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

Grote aantallen Drieteenstrandlopers uit allerlei windstreken bij Griend, nazomer 2011

De wadplaten van de Waddenzee zijn van groot belang voor trekkende steltlopers. Ze tanken er bij op weg naar de broedgebieden in het voorjaar en de overwinteringslocaties in het najaar (o.a. Boere 1977, van de Kam et al. 1999, Reneerkens et al. 2005). Sommige soorten steltlopers die door de Waddenzee trekken, zoals Kanoeten Calidris canutus en Rosse Grutto’s Limosa lapponica, overwinteren massaal in slechts enkele gebieden: de Banc d’Arguin in Mauritanië en de Bíjagos archipel in Guinee-Bissau. In contrast daarmee strekt het overwinteringsgebied van Drieteenstrandlopers Calidris alba, Steenlopers Arenaria interpres en Bontbekplevieren Charadrius hiaticula zich uit langs de hele kust van West-Europa en de westkust van Afrika (Delany et al. 2009). Maar waar komen de in de Waddenzee doortrekkende Drieteenstrandlopers vandaan en waar gaan ze naar toe? De afgelopen jaren zijn veel Drieteenstrandlopers op allerlei locaties langs de Oost-Atlantische trekroute individueel herkenbaar gemaakt met behulp van kleurringen (Reneerkens et al. 2009a). Hierdoor konden we inzicht verkrijgen in de herkomst en bestemming van de Drieteenstrandlopers die in de nazomer van 2011 rond het eiland Griend in de centrale Nederlandse Waddenzee pleisterden. Daarnaast konden we op basis van de fractie gekleurringde vogels een schatting maken van het aanwezige aantal

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

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