Monday, 3 July 2017

Dublin Tern Colonies Bursting With Birds

Tern breeding season is in full swing! We had our first ringing visit of the year to Dublin Port to check up on our summer visitors from Africa. The terns now nest on several structures within the greater Liffey/Port area, such as the disused mooring pontoons near the Poolbeg Chimneys. Most of these support strong numbers of nesting terns, to the extent that some structures near full capacity with adult terns making nests on all available space. As the boat approaches each colony the adults often 'flush' to the skies, screeching and diving. Apart from a small risk of being pecked on the head this is quite a spectacle! It's also a great chance to get a sense of how many terns there are present at the time. From the boat, a count of 290 terns were seen coming off the "ESB Dolphin" - the first established nest site on the Liffey for Common Tern and now protected as part of the many SPA's (Special Area Of Conservation) within Ireland.

The 'ESB Dolphin',
 as seen from the River Liffey Brian Burke 
Adult terns terns flush as the boat approaches the 'CDL Dolphin' Richard Nairn

On a sunny Wednesday afternoon we visited three of the structures in the bay; "Pontoon 1" on the outer Tolka Estuary , "Pontoon 2" and the "CDL Dolphin", both near Poolbeg. Boat transport provided through Dublin Port Co by Jimmy based at Poolbeg Yacht Club, which beats rowing out in the dinghy for sure...thanks Jimmy!

Boat ride with a view of the iconic Poolbeg Brian Burke
Once on the structure the first port-of-call was take a census of all the pulli (young birds that are not yet able to fly) in each section. Then those that were big enough (medium pulli and upwards) were ringed. Common Terns get a metal ring on their right leg and Arctic Terns get a metal ring on their left, so it's easier to differentiate between the two when re-sighted. A "biometrics"  (measurement) are taken for each chick ringed. Wing length is representative of a bird's size so this a good way to keep track of how well they're growing when we visit again.

Pontoon 2. compartments are top real estate for port terns; complete with only the best nesting
gravel, hideaways, chick shelters and not to mention a great view of the port! Brian Burke

Ringing the young terns is a team effort.  Brian Burke
We are sure to spend no more than 30 minutes at each site so as to allow parents to get back to feeding the chicks and all 'round minimise stress on the colony, so we are as efficient as possible when ringing. It's safe to say that it wasn't a bad day's work as c. 150 chicks were ringed and some were even big enough to get colour rings. It's a bonus getting some colour rings on. As demonstrated in the previous blog post, colour rings are so important for re-sighting live birds as they make ring reading so much easier.

"Feed me" - a young Common Tern chick Brian Burke

A young Arctic Tern chick definitely fits in the palm of a hand Brian Burke

A tern nest (using the word "nest" loosely) is just a scrape in the substate and eggs are well camouflaged in the shallow cup, so they can be hard to find but easy to step on. However once you step lightly and know what to look out for the little ones are safe. We are happy with the numbers we've found so far - over 300 nests were found on Pontoon 2 alone. We ringed all suitably robust chicks and will ring the remainder during our next visits.

Although nests are basic, you sometimes see them
decorated with items like this toy plastic fish, which
was probably mistaken for the real thing Brian Burke
A splash of colour. This red/orange colour
 is unusual to see in terns eggs Brian Burke

Creative with crab legs - 
all sorts of materials are used for the nest scrape Brian Burke

So far this season the birds within the wider port colonies are doing a great job and all is going well. In saying that the young terns are sensitive to bad weather conditions and predation events so we'll be eager to get out to the colonies again and keep an eye on their progress. Let's hope those parents keep up the good work! Keep an eye on the blog for updates on how they're doing.


  1. Nice blog. Enjoyed alot to read it. I must say it is very good.

    Miami Video Producer

  2. What happened to the pontoon in the port this winter?

  3. What happened to the pontoon in the port this winter?

  4. What happened to the pontoon in the port this winter?