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Though many recent tracking studies have uncovered considerable variation in the migratory routines of birds, the source of this variation is surprisingly poorly discussed. We hypothesize that a wealth of possible factors, including factors other than genetics, translate into these variable outcomes. To demonstrate how factors that are not inherited can shape migratory routine during development, we performed a translocation and delayed-release experiment with juvenile hand-raised black-tailed godwits Limosa limosa limosa that were carefully matched for ancestral background, releasing siblings 1000 km apart. Translocated juveniles adopted the spatiotemporal pattern of migration that is habitual for the population at the release location rather than the origin. This leads to a rejection of the hypothesis that the migration of inexperienced birds is only shaped by pre-release factors including genes, maternal material in the eggs and a common environment from hatching to fledging. Instead, these findings are consistent with inexperienced migrants also developing their knowledge and capacities through contextual individual learning, the precise nature of which now warrants study. That hand-raised godwits, depending on the context in which they are released, can be induced to show different migratory routines, wintering sites and breeding locations from their siblings, indicates that processes during development offer the substrate for rapid adaptation of long-distance migration., The dataset JuvSouthward contains all first southward-movements of the experimentally released Black-tailed Godwits during 2016&2017. The codename of each bird contains all information about release location and date. Further details about datacollection can be found in the main article. ##The dataset JuvNorthward contains all first northward-movements of the experimentally released Black-tailed Godwits during 2016&2017. The codename of each bird contains all information about release location and date. Further details about datacollection can be found in the main article.

1. Longitudinal tracking studies have revealed consistent differences in the migration patterns of individuals from the same populations. The sources or processes causing this individual variation are largely unresolved. As a result, it is mostly unknown how much, how fast, and when animals can adjust their migrations to changing environments. 2. We studied the ontogeny of migration in a long-distance migratory shorebird, the black-tailed godwit (Limosa limosa limosa), a species known to exhibit marked individuality in the migratory routines of adults. By observing how and when these individual differences arise, we aimed to elucidate whether individual differences in migratory behaviour are inherited or emerge as a result of developmental plasticity. 3. We simultaneously tracked juvenile and adult godwits from the same breeding area on their south- and northward migrations. To determine how and when individual differences begin to arise, we related juvenile migration routes, timing, and mortality rates to hatch date and hatch year. Then, we compared adult and juvenile migration patterns to identify potential age-dependent differences. 4. In juveniles, the timing of their first southward departure was related to hatch date. However, their subsequent migration routes, orientation, destination, migratory duration, and likelihood of mortality were unrelated to the year or timing of migration, or their sex. Juveniles left the Netherlands after all tracked adults. They then flew non-stop to West Africa more often and incurred higher mortality rates than adults. Some juveniles also took routes and visited stopover sites far outside the well-documented adult migratory corridor. Such juveniles, however, were not more likely to die. 5. We found that juveniles exhibited different migratory patterns than adults, but no evidence that these behaviours are under natural selection. We thus eliminate the possibility that the individual differences observed among adult godwits are present at hatch or during their first migration. This adds to the mounting evidence that animals possess the developmental plasticity to change their migration later in life in response to environmental conditions as those conditions are experienced.

The endangered continental Black-tailed Godwit ( Limosa limosa limosa) is a migratory ground-nesting wader breeding in a wide variety of open, wet habitats across Europe. Conservation research has concentrated on the causes of population decline, but we know surprisingly little about whether any resources limit local breeding populations and if so, whether these are resources for the adults or the chicks. We collected data from 63 key breeding sites in five countries across Europe to test whether, after correcting for differences in surveyed areas, the size of Godwit breeding populations was related to environmental variables (vegetation biomass, soil moisture) or food resources for adult birds (soil invertebrates) or chicks (vegetation dwelling arthropods) measured during different times of the reproductive cycle. We found the number of Godwit territories to be positively related to arthropod abundance during the chick-hatching period. We found additional, weaker support for a positive relation between Godwit territory numbers and the abundance of soil-dwelling invertebrates (mostly earthworms) at clutch laying, but not at chick-hatching. These relationships were observed across countries, while we found little support for relationships within countries, possibly due to the smaller range in conditions that exist within countries. Both vegetation growth and soil moisture weren’t related to Godwit territory numbers. Our results suggest that food abundance for chicks, and to a lesser extent adult birds, are key factors determining the size of local Godwit breeding populations. Conservation management aiming to enhance local Godwit populations should therefore consider the impacts of management strategies on the arthropod prey of chicks.

The Dutch breeding population of the black-tailed godwit Limosa limosa limosa has declined substantially over recent decades; the role of contaminants is unknown. We analysed liver samples from 11 adult birds found dead on their breeding grounds in SW Friesland 2016–2020, six from extensive, herb-rich grasslands, five from intensive grasslands. We carried out LC and GC wide-scope target analysis of more than 2400 substances, LC suspect screening for more than 60,000 substances, target analysis for Cd, Hg, Ni and Pb, organo-phosphate flame retardants (OPFRs), dechlorane plus compounds and selected polybrominated diphenyl ether flame retardants (PBDEs), and bioassay for polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/PDBFs) and dioxin-like polychlorinated biphenyls (dl-PCBs). Residues of 29 emerging contaminants (ECs) were determined through wide-scope target analysis. Another 20 were tentatively identified through suspect screening. These contaminants include industrial chemicals (personal care products, surfactants, PAHs and others), plant protection products (PPPs) and pharmaceuticals and their transformation products. Total contaminant load detected by wide-scope target analysis ranged from c. 155 to c. 1400 ng g−1 and was generally lower in birds from extensive grasslands. Heatmaps suggest that birds from intensive grasslands have a greater mix and higher residue concentrations of PPPs, while birds from extensive grasslands have a greater mix and higher residue concentrations of per- and polyfluoroalkyl substances (PFAS). All four metals and two OPFRs were detected. All tested PBDEs were below the respective LODs. Bioassay revealed presence of PBDDs, PBDFs and dl-PCBs. Further research is required to elucidate potential health risks to godwits and contaminant sources.

In this paper, we extend our understanding of the migration of Black-tailed Godwits (Limosa limosa limosa) by describing: (1) the orientation and geographic locations of individual migratory routes and (2) the spatial distribution of godwits across seasons and years. We accomplish this using satellite-tracking data from 36 adult godwits breeding in the 200-ha Haanmeer polder in The Netherlands, from 2015 to 2018. During both southward and northward migration, godwits used a narrow migratory corridor along which most individuals made stops within a network of sites, especially the Bay of Biscay, France and Doñana, Spain. Most sites were used consistently by the same individuals across years. However, sites in Morocco were used during northward migration by 75% of individuals, but not revisited by the same individual across years. After southward migration, a small proportion (15%) of godwits spent the entire non-breeding period north of the Sahara, but most (85%) crossed the Sahara and spent at least part of the non-breeding season among seven coastal sites in West Africa and one site in the Inner Niger Delta. Although site-use patterns varied among individuals, individuals showed high site fidelity and were consistent in the number of sites they used from year to year. The considerable differences in the spatial distribution of individuals that breed within a kilometre of one another raise questions about the causes and consequences of individual migratory differences. We discuss that full annual cycle tracking of juveniles from birth to adulthood is needed to understand the source of these individual differences. Our results on the spatial distribution of godwits throughout their annual cycle lay an important foundation of information that can be used to help conserve this declining species.

Long‐term population studies can identify changes in population dynamics over time. However, to realize meaningful conclusions, these studies rely on accurate measurements of individual traits and population characteristics. Here, we evaluate the accuracy of the observational methods used to measure reproductive traits in individually marked black‐tailed godwits (Limosa limosa limosa). By comparing estimates from traditional methods with data obtained from light‐level geolocators, we provide an accurate estimate of the likelihood of renesting in godwits and the repeatability of the lay dates of first clutches. From 2012 to 2018, we used periods of shading recorded on the light‐level geolocators carried by 68 individual godwits to document their nesting behaviour. We then compared these estimates to those simultaneously obtained by our long‐term observational study. We found that among recaptured geolocator‐carrying godwits, all birds renested after a failed first clutch, regardless of the date of nest loss or the number of days already spent incubating. We also found that 43% of these godwits laid a second replacement clutch after a failed first replacement, and that 21% of these godwits renested after a hatched first clutch. However, the observational study correctly identified only 3% of the replacement clutches produced by geolocator‐carrying individuals and designated as first clutches a number of nests that were actually replacement clutches. Additionally, on the basis of the observational study, the repeatability of lay date was 0.24 (95% CI 0.17–0.31), whereas it was 0.54 (95% CI 0.28–0.75) using geolocator‐carrying individuals. We use examples from our own and other godwit studies to illustrate how the biases in our observational study discovered here may have affected the outcome of demographic estimates, individual‐level comparisons, and the design, implementation and evaluation of conservation practices. These examples emphasize the importance of improving and validating field methodologies and show how the addition of new tools can be transformational.

Variation in migratory behavior is the result of different individual strategies and fluctuations in individual performances. A first step toward understanding these differences in migratory behavior among individuals is, therefore, to assess the relative contributions of inter- and intra-individual differences to this variation. We did this using light-level geolocators deployed on the breeding grounds to follow continental black-tailed godwits (Limosa limosa limosa) throughout their south- and northward migrations over multiple years. Based on repeated tracks from 36 individuals, we found two general patterns in godwit migratory behavior: First, migratory timing in black-tailed godwits varies mostly because individual godwits migrate at different times of the year. Second, individuals also exhibit considerable variation in timing within their respective migratory windows. Although the absolute amount of inter-individual variation in timing decreased over the course of northward migration, individual godwits still arrived at their breeding grounds across a span of more than 5 weeks. These differences in migratory timing among individuals are larger than those currently observed in other migratory bird species and suggest that the selective forces that limit the variation in migratory timing in other species are relaxed or absent in godwits. Furthermore, we could not attribute these individual differences to the sex or wintering location of an individual. We suggest that different developmental trajectories enabled by developmental plasticity likely result in these generally consistent, life-long annual routines. To investigate this possibility and to gain an understanding of the different selection pressures that could be acting during migration and throughout a godwit's life, future studies should track juvenile godwits and other migratory birds from birth to adulthood while also manipulating their spatiotemporal environment during development.

Over the past 50 years, the population of Continental Black-tailed Godwits Limosa limosa limosa breeding of the East Atlantic Flyway has been in steep decline. This decline has previously been documented in trend analyses and six Netherlands-wide count-based population estimates, the last of which was completed in 1999. We provide an updated population size estimate and describe inter-annual fluctuations in the population between 2007 and 2015. To generate these estimates, we integrated a mark-recapture survival analysis with estimates of the densities of colour-marked individuals at migratory staging sites with known proportions of Continental and Icelandic L. l. islandica Black-tailed Godwits within a Bayesian framework. The use of these analytical techniques means that, in contrast with earlier efforts, our estimates are accompanied with confidence intervals, allowing us to estimate the population size with known precision. Using additional information on the breeding destination of 43 godwits equipped with satellite transmitters at Iberian staging areas, we found that 87% (75-95% 95% CI) of the nominate subspecies in the East Atlantic Flyway breed in The Netherlands. We estimated that the number of breeding pairs in The Netherlands has declined from 47,000 (38,000-56,000) pairs in 2007 to 33,000 (26,000-41,000) in 2015. Despite a temporary increase in 2010 and 2011, the population declined by an average of 3.7% per year over the entire period from 2007-2015, and by 6.3% from 2011-2015. We conclude that investing in an intensive demographic programme at a regional scale, when combined with targeted resightings of marked individuals elsewhere, can yield population estimates at the flyway scale., This study was funded mainly by the former Netherlands Ministry of Agriculture, Nature Management and Food Safety, now subsumed in the Ministry of Economic Affairs, by the Province of Fryslân, and by the Spinoza Premium Award 2014 from The Netherlands Organization for Scientific Research (NWO) to TP, with some additional funding by the Prins Bernard Cultuurfonds, the Van der Hucht Beukelaar Stichting, BirdLife Netherlands and WWF-Netherlands through Global Flyway Network and the Chair in Flyway Ecology, FP7-Regpot project ECOGENES (Grant No. 264125), the NWO-TOP grant ‘Shorebirds in space’ (854.11.004) awarded to TP, ExpeER Ecosystem Research, ‘ICTS-RBD’ to the ESFRI LifeWatch, MINECO, and European Union Structural Funds (AIC-A2011-0706).

Annual routines of migratory birds inferred from archival solar geolocation devices have never before been confirmed using GPS technologies. A female black-tailed godwit Limosa limosa limosa captured on the breeding grounds in The Netherlands in 2013 and recaptured in 2014 was outfitted with both an Intigeo geolocator and an UvA-BiTS GPS-tracker. The GPS positions show that, after its breeding season in 2013, the godwit flew 2035 km nonstop from The Netherlands to southern Spain. It then spent the entire nonbreeding season in the southern part of the Iberian Peninsula before returning to The Netherlands the following spring, stopping for 7 days in the delta of the Ebro River in Spain, and again for a day in central Belgium. To compare the geolocation and GPS data, we analysed the geolocation data with two open-source software packages: one using a threshold method (GeoLight) and the other a template-fit approach (FLightR). Estimates using GeoLight, on average, deviated from the individual's true position by 495.5 ± 1031.2 km (great circle distance with equinoxes excluded), while FLightR estimates deviated by 43.3 ± 51.5 km (great circle distance with equinoxes included). Arrival and departure schedules estimated by FLightR were within 12 hours of those determined by the GPS tracker, whereas GeoLight's estimates were less precise. For the analysed track, FLightR represents an improvement over GeoLight; if true for other species and conditions, FLightR will hopefully help establish more precise and accurate uses of geolocation data in tracking studies. To aid future improvements in the analysis of solar geolocation data, we also provide the GPS and geolocation data files together with our R scripts as supplementary material.This article is protected by copyright. All rights reserved.

Publisher's version (útgefin grein), Few studies have been able to directly measure the seasonal survival rates of migratory species or determine how variable the timing of migration is within individuals and across populations over multiple years. As such, it remains unclear how likely migration is to affect the population dynamics of migratory species and how capable migrants may be of responding to changing environmental conditions within their lifetimes. To address these questions, we used three types of tracking devices to track individual black-tailed godwits from the nominate subspecies (Limosa limosa limosa) throughout their annual cycles for up to 5 consecutive years. We found that godwits exhibit considerable inter- and intra-individual variation in their migratory behavior across years. We also found that godwits had generally high survival rates during migration, although survival was reduced during northward flights across the Sahara Desert. These patterns differ from those observed in most other migratory species, suggesting that migration may only be truly dangerous when crossing geographic barriers that lack emergency stopover sites and that the levels of phenotypic flexibility exhibited by some populations may enable them to rapidly respond to changing environmental conditions., We thank the many members of our field crews from 2004 to 2015 for their assistance in the field. We also thank S. Pardal, M. Parejo-Nieto, A. Villegas-Sánchez, and the rest of the teams from Badajoz and Lisboa for help with satellite transmitter instrumentation. A. Stokman, W. Nauta, S. Venema, Staatsbosbeheer, It Fryske Gea, ANV Súdwesthoeke, and Kuststripe, and many other land managers and farmers were gracious in allowing us access to their land. Local bird conservation communities—including Fûgelwachten Makkum, Warkum, Koudum-Himmelum, Oudega, Gaastmeer, and Stavoren-Warns—provided locations of many nests. E. Rakhimberdiev greatly assisted with the geolocator analyses, J. R. Conklin helpfully made available his bar-tailed godwit repeatability data, and T. L. Tibbitts curated the satellite tracking data from 2013 to 2015. Funding for NS, MV, and their fieldwork was provided by NWO-ALW TOP grant Shorebirds in space (854.11.004) awarded to TP. RK is funded by the Royal Society. JA benefited from a Fundação para a Ciência e Tecnologia grant (SFRH/BPD/91527/2012). Long-term godwit research was funded by the Kenniskring weidevogels of the former Ministry of Agriculture, Nature Management and Food Safety (2007–2010, 2012, 2016); the Province of Fryslân (2013–2016); and the Spinoza Premium 2014 of the Netherlands Organization for Scientific Research (NWO) awarded to TP. Additional financial support came from the Prins Bernhard Cultuurfonds (through It Fryske Gea), the Van der Hucht de Beukelaar Stichting, the Paul and Louise Cook Endowment Ltd., the University of Groningen, BirdLife-Netherlands, and WWF-Netherlands. This work was done under license number 6350A, C, and G following the Dutch Animal Welfare Act Articles 9 and 11.

Publisher's version (útgefin grein)., Mechanisms underlying fat accumulation for long-distance migration are not fully understood. This is especially relevant in the context of global change, as many migrants are dealing with changes in natural habitats and associated food sources and energy stores. The continental Black-tailed godwit Limosa limosa limosa is a long-distance migratory bird that has undergone a considerable dietary shift over the past few decades. Historically, godwits fed on an animal-based diet, but currently, during the non-breeding period godwits feed almost exclusively on rice seeds. The latter diet may allow building up of their fuel stores for migration by signifcantly increasing de novo lipogenesis (DNL) activity. Here, we performed an experiment to investigate lipid fux and the abundance of key enzymes involved in DNL in godwits, during fasting and refueling periods at the staging site, while feeding on rice seeds or fy larvae. Despite no signifcant diferences found in enzymatic abundance (FASN, ME1, ACC and LPL) in stored fat, experimental godwits feeding on rice seeds presented high rates of DNL when compared to fy-larvae fed birds (~35 times more) and fasted godwits (no DNL activity). The increase of fractional DNL in godwits feeding on a carbohydrate-rich diet can potentially be enhanced by the fasting period that stimulates lipogenesis. Although requiring further testing, these recent fndings provide new insights into the mechanisms of avian fat accumulation during a fasting and refueling cycle and associated responses to habitat and dietary changes in a migratory species., Te authors acknowledge fnancial support from Fundação para a Ciencia e Tecnologia (FCT) in the form of fellowships to PMA (SFRH/BD/69238/2010), IV (SFRH/BPD/90032/2012) and JAA (SFRH/BPD/91527/2012) and research Project CGL2017-89009-P. NMR data were collected at the UC-NMR facility that is supported by FEDER and FCT (RECI/QEQ-QFI/0168/2012, CENTRO-07-CT62-FEDER-002012) and Rede Nacional de Ressonancia Magnética Nuclear (RNRMN). Tis study benefted from funding by the strategic program of MARE, fnanced by FCT (UID/MAR/04292/2019), and by FTC/MCTES to CESAM, (UID/AMB/50017 – POCI01-0145-FEDER-007638), through national funds.

[Capsule] Most Continental Black-tailed Godwits Limosa limosa limosa using the Doñana wetlands during post-breeding migration appear to begin moult before they arrive and suspend moult before they migrate onwards to West Africa., [Aims] We aim to describe the primary moult strategies and patterns in the Continental Black-tailed Godwits using the Doñana wetlands, a major passage and wintering area for waterbirds in southern Spain., [Methods] Individual godwits were captured, marked and their primary moult was scored in Doñana during the non-breeding season (June–March) in 2011 and 2012. Data from resightings of colour-marked godwits and birds equipped with satellite transmitters were used to estimate stopover duration during post-breeding migration (June–September) to determine if godwits move to West Africa before completing their primary moult., [Results] Average primary moult duration was estimated to be 84 days ± 9 se, during 29 June–21 September and did not differ between sexes. Only 2% of individuals were observed with suspended moult. We estimated stopover duration in Doñana to be 13 days ± 2 se before migrating to West Africa., [Conclusions] Most godwits stage for about two weeks in the Doñana wetlands during southward migration, moult their primaries and appear to suspend moult before crossing the Sahara. Others may complete their primary moult in Doñana, or elsewhere in Europe and overwinter in Doñana where increasing numbers of godwits have been detected in recent years. A few individuals may finish the moult in Doñana and migrate to West Africa late in the post-breeding season.

Sexual size dimorphism (SSD) is common in birds and has been linked to various selective forces. Nevertheless, the question of how and when the sexes start to differentiate from each other is poorly studied. This is a critical knowledge gap, as sex differences in growth may cause different responses to similar ecological conditions. In this study, we describe the sex-specific growth - based on body mass and five morphometric measurements - of 56 captive Black-tailed Godwit Limosa limosa limosa chicks raised under adlibitum food conditions, and conclude that all six growth curves are sex-specific. Females are the larger sex in terms of body mass and skeletal body size. To test whether sex-specific growth leads to sex-specific susceptibility to environmental conditions, we compared the age-specific sizes of male and female chicks in the wild with those of Black-tailed Godwits reared in captivity. We then tested for a relationship between residual growth and relative hatching date, age, sex and habitat type in which the wild chicks were born. Early-hatched chicks were relatively bigger and in better condition than late-hatched chicks, but body condition and size were not affected by natal habitat type. Female chicks deviated more negatively from the sex-specific growth curves than male chicks for body mass and total-head length. This suggests that the growth of the larger females is more susceptible to limiting environmental conditions. On average, the deviations of wild chicks from the predicted growth curves were negative for all measurements, which suggests that conditions are limiting in the current agricultural landscape. We argue that in estimating growth curves for sexually dimorphic species, it is critical first to make accurate sex and age determinations.

SummaryMapping migratory routes and the distribution of species during migration requires information collected over large scales (e.g. survey data), or the ability to follow specific movements (e.g. using tracking devices), which is often limited to a few individuals. For endangered species, such techniques may be impractical, but developments in flight range modelling allow inferences about migratory routes and potential site occupancy, given a few morphological parameters. We modelled flight range in a rapidly declining population of continental Black-tailed Godwits Limosa limosa limosa departing from a staging site in Iberia during spring migration and found that the vast majority of godwits are able to reach the breeding grounds in a single flight. Contrary to the traditional use of staging sites in France (and Morocco), godwits currently staging in Iberia are predicted to fly directly to The Netherlands and be present at breeding locations earlier than previously expected and observed. Despite harbouring approximately 75% of the total population during spring migration, Iberian staging sites currently lack any legal protection. Our example of the Black-tailed Godwit illustrates the potential of this approach to identify migration strategies and locate staging sites for species of conservation concern for which such information may be virtually absent.

Conservation of long-distance migratory shorebirds is complex because these species use habitats spread across continents and hemispheres, making identification of critical habitats and potential bottlenecks in the annual cycle especially difficult. The population of Black-tailed Godwits that breeds in Western Europe, Limosa limosa limosa, has declined precipitously over the past few decades. Despite significant efforts to identify the root causes of this decline, much remains unclear. To better understand the migratory timing, use of stopover and nonbreeding sites, and the potential impact of breeding success on these parameters, we attached 15 Argos satellite transmitters and 10 geolocation tracking devices to adult godwits nearing completion of incubation at breeding sites in southwest Friesland, The Netherlands during the spring of 2009. We successfully tracked 16 adult godwits for their entire southward migration and two others for part of it. Three migration patterns and four regions of use were apparent. Most godwits left their breeding sites and proceeded south directly to stopover sites in the Mediterranean — e.g. Spain, Portugal, and Morocco — before flying on to non-breeding sites in West Africa. Other individuals spent the entire nonbreeding season in the Mediterranean. A third pattern included a few individuals that flew nonstop from their Dutch breeding sites to nonbreeding sites in West Africa. Tracking data from this study will be immediately useful for conservation efforts focused on preserving the dispersed network of sites used by godwits during their southward migration.

Over the last decades the Continental European population of black-tailed godwits, Limosa limosa limosa, has shown steep declines as a consequence of agricultural intensification on the breeding grounds. Although numbers have also declined in their traditional wintering areas in West-Africa, in the Doñana wetlands of southwestern Spain high nonbreeding numbers have persisted. Here we provide a long-term (35. year, 1977-2011) analysis of godwit numbers in Doñana. In fact, from the mid 1990s there has been a steep increase in numbers so that the fraction of godwits along this flyway that winters in Doñana increased from 4% in the late 1980s to 23% in 2011. These changes were not correlated with climatic conditions in Spain, nor in Sahel, but they were associated with changes in habitat availability - mainly an increase in man-made artificial wetlands. Commercial fish-farms and rice fields provide alternative habitats to the original seasonal marshlands for daytime roosting (mainly in the fish ponds) or nocturnal foraging (probably rice fields in addition to fish ponds). For migrating waterbirds, degradations of natural wetlands can thus be compensated by man-made alternative habitats. As the availability especially of such man-made areas is highly sensitive to short-term political/economic driven decision-making, they should be given greater consideration in global conservation plans. © 2014 Elsevier Ltd.

Recently, Schroeder etal. (2010, Ibis 152: 368-377) suggested that intronic variation in the CHD1-Z gene of Black-tailed Godwits breeding in southwest Friesland, The Netherlands, correlated with fitness components. Here we re-examine this surprising result using an expanded dataset (2088 birds sampled from 2004 to 2010 vs. 284 birds from 2004 to 2007). We find that the presence of the Z* allele (9% of the birds) is not associated with breeding habitat type, egg size, adult survival, adult body mass or adult body condition. The results presented here, when used in synergy with the previously reported results by Schroeder etal., suggest that there might be a tendency towards female adults with the Z* allele laying earlier clutches than adult females without the Z* allele. The occurrence of the Z* allele was also associated with a higher chick body mass and return rate. Chicks with the Z* allele that had hatched early in the breeding season were heavier at birth than chicks without the Z* allele and chicks with the Z* allele that had hatched late. Collectively, the results suggest that variation in the CHD1-Z gene may indeed have arisen as a byproduct of selection acting on females during the egg fase and on chicks during the rearing stages of the reproductive cycle.

In sexually dimorphic species, males with more exaggerated plumage ornamentation generally have higher body condition, are preferred by females, and have higher reproductive output. In contrast to the majority of studies, we describe that less ornamented males of the monogamous and sexually dimorphic black-tailed godwit Limosa limosa were larger and heavier during late incubation than more ornamented males and were mated with females that laid larger eggs. In females, we detected no such correlations. If paler and larger males indeed have higher fitness, this suggests ongoing selection for a reduction in male ornamentation, leading to a decrease in plumage ornamentation. We found evidence for such a change since 1840: Male ornamentation in museum specimens became progressively less in all our measured plumage traits. One explanation for this could be that formerly sexually selected plumage traits are now selected against and that the sexual plumage dimorphism of WestEuropean breeding black-tailed godwits might be waning. Concomitant with this change in plumage coloration, this species has experienced enormous human-mediated changes in both breeding and nonbreeding habitat, and we suggest that these might have led to increased costs or reduced fitness benefits for highly ornamented male godwits. Key words: contemporary evolution, egg size, Limosa limosa limosa, meadow bird, plumage coloration, sexual selection. [Behav Ecol]

SUMMARYThe karyotypes of five species of charadriiform birds (three of which are new to cytology) belonging to two families, Charadriidae (Vanellus spinosus duvaucelii, Pluvialis squatarola, Pluvialis dominica fulva, Charadrius alexandrinus alexan-drinus) and Scolopacidae (Limosa limosa limosa) are described. For the sake of comparison, the karyotype of Vanellus malabaricus is also described. The karyological relationships in both the families are discussed in detail.

Capsule Black-tailed Godwits first return to the nest location of the previous year, even when moving to a different nest location later that season.Aims To examine the use of space by Black-tailed Godwits during the two months before egg-laying to two weeks afterwards.Methods We compare the spatial distribution of sightings of eventually site-faithful birds with birds that changed nest location, and relate this to the change of the distance to their previous year's and current nest-site in the period until egg-laying. Using a log-likelihood model we establish how the differences in distance to the respective nests change over the course of the season.Results All birds were observed first near their previous year's nest-site, and remained there for most of the pre-laying period. Birds that subsequently changed nest location made the move only about five days before egg-laying and were more wide-ranging earlier on.Conclusion The return to the previous nest-site suggests that a decision to move is made only after considerable time investment near the previous nest-site. This indicates that site-faithfulness in Black-tailed Godwits is conditional on experiences after return to the nesting area.