Monday, 27 July 2015

A Kestrel visits Rockabill, and the tables are tern-ed.....

*Warning - this is nature at its most impressive and unforgiving. The pictures and story below mightn't be for everyone....*

We've had quite a few visitors to Rockabill in the past few weeks - people coming to help us with our work and research, or to carry out conservation research of their own, and some peopLe just for a quick visit!

As well as human visitors we've had some colourful invertebrates coming and going, in the shape of Hummingbird Hawk Moths and Small Tortoiseshell Butterflies. The air has been a bit cooler - a sign that autumn is on its way - and we've had some Whimbrel and Redshank passing by the island too, getting a headstart on moving to their wintering grounds. Both were duly added to our species list, along with another less-expected visitor - a young Kestrel!

Our first glimpse of the visiting Kestrel, minutes after arriving from the mainland (AP)
It wasn't long before it was on the move....but not back to Skerries.... (AP)

Kestrels are members of the falcon family, most often associated with farmland. Unfortunately like most farmland species, Kestrels are suffering from widespread agricultural intensification and are in decline both in Ireland and the UK. As agriculture intensifies across the country, complex habitats are 'simplified' and theres no suitable food or habitat left for the birds, mammals and invertebrates that formerly had our landscapes buzzing through the summer months. So with that in mind, I'm always delighted to see a Kestrel!

Kestrels have always been one of my favourite birds - along with Peregrines actually! But on Rockabill, both of these fantastic falcons have their sights set on the birds we're trying to conserve and protect! Now Kestrels and Peregrines have to eat too, and to be honest they're such excellent hunters and flyers that theres not a huge amount we can do about them anyway. It didn't take this young Kestrel long to become quite an efficient hunter on Rockabill, with plenty of chicks running round on the ground for the Kestrel to pounce on! By our count it was taking 1-2 chicks per day, usually taking its time to pluck its prey in-situ, despite the aggressive dissatisfaction of all of the adult Terns in the vicinity. Once it had removed the unimportant bits of little food value (the wings and legs) it would fly to the back of the Bill to eat its catch in peace.

Kestrel with a small chick as prey. (BB)
The Terns made plenty of noise, the Kestrel didn't really care! (BB)
This pattern continued over 4 or 5 days - the Kestrel would cause commotion from time to time, eventually get a chick and retreat back to the Bill after a few minutes of preparation/snacking. Silence again for a few hours, and then the Kestrel would move and cause the Terns to go mental again! It's worth noting that predation by Kestrels and Peregrines isn't a major worry - there are a lot more Terns here than a falcon could eat in an entire summer, and their visits are usually few and far between. Part of the reason seabirds live in these big colonies is to minimise the risk and impact of predators. On a few occasions we'd see the Terns all lifting off the ground and taking it in turns to swoop at something on the ground.....which turned out to be a rather confused and lost pigeon....but more often than not it was the Kestrel. This all continued until Wednesday evening......

As I was doing my nest rounds I noticed a sudden commotion as the Terns all noisily lifted off the ground and flew quickly out to sea - their usual tactic when a predator is in the air. I ran to take a closer look, but when I looked out to sea I realised a flock of hundreds of Terns were swooping and calling at a bird in the water. This is often what you see when a Gull has taken a chick, but this time it wasn't a Gull - it was the Kestrel!

The Terns had obviously landed a hit on the Kestrel, knocking it into the sea. Their continued bombardment of attacks left the Kestrel no opportunity to lift itself out of the water. As a result its feathers became more and more waterlogged, getting heavier and heavier. This continued for up to 20 minutes, the Kestrels struggles becoming more and more futile until it eventually drowned. The Terns were presented with an opportunity to get rid of their predator once and for all, and they seized it! No single tern is a match for a Kestrel, but hundreds of Terns are a different story entirely! On land the Kestrel can look after itself, but once it hit the water the tide turned, figuritively speaking.

The Terns knocked the Kestrel into the water and kept mobbing it (BB)

Once the Kestrel hit the water it was always going to be in trouble. (BB)

I'll be honest - I didn't like seeing this happen the Kestrel, despite the trouble its been causing the Terns. But that being said, it's nature! In nature you have predators that kill prey, but those predators aren't invincible either. This is how predators have evolved to be as fast, cunning and deadly as they are - the best survive and reproduce, and those that aren't on top of their game don't live that long. This was very much a once-off incident. Like the Kestrel won't have a significant impact on the Terns population, the loss of this one Kestrel won't make or break the local Kestrel population either - particularly at this time of year. It was certainly one of the most impressive wildlife moments I've ever witnessed, and I've seen a few!!

So that was the end of the Kestrel. I should point out that while hundreds of Terns were concerning themselves in this epic battle, a Peregrine flew in and took a Tern and flew away again! Talk about timing!

By the nest morning we were adjusting to life on Rockabill post-Kestrel, when we saw something on the Bill.....another juvenile Kestrel..............but this one left after a few hours thankfully!

An ex-Roseate Tern chick, thanks to Kestrel #2(AP)

Monday, 20 July 2015

Parental instinct taken to a whole new level...

Many of you by now will have seen the nest camera footage below of a Roseate Tern chick happily being cared for and fed by two adult Common Tern parents. This is very unusual, not just because of the fact that the Terns are now looking after a chick that isn't theirs, but the fact that it's a chick of a different species altogether, and lastly because the Commons moved into a nestbox - they never do that!

So this series of very unusual events is an extreme example of parental instincts gone into overdrive! What we presume happened was that the Common Tern adults had laid an egg near this nestbox but their egg got stolen, crushed, or lost somehow. They then mistook the nearest egg for their own, which just so happened to be a Roseate Tern egg in an open-fronted nestbox. We don't know how the Roseate Tern parents took to this, but we know Commons can be quite aggressive so presumably saw them off fairly quickly! 

We see plenty of less-extreme examples of parental instinct-induced silliness around the colony every year. We usually come across Common Tern nest where eggs have been stolen from their neighbours. Common Terns uusally lay 2-3 eggs, but we've found a few clutches that jumped from 3 to 5 to 7 eggs in a short space of time, and even one with 9 eggs, all at the expense of neighbouring nests. Unfortunately it's not possible for a Common Tern to incubate such a large clutch and most of the extra eggs go cold and are rolled out of the nest. 

Parental instinct led this Common Tern to kleptomania! She laid three eggs, then stole another four!! (Picture taken under NPWS license)

We also had another inter-species mix-up, similar to the above where an adult Common Tern saw a neighbouring egg and hurridly rolled it in with their own eggs, not realising that it belonged to a neighbouring Roseate Tern! 

Spot the odd one out! Two Common Tern eggs, with a Roseate Tern egg in the middle! (picture taken under NPWS license)
The same nest after hatching - again, spot the odd one out! Note how welll camouflaged the chicks are too. (picture taken under NPWS license)

The above clutch hatched successfully and all three chicks were progressing as normal. Unlike the video above, the Roseate Tern in this clutch had to make-do with sitting in a a nest that was out in the open, as opposed to a shaded or covered area that a Roseate Tern would usually lay eggs and raise chicks in. Unfortunately the chicks from this clutch succumbed to poor weather earlier in the summer.

Of course, the most obvious (painfully obvious sometimes!) example of parental behaviour we beare witness to is the Common Terns attacking the wardens and anyone else who gets too close to a nest! They'll defend their eggs at almost all cost and will continue to be like this until the chicks are close to fledging. They invest a lot of time and energy into flying to Rockabill from Africa,  laying eggs and looking after them until they hatch, then feeding them and keeping them out of trouble until they're able to fly and fend for themselves. So they don't want to lose all of that evolutionary investment, not without a fight! And of course, we want them to succeed too, so we can't be angry with them - just begrudgingly admire them as we duck and dive out of their way!

Andrew suffering at the hands (and beaks!) of some angry parents!

Tern wardening - sponsored by Panadol! (?)

Of course, they don't just peck us.....
...plenty of good clothes ruined over the years....

Wednesday, 15 July 2015

Dinner time!

This week on Rockabill we'll be doing the second of our all-day feeding watches to gather important data on the food our Roseate chicks are being fed - that is, what types of fish the adults are bringing back and the rate they're supplying them at. We start at 5am and finish at 10pm, taking it in shifts to account for all food items brought back to around 25 of our Roseate Tern nests. Later on in the week we'll be doing similar studies for Common Terns as there is usually a slight difference in the food they manage to get.

This kind of data has been gathered every year on Rockabill and so we've amasssed a very informative long-term dataset that will help us learn more about the Terns, their preferences and what they rely on. 

Check out these short videos below of Tern chicks being fed:

First, one of our oldest Roseate Tern chicks comes running out of its box to greet an adult with food:


Next, a hungry Common Tern chick beats its sibling to the incoming food:


Many of the small fish the Terns feed on are also eaten by the larger fish that humans eat. While there aren't enough Terns to have an impact on the numbers of those small fish, the Terns act as an indicator species for the larger food web in the Irish Sea - if they can't find small fish to eat, then neither can the bigger fish and that could help explain declines in commercially exploited fish. Sometimes these are short-term problems, sometimes they're longer-term changes like overfishing or the knock-on effects of climate change.

Common Tern coming in with a sandeel (BB - picture taken under NPWS license)
Common Tern delivering food to hungry chicks (BB - picture taken under NPWS license)

Roseate Tern with a sprat (BB - picture taken under NPWS license)

Here are some of the fish species brought into the colony by adult Terns:

Sandeel (AP)

Pipefish - they offer no food value to chicks and can be a choking hazard! (AP)

Clupeid - the most common prey species (AP)

Stickleback (AP)

One of the more colourful food items brought back to the colony!

Wednesday, 8 July 2015

The dark side of Rockabill..... (Tystie picture gallery)

So it's no secret that our main focus out here are the Terns - all three species nest on the ground and require some level of habitat management and general protection from us to ensure a successful breeding season. In addition to the Terns, we have two other very ecologically different seabird species to monitor - namely Black Guillemots and Kittiwakes. We spent last Friday afternoon recording and ringing our Black Guillemot chicks, so here's a bit more about them: 

Adult Black Guillemot (BB - picture taken under NPWS license)

A young Black Guillemot chick (BB - picture taken under NPWS license)

Black Guillemots (or 'Tysties') are a member of the Auk family - related to Puffins, Razorbills and Common Guillemots, and they fill the same ecological niche in the northern hemisphere as the penguin family does in the southern hemisphere. They have a small, fine, pointed bill, short oval-shaped wings with white patches on the upper-wing and a noticeably tubby body (particularly noticeable then they're chicks!). Their legs and feet are a crimson red, as is the inside of their mouths.

Black Guillemot with food (left) and it's 'cousin', a Razorbill (right) (AP - picture taken under NPWS license


Black Guillemots outside the boulders area in which they nest. (AP - picture taken under NPWS license)

A range of Black Guillemot nestboxes on Rockabill.
On Rockabill this year we have 60 pairs breeding on both the Rock and the Bill. They prefer to breed amongst boulders and in crevices, so we put out L-shaped boxes for them on Rockabill that mimic this sheltered, cave-like preference. As well as amongst boulders and in specially designed nestboxes, we have Black Guillemots nesting in a number of wall holes around the island, occasionally peeking their head out when they hear a disturbance. They also nest in small holes, some specially designed, in piers and ports around Ireland.

Black Guillemot sticking its head out of its nest-hole. (BB - picture taken under NPWS license)

Black Guillemot eggs under boulders on Rockabill
(AP - picture taken under NPWS license)

Black Guillemots usually lay clutches of 1 or 2 eggs. When our Tern and Kittiwake chicks are old enough to fledge, they will still hang around on Rockabill on the outer parts of the colony. By contrast, when Black Guillemot chicks fledge they do so in the middle of the night - clambering out of their nesting holes and boxes until they reach the sea, and moving off before sunrise - so we don't actually get to see them again until they hopefully return in a couple of years time to breed here themselves.

A Black Guillemot chick, less than a week old (BB - picture taken under NPWS license)
Andrew with a BG chick.
Brian with a BG chick.
BG chick, close to fledging.

BG chick, close to fledging, having its wing measured.

Some BG nest-holes are quite can be hard to find the chicks.....

Black Guillemot chick, very close to fledging and looking very similar to an adult. (BB - picture taken under NPWS license)

In summer they come to our shores and islands to breed in 'loose' colonies, usually foraging within a few kilometres of those sites, but in winter they can move further out to sea - though generally don't migrate too far away.  During the breeding season they face a number of threats including predation by rats and mink, human disturbance close to the breeding site, offshore developments in foraging areas, and water pollution. Later in the year prolonged and heavy storms also pose a serious threat. The terrible storms in winter 2013/14 unfortunately killed a lot of birds that were feeding out at sea, and Black Guillemots that were born and ringed on Rockabill were found washed up on the west, north and east coasts of Ireland, giving us a interesting glimpse into their winter movements. Those storms almost halved the Rockabill population of Black Guillemots, and it will take several good years to get their numbers back.

Black Guillemots catch food by 'pursuit-diving', propelling themselves through the water using their wings. In this part of their range they eat a number of marine fish and crustaceans, depending on what's available, and usually stay within a couple of kilometres of the breeding site. Once their chicks hatch they are mostly fed 'butterfish' - a small eel-like fish found amongst rocks and seaweed. 

Adult Black Guillemot with a 'butterfish' to feed to its chicks. (AP - picture taken under NPWS license)
Butterfish - preferred food of Black Guillemot chicks (BB)

From late July onwards they change from being predominantly black to mostly white - we get to see the start of that change here on Rockabill......

Adult Black Guillemot starting to come into winter plumage (BB - picture taken under NPWS license)

Saturday, 4 July 2015

The numbers are in.....great news!

Apologies for the lack of updates - most of our nests have chicks now so its absolute chaos out here, in the best way possible! Every morning and evening we spend several hours ringing chicks and taking weights and wing lengths so we can analyse their growth rates. Thankfully, this season looks to be going a bit better than last year in terms of chick survival, so fingers crossed that continues to the end of the summer!

We also found the time to do the second part of our nest census, to count all of the nests on the island, and the results are in......

Roseate Terns

Roseate Tern (picture taken under NPWS licence)

Numbers of Roseate Terns breeding here over the last two years have been levelling out a bit as the island reaches maximum capacity. With that in mind we would have been happy with similar numbers to last year's 1,250 pairs. You can imagine our delight then to get a final count of 1390 Roseate Tern nests this year!! That's the highest number every recorded here, a jump of almost 150 pairs from last year, further cementing Rockabill's importance as the single biggest Roseate Tern colony in Europe! Woo!

It's worth noting that around 90% of the nestboxes we put out have Roseate Tern nests in them, so a big thanks to everyone who has donated to the Seabird Appeal this year to help us get new boxes for future years, and to the staff and pupils of Balbriggan Community College for the boxes they gave us this year!

Common Terns

Common Tern (picture taken under NPWS licence)
 Last year we had around 2,100, and like the Roseates we have been getting the impression over the last few years that their numbers have been levelling off as all available space gets filled. This year we have 1,950 pairs of Common Terns, so their numbers here are down. Needless to say we still have a lot of them! And they still do an excellent job providing a bit of security for the Roseates. And with the amount of peck and poo attacks we're getting, it certainly doesn't seem like their numbers are any lower!! 

The Common Terns in Dublin Port seem to be doing quite well too, so despite the bit of a drop in numbers out here, they should be ok!

Arctic Terns

Nesting Arctic Tern (picture taken under NPWS licence)

 Last year we had somewhere in the region of 30 Arctic Tern nests at any one time, down from around 100 only a few years ago, due to gull predation. Unfortunately the Arctics tend to pick the rockier parts of the edge of the colony, as well as our neighbouring island ('the bill'), where they're easier pickings for opportunistic predators than if they were in the middle of the colony. We had somewhere in the region of 50 nests last week, though some of these have since been lost to gulls again. There is a ray of light though as we do have some Arctic chicks that are growing and surviving quite well. Last year we none of their eggs progressed to hatching, so this year is a bit of an improvement. We're also learning from our RSPB colleagues on Coquet Island in the UK on how to deal with the issue of gull predation, so the future should be a bit brighter in that regard. Like the Common Terns, Arctics aren't doing too bad in Dublin Port either, so fret not!

Black Guillemots

Black Guillemot (picture taken under NPWS licence)
Some of our followers might remember that last year our Black Guillemot population nearly halved due to high mortalities in the strong winter storms of 2013/14. Numbers this year are up to 60 pairs, up by around 5 pairs. A lot of young birds are likely to have died that winter, so we were expecting to 'recruit' less birds into the breeding population for a few years. Still, 60 pairs of these fantastic birds is still pretty good - fingers crossed for a few easier winters though!


Kittiwakes (picture taken under NPWS licence)

220 nests - our highest every count on Rockabill! We're delighted to have more of these fantastic cliff-nesting gulls. A lot of other colonies in the Irish Sea have noted decreases in their Kittiwake populations, so at least the Rockabill populaton is going strong.

So yay! Record-breaking years for both Roseate Terns and Kittiwakes, and not bad years for everything else. We have to send a big thanks to Peter Cutler, Jennifer Lynch, Niall T. Keogh and Dr. Steve Newton for their help over the last two weeks, both for censusing and ringing. After a few tough days you can imagine our delight when Jennifer brought us out some chocolate brownie cake, and Eoin from Skerries Seatours brought us out two Apache pizzas!! We'd like to think we've earned them!  

Andrew, and pizza!! (picture not taken under NPWS licence....)