Tuesday, 18 December 2018

And a... godwit... in a pear tree?

When you think of Christmas the first bird that comes to mind is probably not the Bar-tailed Godwit. Yet there is one similarity between this bird and the jolly bearded man who delivers Christmas from the Arctic Circle - the journeys each undertakes.

The Bar-tailed Godwit subspecies, Limosa lapponica baueri, holds the record for the single longest non-stop migration of any avian species, clocking up between 10,000 and 11,000 km as it crosses the Pacific Ocean from its breeding grounds in Alaska to its wintering grounds on the shores of Australia and New Zealand. Closer to home, ‘our’ Bar -tailed Godwit subspecies, Limosa lapponica, admittedly has a slightly easier time of it, migrating from the Arctic Circle in Norway to overwinter on Irish shores from late August until March or April. That being said, I don’t think I’d fancy swapping my daily commute for their biannual trek.

Bar-tailed Godwit in winter plumage with satellite tracking device attached to its back.
John Fox.
Prior to undertaking such long migrations, these little birds must first ‘bulk up’. Their fat reserves increase phenomenally, finally comprising over half their body weight while their digestive organs shrink to accommodate this increase. As  Bill Bailey so aptly put it, this is a ‘form of self- cannibalisation’ (1), a gory feat which Santa Claus has thus far been able to forego.

The Dublin Bay Birds Project colour-ringing scheme, which began in 2013, has shed some light on the migration patterns of Limosa lapponica. With the aid of volunteers, one Bar-tailed Godwit, (DH), ringed on Sandymount Strand, has been recorded in Norway in the months of May and July over four consecutive years. This suggests that 'DH' is breeding in Norway, a finding supported by ‘An Atlas of Wader Populations in Africa and Western Eurasia’(2).

Bar-tailed Godwit ‘DH’ in breeding plumage – photo taken in Denmark.
Kim Fischer.
Colour-ring resightings have also revealed the potentially significant sites for these birds during their migration, with reports of Bar-tailed Godwits ringed by the Dublin Bay team submitted by volunteers in Denmark, the Netherlands and, most recently, England, prior to or following the breeding season.

Resighting locations of Bar-tailed Godwits outside Ireland.

Colour-ringing has also revealed some interesting patterns in terms of how Bar-tailed Godwits use Dublin Bay. Although all the Bar-tailed Godwits colour-ringed by the scheme so far were ringed on Dublin’s southside at Sandymount Strand, these marked individuals have been recorded using both the north and south sides of the bay. This is in contrast to the Oystercatcher which appears to be a bit more site-faithful. Many Oystercatchers ringed by the Dublin Bay Birds Project at either Sandymount Strand or Bull Island on Dublin’s northside, have only ever been resighted in Ireland at or near to these sites. For instance, two - hundred and fifty Oystercatchers ringed at Sandymount Strand have been resighted in Dublin Bay since 2013, with only 42 of these birds observed in the northern portion of the bay. Therefore, while Oystercatchers appear to largely conform to Dublin’s northsider/ southsider divide, Bar-tailed Godwits seem a more flexible bunch, availing of foraging and roosting opportunities on both sides of the bay.

Resighting locations of Bar-tailed Godwits in Dublin Bay. All Bar-tailed Godwits were ringed at Sandymount Strand on Dublin's southside.

Understanding the sites which are important to these incredible little birds on their migration to and from the Arctic and on our own shores outside the breeding period, enables greater national and international cooperation in protecting these sites. Colour-ring resightings feed into these conservation efforts and are a vital way to make a difference. Also, I have it on good authority that Bar-tailed Godwits act as spies for Santa Claus (courtesy of a five-year-old from Australia), so getting out and ring-reading may not only aid waterbird conservation but also pay off next Christmas!

Finally, from everyone in the Dublin Bay Birds Project, we wish you a Merry Christmas and Happy New Year. A massive thank you to everyone who has submitted ring resightings over the last number of years, your help really is invaluable!

(1) Bernhardt, A. (2016). ‘Interview: Bill Bailey on birdwatching, bar-tailed godwits and Brexit’ Country and Town House.
(2) Delaney, S., Scott, D., Dodman, T., & Stroud, D. 2009, An atlas of wader populations in Africa and Western Eurasia, 1st edn, Wetlands International, The Netherlands.