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)

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