Great skua behaviour and Fair Isle’s lifeline

Fair Isle is Britain’s most remote inhabited island, 38 km from the next nearest island and 125 km from the northernmost tip of the UK mainland. A boat runs from the island but most visitors and most of the 60 or so island residents (including school children) travel mainly by light aircraft. The scheduled air service of Britten Norton Islander planes, a twin engine 8 seat prop plane, flies from Shetland Mainland, and in the summer months there is also a link to the Orkney Islands. Glen Tyler from our Shetland office and Aberdeen University student, Bethaney Stonier, tell us about a project they’re working on which aims to ensure that this lifeline to the island can continue to operate safely with minimal effect on the islands’ wildlife.

AirTask's BN Islander on Fair Isle airstrip (Photo David Parnaby)

AirTask’s BN Islander on the Fair Isle airstrip (Photo David Parnaby)

As well as being the most remote inhabited island in Britain, Fair Isle is also famous for birds. Not only for rare ‘off course’ vagrants but also for the huge colonies of seabirds that nest on the island and its towering cliffs. One of the most important seabird populations is that of the great skua, or ‘bonxie’ as it is known in Shetland. Up to 500 pairs of the large, gull-like predators nest on the moorland which covers much of the northern end of Fair Isle. Their numbers have been increasing on the island for nearly 100 years since they colonised in 1921. Approximately half the world population of this species breeds in the UK. Consequently great skua is a strongly protected species, and the internationally important Fair Isle Special Protection Area has them as one of its qualifying interests.

Great skua on moorland at sunrise (photo - Glen Tyler)

Great skua on moorland at sunrise (photo – Glen Tyler)

Bonxies are disturbed by the light aircraft flights though, and in response to the approach of the plane will fly up and circle around. As the number of birds has increased over the years more and more nest close to the airstrip and the number of these birds flying up to greet the plane arriving has recently caused pilots to voice safety fears.

To understand more on this issue, we are undertaking a study of the bonxies’ breeding distribution around the Fair Isle airstrip and their behaviour in relation to flight arrivals and departures.

Beth Stonier (Aberdeen Uni) scanning for great skua settlement sites near Fair Isle Airstrip (Photo Glen Tyler)

Beth Stonier (Aberdeen Uni) scanning for great skua settlement sites near Fair Isle Airstrip (Photo Glen Tyler)

Bonxies arrive in April and lay eggs in May, and we wanted to investigate the relationship between the early season settlement positions of birds and their eventual nest site selection. For this investigation we used rangefinder binoculars combined with a compass bearing to accurately and rapidly plot the position of a stationary bonxie from a remote or concealed position. This was important as we did not wish to influence where the birds were settled.

As well as determining the relationship between settlement and nest location we are also interested in the distance at which great skuas react to various stimuli, be that approach by a human, vehicle or plane. To do this we are also using the rangefinders taking a reading of any birds seen taking flight while we are moving about the island. These opportunistically sampled readings give us an idea of how the birds might respond when a plane approaches.

Great skua or bonxie in flight (Photo – Glen Tyler)

Besides these elements we are also looking at the behaviour of ‘club’ birds. Some bonxies do not have a nest, either because they are young and waiting for an available territory, or they are skipping a breeding season (sabbaticals as they are termed). When in this state birds gather in groups or ‘clubs’ and it is quite possible that these birds may behave differently with respect to the approaching plane compared to the birds with nests and young.

The first phase of data gathering for this work is now completed, although the data analysis is only just started. In June a second period of field study will take place, and we are hopeful that some answers to questions of how birds react to the plane, and how birds breeding distribution is affected by their settlement pattern will be clearer. The aim of this study is to keep the life-line airlink to Fair Isle operating as safe as possible and at the same time protect the population of breeding skuas.

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