Home and Away with Bar-tailed Godwits

Despite glimpses of an Indian summer over the last several weeks, building waterbird numbers on our shorelines herald the turning of the seasons. Many of the returning wading species are still sporting their summer finery or vestiges of it. To say they are stunning at this time of year, is an understatement. One example is the Bar-tailed Godwit.

       Bar-tailed Godwit in full breeding plumage (Andreas Trepte).

Bar-tailed Godwit in non-breeding plumage (Colm Fitzpatrick).

There are five subspecies of Bar-tailed Godwits worldwide (although the classification of one of these subspecies is contested) (Tomkovich & Serra 1999). The subspecies that occurs in Ireland is Limosa lapponica lapponica. Internationally important numbers of this subspecies are found in Dublin Bay during the winter months. This means that 1% or more of the East Atlantic Flyway population of this subspecies is found in the bay.

Flyway populations. The East Atlantic Flyway is marked in green in the centre of the map (Wetlands International).

On average, the highest numbers of Bar-tailed Godwits are found in Dublin Bay between December and February, and numbers drop steeply between March and April. We start seeing a small increase in July, with generally the failed breeders returning first.

Bar-tailed Godwits in Dublin Bay: mean peak numbers per month 2013-2020. Note due to Covid-19 restrictions, no counts were carried out in April 2020 (Dublin Bay Birds Project).

These birds are returning from the breeding grounds in northern Norway, Sweden, Finland, and northwestern Russia.

Distribution of Bar-tailed Godwits in Europe, Africa and western Asia. The distribution of Limosa lapponica lapponica occurs within the blue lines. The yellow highlighted area refers to the breeding distribution of this Bar-tailed Godwit subspecies (Delaney et al.2009). 

Two Bar-tailed Godwits, colour ringed by the Dublin Bay Birds Project (DBBP), (funded by Dublin Port Company), have been resighted on the breeding grounds. One was resighted at the breeding grounds in Porsanger, Norway. Three Bar-tailed Godwits originally ringed at Porsanger, Norway as adults have also been resighted in Dublin Bay*.

The second bird spotted on the breeding grounds, was unfortunately found dead in the Tersky District, Russia in June 2020. This is our only record to date of a Dublin Bay ringed Bar-tailed Godwit in Russia. Although this is a very small sample size, it does feed into a broader understanding of the significance of these sites to L.l lapponica across their breeding range.

Dublin Bay colour ringed Bar-tailed Godwit (Kim Fischer).

Resightings map of Dublin Bay Birds Project colour ringed Bar-tailed Godwits (Dublin Bay Birds Project).

When L. l. lapponica departs to or from the breeding grounds, they don’t fly directly to their destination. Instead, they take their migration in stages, using a small number of sites to refuel as they go (Atkinson 1996). By dividing their migration into several shorter stages, L. l. lapponica reduces the energetic cost of their migration, as they don’t have to carry a lot of extra weight in the form of fat, a long distance (Green et al. 2003). This is an energy-minimising migration strategy (Duijns et al. 2009).

Bar-tailed Godwits (John Fox).

DBBP colour ringing efforts have provided further information on staging sites used by this subspecies en route to and from the breeding grounds.

The Wadden Sea is one such staging site, and indeed is the most important staging site overall for waterbirds on the East Atlantic Flyway. Most of the European population of Bar-tailed Godwits are thought to pass through it on passage to and from the breeding grounds. Dublin Bay ringed Bar-tailed Godwits are no exception, with 30 resightings of 7 individual birds to date.

A map of the Wadden Sea (Wadden Sea Forum).

Bar-tailed Godwits have been assumed to fly directly from the Wadden Sea to the breeding grounds in northern Europe. However, small flocks have been observed foraging on tidal flats in southern Sweden in early spring. The regularity of these flocks year on year and the lack of correlation with severe weather events, suggests these are not emergency stopovers, but are a regular stopover for some Bar-tailed Godwits en route to the breeding grounds (Green 1999).

Flock of Bar-tailed Godwits (John Fox).

On the 7^th of May 2020, a Dublin Bay ringed Bar-tailed Godwit was spotted in a flock of 37 birds near Loviisa, on Lehtinen Island in Finland, presumably en route to the breeding grounds further north. Unlike the birds observed in Sweden, this is assumed to have been an emergency stopover, as the observer, Veronica Strömberg wrote; “Bar-tailed Godwits on Finnish gulf archipelago islands or at islets are seen usually when they drop down due to rain or wind.” These emergency stopover sites serve a slightly different function than more regular stopover sites, but they are nonetheless critical to the survival of migratory species should they run into trouble when on passage.

Dublin Bay ringed Bar-tailed Godwits have also been resighted at Rogaland, Norway, a well-known passage site for migrating Bar-tailed Godwits. Interestingly, one of the Dublin Bay Bar-tailed Godwits, resighted at Rogaland, Norway on the 11^th of July 2016, was then subsequently observed at the Wadden Sea in Denmark on the 4^th of August of the same year. This gives us an indication of a part of the path this male Bar-tail took, before returning to Dublin Bay for the winter.

Resightings map of Dublin Bay Birds Project colour ringed Bar-tailed Godwit, ‘DH’ (Dublin Bay Birds Project).

The final passage site that has been identified for Dublin Bay ringed Bar-tailed Godwits is Merseyside in England. We know that some population exchange occurs between Dublin Bay and Merseyside, as three Dublin Bay ringed Bar-tails have been spotted at Merseyside when on passage, to and from the breeding grounds.

In addition, an immature two-year-old Bar-tailed Godwit (‘EH’) ringed at Altcar, Merseyside in March 2018, was spotted in Dublin Bay in May, June and July of the same year, and subsequently overwintered here. Tracking and colour ringing work undertaken in New Zealand indicates that immature Bar-tailed Godwits explore a variety of non-breeding sites before settling on a final site (Battley et al. 2020). Therefore, it is possible that ‘EH’ was exploring a range of non-breeding sites across the British Isles, before settling in Dublin Bay.

But why does an understanding of passage sites used by Bar-tailed Godwits matter? Adult Bar-tailed Godwits are thought to be highly site faithful to stop-over sites, particularly in spring (Scheiffarth 2001). As they rely on a limited number of sites when on passage, they are considered vulnerable to changes in these environments. Therefore, identifying these sites can help inform better protection measures between nations and safeguard the flyway population.

Bar-tailed Godwit (Billy Clarke)

Back in Ireland, the majority of resightings of Dublin Bay ringed Bar-tailed Godwits have come from Dublin Bay, with one resighting in Malahide Estuary, less than 20km north. These colour ring resightings provide an insight into how this species uses the wintering grounds. All Bar-tailed Godwits were colour ringed on the south side of Dublin Bay, but are found roosting and foraging across much of the bay. Although our understanding of sites of importance to these ‘Irish’ overwintering flocks outside Dublin Bay is limited, we do know that they are highly mobile within the bay.

Resightings map of Dublin Bay Birds Project colour ringed Bar-tailed Godwits in Dublin Bay (Dublin Bay Birds Project).

And why does this matter? For waterbirds over-wintering in colder regions such as Ireland, the highest number of deaths occur not on migration as you might expect, but actually at the wintering sites, where conditions can be quite difficult (Scheiffarth 2003). Contributing factors aside from climate can include disturbance, food availability and development pressure. By understanding habitat use, it is possible to better inform management decisions at a site level to protect these species.

Much of this work is not possible without the generous help of ring readers both home and abroad. So, from all in the Dublin Bay Birds Project Team, many thanks to all ring readers for your help! Thanks also to Dublin Port Company for their continued funding and support for the Dublin Bay Birds Project!

*Two of the resightings of Norwegian colour ringed Bar-tailed Godwits were provided by Peter Knight and Rose Maciewicz.

References

Atkinson, P. 1996. The origins, moult, movements and changes in numbers of Bar-tailed Godwits Limosa lapponica on the Wash, England. Bird Study 43: 60-72.

Battley, P.F., Conklin, J.R., Parody-Merino,A.M., Langlands, P.A., Southey, I., Burns, T., Melville, D.S., Schuckard, R., Riegen, A.C., Potter, M.A., 2020. Interacting roles of breeding geography and early-life settlement in godwit migration timing. Frontiers in Ecology and Evolution 8: 52.

Delany, S., Scott, D., Dodman, T. & Stroud, D. (eds). 2009. An Atlas of Wader Populations in Africa and Western Eurasia. Wetlands International, Wageningen, The Netherlands.

Duijns S., Jukema J., Spaans B., van Horssen P. & Piersma T. 2012. Revisiting the proposed leap-frog migration of Bar-tailed Godwits along the East-Atlantic Flyway. Ardea 100: 37–43.

Green, M. 1999. Bar-tailed Godwits Limosa lapponica on south Swedish shore in spring–emergency stopovers or a regular occurrence? Ornis Svecica 9: 133–142.

Green, M., Blomqvist, S. & Lindstrom, A. 2003. The spring migration of two Bar-tailed Godwit Limosa lapponica populations in Sweden. Ornis Svecica 13: 1-15.

Scheiffarth, G. 2001. Bar-tailed Godwits (Limosa lapponica) in the Sylt-Rømø Wadden Sea: which birds, when, from where, and where to? Vogelwarte 41: 53–69.

Scheiffarth, G. 2003. Born to fly – Migratory strategies and stopover ecology in the European Wadden Sea of a long-distance migrant, the Bar-tailed Godwit (Limosa lapponica). PhD thesis.

Tomkovich, P. S. & Serra, L. 1999. Morphometrics and prediction of breeding origin in some Holarctic waders. Ardea 87: 289–300.