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

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

Age-dependent timing and routes demonstrate developmental plasticity in a long-distance migratory bird

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. 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. 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. 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. 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

Spring migration of Black-tailed Godwits in Iberia 2015:Mission Report Sado, Tejo and Extremadura

In 2004 the University of Groningen has started a long-term demographic project on a partly colourringed breeding population of Black-tailed Godwits Limosa limosa in SW Friesland, The Netherlands (readmore on http://www.rug.nl/research/gelifes/ceg/_piersma/meadow-birds). Mainly from Decemberonwards, Black-tailed Godwits leave their wintering areas in West-Africa to stopover areas in southernIberia. Here they are confined to three main areas: Doñana NP and Extremadura in Spain and the ricefields surrounding the Tejo and Sado estuaries near Lisbon in Portugal. Resighting color marked birdsduring the stopover period is necessary for several reasons. Firstly, if a godwit disperses outside ourstudy area, the chance that it will be resighted elsewhere in The Netherlands is small. Without theresightings in the stopover area, we would assume that this individual is dead and thereforeunderestimate annual survival. Secondly, with enough resightings in the Iberian Peninsula we cancalculate seasonal survival. In other words, we can calculate in which period mortalities occur moreoften. Thirdly, by measuring the density of individuals with colour marks, we can monitor the populationsize of the western European part of the Black-tailed Godwit population. Below you will find a summaryand detailed day-to-day trip report of our work in Portugal and Extremadura in 2015

Spring migration of Black-tailed Godwits in Iberia 2014:Mission Report Sado, Tejo and Extremadura

In 2004 the University of Groningen has started a long-term demographic project on a partly colour-ringed breeding population of Black-tailed Godwits Limosa limosa in SW Friesland, The Netherlands(read more on http://www.rug.nl/research/animal-ecology/research/piersma-lab/meadow-birds).From half December onwards, Black-tailed Godwits leave their wintering areas in West-Africa to theirstopover areas in southern Iberia. Here they are confined to three main areas: Doñana NP andExtremadura in Spain and the rice fields surrounding the Tejo and Sado estuaries near Lisbon inPortugal. Resighting color marked birds during the stopover period is necessary for several reasons.Firstly, if a godwit disperses outside our study area, the chance that it will be resighted elsewhere inThe Netherlands is small. Without the resightings in the stopover area, we would assume that thisindividual is dead and therefore underestimate annual survival. Secondly, with enough resightings inthe Iberian Peninsula we can calculate seasonal survival. In other words, we can calculate in whichperiod mortalities occur more often. Thirdly, by measuring the density of individuals with colourmarks, we can monitor the population size of the western European part of the Black-tailed Godwitpopulation. Below you will find a summary and detailed day-to-day trip report of our work inPortugal and Extremadura in 2014