The work presented in this thesis investigates the implications of migration strategies and choice of winter location in a population of a migratory shorebird, the Icelandic Blacktailed Godwit Limosa limosa islandica. Measures of the environmental conditions experienced by individuals in different parts of the winter range are used to explore the energetic trade-offs associated with choice of winter location. The costs of migrating different distances to the Icelandic breeding grounds are also explored, as winter locations range from Britain and Ireland to Iberia. These studies suggest that winter locations in the south of the range are energetically more favourable, and that the resources available at these sites are more than sufficient to fuel migration. However, Icelandic godwits wintering in Iberia have to fly more than twice the distance to reach Iceland than their conspecifics in the north of the winter range, and models of potential flight range indicate that most birds from Iberia have to stop and refuel during spring migration. Despite this, population-wide tracking of marked individuals indicates that godwits from southern winter locations are able to reach Iceland earlier than birds from more northerly winter sites. In the Iberian winter sites, Icelandic black-tailed godwits overlap with continental black-tailed godwits (Limosa limosa limosa), but detailed field studies in Portugal indicate clear habitat segregation between these two subspecies, with Icelandic godwits primarily foraging on estuarine mudflats and continental godwits foraging in rice-fields. Estuarine prey resources vary in availability and profitability and, as in most shorebird species, female godwits are larger than males and have higher energy requirements. Thus, the extent and implications of sex differences in distribution and resource use are explored in this thesis. Finally, the impact of ongoing efforts to reduce organic inputs to the Tejo estuary, west Portugal (the main Iberian winter site), on the distribution of black-tailed godwits and their invertebrate prey are explored.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:522397 |
| Date | January 2009 |
| Creators | Alves, Jose Augusto Belchior |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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