Wednesday, 16 September 2015

Roseate Terns on Rockabill, 2015. (Good news!!!)

We've told you all about how our breeding Black Guillemots, Kittiwakes, Oystercatchers, Arctic Terns and Common Terns did on Rockabill during the 2015 breeding season - now it's time for the pièce de résistance - how did our Roseate Terns get on? 

Roseate Tern on Rockabill. (picture taken under NPWS license)

Rockabill Island is synonymous with Roseate Terns in this part of the world. This football pitch-sized island in the Irish Sea has held Europe's largest Roseate Tern colony for quite a while, and so the future of this species in Europe is highly dependant on their fortunes on this rocky outcrop of county Dublin. In 1989 Rockabill had 180 pairs of Roseate Terns, and through a lot of hard work over the years by Birdwatch Ireland and with help from the NPWS (and RSPB in the past too), the Rockabill population reached a peak of almost 1250 pairs last year. Thats what you call successful conservation! But that was last year, what about this year....?

Breeding Pairs:
To have reached 1250 pairs last year was fantastic! The last few years numbers have hovered roughly around the 1200 mark, and we began to wonder if that was as many as Rockabill could hold, so if we got 1250 pairs again we would have been delighted. Imagine our surprise when we found 1388 Roseate Tern nests this June! That a jump of 140 pairs in a year and further cements Rockabills position as Europes most important colony. But thats not all folks......

Roseate Terns quarrel outside a nestbox on Rockabill. (picture taken under NPWS license)

The other two Roseate Tern colonies in north-west Europe are NPWS-managed Ladys Island in Wexford, and RSPB-managed Coquet Island off the Northumerland coast in England. Not only did Rockabill have a record-breaking year, but so did Ladys Island and so did Coquet! Ladys Island reached 215 pairs this year, their first time clearing the 200-mark. Not only that, but Coquet reached over 100 pairs for the first time, finishing on 111 pairs. So thats fantastic news for Roseate Terns in Britain and Ireland this year. Congratulations to everyone who has put in so much hard work over the years to get us to this point - to Dr. Steve Newton and all of the former Rockabill wardens and volunteers, to Dave Daly and Tony Murray and past wardens at Ladys Island, and to Paul Morrison and everyone on the RSPB team at Coquet Island. Fingers crossed we can push on a bit more next year!



The average number of eggs laid on Rockabill this year was a bit lower than usual, though not worryingly so. This could be down to low food availability early in the summer (all that wind and rain might have made fishing hard!), or it could be down to the age-structure of the population changing a bit as younger pairs tend to lay fewer eggs. 

Roseate Tern egg 'pipping' (picture taken under NPWS license)
Roseate Tern chick on day of hatching. (picture taken under NPWS license)

Chicks and Productivity:

Roseate Tern productivity was quite low last year, averaging less than 1 chick fledging per nest. Things were back to normal this year however, with around 1.1 chicks fleding per nest. It's productivity around this level that has allowed the Rockabill population to go from strength to strength over the last 26 years, so hopefully this bodes well for the future. Chick growth was much better than last year, indicating that a lack of food was the problem last year. While last year was a bad year, this year will help balance things out a bit, and it goes to show the importance of long-term conservation projects. One good or bad year won't make or break a project or a species - if you keep at it over time the rewards will come.

The guys at Ladys Island report having a good year, and productivity at Coquet wasn't too bad either, so it's pretty good news all around, and hopefully the future will continue to be bright for this fantastic, elegant species in the coming years!

Roseate Tern fledglings. (picture taken under NPWS license)

Roseate Tern adults and fledlgings. (picture taken under NPWS license)


Many of you have been kind enough to donate to Birdwatch Ireland's Seabird Appeal this year (see link here). One of the things we'll be using your donations for is to help pay for materials to build more Roseate Tern nestboxes. This year nearly 90% of our Roseate Tern nestboxes were occupied, the highest occupation rate we've had! Not only that, but on average the pairs in nestboxes laid more eggs and fledged 25% more chicks than the pairs not using nestboxes. Nestboxes have been truly vital to the conservation of Roseate Terns not just on Rockabill, but on all of the nearby colonies too. As the population grows, and older nestboxes get broken, its vital that we can get new nestboxes year-on-year to ensure this success continues. So a heartfelt thanks from the wardens, and the Roseate Terns, to everyone who donated! And to anyone who hasn't, there's still time..... (Click here)

Adult Roseate Tern coming out of its nestbox. (picture taken under NPWS license)

A sincere thanks too to Sean Pierce, Jim Boylan and the pupils of Balbriggan Community College for supplying us with a much-needed batch of nestboxes this year. They've been very good to us over the years, and this year supplied reached the 1000 nestbox landmark. Not only that, but this years were perhaps the most solid and well-decorated we've ever had! So a big thanks to them, and to Noel Harford, Eugene Macken and the Birdwatch Ireland Fingal branch for everything over the years! 

One of our study areas, with specifcally placed and numbered nestboxes.
Nestboxes provided by Balbriggan Community College in 2015.


We ringed over 1450 Roseate Tern chicks this year, though we know at least 5% of these didn't manage to fledge. A certain amount will be lost to perilous conditions on their migration to Africa, and over the next couple of years before they eventually return to Ireland and Britain to breed. This ringing programme continues to provide us with valuable data in the conservation of this species - telling us how old each bird is, where it was born/ringed, if it has previously been found breeding elsewhere etc. We look forward to the class of 2015 returning from around 2018 onwards! 

Adult Roseate Tern with special ring (right leg) and BTO ring (left leg). (picture taken under NPWS license)

Take a look at the graph below from the RSPB team at Coquet Island for some of the interesting information, and important from a conservation point of view,  we can get from a long-term ringing and resighting programme. In the early years, birds originally from Rockabill formed the majority of the Coquet population, but over time and with increasing numbers the proportion of Coquet-origin birds is increasing there and the population is starting to 'stand on its own' and self sustain.

 Thanks to RSPB Coquet Island for the graph. Follow their work @RSPBCoquet on twitter.

So thats it for our Roseate Terns this year. Most are now en route to Africa after what was a very successful year. After the bad news about our Arctics, and average enough performance of our Common Terns, its great to have plenty of good news about this rare, amber-listed species!
Mr. Noel Harford and Mr. Eugene Macken
Mr. Noel Harford and Mr. Eugene Macken

Sunday, 13 September 2015

Common Terns on Rockabill, 2015

Our penultimate species update is about our breeding Common Terns. We have more Common Terns on Rockabill than all of the other species put together, which is somewhat inconvenient for the wardens when you realise that they're the species that attacks us day in, day out! That being said, Common Terns are full of character with their varying levels of cheekiness and aggression and so we grow quite fond of them over the course of the season - a real love/hate relationship! That same aggression also benefits the nesting Roseate Terns all over the island, as the Commons do all of the hard work when it comes to scaring off predators of various sorts. In the 27 years of the Rockabill Tern conservation project the numbers of Common Terns have gone from a few hundred pairs to more than 2,100 pairs in recent years. So how did they get on in 2015.......?

Common Tern on Rockabill, Summer 2015. (picture taken under NPWS license)

Breeding Pairs:
In 1989 there were 109 pairs of Common Terns on Rockabill. Thats the year that the conservation project started here, and  by 2011 there were 2191 pairs. Thats what we call conservation!! Numbers dipped a bit in some of the years since, though we had 2150 nests early in the season last year, so still no shortage of Common Terns! This year we had 1950 breeding Common Tern pairs. In the short term that might not seem great - 200 less than last year. But with a species like this there will be some variation in numbers from year to year for a variety of reasons, including poor productivity several years ago, Commons deciding to breed elsewhere, and there being limited room for all of the birds on Rockabill! Though numbers were good last year, they were around 160 pairs lower the previous year, showing that there is often fluctuation. The fact that the birds on Rockabill have been protected and monitored for over 25 years in a row means we have considerable data and information on them, and can take a long-term view of whats happening. As long as they stay at around 2,000 pairs, and productivity is ok, then there shouldn't be anything to worry about. That being said, we'd certainly welcome a couple of hundred more if they turned up next summer!

Common Tern mating 'dance'. (picture taken under NPWS license)
Common Tern on its nest. (picture taken under NPWS license)

Average clutch size was 2 eggs, which is similar to the last two years, though in other years it has been higher. Like with total pair numbers, a certain amount of variation between years is to be expected. Factors that can influence the number of eggs include food availability early in the season and also the age-structure of the adult population - more 'old' pairs will lay more eggs than younger pairs. 
Around 75% of eggs hatched, which is quite similar to previous years. Whether or not eggs hatched are mostly impacted by weather and predation, though the amount of food available to adults before the egg was laid will also have played a part in determining the viability of the egg.

Common Tern clutch. (picture taken under NPWS license)
Common Tern egg hatching. (picture taken under NPWS license)

 Productivity  - that is the average number of chicks that survived per nest - was a bit over 0.77. This might seem low but its the same as the average over the last five years. I've mentioned it in previous blogs, but when Common Terns lay two or three eggs they're banking on one of those eggs surviving to be a fledged chick at the end of the season, so 0.77 is a bit below that aim for each pair.

Common Tern adult and chick, a day or two old. (picture taken under NPWS license)

Factors impacting chick survival again include weather, predation and age of adults, amongst others. This year some of the worst days of rain and wind hit when many of the chicks were 2-3 weeks old. At this age they were too big to be effectively sheltered by their parents, so Common Tern chicks in areas with little natural shelter were exposed to the elements and many died. A certain number of fledglings later died due to strong winds blowing them around when they were still inexperienced at flying, though this is a regular annual occurrence and is one of the hurdles young Terns will inevitably face in their first few days in the air. Adult Terns that are young usually have lower success rates than more experienced adults, so this might have been a factor this year too. 

Common Tern chick, 1-2 weeks old. (picture taken under NPWS license)
Common Tern fledgling. (picture taken under NPWS license)

If it seems like I'm painting a very negative picture of how our Common Terns got on this year, thats certainly not the case. It was simply an average year for them on Rockabill, which is nothing to worry about, but we'll just be hoping theres a couple of better years to come in the not too distant future to balance things out a bit!

Check out our work on Rockabill on 'Animal Rescue' on TV3 tomorrow (Monday 14th Sept 2015) on TV3 at 8.30pm, and check back in with the blog later in the week to hear how our Roseate Terns got on this year - our top priority species at their biggest European colony! 

Monday, 7 September 2015

Arctic Terns and Oystercatchers on Rockabill, 2015

So we've had two end-of-season species reports so far - the Black Guillemot population on Rockabill is bouncing back after a rough winter in 2013/14, and our Kittiwake population hit a record high, though productivity was a bit below average. Still, all things considered there has been much to be positive about in our previous two blogs!

With that in mind, we've paired up Arctic Terns and that one pair of Oystercatchers in this blog. . . . . just so we can keep the negativity to a minimum. . . . . . . . . . 

Arctic Terns

Arctic Terns are one of the longest migrants in the world - thought to see more daylight in a year than any other species as they migrate from one pole to the other - breeding in the northern part of the northern hemisphere and returning to the South Pole for the winter. This feat is ridiculously impressive when you consider that this little bird weighs less than 100g! I personally weigh much more than 100g, and would struggle to get to the south pole despite all of the modern conveniences and technology us humans enjoy. . . . . . . .

Arctic Tern on Rockabill, 2015. (picture taken under NPWS license)

We have three species of Tern on Rockabill, and Arctic Terns have always been the least numerous. They peaked at around 230 nests five years ago, but generally have ranged between 100 and 200 pairs. In recent years that number has been closer to 100 pairs, with only around 50 nests recorded at any one time. Our Arctics prefer the rockier, outer parts of the island away from the chaos of the middle of the colony, with their main stronghold being the Bill and a few other nests around the helipad. Unfortunately, being on the Bill means they are only a hop, skip and a jump from the Gulls that hang around on the other end of the Bill waiting for fishing boats to go by. You can see where this is going. . . . . . . . 

Nesting Arctic Tern (picture taken under NPWS license)
Arctic Tern egg - more round, blotchy and blue/green that Common Tern eggs. (picture taken under NPWS license)
A predated Arctic Tern egg.
Unfortunately a small number of those Gulls have perfected the art of taking Arctic Tern eggs within hours of them being laid. The most we found on the Bill this year was two nests of one egg each, and they didn't last long! Having carried out counts of adults and pairs on the Bill around the time egg laying began we know there were more pairs trying to breed but the Gulls had other ideas. We had something in the region of 50 Arctic Tern nests at any one time on the Rock - the usual ones around the Helipad and a few more that may have originally tried laying on the Bill. The fact that they laid on the rockier parts of the island meant that occasionally heavy rain flooded many nests, and being on the outer edges of the colony meant they were easier for the Gulls to get as there were few neighbouring terns to help them defend their nests. We managed to ring a small number of Arctic Tern chicks (they didn't even get that far last year!), but again rain and predation hit them hard and only a small number are likely to have fledged in the end. No Arctic chicks fledged last year, only a handful fledged this year, but we've learned from this and we'll be putting specific recommendations in our report to help ensure things improve for them from next year onwards.

Arctic Tern chick (picture taken under NPWS license)
Arctic Tern adult and chick (picture taken under NPWS license)

Brian and Andrew with two Arctic Tern chick siblings. (picture taken under NPWS license)


Some of you will remember the story of our Oystercatcher pair, but for the sake of completeness here's a quick recap: A pair of Oystercatchers were the first species to lay eggs on Rockabill this season - only the day after we arrived! Unfortunately, and I'm sure much to their surprise, around three weeks later they were completely surrounded by Common Tern nests. That wasn't a problem for the adults - Oystercatchers are much bigger than Common Terns, with much bigger bills, and in general there seems to be a certain amount of 'nesting bird ettiquette' at large breeding colonies -  "You stay out of my nest, I'll stay out of yours, and if you see a predator flying over let us know!!". Everything was going well and both eggs hatched in early June. Unfortunately Oystercatcher chicks tend to run from their nest pretty much once they're able to run and our two Oystercatcher chicks ran into the path of an aggressive nesting Common Tern, and both died from the injuries. This was the first time we've had Oystercatchers nesting on the Rock, and as with the Arctic Terns we'll be making specific recommendations in our report to make sure they don't meet the same fate if they come back next year.
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So thats the really bad news out of the way! It really shows how complicated things are at a colony like this and so many factors come into play over the course of a season that determine whether things end on a good or a bad note. You'd think the success of our breeding Terns would be tied together, given how similar they all are, but the location of nests combined with weather, has led to huge problems for our Arctic Terns. You'd also think Oystercatchers would be able to hold their own in a colony of much smaller birds, but again nest location and the vulnerability of their chicks meant they were unlucky this season.

Stay tuned this week to hear about how our Roseate and Common Terns did in 2015. . . . . . . . .