New Tern raft

You may be wondering about the new structure in the Tolka Estuary? 

In May this year, a raft was moored in the Tolka Estuary by the Dublin Port Company, with welcome assistance from members of the Clontarf Yacht and Boat Club.

Dublin Port Company’s tern raft near Clontarf. Richard Nairn

This large steel pontoon, last used for the Tall Ships’ visit to Dublin Port, has been specially adapted for breeding terns, by adding timber walls and a gravel layer, to mimic a single beach. 

Common Terns carrying fish to chicks on the tern raft. John Fox

Up to 12 Common Terns have been recorded on the raft over the summer, with one pair successfully raising young. 

Tern chicks prepare for takeoff!

On the third monitoring visit to the Dublin Port Tern colony, most of the eggs had hatched and there was a good mix of ages, from one day old fluffies (to use the technical term!) to those almost ready to fledge.

Two fluffies and an adolescent! Niall Tierney

Most had been ringed in the previous monitoring visit and looked in great shape, and we managed to round up and ring the majority of the others. No signs of predation to report once again, which is great, especially after the devastating year they had last year when the high rainfall and unprecedented predation effectively wiped out the entire colony. Terns are long-lived and therefore have the ability to cope with terrible years like 2012, and hope to get luckier the following season. We ringed 186 Common and 19 Arctic Tern chicks, giving us a total of 450 Commons and 32 Arctics for the season. 

Arctic Tern. Dick Coombes

So what did we learn? Well, one key lesson is to always wear a hat when ringing in a tern colony (ouch!), but more importantly, ringing these chicks will allow us to learn a great deal about where these birds go, where they subsequently breed and how long they live. Who knows, we may have just ringed the future Common Tern longevity record holder!

Typical Common Tern life expectancy is about 12 years, but the maximum recorded age, according to BTO records, is 33 years and 6 days. This bird was ringed as a nestling in Northumberland on the 1st July, 1963 and it’s ring was read through a telescope in Liverpool on the 7th July 1996! 

Common Tern. Dick Coombes

Other notable bird sightings on the day included Black Guillemot, Common Sandpiper and two Sandwich Terns. The Pigeon House Kestrel nest ledge was empty and the three young were known to have fledged the previous week.

Celtic links

Ninety one of the 119 Oystercatchers that we ringed on Sandymount Strand last February have now been re-sighted at least once. The majority of these re-sightings have been from locations on Sandymount Strand itself, but there have also been several reports from some playing pitches in south Dublin and individual sightings at Bull Island, Dalkey Island and Baltray, Co. Louth.

And we’ve just heard about two birds that have been re-sighted in Scotland, providing an international context to the study. JL was re-sighted in Argyll on the 10^th April, and DJ was photographed in Orkney on the 1^st May.

Re-sighting locations for JL (green) and DJ (red).

We’re not surprised that these birds have been seen in Scotland, but these records are notable as they are our first international re-sightings. Who knows where our next international records will come from? 

DJ at St Peter's Pool, Deerness, Orkney on 1st May, 2013. Colin Corse.

Meet LV

We ringed this guy and his two siblings last week in Kilcoole, Co. Wicklow. It will be interesting to see if he turns up in Dublin Bay this winter. 

Oystercatcher "LV" foraging with parent. Niall T. Keogh

Looks like he’s getting a foraging lesson from one of his parents. Who knows, today’s lesson could be on whether he’s going to be a smasher or a splitter! It has long been thought that juvenile Oycs learn their foraging strategy from their parents, i.e. whether they gain access to mussel shells by hammering at them or by prising them open. However, it now seems that things are more flexible, and that the birds can switch between foraging approaches. 

Don't mind Evelyn Cusack…

It’s officially autumn…the breeding season, and therefore the summer, is over.

OK, this may not be strictly true, but it may make you think twice about the way that we define the seasons. The reason I say this is because for some waders, the breeding season is already at an end, and northern breeders are starting to trickle in to our wetlands once again. Failed breeders start to arrive on our shores from as early as late June, and as July progresses this passage of waders will increase.

With that in mind, I want to mention a colour-ringing project that is hoping to get to grips with the migration ecology and wintering areas of the Scottish breeding population of Greenshank. The researchers are very keen to get any records they can of their Greenshanks passing through or wintering in Ireland, and these movements are already likely to have begun. So, please keep an eye out for colour-ringed Greenshanks if you are out and about. Please send details (date, location, etc.) and any photographs to Brian Etheridge (brian@milvus.myzen.co.uk).

And if you happen to come across some of our colour-ringed Oystercatchers on your travels, all the better! The latest reports we have suggest that as many as 18 colour-ringed Oycs have summered in Dublin Bay. So get out there - there really is no better weather for ring-reading!

First Tern chicks hatch at Dublin Port

Our second monitoring visit to the Dublin Port Tern colony showed that things are progressing well. On a warm sunny day in the first week of July, we ringed the majority of the ringable Common and Arctic Tern chicks.

So why ring these chicks? Well, it allows us to find out how many young birds leave the nest each year and survive to become adults, how long these adults live and where they breed in subsequent years. To learn more about ringing click here.

As we approached platform, we estimated the flock size to be 285 adult Common Terns (but bear in mind that a good deal of the colony will have been off foraging). On climbing up onto the platform, we could immediately see that things were going really well - there were good numbers of chicks and quite a few already on the run - it only takes a couple of days before these guys are mobile. We ringed 262 Common  and 13 Acrtic Tern chicks.

Arctic Tern nestling. Niall Tierney

Thankfully, there was no evidence of the egg predation that we reported in the last post. Now that the colony is in full swing, let’s hope that the terns can drive off any intruders. A passing Great Black-backed Gull got the “tern treatment” while we were ringing, and it made as fast an escape as possible!

Tern eggs show remarkable variability, but these erythristic Arctic Tern eggs were interesting.

Erythristic Arctic Tern eggs. Niall Tierney

Other bird sightings included Cormorants, Black Guillemots, Common Sandpipers and three well grown Kestrel nestlings in ‘window-nest’ at old Pigeon House power station. A Peregrine was heard calling briefly as well.

Breeding terns update

The main tern nest census was carried out on a fine day last week, and showed good increases in the number of nests and clutch sizes since our last visit.

As we rowed out to the platform, we could see that something was distressing the terns – they were repeatedly diving at an unseen intruder towards the eastern end of the platform – and we immediately suspected a pillaging corvid. We climbed the ladder to the platform and carefully picked our way (tern eggs are almost invisible on the shingle substrate) to the eastern end to find a Kittiwake spread-eagled across one of the nests. A quick examination revealed that the bird was very freshly dead, but showed no signs of external injury. Whatever the cause of death, this bird picked a less than peaceful refuge for its final moments... 

Common Tern nest in Dublin Port. Niall Tierney. 

Anyway, we promptly got back to the job in hand – the nest census. This is simply a count of the number of nests and the number of eggs per nest. This, along with the estimation of the number of adult birds present, allows us to see how the colony is faring from year to year. On the main platform, 418 Common Tern nests were recorded, with clutch sizes ranging between 1 and 4. There were 25 Arctic Tern nests, with clutch sizes of 1-2. There was an increase in the number of cached depredated egg shells, indicating that the (still unidentified) avian predator had been on the platform since the earlier visit (see previous post).

Two Arctic Tern nests in Dublin Port. Niall Tierney.

Once the census was complete, we quickly vacated the platform to allow the adults to resume incubation. Peak hatching is expected to be around the turn of the month. We’ll check back in on the colony again in the coming weeks to monitor breeding success and will post another update then.