Dalkey Islands
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The Arctic Tern (Sterna paradisea) is an Amber listed species in the Republic of Ireland and UK. The principal threats to this seabird are lack of suitable breeding habitat, mammalian predation and changes in the availability of preferred prey (sandeels, herring and sprat), particularly in the North Sea.
They are the world’s greatest long - distance traveller, migrating further than any other animal. These small seabirds breed in the Northern Hemisphere as far as the Arctic Circle, then fly south along the coast of Africa to the shores of Antarctica, where they wait out the northern winter. The longest-lived Arctic Tern to date was recorded as 30 years of age. Over the course of their lives, Arctic Terns can migrate the equivalent distance of 3-4 round trips to the moon.
Photo credit: Brian Burke
Three species of large gull nest on the Dalkey islands. These birds play an essential role in a natural ecosystem.
Photo credit: Billy Clarke (Great Black-backed Gull)
Photo credit: Paul Troake (Lesser Black-backed Gull)
The Great Black-backed Gull is the largest gull in the world with a wingspan of 1.5-1.7m. Both the Great Black-backed and Lesser Black-backed Gull are amber listed as a species of conservation concern across the British Isles.
Photo credit: Michael Finn (Herring Gull)
The Herring Gull is the only large gull in the British Isles to ‘dance for its food’. It simulates rain falling by rapidly stamping its feet which encourages earthworms to rise to the surface. It then gobbles them up.
The Herring Gull is perhaps the best known gull species in Ireland and the UK due to its recent move into urban areas during the breeding season. This species is actually red listed as a species of conservation concern across the British Isles due to a severe population decline, with 90% of Herring Gulls in Ireland lost between 1968 and 2002. Therefore it is essential that we protect these existing colonies on natural sites such as Dalkey Island. Factors which led to their colonisation of urban areas during the breeding season are overfishing and habitat loss.
Common Terns (Sterna hirundo) are found nesting not only on coastal islands, but also at inshore lakes and on man-made structures such as pontoons, piers and even boats. Common, Arctic and Roseate Terns are affectionately referred to as ‘Sea Swallows’, but Common Terns have this pet name built into their Latin name, as hirundo is the Latin term for swallows and martins. This swallow-like buoyant flight is not only beautiful to see but is essential to the ability of these birds to migrate to and from the west coast of Africa, where they overwinter.
Photo credit: John Fox
A Martello Tower stands on Dalkey Island. Dating from the Napoleonic Wars, this defensive tower was built between 1804 and 1805 and forms part of a chain of 50 towers running along a portion of Irelands eastern coast. Two 24-pound cannons were placed on the roof of the tower, each of which could fire up to a mile out to sea.
The Dalkey Island Martello Tower is unusual as it is the only Martello Tower built without a door. Instead, soldiers climbed up the side of the tower and entered it using a hatch on the roof. The reason for this was that the Martello Tower is exposed on all sides, and a door would have been extremely vulnerable under heavy cannon fire. Napoleon never invaded the British Isles and these Martello Towers are credited as one of the reasons, acting as a deterrence.
Photo credit: Tara Adcock
A secondary defence structure, a Battery Fort, was also built on Dalkey Island between 1804 and 1805. Three 24-pound cannons faced south across the sea. The combination of the Battery Fort and Martello Tower meant that this was the most heavily fortified position in Ireland’s eastern chain of defence. Nowadays, the Battery Fort has more peaceful occupants, with the herd of goats, sleeping in the former soldier’s barracks.
Photo credit: Tara Adcock
A small herd of feral goats lives all year round on Dalkey Island. These goats form an important social and community value on the island. The goats also contribute to the sense of “wildness” and character of the islands through grazing
Dalkey’s islands contain some interesting habitats including semi- natural dry grassland, wet grassland, rock outcrops, dense bracken, sea cliffs and rocky shores with internationally important exposed reef habitats. Dalkey Island holds a significant diversity of species in six key habitats, with some rare species recorded including Trifolium ornithopodioides (Bird’s-foot Clover), T. scabrum (Rough Clover), T. occidentale (Western Clover), a rare hybrid of Spurgularia rupicola (Rock Sea-spurrey), Spurgularia marina (Lesser Sea-spurrey), Vicia lathyroides (Spring Vetch) and Juncus ranarius (Frog Rush).
Bird’s-foot Clover (Trifolium ornithopodiodes). Jenny Seawright.
The Dalkey Islands are not only important for breeding seabirds but are also rich in history. In the 10th century a church, named after St. Begnet, was built on Dalkey Island. The church, like that in the town of Dalkey, is dedicated to Saint Begnet, (also referred to as Begh or Bee) and is associated with Saint Bea’s Head in Cumberland and Killibeaes in Scotland. St. Begnet was an Irish princess in the 7th century whose family ruled much of the Irish province of Leinster. The church was later repurposed to house soldiers during the Napoleonic War.
Photo credit: Tara Adcock
Dalkey Island meaning ‘Thorn Island’ was home to some of the first Stone Age settlers on the east coast of Ireland. There is evidence of activity from the Neolithic and Bronze Periods. Arrowheads, axes and pottery from these periods have been discovered during the archaeological excavations of the island. Uncovered evidence from later periods revealed 5th and 6th century glass from Belgium and France, English pottery and an 11th century silver coin from Normandy. There are also signs that the island was once used for farming.
Vikings are also an intrinsic part of the islands’ history. During the late 8th/9th century, they are known to have used Dalkey Island to hold slaves until ransoms were paid, or they could be sold to slave markets. Although Dalkey Island lies only roughly 400m from the mainland, the strong currents made escape treacherous, as an unfortunate Abbot learned to his own peril.
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Photo credit: Tara Adcock
BirdWatch Ireland and Dún Laoghaire-Rathdown County Council, with support from the Roseate Tern LIFE Recovery Project manage these islands to create a safe haven for breeding terns.
Prior to the tern’s arrival, the warden and volunteers prepare the islands by adding nesting substrate (e.g. gravel) to prevent the tern eggs rolling down the bare rock. Nest boxes are deployed to simulate crevices for Roseate Terns and protect tern chicks from the weather. Canes are erected throughout much of the tern colony to deter avian predators from taking chicks. Throughout the winter, BirdWatch Ireland carry out removal of Brown Rats which are an invasive predator.
Photo credit: Tara Adcock
During the breeding season, the team are busy monitoring the terns. This involves counting the number of nests, eggs, chicks and subsequently fledged young which allows us to gain information as to whether the colony is doing well on the islands. Trail cameras are used to monitor the colony when no warden is on site. Ringing the chicks allows the warden to keep track of them and measure survival and growth rates. Ring resightings of fledged chicks enables us to measure survival, longevity, migration and recruitment to breeding sites.
Roseate Terns (Sterna dougallii) are one of Europe’s most endangered seabirds. During the 19th century, these birds were hunted almost to extinction in Britain for the millinery trade. Thanks to habitat management, three colonies across the British Isles now support a significant proportion of Europe’s breeding population of Roseate Terns (1,884 pairs as of 2019). One of these colonies, Rockabill Island off the coast of Co. Dublin, Ireland supports approximately 80% of north-western Europe’s breeding population of Roseate Terns. This colony is managed by BirdWatch Ireland.
On the Dalkey Islands, Roseate Terns have nested on Maiden Rock in the recent past, with a maximum of 11 pairs recorded in 2004. Since 2017, no Roseate Terns have bred at this site. Conservation measures are ongoing to create safe habitat for this beautiful seabird with the aim of reintroducing a breeding population of Roseate Terns to the Dalkey Islands.
Roseate Terns migrate to western Africa at the end of each breeding season, returning to the British Isles in April.
Photo credit: Lorna Gill
Terns lay their eggs on bare rock or in a small scrape in short turf making them highly vulnerable to human disturbance, weather, flooding and predators. By nesting on islands, terns are usually safe from mammalian predators like foxes and stoats. Therefore, they have evolved defences against avian predators (aerial mobbing behaviour) but not against ground predators. Unfortunately, Brown Rats are present on the Dalkey islands. The presence of this species in the recent past has had serious consequences for the tern colony.
Photo credit: Tara Adcock. Flavoured wax block with signs of rat teeth marks.
The Dalkey Tern Project, with funding from the Roseate Tern LIFE Recovery Project and Dún Laoghaire – Rathdown County Council, have undertaken rat control on the islands. Rat control occurs during the winter months. This work benefits breeding terns on the island, along with other ground and burrow nesting bird species.
To monitor for the presence of rats, small, non-toxic wax blocks flavoured with coconut or chocolate are placed across the islands as part of the biosecurity monitoring. Rats find these wax blocks irresistible and if present, we should find their teeth marks on these blocks. This presence/absence data allows the team to monitor the success of the rat control project.
Boat trips are available to Dalkey Island from May to September. During these months, the Cunningham brothers have supported our conservation efforts by providing free transport to the warden and volunteers to the islands. Lamb Island and Maiden Rock are closed to the public during these months to protect nesting terns.
The opening of Dalkey Island to the public coincides with the tern and gull breeding seasons. With the first ever tern chicks surviving to fledging on Dalkey Island in 2019, it is even more important that visitors are aware of these birds and how they can minimise disturbance. Two ways are; leaving dogs at home and keeping a distance from nesting birds.
Dogs are not allowed on the island to protect ground nesting birds and the small population of feral goats on the island. Each season, fencing and signage is put in place around tern and gull nest sites. Guided walks run by BirdWatch Ireland also take place and are an excellent way to learn about the biodiversity, ecology and history of the site. If planning a visit to Dalkey Island, please see our Code of Conduct sign below…
Image courtesy of Anne Murray
Ken the boatman
A wide range of marine mammals are found in the waters surrounding the islands, including Harbour Seals, Grey Seals, Harbour Porpoises, the Common Dolphin and Bottle-nosed Dolphins. Grey Seals are often ‘hauled-out’ basking in the sun. In the sound, a fleeting glimpse of a dorsal fin is usually that of Ireland’s smallest cetacean, the Harbour Porpoise. These species occur so regularly that an area around the islands extending northwards to Rockabill, 35 km away, was designated a ‘Special Area of Conservation’ under the EU Habitats Directive.
Harbour porpoise. Photo credit: Brian Burke
Black Guillemots nest in the walls of Coliemore Harbour and over the course of the breeding season are a regular sight, flying rapidly to and from the nest sites, or resting up on the harbour walls and sea. During the breeding season these birds have a striking appearance: jet black, with large white wing patches offset by beautiful dark red legs.
A small number of Shelduck also nest on Dalkey Island. This burrow nesting species takes advantage of the abundance of rabbit burrows found on the island. In 2019, a Shelduck with young was spotted swimming across the sound. This was the first confirmation of young surviving to fledge from Dalkey Island in many years. Rock Pipit also benefitted from rat eradication carried out in 2019 on Dalkey Island, with chicks confirmed late in the breeding season.
Oystercatchers nest on Maiden Rock, Lamb and Dalkey Island. One Oystercatcher was ringed by BirdWatch Ireland and has nested on Maiden Rock for many years
Photo credit: Laura Glenister
Maiden Rock and Lamb Island are the traditional stronghold for the tern colony on the Dalkey islands. As a result, there is no access to these sanctuaries in order to protect the breeding terns. To connect people with these fabulous birds, tern watch events from Coliemore Harbour have been held for the last number of years. Telescopes are provided at the events which allow visitors to watch their antics throughout the summer and take in a host of other wildlife including Black Guillemots, Grey Seals, and even on occasion, Harbour Porpoises.
Dalkey tern watches. Photo credit: Tara Adcock.
Photo credit: Karen Varnham
The Dalkey islands comprise 5 islands and islets. Dalkey Island is the largest (11.2 hectares). Immediately north are Lamb Island, the islet Clare Rock, and Maiden Rock. Muglins Island lies to the east of Dalkey Island. These islands are a Special Protection Area (SPA) for terns. This is a European Union designation for sites supporting important populations of birds.
Three species of terns have bred on the Dalkey Islands. Prior to 2016, Common Terns were the most abundant species. They were found on Maiden Rock alongside one to two pairs of Roseate Terns. Arctic Terns are now the most abundant tern species on the islands, and are found on Maiden Rock, Lamb Island and Dalkey Island. In 2019, the first ever tern chicks (Arctic) fledged from Dalkey Island. BirdWatch Ireland is working to encourage terns to nest on Dalkey and Lamb Island instead of Maiden Rock, as this low-lying island is increasingly vulnerable to sea surges.
Clare Rock is a series of outcrops which are exposed at low tide, during which time many birds use it as a roost site. Herring Gulls nest on Muglins Island alongside roosting Cormorants and Shags. Muglins is also the resting place of two pirates who were hanged on the island in 1765 after murdering the passengers on board the ship, the ‘Earl of Sandwich’.