Waders perform some of the longest migratory flights amongst all birds, traversing hemispheres between their breeding and wintering grounds. Despite the relatively narrow latitudinal span in breeding distributions, most species show extensive wintering ranges and also use, along their migratory routes, numerous sites that act as refuelling stops - the staging areas. Such diversity in geographical distribution and in habitat use has important ecological and evolutionary implications for population segregation and allopatric subspeciation. However, among waders, distinct populations or subspecies are virtually impossible to identify, given the high overlap in morphological and plumage characteristics and the high degree of population mixing at staging areas. This situation precludes a thorough understanding of dispersal and connectivity of specific migratory populations, with crucial implications for their conservation and management.

During spring (pre-nuptial) migration, several sites across the migratory flyways harbour a mixture of wintering and staging birds, the later just arrived from their wintering locations (further south) and on their way to the breeding grounds. To date, the inability to discriminate wintering and passage populations (possibly originating from a variety of sites) has prevented the interpretation and estimation of relevant migration-related parameters, such as timings of arrival and departure, residence periods, and ultimately, of the overall number and origins of the birds using a particular site. As a consequence, comparison of migratory strategies among populations, namely of migratory schedules and of potential physiological specializations are as yet poorly known.

The main aims of this project are (1) to develop interpreted isotopic profiles of the trophic webs (leading to waders) in different tidal wetlands across the East Atlantic Flyway and (2) to use this knowledge to identify the wintering grounds of migratory waders at staging areas during spring migration. We will combine standard field methods (e.g. behavioural observations, invertebrate sampling) with extensive use of intrinsic markers (stable isotopes of nitrogen, carbon and to a lesser extent hidrogen) to develop interpreted signatures for the main components of the bird's trophic web in each area, with the aim of building isoscapes on a significant part of the east Atlantic Flyway. This approach will allow us to address relevant issues and hypotheses such as (1) how do food webs in tidal wetlands compare in terms of main paths of nutrient sources (carbon, nitrogen and hidrogen) and what drives the geographical and interannual variability from tropical to temperate environments?, (2) can mixed populations of wintering and migrant waders be discriminated at staging areas and assigned to specific wintering grounds by their isotopic signatures?, (3) is geographic segregation found in wader populations wintering in West Africa propagated at northern staging areas?, (4) can we efficiently assess the phenological patterns of migrants using stable isotopes? and (5) are there differences in the physiological profiles of staging waders, and do they relate to their wintering grounds?

The vast majority of studies have used isotopic ratios in feathers for investigate the geographic origin of birds. However, this tissue proved to be unsuitable to track movements of migratory waders, since their moult schedules are still poorly investigated but clearly very variable. For the first time, we will use toenails to identify the wintering origins of migratory waders and thus assess the degree of mixing of migratory populations along the East-Atlantic Flyway. Recent preliminary analyses from ongoing work (T.Catry & J.P.Granadeiro) strongly indicates this to be a successful approach.

The use of stable isotopes will enable a comprehensive and integrative approach to the study of food web of tidal wetlands in contrasting ecological contexts, offering insightful overviews at a flyway scale. By covering a variety of species, occurring on vast geographical areas, the project will bring data with potential application in wetlands worldwide. The relevance of this work extends well beyond the objectives and duration of this project. In fact, the data to be collected has the potential to act as a base to monitor the foreseeable variation in isotopic landscapes, which are expected to arise due to the increasing natural and man-made changes in coastal wetlands.

Due to the extensive geographical scope, the work will be based on a selection of representative study sites, which include important wetlands at Guinea-Bissau, Mauritania, Morocco, Portugal and the UK. We will select two species for deeper analysis at these sites: the Dunlin Calidris alpina and the Grey Plover Pluvialis squatarola. They both breed at high latitudes and winter over a very large number of sites from the UK to Guinea-Bissau.

CESAM members on this project

José Pedro Granadeiro
Team Member

Teresa Catry
Principal Investigator