Understanding species responses to environmental changes, and particularly shifts in their range size and distribution, is a major current challenge for ecologists and conservationists. The capacity of species to shift distribution will depend upon the constraints imposed by habitat quality and availability, and the fitness benefits associated with the occupation of new sites. Among birds, most species are philopatric as adults and so the settlement decisions of juveniles are likely to be critical in determining local population processes, and rates and patterns of colonisation of new sites. In migratory species, fitness can also be greatly influenced by the interactions between conditions experienced in summer and winter, and the migratory trade-offs resulting from differences in energetic balance among wintering locations. The fitness consequences of juvenile settlement decisions may therefore be considerable, particularly when the available breeding and winter habitats vary greatly in quality.

Juvenile settlement decisions may be influenced by both site quality and the factors influencing their capacity to exploit resources within those sites. For example, the time of arrival of juveniles on wintering sites may influence their capacity to learn about the distribution and quality of food resources, and this may influence their subsequent habitat selection, foraging success and survival.

Icelandic black-tailed godwits have been the subject of a long-term (~20 year) study of the links between individual behaviour and population processes1-5. This population has been increasing over the last century, and new sites have been colonised in summer and winter. Large numbers of individuals throughout the population are individually marked and tracked on their annual migratory journeys between Iceland and western Europe, including birds ringed as chicks in Iceland. This study will focus on the most recently colonised winter locations, and will explore patterns of adult and juvenile arrival in autumn, distribution, habitat use and foraging behaviour. Foraging and thermoregulatory models will be used to quantify the energetic trade-offs experienced by different age groups on these locations, and to contrast with the trade-offs that have been established on traditionally occupied sites elsewhere in the winter range.

1.     Gill, J.A., Norris, K., Potts, P.M., Gunnarsson, T.G., Atkinson, P.W. & Sutherland, W.J. (2001) The buffer effect and large-scale population regulation in migratory birds. Nature, 412, 436-438.

2.     Gunnarsson, T.G., Gill, J.A, Newton, J., Potts, P.M. & Sutherland, W.J. (2005) Seasonal matching of habitat quality and fitness in migratory birds. Proceedings of the Royal Society of London B, 272, 2319-2323.

3.     Gunnarsson, T.G., Gill, J.A., Petersen, A., Appleton, G.F. & Sutherland, W.J. (2005) A double buffer effect in a migratory population. Journal of Animal Ecology, 74, 965-971.

4.     Gunnarsson, T.G., Sutherland, W.J., Alves, J.A., Appleton, G.F., Potts, P.M., & Gill, J.A. (2012) Rapid changes in the distribution of phenotypes in an expanding population of a migratory bird. Proceedings of the Royal Society of London B, 279, 411-416.

5.     Alves, J.A., Gunnarsson, T.G., Potts, P.M., Gélinaud, G., Sutherland, W.J. & Gill, J.A. (2012) Overtaking on migration: does longer distance migration always incur a penalty? Oikos, 121, 464-470.