Dublin Bay is an internationally important wetland complex, and is designated as a Special Protection Area (SPA) based on the wintering waterbirds that it supports. It is internationally important for Light-bellied Brent Goose Branta bernicla hrota, Knot Calidris canutus, Black-tailed Godwit Limosa and Bar-tailed Godwit Limosa lapponica, and supports nationally important numbers of a further 18 species.
In our last Sustainability Report we provided details on the Dublin Bay Birds project which commenced in 2013. DPC are supporting Bird Watch Ireland (BWI) to complete this 3.5 year programme which monitors and researches the waterbirds within Dublin Bay. The programme was initiated because Dublin Bay is among the top-ten most important wetlands in Ireland for migratory wintering waterbirds. The programme involves comprehensive counts and observations.
During 2014, bi-monthly waterbird counts of the entire Dublin Bay which commenced in July 2013, have taken place as planned in the July to December 2014 period.
- All-day surveys
- Gull survey roost
- Tern foraging movements
- Spring low tide observations
- Monitoring of breeding terns
- Monitoring of post-breeding tern aggregations
- Wader catching and ringing
- Wader re-sighting database
A series of additional surveys are taking place in the proximity of the port area (between the two sea walls) and will continue on a seasonal basis for the duration of the project.
The bird populations of Dublin Bay are at constant risk from disturbance as the bay adjoins the capital city of Ireland with a population of 1.5 million people. In order to facilitate adequate assessment of potential impacts, more detail on how birds use the bay and its surrounds is vital. There is currently insufficient available information about some very important aspects of the waterbirds using Dublin Bay. The programme is aimed at compiling information on how waterbirds are distributed in Dublin Bay. It aims to describe spatial and temporal patterns of usage of Dublin Bay by waterbirds, across a variety of tidal states. It will also inform on measures that may reduce impacts of disturbance, development and climate change. The programme's aim is to gather detailed information about how wintering waterbirds use Dublin Bay and specifically the Port area for roosting and foraging, during the day and at night, to identify areas that are used regularly by large numbers of waterbirds, and/or during specific conditions that may render these areas particularly sensitive, to gather information about the importance of Dublin Bay for waterbirds in the context of neighbouring estuaries and to initiate a marking-resighting programme of a selection of wader species aimed at identifying how individuals use Dublin Bay throughout the winter, and the extent of movement between Dublin Bay and neighbouring estuaries.
1. Core surveys
Four waterbird species were present in internationally important numbers in 2015: Light-bellied Brent Goose, Knot, Black-tailed Godwit and Bar-tailed Godwit. In total, 54 waterbird species were recorded throughout the year, with the highest species diversity occurring during surveys in November and December, when 41 species were present in Dublin Bay. As expected, the lowest species diversity on a single survey day occurred during the mid-summer count in June, when 21 species were recorded.
In 2015, the colour-ringing re-sightings database grew to 1,800 records. Of the 397 birds that were colour-ringed since 2013, a high proportion (84%) has been re-sighted, at least once, and some birds have been seen 20 times or more. This information is allowing us to track how these birds are using the resources in Dublin Bay and will lead to the identification of areas that are particularly important, and those that are used less frequently. The majority of the sightings continue to come from locations within Dublin Bay, but reports of colour-ringed birds have continued to be received from Scotland, Iceland, the Faroe Islands and Norway. This adds an interesting international context to the project and allows us to ascertain where these Dublin-wintering birds are breeding, and passing through on migration.
3. Breeding terns
Common Terns and Arctic Terns have been known to breed in the Dublin Port area since at least 1949 and each year since 1994, the breeding Common and Arctic Terns at Dublin Port have nested on two isolated mooring dolphins situated on the south side of the port. In 2013, a raft was customised to accommodate breeding terns and was floated on the Tolka estuary. In 2015, a second floating raft, designed to facilitate breeding terns, was installed in the Liffey at the Great South Wall.
In total, at least 548 tern pairs laid eggs in the Dublin Port colony in the 2015 breeding season. The majority of the nests (416) were on the ESB Dolphin, with 73 on the Tolka raft, 58 on the CDL dolphin and a single nest on the Great South Wall Raft. Productivity (the number of chicks raised per pair) on the ESB dolphin was estimated at 1.13 chicks per egg-laying pair, and 0.81 chicks per egg-laying pair on the concrete platform. On the CDL dolphin, where 58 Arctic Tern pairs laid eggs, productivity was zero due to predation at the chick stage. It is estimated that 0.48 chicks per egg-laying pair fledged on the Tolka raft. Despite several egg-laying bouts involving both Common and Arctic Terns on the new Great South Wall raft, productivity is likely to have been close to zero. It is expected that it will take several years for stable colonies to form on the new rafts. These new structures are likely to be initially occupied by younger, inexperienced breeders and are therefore inclined to be less successful.
Evidence of mammalian predation was detected on three of the four nesting structures and avian scavenging and/or predation was observed on the CDL dolphin and on the Great South Wall raft. This caused the desertion of the Arctic Tern colony on the CDL dolphin. As well as predation, the premature fledging of chicks into the water continued to be a problem in 2015. Maintenance of each of the nesting structures is paramount in order to maintain suitable nesting substrate for the birds, prevent mammalian predation and avoid the premature fledging of chicks into the water before their feathers are waterproof.
In 2015, 268 chicks were fitted with individually identifiable colour-rings, which will allow them to be identified at a distance, without the need for recapture. This will allow the movements of individual birds to be tracked from their natal structures to their breeding sites, when they are recruited into the breeding population. This will measure how the tern population responds to the presence of the new structures and will ascertain whether the provision of these structures will result in an overall increase in the Dublin Port colony population or simply its redistribution to a larger number of structures.
The total number of gulls recorded during a roost survey across Dublin Bay in February 2015 was 18,758. Six species of gull: Black-headed, Common, Herring, Lesser Black-backed, Great Black-backed and Mediterranean Gull were recorded. This is lower than that recorded in 2014 and in other in previous surveys. For example, 29,564 gulls were recorded in February 2014, 42,228 in 2012 and 41,293 was recorded in 2009. However, direct comparison between these surveys is not possible, as the 2009 and 2012 surveys covered a larger area than in the current project.
5. Post-breeding tern aggregations
Five species: Black Tern, Roseate Tern, Common Tern, Arctic Tern and Sandwich Tern were recorded during the dusk surveys August and September 2015.
A peak count of 4,035 terns was recorded on the 26th August 2015. The numbers of roosting terns recorded as part of this project are broadly consistent with the peak counts recorded in 2013 and 2014, as part of this study. However, these numbers are much lower than the peaks of 11,700 and 9,025, which were recorded in 2006 and 2007.
It is anticipated that there is considerable turnover in the roosting flocks throughout the post-breeding season, and that particularly high numbers are present only on some evenings, and therefore may be missed by the current survey methodology, which includes six counts per season. We have shown through ringing work that Sandymount Strand supports terns not just from the Dublin colonies, but from at least as far away as Scotland and Norway.
6. GPS tracking
In August 2015, BirdWatch Ireland submitted a proposal to the Sustainable Energy Authority of Ireland’s Ocean Energy Development Unit for grant funding towards the deployment of pioneering tracking technology on seabirds and coastal waterbirds along the east coast of Ireland in order to determine the potential requirements for delivery of a Bird Sensitivity Map for offshore renewable energy infrastructure. This proposal aims to track a sample of wintering waterbird species from Dublin Bay as well as a selection of seabirds from key Dublin nesting colonies.
The Dublin Port Company is keen to be involved in the wintering waterbird work - deploying GPS-telemetry on waders (Oystercatchers and Curlew) within Dublin Bay - as the data collected from these innovative devices will proliferate our knowledge of how these birds use Dublin Bay during the winter months, and also when they leave Dublin on migration.
For further information please see http://dublinbaybirds.blogspot.ie/.
In 2015 DPC finalised a Tern Colony Management Plan. As part of this plan we expanded our successful experiment to attract terns to nest on a floating raft in the Tolka Estuary to include a similar initiative in the Liffey. The Tolka Estuary pontoon colony proved to be a complete success in 2015 with over 100 plus nests recorded. The Liffey pontoon colony had initial success and will be monitored again in 2016 to see if it progresses further.
During 2016 we will start the design for a major tern colony installation in the river with the intention of using this in the future to move populations of terns from areas where their presence could prevent future Masterplan development works.