Monday, 28 August 2017

The worst named bird in Dublin Bay!

At this time of year thousands and thousands of Terns gather and roost in Dublin Bay before migration, providing an unforgettable spectacle for birdwatchers and Dublin residents alike! It's one of the most important tern gathering points for Europe and we've been monitoring it for several years to find out how many Terns use it, what species are there, how long they stay, and what kind of threats the birds and the site might face. So this blog is inspired by our late-summer evenings spent on Sandymount Strand, but it's not about Terns....

Black-headed Gulls roosting on Sandymount Strand - August 2017 (B Burke)

The Terns spend their day feeding out in the Irish Sea and return to roost around 8pm, arriving bit-by-bit in their 10's and 100's until after dark when there are several thousand present. Before they get there however, we see the arrival and gathering of their Larid (Terns & Gulls) cousins, including large flocks of the humble Black-headed Gull! The Black-headed Gulls also gather in Dublin Bay in their hundreds and thousands, but rather than coming from the middle of the Irish Sea, most arrive here from rivers, ponds, parks inland, as well as coastal sites, around county Dublin. Unlike our Terns they'll be here with us through the winter.

A Black-headed Gull beginning to come out of its summer plumage - changing from brown head to white. (B Burke)

Black-headed Gulls are one of the small gull species, much smaller and very different from an ecological point of view to the sometimes-controversial large Gulls. Black-headed Gulls don't nest in urban areas, but like Terns they nest in colonies on offshore and inland-lake islands around the country. They have a brown head during the breeding season, a mostly white head in winter, and show various shades in between during the spring and autumn months. During winter they're very common pretty much everywhere there's water - the coast, inland lakes, rivers, turloughs and even ponds in parks. Don't let this seasonal abundance fool you though, they're red-listed in Ireland and like most of our ground-nesting species they're under threat and losing ground year after year.
Black-headed Gull in late summer, changing from brown to white head (B Burke)

Black-headed Gull in late summer, having lost most of its brown head (B Burke)

A winter plumage Black-headed Gull - the dark smudge at the back of the head is the only hint of it's alternative summer plumage (B Burke)

The reason for their ubiquity from August to March is because we get a huge influx from all over Europe. Before our Autumn Tern counts at Sandymount and Merrion we set aside some time to look for Gulls and Waders that have been colour-ringed, and we haven't been disappointed. We've seen Black-headed Gulls with yellow, white and green rings; some with letters, some with numbers, and some with both! A bit of googling and a few emails later we found that our Black-headed Gull flock in Dublin last week consisted of birds from colonies as far away as the UK (2), Belgium (1), Norway (2) and Poland (3)! A lot of last week's birds have been ringed in the last five years, though given that many of them were ringed as adults they are likely a good bit older than that. The BTO tell us that their typical lifespan is around 11 years old, though the oldest Black-headed Gull on record was over 32 years old!

A juvenile Black-headed Gull - they're Red Listed as a breeding species in Ireland (B Burke)

In Ireland we also have two other small-to-medium sized gulls that offer a glimpse into how confusing some bird names can be. One of our other resident Gulls is the Common Gull - but it's much less Common than the Black-headed Gull. We also have a growing population of Mediterranean Gulls who actually have a black head during the summer, in contrast to the brown head of the Black-headed Gull! So we have Black-headed Gulls that aren't actually black-headed, and are much more common than the Common Gull! 

Winter plumage Black-headed Gull (B Burke)

Keep an look out for these birds next time on your walk along the coast or in a suburban park, take a look at the variety of head-plumages on show, and keep your eyes peeled for a colour-ring that might give you an insight into the history and travels that bird has taken to get there!

For further information about Black-headed Gulls, see the links below:

  • Our South Dublin BirdWatch Ireland Branch will be meeting at 7pm this Thursday to go and see the Tern roost at Merrion Strand - if you haven't seen it before then this is your chance!