Tuesday, 1 September 2015

Black Guillemots on Rockabill, 2015

Apologies for the radio silence! The breeding season might be over, but a wardens work is never done. . . . . . Or at least thats what it feels like at the moment! We've been back on the mainland for a little while now, but chained to our respective desks going through the huge amounts of data we've gathered through the season to be able to scientifically report on how the season went. So as we go through everything, we'll keep you updated on how each species fared on Rockabill during the 2015 breeding season. First up, Black Guillemots a.k.a. 'Tysties'..........

Adult Black Guillemot on Rockabill, 2015. (picture taken under NPWS license)

Some of you may remember the fortunes of our Black Guillemots in previous years - the population was slowly rising to almost 100 pairs in 2013, but then the severe winter storms of 2013/14 caused huge mortality of Black Guillemots and other related species, almost halving the Rockabill population to 55 breeding pairs last year. Thankfully we had no such trouble last winter and the Rockabill population reached 63 pairs in 2015. Its somewhat slow recovery, but since Black Guillemots take a few years to mature and start to breed, it was to be expected. Hopefully we'll continue to see increases in the coming years and the population here will be back to full strength in a few years time.

Black Guillemot sticking its head out of a wall hole where it's nesting. (picture taken under NPWS license)

Black Guillemot stretches outside its nestbox. (picture taken under NPWS license)

Black Guillemot sticking its head out of a wall hole. (picture taken under NPWS license)

A Black Guillemot nestbox, designed to replicate a hole and cave.

So thats how things stood early in the season - how did things go from there? Well we'd expect Black Guillemots to usually lay two eggs, sometimes one, and that was no different this year with a mean clutch size of almost 1.8 eggs per pair - exactly as things should be!

A clutch of two Black Guillemot eggs in a wall hole. (picture taken under NPWS license)

And the chicks? Well one of the advantages Black Guillemots have over other seabird species is that they nest in holes and caves (and specially designed nestboxes), so that offers a higher degree of shelter to their chicks than some other species get. With that in mind, and one less thing to worry about, you'd expect most chicks to do fairly well. This year a little over one Black Guillemot chick per nest on average fledged from each nest, again exactly as we'd expect and hope, so that should help the population to grow in the coming years - fingers crossed for no sever winter storms though!

Black Guillemot chicks start off cute.....
.....small, black balls of fluff.......
.....though that doesnt last for long.......
......starting to look a bit more adult like as they lose their 'fluff'......
After around four weeks they look very similar to adults in winter plumage.

We've also ringed most of our Black Guillemot chicks, so if/when they return to Rockabill in the coming years we'll know who they are! 

Andrew retrieving a Black Guillemot chick from one of the higher wall holes.

Volunteer Kristina ringing a Black Guillemot chick . (picture taken under NPWS license)

A ringed adult Black Guillemot changing into white winter plumage. (picture taken under NPWS license)

 So a good season overall for Black Guillemots on Rockabill - breeding numbers up, and in terms of eggs and chicks surviving to fledge everything went according to plan! These guys will change from mostly black to mostly white in the coming weeks as they change into their winter plumage. If you happen to find one washed up on a beach during your autumn or winter walks, make sure to check if its leg is ringed! If it is, get in touch with us here or on the Birdwatch Ireland Facebook Page.  And whether its ringed or not, get in touch with Heidi at the Republic of Ireland Beached Bird Survey - Heidi is studying plastic ingestion by seabirds and is always on the lookout for more samples to inform her research to get a better picture of what kind of impact marine litter is having on our wildlife - so go like her facebook page to keep up to date with her work!

Black Guillemot with their favoured food - 'butterfish' (AP - picture taken under NPWS license)


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