Monday, 16 May 2016

Running Rings Around Me

A Dublin Port Common Tern colour-ring has been recovered on Rockabill, but all is not as it seems.  

Part of our routine monitoring of our tern colonies involves ringing (and sometimes colour-ringing) the chicks before they fledge. And a good proportion of the chicks that hatch on the east coast of Ireland each year are ringed. Over time, this allows us to build a picture of where these birds go, but also whether they return to breed in the colony where they hatched, or in a different colony. By keeping track of this, we can work out what level of mixing happens, and which colonies are acting as population sources or population sinks. Terns don’t start to breed until they are three years old, so we have to play a waiting game between ringing the chicks and re-sighting the adult birds when they return to breed.   

Ringed adult Roseate Tern Dick Coombes

Earlier this week we received word from the tern wardens on Rockabill, saying that they had found a tern colour-ring out there. We knew from the colour of the ring and the inscription (PST) that it was a ring that has been assigned to the Common Terns breeding on the ESB Dolphin in Dublin Port. And while it was disappointing to find out that the blue ring with white inscription “PST” hadn’t managed to get any further than Rockabill, it caused us to wonder if Dublin Port-ringed birds often visited Rockabill between fledging and migrating southwards for the winter.

Rockabill Island (30 km fro Dublin Port) Brian Burke

Of course one recovery or a ring cannot answer all of our questions, but it seemed like a good start… However, a quick look at the database, resulted in alarm bells, and more questions - PST wasn’t there! Was the database working incorrectly? Or was it human error, and had we sent birds off to Africa without keeping a record of their details? We were starting to feel pretty PST off!! But thankfully, after checking the record of broken rings, we realised that this wasn’t the case. PST had snapped during ringing and had never made it to a bird’s leg at all – one of us picked up the broken ring and pocketed it. 

"PST" colour-ring found on Rockabill Island 
on May 8th, 2016 Brian Burke

The ring didn’t get to Rockabill, 30 km away, by wing as we initially thought -  it made the trip in a powerboat with the same ringers the following week! Presumably, it then fell out of on of our pockets, and was later picked up by one of Rockabill wardens.

So, the two take-home messages are:
  • We definitely, definitely didn’t doubt ourselves or our record keeping for a second
  • Those Rockabill wardens know every inch of that island and don’t miss a thing

The observation hide overlooking the Kilcoole
 Little Tern colony Paddy Manley

As the number of terns build up, this is a great time to get out to the Tolka Estuary in Dublin, Kilcoole Beach in Wicklow or Lady's Island in Wexford to see these beautifully delicate, but still totally badass, seabirds breeding along our coasts. Keep an eye out for our colour-ringed ones too!