throated sparrows at a migration monitoring station

The Canadian Migration Monitoring Network consists of several fixed migration monitoring stations (MMS) that apply constant-effort protocols to track changes in the abundance of migratory birds. Such monitoring will be important for tracking long-term population trends of songbirds, especially for species breeding in remote areas such as the North American boreal forest. The geographical catchment sampled by individual MMS, however, remains largely unknown. Here, we used hydrogen isotope measurements (δD) of feathers of white-throated sparrows (Zonotrichia albicollis) moving through Delta Marsh MMS in Manitoba, Canada, to determine both wintering and breeding ground catchment areas monitored by this station. The δD of tail feathers, collected from spring and fall migrants delineated previous breeding or natal latitudes, ranging from the northern to the southern extremes of the western boreal forest. The δD values of head feathers grown on the wintering grounds and collected during spring migration revealed that individuals wintered in a broad region of the southeastern United States. The isotope data showed no relationship between estimated breeding/natal and wintering latitudes of white-throated sparrow populations. Stable isotope data provided little information on longitude. Band-encounter analyses, however, indicated a clear east–west segregation of these sparrows across Canada, supporting connectivity among breeding/natal and wintering longitudes over the entire scale of this species' range. Isotope analyses of multiple feather types representing different periods and geographic regions of the annual cycle can provide key information on migratory connectivity for species moving through dedicated MMS.     

Assigning birds to wintering and breeding grounds using stable isotopes: lessons from two feather generations among three intercontinental migrants

Geographic origins of populations and migration patterns of several vertebrate and invertebrate species have been inferred from geographically distinct isotopes in their tissues. To test the hypothesis that feathers grown on different continents would reflect continental differences of δD in precipitation and have significantly different stable isotope ratios, we analyzed stable isotopes in two generations of feathers from three bird species (American and Pacific golden-plovers, Pluvialis dominica and P. fulva, and northern wheatears Oenanthe oenanthe) that breed in North America and winter in South America, the South Pacific and Asia, and Africa. We found significant differences in stable isotope signatures between summer- and winter-grown feathers in the plovers, and our use of two generations of feathers provided similar variation to that reported in studies using larger sample sizes. In contrast to plovers, no differences were detected in isotope values between summer- and winter-grown feathers in wheatears. Discriminant analyses separated 80% of summer- and winter-grown feathers for each plover species. Nonetheless, an “assignment with exclusion” method adapted from population genetics to impart a measure of confidence in assigning individuals to groups of origin resulted in an overall accuracy among plovers of only 41%, compared with a 63% assignment accuracy when the exclusion criterion was removed. Thus, we were unable to accurately assign feathers to origin of growth on the continental scale. Moreover, using δD expectations for North America, we were unable to assign summer-grown plover feathers to within better than several thousand kilometers of their true origins. We urge researchers to carefully consider the ecology and physiology of their study organisms, statistical methodology, and the interpretation of results when using stable isotopes to infer the geographic origins of feather growth.     

Solving a Migration Riddle Using Isoscapes: House Martins from a Dutch Village Winter over West Africa

Background

The ability to connect breeding, stopover and wintering locations of populations of migratory birds greatly enhances our understanding of the phenomenon of migration and improves our chances of effectively conserving these species. Among Palearctic-Afrotropical migratory species, aerial insectivores like the house martin (Delichon urbicum) are sensitive to factors influencing the availability of flying insects, and have declined in recent decades. The strict aerial behaviour of martins severely limits ring recoveries on wintering grounds and so there is a dearth of information on where European breeding populations over-winter in Africa, and the relative effects of population regulation on breeding vs. wintering grounds. We used a newly developed multi-isotope (δ ²H, δ ¹³C, δ ¹⁵N) feather isoscape for Africa together with inferences from summarized ring return data based on longitude, to assign winter origins to birds captured at a breeding colony in The Netherlands.

Principal Findings

Based on isotopic analyses of winter-grown martin feathers, we used a likelihood-based assignment approach to describe potential wintering locations where molt occurred of individual house martins from a Dutch colony by assigning them to four potential isotopically distinct clusters in Africa. We found the overwhelming majority of Dutch martins were assigned to a geographical cluster associated with West Africa.

Conclusions/Significance

The existence of strong isotopic gradients and patterns in African foodwebs that support migratory wildlife allows for the spatial assignment of tissues grown there. The assignment of Dutch house martins to wintering grounds primarily in West Africa was in strong agreement with independent and indirect methods used to infer winter origins of this species based on the association between the Normalized Difference Vegetation Index (NDVI) in Africa and population patterns in Italy and the United Kingdom. These confirmatory data-sets underscore the importance of suitable habitats in West Africa to the conservation of migratory aerial insectivores and other species.     

The strength of migratory connectivity for birds en route to breeding through the Gulf of Mexico

The strength of migratory connectivity is a measure of the cohesion of populations among phases of the annual cycle, including breeding, migration, and wintering. Many Nearctic‐Neotropical species have strong migratory connectivity between breeding and wintering phases of the annual cycle. It is less clear if this strength persists during migration when multiple endogenous and exogenous factors may decrease the cohesion of populations among routes or through time along the same routes. We sampled three bird species, American redstart Setophaga ruticilla, ovenbird Seiurus aurocapilla, and wood thrush Hylocichla mustelina, during spring migration through the Gulf of Mexico region to test if breeding populations differentiate spatially among migration routes or temporally along the same migration routes and the extent to which within‐population timing is a function of sex, age, and carry‐over from winter habitat, as measured by stable carbon isotope values in claws (δ¹³C). To make quantitative comparisons of migratory connectivity possible, we developed and used new methodology to estimate the strength of migratory connectivity (MC) from probabilistic origin assignments identified using stable hydrogen isotopes in feathers (δ²H). We found support for spatial differentiation among routes by American redstarts and ovenbirds and temporal differentiation along routes by American redstarts. After controlling for breeding origin, the timing of American redstart migration differed among ages and sexes and ovenbird migration timing was influenced by carry‐over from winter habitat. The strength of migratory connectivity did not differ among the three species, with each showing weak breeding‐to‐spring migration MC relative to prior assessments of breeding‐wintering connectivity. Our work begins to fill an essential gap in methodology and understanding of the extent to which populations remain together during migration, information critical for a full annual cycle perspective on the population dynamics and conservation of migratory animals.     

87Sr/86Sr Chronostratigraphy and dolomitization history of the Seroe Domi Formation,Curaçao (Netherlands Antilles)

Summary The Seroe Domi Formation is a 350 m-thick sequence of Neogene marine limestones and silicilastic sandstones cropping out on the leeward coast of Cura?ao, Netherlands Antilles. Integrated analyses of lithofacies, biostratigraphy, geochemistry and Sr isotope model age analyses indicate that Seroe Domi Formation has experienced three major episodes of limestone diagenesis and dolomitization (Dolomites I, I′, and II) that have taken place after successive Mio-Plio-Pleistocene depositional and subaerial exposure events (Subunits 1, 2, and 3). Subunit 1, the lowermost 30 to 100 m of the Seroe Domi Formation, is composed of interbedded coralgal grainstone gravity flows, pelagic wackestones, and allochthonous blocks deposited in Middle Miocene deep-water (>500 m) fore-reef and carbonate slope environments. Subunit 2, the uppermost 250 m of the Seroe Domi Formation, consists of coralgal packstones with basement-derived siliciclastic sands that were deposted in shallowing fore-reef to reef-front environments during the Late Miocene to Pliocene. Subunit 3 siliciclastic sandstones were deposited during the Early Pleistocene within erosional cavities in the Subunit 2 limestones, and are overlain by Late Pleistocene Quaternary Limestone Terraces. The petrography, distribution and geochemistry of Dolomites I, I′ and II indicate that they were precipitated from seawater-freshwater mixing zone fluid environments. Dolomite rhombs and meteoric calcite cements within biomolds illustrate that the host Seroe Domi Formation limestones were subaerially exposed prior to each dolomitization event. Dolomite I (δ¹⁸O = +1.04 to +2.46% PDB; δ¹³C = −2.55 to −6.79 PDB;⁸⁷Sr/⁸⁶Sr=0.708866 to 0.708915; Zn=0 ppm; Cu=0 ppm) was precipitated from mixtures of seawater with isotopically-depleted freshwater during the late Middle Miocene. Dolomite I′ (δ¹⁸O = +2.08 to +3.55 PDB, δ¹³C = −1.53 to 1.69 PDB,⁸⁷Sr/⁸⁶Sr=0.708981−0.709030; Zn=0 ppm; Cu=0 ppm) was also precipitated from mixtures of seawater with isotopically-depleted freshwater, but during late Late Miocene. In contrast, Dolomite II (δ¹⁸O = +2.69 to +3.51 PDB; δ¹³C = −0.34 to +1.53 PDB;⁸⁷Sr/⁸⁶Sr=0.708954 to 0.709088; Zn=20 ppm; Cu=20 ppm) precipitated from late Early Pliocene mixtures of seawater with isotopically-depleted freshwater that had derived Zn, Cu, and less-radiogenic Sr from basalts comprising the Cura?ao basement.     

Fish scale δ<Superscript>15</Superscript>N and δ<Superscript>13</Superscript>C values provide biogeochemical tags of fish comparable in performance to element concentrations in scales and otoliths

Natural variability in stable isotope ratios and element concentrations in calcified structures of fish (e.g. scales and otoliths) has provided biogeochemical ‘tags’ for studying origins and movements of marine species, but has been little used in freshwater studies. We examine whether variability in scale δ¹⁵N and δ¹³C values of Salmo trutta L., could provide a tag of fish over small spatial scales in a small river catchment (River Dee, U.K.) and compared their performance as tags with that of scale/otolith element concentrations. Whole scale δ¹⁵N and δ¹³C values differed among six study sites and fish could be classified to their site of origin with a high degree of accuracy. Classifying fish to their site of capture was marginally superior using scale δ¹⁵N and δ¹³C values compared to that achieved using Sr, Mn, Ba and Mg in scale hydroxyapatite or otolith aragonite. Scale δ¹⁵N and δ¹³C values could therefore provide non-lethally collectable biogeochemical tags superior in performance to element concentrations in otoliths and scales. A comprehensive study of δ¹⁵N and δ¹³C values within freshwater systems would develop our understanding of factors influencing geographical variability in baseline δ¹⁵N and δ¹³C signatures.