Science unravels mystery of eastern visitor

A rare warbler spotted in Ballasalla in January has now been identified as being from the Central Asian population found in Kazakhstan.

Eastern
Eastern 'blythi' Lesser Whitethroat (Paul Bromley)

Ballasalla resident Paul Bromley first spied the diminutive warbler on 30th January 2017 when it was feeding on fat balls put out by his neighbours in their back garden. Paul alerted local birdwatcher Peter Christian who in turn contacted Manx BirdLife.

From its appearance, it was presumed that the bird was most probably a form of Lesser Whitethroat of an unknown eastern origin. To solve the identity, Neil Morris, Managing Director of Manx BirdLife, collected a sample of the bird’s faeces – conveniently deposited on the garden fence by the bird – and sent it for analysis to Professor J. Martin Collinson at the University of Aberdeen. Professor Collinson is a leading authority on the DNA profiling of wild birds from around the world.

Taking a wrong turn

On 22 March, after detailed DNA analysis, Professor Collinson confirmed to Manx BirdLife that the bird was a Lesser Whitethroat of the sub-species blythi. The population of this form of Lesser Whitethroat breeds in central Asia in and around Kazakhstan and further northwards.

It is likely that the bird got its migratory instincts wrong, heading north and west last autumn instead of south to its usual wintering grounds in southern Asia and east Africa. The journey from Kazakhstan to the Isle of Man (as the ‘Whitethroat’ flies) is approximately 3,200 miles. The bird was last seen in mid-February. It can only be hoped that it will find its way back to its nesting grounds in Asia this spring.

A previous sighting?

A similar-looking bird was spotted a few years ago by local birdwatcher Pete Hadfield. Although the bird stayed for two days in February 2014, it was not possible to get a DNA sample and so its identity remains unproven.

Hence this year’s bird is the first ever ‘Eastern’ Lesser Whitethroat proven to have occurred in the Isle of Man.

About Lesser Whitethroats

Nominate Lesser Whitethroat Sylvia curruca curruca is an extremely rare summer visitor (one to eight pairs breed each year) and a very scarce passage migrant to the Isle of Man.

Across the European continent there are half-a-dozen or more forms of Lesser Whitethroat. According to different scientific authorities, these are recognised variously as sub-species, clades or even full species. The identification of these different types, including blythi – also known as 'Siberian Whitethroat' – is often only possible through DNA analysis, as pioneered by Professor J. Martin Collinson, Professor in Genetics of the School of Medicine, Medical Sciences and Nutrition at the University of Aberdeen.

Acknowledgements

We are indebted to the garden’s owners, Peter and Lynne Cain, for allowing access to photograph and collect a faecal sample from the bird; to Professor Collinson for undertaking the DNA analysis; and to Paul Bromley and Peter Christian for contacting Manx BirdLife.