Ecology of migratory populations
Long-term individual-based studies are the only means by which to address many key problems in ecology and evolution. Such studies allow researchers to link life history stages, explore social structure, derive lifetime fitness measures and in the case of migratory populations - link events which operate on individuals in far-between places. Iceland, being an island in the middle of the North Atlantic, has a high proportion of migratory landbirds and highly suitable conditions to study population processes in migrants. These include unusual geology which provides useful stratification in landscapes and habitats, variable climate and isolation which provides high contrast in measures of phenology such as timing of migration and breeding. And for migratory waders, the accessibility of field sites and the comfort by which they can be operated (no polar bears or mosquitoes) is fortunate.
A key part of our work are longitudinal studies of several wader populations which span a gradient of migratory strategies and life-histories from being partial migrants to being long-distance migrants. Those range in time from studies of Black-tailed Godwits first individually marked in Iceland in 1999, to more recently initiated studies of Ringed plovers, Oystercatchers and Whimbrels. Longitudinal studies take some time to pick up pace but once they do they can provide novel insights. Below is a short account of each study system.
Black-tailed Godwits have been our flagship species for a long time. Godwit studies are run in close collaboration with Jenny Gill at the University of East Anglia and Pete Potts at the Farlington Ringing group in the UK with contributions from many others through the years. It is from this system we have learned most about population processes in migratory birds. Studies of Godwits have produced many publications in international journals, including in Nature, Proceedings B, J. Animal Ecol. and Ecology. What makes the Godwit system special is the unusually high resighting rate of marked birds on their winter grounds across Europe which allow us to link population processes at the individual level throughout the year. For an excellent account of the contribution of the observers which send us those sightings see the blog of Graham Appleton Wadertales. Godwit research has revealed how inherently linked events in different seasons are at the individual level. Individual variation often makes little sense except in a population perspective.
The whimbrel is one of Iceland's most common land birds and the country holds a large proportion of the world population. Unlike the related Godwit which only migrates to W-Europe the Whimbrel is a long-distance migrant, travelling 6000 km to W-Africa in autumn. And they make this long trip in a single impressive flight. Whimbrels provide an interesting contrast to Godwits as these species are on very different annual schedules but still face many of the same challenges during the breeding season. Studies into population processes in whimbrels started in 2009 with the MSc project of Borgný Katrínardóttir who studied their demography and effects of volcanic eruptions across South Iceland. These studies have since expanded with individual tracking by geolocation led by José Alves and later Camilo Carneiro who currently carries out his PhD in collaboration with the University of Aveiro. The aim of the current studies is to link individual migration strategies and annual schedules to population processes.
Common Ringed plover
All study systems have pros and cons. Godwits for example, have a very high resighting rate across the year but detailed demographic data is hard to get due to their cryptic behaviour during breeding. Ringed Plovers on the other hand are very cooperative and it is easy to mark large numbers of breeding adults and measure their breeding success which can give unique insights into drivers of fitness. In contrast to Godwits and Whimbrels, Ringed Plovers show a very interesting gradient in migration as they winter both in S-Europe and W-Africa. Studies of Ringed plovers commenced in 2004 with Böðvar's MSc project and have mostly carried on since. Ongoing developments are studies using geolocators to link individual migration strategies to breeding season processes and analyses of the role of renesting in fitness.
Changes in the migratory behaviour of bird species in response to climatic change are being widely reported throughout the world, but the causes and consequences of these changes are largely unknown. Understanding the complex ecological and behavioural processes that drive species responses to climatic change is key to developing robust conservation strategies, but this requires model systems in which different migratory strategies exist within the same population, and can be linked to individual fitness. Studies of Oystercatchers are the most recent of the individual species projects but they started in 2012 in South and NW-Iceland and have expanded around Iceland since then. Oystercatchers are partial migrants in Iceland and provide a unique opportunity to study drivers of migratory behaviour. Veronica Méndez is carrying out post-doctoral studies on migratory decisions in Icelandic Oystercatchers in collaboration with Jenny's lab and these studies are expanding to other aspects of their life. A nice account of these studies can be found on the Wadertales blog.