On the behaviour and ecology of the Black-tailed Godwit

Migration: The large variation in the migration of godwits is mostly the result of consistent differences between individuals. These differences are large compared to other migratory bird species. The survival of godwits during migration is also higher compared to other bird species. The mortality that does occur on migration is mostly the result of adverse wind conditions during northward Sahara crossings.The considerable variation in the migration of godwits might therefore result from an absence of a consistent selection pressure during migration. The consistent differences among individuals develop during multiple years of life. A translocation experiment to Poland with naïve juveniles from The Netherlands showed that the development of their migratory direction and wintering location was not merely inherited. Polish individuals are less consistent in their migration than those from The Netherlands. This might be because there is less canalization through social factors in the lower density Polish population. Population: Godwits are monogamous, but do sometimes lay eggs in the nests of other godwits. Individuals lay similarly sized eggs every year. Our traditional observation methods often fail to capture the first nest and the renests of individual godwits. This observational bias has led to biased estimates in the past. Even though the sex ratio at hatch is equal, higher survival of male chicks and adults leads to a surplus of males. Sexual dimorphism develops during the chick phase in godwits and needs to be accounted for when evaluating the condition of chicks

Earthworm abundance and availability does not influence the reproductive decisions of black-tailed godwits in an agricultural grassland

Maintaining the biodiversity of agricultural ecosystems has become a global imperative. Across Europe, species that occupy agricultural grasslands, such as black-tailed godwits (Limosa limosa limosa), have undergone steep population declines. In this context, there is a significant need to both determine the root causes of these declines and identify actions that will promote biodiversity while supporting the livelihoods of farmers. Food availability, and specifically earthworm abundance (Lumbricidae), during the pre-breeding period has often been suggested as a potential driver of godwit population declines. Previous studies have recommended increasing the application of nitrogen to agricultural grasslands to enhance earthworm populations and aid agricultural production. Here we test whether food availability during the pre-breeding period affects when and where godwits breed. Using large-scale surveys of food availability, a long-term mark-recapture study, focal observations of foraging female godwits, and tracking devices that monitored godwit movements, we found little evidence of a relationship between earthworm abundance and the timing of godwit reproductive efforts or the density of breeding godwits. Furthermore, we found that the soils of intensively managed agricultural grasslands may frequently be too dry for godwits to forage for those earthworms that are present. The increased application of nitrogen to agricultural grasslands will therefore likely have no positive effect on godwit populations. Instead, management efforts should focus on increasing the botanical diversity of agricultural grasslands, facilitating conditions that prevent hardening soils, and reducing the populations of generalist predators. </ol

Fuelling and moult in Red Knots before northward departure:A visual evaluation of differences between ages, sexes and subspecies

The departure of migratory birds from their non-breeding grounds is thought to be driven by the phenology of their breeding destination. In north-west Australia, two plumage morphs of Red Knot (Calidris canutus) prepare for a 5500-km journey to Yellow Sea staging areas. These morphs are recognised as the subspecies C. c. piersmai and C. c. rogersi, which breed at different latitudes and have different seasonalities. From February to May 2011, we observed the migratory preparation of individually marked birds of known age, sex and type. This enabled a comparison of fuelling rates and pre-alternate moult among these classes. First-year birds did not prepare for migration. Second-year birds accumulated smaller fuel stores and reached lower plumage scores than adults. Adults of both types reached their highest abdominal profile scores by the end of April when they were last observed in Roebuck Bay. This lack of difference between types in the timing of fuelling and departure is surprising. Based on the differences in staging and breeding phenology, C. c. rogersi is expected to leave north-west Australia 2–4 weeks before C. c. piersmai. Assuming that types and subspecies are equivalent, our findings in combination with other research on Red Knots in the East Asian–Australasian Flyway suggest that it takes more than breeding origin alone to explain annual cycles in migratory birds. Concurrent migratory schedules imply that, during northward staging in the Yellow Sea, there is strong variation in fuelling rates between and within subspecies depending on non-breeding origin. The ongoing loss of staging habitat may therefore have differential effects on Red Knots in the East Asian–Australasian Flyway

Adverse wind conditions during northward Sahara crossings increase the in-flight mortality of Black-tailed Godwits

Long-distance migratory flights are predicted to be associated with higher mortality rates when individuals encounter adverse weather conditions. However, directly connecting environmental conditions experienced in-flight with the survival of migrants has proven difficult. We studied how the in-flight mortality of 53 satellite-tagged Black-tailed Godwits (Limosa limosa limosa) during 132 crossings of the Sahara Desert, a major geographical barrier along their migration route between The Netherlands and sub-Saharan Africa, is correlated with the experienced wind conditions and departure date during both southward and northward migration. We show that godwits experienced higher wind assistance during southward crossings, which seems to reflect local prevailing trade winds. Critically, we found that fatal northward crossings (15 deaths during 61 crossings) were associated with adverse wind conditions. Wind conditions during migration can thus directly influence vital rates. Changing wind conditions associated with global change may thus profoundly influence the costs of long-distance migration in the future

Current breeding distributions and predicted range shifts under climate change in two subspecies of Black-tailed Godwits in Asia

Habitat loss and shifts associated with climate change threaten global biodiversity, with impacts likely to be most pronounced at high latitudes. With the disappearance of the tundra breeding habitats, migratory shorebirds that breed at these high latitudes are likely to be even more vulnerable to climate change than those in temperate regions. We examined this idea using new distributional information on two subspecies of Black-tailed Godwits Limosa limosa in Asia: the northerly,bog-breeding L. l. bohaii and the more southerly, steppe-breeding L. l. melanuroides. Based on breeding locations of tagged and molecularly assayed birds, we modelled the current breeding distributions of the two subspecies with species distribution models, tested those models for robustness, and then used them to predict climatically suitable breeding ranges in 2070 according to bioclimatic variables and different climate change scenarios. Our models were robust and showed that climate change is expected to push bohaii into the northern rim of the Eurasian continent. Melanuroides is also expected to shift northward, stopping in the Yablonovyy and Stanovoy Ranges, and breeding elevation is expected to increase. Climatically suitable breeding habitatranges would shrink to 16% and 11% of the currently estimated ranges of bohaii and melanuroides, respectively. Overall, this study provides the first predictions for the future distributions of two little-known Black-tailed Godwit subspecies and highlights the importance of factoring in shifts in bird distribution when designing climate-proof conservation strategies.</p

Individual Black-tailed Godwits do not stick to single routes:A hypothesis on how low population densities might decrease social conformity

The miniaturization of tracking devices is now rapidly increasing our knowledge on the spatiotemporal organization of seasonal migration. So far, most studies aimed at understanding within- and between-individual variation in migratory routines focus on single populations. This has also been the case for continental Black-tailed Godwits Limosa l. limosa (hereafter Godwits), with most work carried out on individuals from the Dutch breeding population, migrating in relatively large numbers in the westernmost part of the range. Here we report the migratory timing and routes of four adult individuals of the same subspecies from the low-density population in eastern Poland and compare this with previously published data on Godwits breeding in The Netherlands. During northward migration, the birds from Poland departed and arrived later from their wintering and breeding grounds. However, on southward migration the Polish breeding Godwits departed earlier, but arrived one month later than the Dutch birds on their wintering grounds in sub-Saharan Africa. Despite the small sample size of tracked birds from Poland, we find a significantly higher between-individual variation in timing during southward migration in Polish Godwits as compared to the Dutch Godwits. Furthermore, not only did migratory routes differ, but the few Polish Godwits tracked showed a higher level of between- and within-individual variation in route choice during both southward and northward migration. To explain this remarkable discrepancy, we propose that the properties of transmission of social information may be different between Godwits from a high-density population (i.e. the one in The Netherlands) and a low-density population (in Poland) and that this leads to different levels of canalization. To examine this hypothesis, future studies should not only follow individuals from an early age onwards, but also quantify and experimentally manipulate their social environments during migration

Misidentification errors in reencounters result in biased estimates of survival probability from CJS models: Evidence and a solution using the robust design

Misidentification of marked individuals is unavoidable in most studies of wild animal populations. Models commonly used for the estimation of survival from such capture–recapture data ignore misidentification errors potentially resulting in biased parameter estimates. With a simulation study, we show that ignoring misidentification in Cormack–Jolly–Seber (CJS) models results in systematic positive biases in the estimates of survival and in spurious declines of survival over time. We developed an extended robust design capture mark–resight (RDM) model that includes correct identification parameters to get unbiased survival estimates when resighting histories are prone to misidentification. The model assumes that resightings occur repeatedly within a season, which in practice is often the case when resightings of colour-marked individuals are collected. We implemented the RDM model in a state-space formulation and also an approximate, but computationally faster, model (RDMa) in JAGS and evaluated their performances using simulated and empirical capture–resight data on black-tailed godwits Limosa limosa. The CJS models applied to simulated data under an imperfect identification scenario data produced strongly positively biased estimates of survival. For a range of degrees of correct identification probabilities, the RDM model provided unbiased and accurate estimates of survival, reencounter and correct-identification probabilities. The RDMa model performed well for large datasets (>25 individuals), with high resighting (>0.3) and high correct identification (>0.7) probabilities. For the empirical data, the CJS model estimated average juvenile survival at 0.997% and adult survival at 0.939% and also detected a strong decline in adult survival over time at a rate of −0.14 ± 0.029. In contrast, the RDMa model estimated a probability of correct identification of 0.94, annual juvenile survival at 0.234%, adult at 0.834% and less strong decline over time (−0.046 ± 0.016). We conclude that estimates of survival probabilities obtained from data that include misidentification errors and analysed with standard CJS model are unlikely to be correct. The bias in survival increases with the magnitude of misidentification errors, which is inevitable as datasets become longer. Since misidentification due to tag misreads is common in empirical data, we recommend the use of the here presented RDM model to provide unbiased parameter estimates

Migration route, stopping sites, and non-breeding destinations of adult Black-tailed Godwits breeding in southwest Fryslân, The Netherlands

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

Predicting the non-breeding distributions of the two Asian subspecies of Black-tailed Godwit using morphological information

Until recently, Limosa limosa melanuroides was thought to be the only subspecies of Black-tailed Godwit in the East Asian–Australasian Flyway. For this reason, all previous occurrences and counts of Black-tailed Godwits in the flyway have been assigned to melanuroides. However, a larger-bodied subspecies, bohaii, has recently been discovered in the flyway. As a result, the occurrence of Black-tailed Godwits in the flyway needs to be reconsidered such that the specific distribution of each subspecies becomes known. To this end, we developed a simple discriminant function to assign individuals to subspecies based on their bill and wing length. Cross-validation with individuals known to be bohaii or melanuroides, based on molecular analysis, showed the developed function to be 97.7% accurate. When applied to measurements of godwits captured at 22 sites across 9 countries in East–Southeast Asia and Australia, we found that bohaii and melanuroides occurred at most sites and overlapped in their distribution from Kamchatka to Australia. We examined photos from all along the flyway to verify this surprising result, confirming that both subspecies co-occur in most locations. Based on these results, we hypothesise that bohaii and melanuroides from the west of their breeding ranges mostly migrate over Chinese mainland. Birds of both subspecies from the east of their ranges are expected to migrate along the Pacific Ocean. We encourage ringing groups in East–Southeast Asia and Australia to use this simple method to keep adding knowledge about Black-tailed Godwits in the East Asian–Australasian Flyway