The Roseate Tern (Sterna dougallii) is considered to be Europe’s rarest breeding sea bird by the EU LIFE project. These birds were driven to the brink of extinction in the 19th century due to exploitation for the millinery trade (1). Legislation and management provided them protection and their numbers rose considerable up into the 1960s. The Roseate Tern then experienced population decline in Europe in the 70s and 80s, from 3,812 pairs in 1968 to only 561 pairs in 1987. Reasons for decline are thought to be from a multitude of factors affecting their breeding grounds such as human disturbances, high tides, coastal erosion and depredation by gulls, rats and various waders as well as trapping in their wintering grounds in Ghana (2). This dramatic loss in numbers led to a conservation project being set up at several locations in an attempt to protect the terns.
Rockabill Island consists of two islets, named the Rock and the Bill, located about 7km East-North-East of Skerries, Co. Dublin. The island belongs to the Commissioners of Irish Lights and Rockabill lighthouse is located on the larger of the two islets – the Rock. In 1860 the lighthouse building was completed. In April of 1989, the lighthouse was converted to automatic operation and lightkeepers were withdrawn (3).
That same year, 1989, Rockabill Island had its first Tern Wardens on the island for the summer, providing nest boxes, monitoring and protection to the terns nesting on the island. Rockabill is ideally located as it is isolated from predators, such as rats or mink, on the mainland and is a Special Protected Area under the EU Birds Directive. In the UK the Roseate Tern in just one of three seabirds on the UK’s national Red List. Here in Ireland, the Roseate is listed as Amber (1).
The Roseate Tern looks very similar to the Common Tern (Sterna hirundo) but is distinguished by its black bill and a slight rosy blush on its chest, giving it its name. Common and Arctic Terns (S. hirundo & S. paradisaea respectively) are very defensive of their nests and will mob any potential threats. Roseate Terns tend to nest with these birds as they get protection from predators through this behaviour. They nest in sheltered spaces, such as the nest boxes provided for them here on Rockabill.
I am fortunate enough to be working as a Tern Warden on Rockabill this year. I have been out here since April 25th and will stay until mid-August. As well as the three species of tern breeding on the island, we also have nesting Black-legged Kittiwakes (Rissa tridactyla) and Black Guillemots (Cepphus grylle). We have daily visitors to the island such as Puffins (Fratercula arctica), Common Guillemots (Uria aalge), Razorbills (Alca torda) and Northern Fulmars (Fulmarus galcialis), along with Greater Black-backed Gulls (Larus marinus), Herring Gulls (Larus argentatus), , Oystercatchers (Haematopus ostralegus) and Ruddy Turnstones (Arenaria interpres) who are known to predate on tern eggs.
At the beginning of the season, most of our work consisted of clearing out all of the tree mallow (Lavatera arborea) that grows around Rockabill as it grows too dense for the birds to nest in. Then, we began setting out the 800+ nest boxes for the Roseate Terns around the island.
While I am not yet half way through the field season, my field clothes have gone from a dark navy colour to a lovely shade of white as defecation is a defence mechanism of Common Terns who feel threatened by the wardens coming into study areas to do their twice daily nest checks. In addition to this, their mobbing behaviour means we wear about four hats on our heads to soften the repeated blows. During these nest checks we are noting any new nests and looking at previously known nests to check for new eggs within a clutch or to see if any eggs have been predated. We spend a lot of time at the moment ring reading the nesting adult birds to determine how many of them were born here vs born in other colonies around Ireland or in the UK. In previous years, birds ringed in Africa have been found nesting on the island.
Soon our eggs will start to hatch and that is when the fun will really start. When we have chicks, we will ring them and begin observing hatchling feedings. We will be looking at the different prey species and size of the fish the parents are providing to the chicks. We will also be recording growth of those chicks.
In 1989 when the first Tern Wardens arrived on Rockabill Island, there were only 152 breeding pairs (2). Last year, in 2018, there were 1,633 breeding pairs of Roseate Terns on Rockabill (4). Rockabill is now a breeding site for 80% of the European Roseate Tern population according to the EU LIFE project and is known around the world to be a conservation success story. The early success of the project on Rockabill was aided by an influx of birds from Northern Ireland and Wales, where there were higher levels of predation at the time. The EU LIFE project, with support from the NPWS that currently funds Rockabill, is hoping that similarly now the birds on Rockabill will begin to disperse back to the other colonies they formerly occupied and thus increase their range. Their overall purpose is “to improve the conservation prospects of Roseate Tern (Sterna dougallii) in the UK and Republic of Ireland”. Their long-term goal being to improve the conservation status of Roseate Terns all across Europe. While Rockabill is a resounding success, the importance of these other colonies taking hold is vital to the survival of the Roseate Tern because, as they say, don’t keep all your eggs in one basket!
References:
- http://roseatetern.org/roseate-tern.html
- Seward, A., Ratcliffe, N., Newton, S., Caldow, R., Piec, D., Morrison, P., Cadwallender, T., Davies, W. and Bolton, M., 2019. Metapopulation dynamics of roseate terns: Sources, sinks and implications for conservation management decisions. Journal of Animal Ecology, 88(1), pp.138-153. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2656.12904
- https://www.irishlights.ie/tourism/our-lighthouses/rockabill.aspx
- Rockabill report 2018, available on request from BirdWatch Ireland.
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