A Model Migrant

Millions of birds are now embarking on journeys to distant wintering grounds. Wheatears, distant relatives of the robin to which they are similar in size, undertake extraordinary migrations of several thousands of kilometres. Most extreme are those travelling from Alaska, west across Asia, reaching East Africa after a voyage of 10,000 kilometres. Or the Greenland race, which flies from Greenland and Canada, across the northern Atlantic to Europe before veering south to Africa. All wheatears spend the winter in Africa, south of the Sahara Desert around the dry Sahel region. Standing tall and recognised by the flash of the white rump, the Olde English name of white arse was an apt name that has since been replaced by the less vulgar – but entirely misleading – name of wheatear. Their ears have nothing to do with wheat, and in fact you would be unlikely to find a wheatear in a field of wheat even – they prefer moorland or grass cropped well by sheep, helping them find their insect prey.

Pair of wheatears: female on the left, male on the right.

Pair of wheatears: female on the left, male on the right.

Wheatears have been well studied in recent years and were the subject of my PhD at Cardiff University and James Hutton Institute. I investigated how changes in food supply affect different aspects of behaviour and life history that affect the life time success of individuals (passing on more genes over a life span = more successful). Changes in food supply are a major way in which environmental changes such as climate change and land use change affect not only wheatears, but other migratory birds too and in fact any organism in some way or another. Wheatears are a great bird to study to get into the detail of such issues for several reasons. For one thing, you can very easily see them! It sounds simple but is vital for following individual animals without needing to capture them whenever you want to know if particular individuals are around or not. Knowing whether individuals survived the winter, when they started breeding and how many offspring they produced in a season were vital statistics for my study. Unlike forest species that are hard to spot because of all the trees in the way, wheatears always live in open habitats where I could spot them from a distance and get their colour ring combinations down with the aid of a telescope. Being able to capture wheatears and tag them with unique combinations of colour rings enabled me to follow them over several seasons without needing to catch them again.

Male wheatear with identifying plastic colour rings.

Male wheatear with identifying plastic colour rings.

Study sites were also important. My supervisors Dr Rob Thomas and Dr Colin Beale (later also joined by Dr Hefin Jones and Dr Lucy Gilbert) had decided that Fair Isle would be an ideal place. They were right. Blessed with a plentiful supply of wheatears arriving each spring to breed, this small island of Shetland off the northern coast of Scotland is also the site of a world-famous bird observatory. The extra pairs of eyes and experienced bird ringers helped with the jobs of catching and colour-ringing the birds and also spotting them again over the several years of my study. It was also an amazing environment in which to study, with a welcoming community, plenty of other wildlife to prevent wheatear tunnel-vision setting in (too much) and other researchers and visitors to share a beer and stories with.

Fair Isle Bird Observatory

Fair Isle Bird Observatory

Much of my time was spent feeding randomly selected pairs of wheatears with supplementary mealworms. By laying on this extra food I could find out whether key parameters such as survival or breeding success were being limited by the amount of natural food available. What would happen in the future were environmental changes to cause an increase or decrease in this available food? By having birds visit these feeding stations, it was also possible to weigh the birds by placing a balance under the bowl and filming these visits with a video camera. Each individual was of course recognisable once they’d been fitted with their colour rings.

Female wheatear being weighed while taking mealworms at a feeding station.

Female wheatear being weighed while taking mealworms at a feeding station.

I’ll be blogging more about wheatears over the coming months, while I’m still in the process of getting more papers out so that the scientific community is able to read about our findings.  These blogs are one way in which I can share my work outside of the realm of scientific literature!

I first posted this to http://earthinfocus.com on 14th September 2013

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