Invisible links
Unveiling origins of migratory waders using biogeochemical markers
2012-2016
Background
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.
Faísca
Objectives
The main aims of this project were:
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(1) to develop interpreted isotopic profiles of the trophic webs (leading to waders) in different tidal wetlands across the East Atlantic Flyway;
(2) to use this knowledge to identify the wintering grounds of migratory waders at staging areas during spring migration.
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We combined 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 allowed 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?
(5) are there differences in the physiological profiles of staging waders, and do they relate to their wintering grounds?
Funding
Fundação para a Ciência e Tecnologia (FCT). Portugal.
