Seasonal variations in the diet and foraging behaviour of dunlins Calidris alpina in a South European estuary: improved feeding conditions for northward migrants

During the annual cycle, migratory waders may face strikingly different feeding conditions as they move between breeding areas and wintering grounds. Thus, it is of crucial importance that they rapidly adjust their behaviour and diet to benefit from peaks of prey abundance, in particular during migration, when they need to accumulate energy at a fast pace. In this study, we compared foraging behaviour and diet of wintering and northward migrating dunlins in the Tagus estuary, Portugal, by video-recording foraging birds and analysing their droppings. We also estimated energy intake rates and analysed variations in prey availability, including those that were active at the sediment surface. Wintering and northward migrating dunlins showed clearly different foraging behaviour and diet. In winter, birds predominantly adopted a tactile foraging technique (probing), mainly used to search for small buried bivalves, with some visual surface pecking to collect gastropods and crop bivalve siphons. Contrastingly, in spring dunlins generally used a visual foraging strategy, mostly to consume worms, but also bivalve siphons and shrimps. From winter to spring, we found a marked increase both in the biomass of invertebrate prey in the sediment and in the surface activity of worms and siphons. The combination of these two factors, together with the availability of shrimps in spring, most likely explains the changes in the diet and foraging behaviour of dunlins. Northward migrating birds took advantage from the improved feeding conditions in spring, achieving 65% higher energy intake rates as compared with wintering birds. Building on these results and on known daily activity budgets for this species, our results suggest that Tagus estuary provides high-quality feeding conditions for birds during their stopovers, enabling high fattening rates. These findings show that this large wetland plays a key role as a stopover site for migratory waders within the East Atlantic Flyway.This study was supported by Fundação para a Ciência e a Tecnologia (http://alfa.fct.mctes.pt/) through Project PTDC/MAR/119920/2010 and grants to RCM (SFRH/BD/44871/2008), TC (SFRH/BPD/46967/2008) and CDS (SFRH/BPD/64786/2009). JPG was under a research contract within project “Sustainable Use of Marine Resources - MARES” (CENTRO-07-ST24-FEDER-002033), co-financed by “Mais Centro” Regional Operational Programme (Centro Region) and European Regional Development Fund (ERDF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.publishe

Estimating the size of the Dutch breeding population of continental black-tailed godwits from 2007–2015 using resighting data from spring staging sites

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

Do different subspecies of Black-tailed Godwit Limosa limosa overlap in Iberian wintering and staging areas? Validation with genetic markers

<p>Resolving the migratory connectivity (identifying non-breeding grounds) of migrating bird populations that are morphologically similar is crucial for an understanding of their population dynamics and ultimately their conservation. Such is the case in Black-tailed Godwits Limosa limosa, where the Iceland-breeding subspecies islandica shows overlap during the non-breeding season with the continental-Europe-breeding limosa. On the basis of variation in the control region of mitochondrial DNA, it was already shown that there is a cleat geographic structure in their phylogeography and a clear discrimination between the haplotypes of the two subspecies. We can thus assign subspecies of non-breeding individuals on the basis of a molecular assay. Here we validated this approach using samples of 113 birds with known breeding origin, and on the basis of haplotype variation, all birds were properly assigned to each subspecies. We then tested for overlap during non-breeding season using a sample of 278 birds from an Iberian wintering and staging area, the inland rice fields in southwest Iberia (Extremadura, Spain). We showed that even in this inland area, 6.5 % of the birds belonged to islandica subspecies, thus demonstrating the usefulness of genetic markers as an alternative or supplementary method to the most common approach, individual colour-ringing.</p>

Primary moult of continental Black-tailed Godwits Limosa limosa limosa in the Doñana wetlands, Spain

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.</p

Latitudinal-related variation in wintering population trends of greylag geese (Anser Anser) along the Atlantic flyway: A response to Climate Change?[Dataset]

The high quality of available census data for wintering greylag geese in Europe facilitates the study of how population change varies across the Atlantic flyway and relates to global change. Files contain information of greylag geese winter counts, mean January temperatures and surface areas of the main crops used by wintering geese (1980-2009), and of the first arrival of greylag geese in autumn to the Guadalquivir marshes (1961-2012).-- et al.Peer reviewe