Monday 25 May 2020

Guest blog: The Knotty and intricate origins of Ireland's east coast wintering waders

We are excited to have a guest blog this month from Peter Knight and Rose Maciewicz from the UK about their research, and trials and tribulations relating to Red Knot Calidris canutus, with particular focus on Ireland and Dublin Bay.  

Red Knot is one of the few species which can strike fear into the heart of the most seasoned of counters. In Dublin Bay, flocks numbering in their thousands can be found bunched tightly together, their grey, non-breeding plumage nearly invisible against the backdrop of an Irish winter morning. To make a difficult job even tougher, these little birds are given to flightiness (an anti-predator defence). Halfway through surveys they can suddenly wheel into the air leaving exasperated counters frantically trying to count them mid-flight.

Mixed flock of Red Knot and Bar-tailed Godwit in flight. Photo credit: Dick Coombes.

For certain inquisitive souls, however, the sight of thousands of Knot - rather than calling forth terror - instead leads to questions. And like all great scientists, these questions rest on the shoulders of inquiry from previous generations and fellow ecologists.  

The Red Knot we see in Ireland breed in Greenland and northern Canada, and we are aware that these medium-sized waders stop-over at key sites to moult (replace worn feathers with fresh plumage), and that some then continue on to other sites where they see out the winter. 

Red Knot colour-ringed in the UK. Photo credit: Howard Stockdale

Building on this information, Peter Knight and Rose Maciewicz who are amateur ornithologists with a long-standing interest in wader migration, began to wonder: 

  • Where do individual Knot stop-over to moult both pre- and post-breeding?
  • After moulting, do individuals migrate to the same locations each year, or do they randomly disperse? 
  • If the weather is bad in one location, will Knot just stick it out at that site or do they move to another location within their winter range?    

Rose Maciewicz. Photo credit: Peter Knight.

Peter Knight. Photo credit: Rose Maciewicz.

You can read another one of our Knot-themed Dublin Bay blogs (by Brian Burke) here but now let’s turn the story over to Rose and Peter.... 

It is well documented that waders such as Red Knot winter every year in Ireland. Data from I-WeBS (Lewis et al. 2019) shows their major Irish wintering sites to be along the east coast, from Dublin to Dundalk.  They typically arrive in November after completing their autumn moult and depart in March.   

Distribution map of Red Knot in Ireland. Credit: Irish Wetlands Bird Survey: Waterbird Status and Distribution 2009/ 10 - 2015/ 16.

But where do these Knot come from and where do they go? Is this post-moult movement to Ireland undertaken every year by the same individuals or is it just a random dispersal of birdsDo additional birds arrive if there is inclement weather elsewhere in their winter range?   

One way to address such questions is to undertake colour-ring reading which can provide detail about the migration history of individual birdsIn the past a very small number of colour-ring resightings had indicated that at least some of the Knot that winter in Ireland had moulted in The Netherlands. 

Red Knot colour-ringed by the Royal Dutch Institute for Sea Research. Photo credit: Matt Thomas. 

In September 2017, we worked with a team jointly led by Steve Dodd and Richard du Feu to colour-ring about 500 Knot at Altcar, Merseyside, UK, during their autumn moulteach bird being fitted with an inscribed orange ‘flag’ above a pale blue ring. We caught a similar number in March 2018, again using an inscribed orange flag but this time over a dark green ring.  

Map showing location of Altcar ringing site. Credit: Rose Maciewicz and Peter Knight.

Jacquie Clark and Steve Dodd inspecting wing plumage on a Eurasian Curlew, Altcar, March 2019. Photo credit: Rose Maciewicz

Resightings of the Knot ringed at Altcar, indicated that some of the Knot ringed at this site make a short flight from moulting grounds on the east side of Liverpool Bay into the Dee Estuary during winter. But do they go further west?  Some support for this notion was that a Knot in the March 2018 Merseyside catch had been metal-ringed in Dublin Bay in January 2014 by the Dublin Bay Birds Project 

To answer this question, we traveled to both Dublin and Dundalk Bay in late February and early March 2019. Here we were joined by Jim Wilson from Norway for a week of intensive Knot colour ring reading, guided by local experts Helen Boland and Tom Cooney. Jim, another amateur ornithologist, has studied Knot migration for over 50 years. For many years he has been fitting them with inscribed yellow flags at their spring staging sites in Iceland and arctic Norway, and the Altcar catches build on this foundation.  

Jim Wilson and Peter Knight recording colour-rings in Dublin Bay. Photo credit: Helen Boland.

Over the course of the week, widentified 68 colour-ringed Knot: 35 of these were in Dublin Bay and 33 in Dundalk Bay. They included 38 of our Merseyside-ringed birds, 17 Knot which had been ringed in Iceland, Knot ringed in Norway and 12 Knot ringed in the Netherlands.  

Resighting histories show that all of the Dutch and 2 of the Icelandic Knot were known to make their autumn moult in the Netherlands, and were then subsequently seen only in Ireland, confirming a post moult movement from the North Sea to Ireland.  

Nineteen of the Merseyside-ringed Knot seen in Ireland in 2019 were known to moult in Merseyside. This showed a previously unknown post-moult movement across the Irish Sea.  

We got close to saturation, reading every Knot ring in Dublin Bay. We found 20 Merseyside colour-ringed birds among about 3,000 Knot. During the autumn moult of 2018 in Merseyside, we estimated that there were about 50 unringed Knot for every one Merseyside-ringed Knot. Therefore, the presence of 20 Merseyside colour-ringed Knot in Dublin Bay during our ring reading session in 2019 could indicate that about 1,000 Knot had moved from Merseyside across to Dublin Bay, potentially making up about a third of the flock in Dublin Bay.  

Red Knot colour-ringed in the UK. Photo credit: Howard Stockdale.

At Dundalk Bay the proportion of Merseyside birds among colour ringed Knot was similar to Dublin Bay, so we think a third of that flock could also be Merseyside moulters.  

After the week in Ireland we checked the Knot flocks on Merseyside frequently until they departed in early May to breed in the Arctic and managed to find 24 of the 38 Merseyside colour-ringed birds that we had seen in Ireland. An additional seven of the Merseyside colour-ringed Knot wintering in Ireland had previous history of Spring-presence on Merseyside. This shows that a sizeable part of the Irish wintering flock likely shuttles back to Merseyside to fuel up before the flight north.  

On the other hand, of the 30 colour-ringed Knot from other schemes (Netherlands, Norway and Iceland) that we saw in Ireland, only one was seen on Merseyside in the spring of 2019. This shows that the flocks containing these birds likely fly over to the North Sea, probably to the Wadden Sea where huge numbers of Knot fuel up in spring. 

Red Knot colour-ringed in Norway. Photo credit: Howard Stockdale.

This first visit showed the importance of understanding the whole flyway (routes taken by migratory birds) of migratory waders like Knot. It also emphasised the importance for wader conservation of knowing which populations of waders are using our estuaries and at what times of year.  The results also raised two further questions:   

  • Do the same individual Knot make the post-moult winter trip to Ireland every year? 
  • If they do, do they go to the same location? 

To address these questions, we made a follow-up visit, mainly to Dublin Bay, in the first week of March 2020. During our week’s stay we encountered 158 colour-ringed birds of 11 species and by seeing some birds on several dates, amassed a total of 257 bird-days.  

Our arrival coincided with Storm Jorge which made ring-reading challenging, and there was a marked drop in numbers of Knot and Bar-tailed Godwit as the wind subsided, so we missed reading a lot of the wintering flock, and numbers at Blackrock in Dundalk Bay were also low.  

Nevertheless, ifive days of fieldwork in Dublin Bay in 2020, we re-sighted 60% (21 out of 35) of the colour-ringed Knot observed there on our visit in the previous winter, involving birds from all of the ringing schemesThis confirms the likelihood that the same individual Knot make the post-moult winter trip to Ireland every year and that they go to the same location.  

Colour-ringed Red Knot as seen through a telescope lens. Photo credit: Helen Boland.

Furthermore, 39 colour-ringed Knot were sighted in Dundalk Bay during the whole 2018/2019 winter season, yet we saw only one of them in Dublin Bay in 2020 and that one had also been seen in Dublin Bay in the winter of 2018/2019.  So it seems that there is little interchange of Knot between these two major sites. 

This second ring-reading visit confirmed the previously unknown Irish Sea winter shuttle, with 19 Merseyside-ringed Knot seen. Among these, 12 had been seen in Dublin Bay in 2019 (60% of the 20 seen in 2019), so were wintering again in the Dublin Bay area. A few Merseyside-ringed Knot were then re-sighted back in the Liverpool Bay area before the coronavirus lockdown put a stop to fieldwork.  Our data, though based on just two winters, thus indicates that Knot that winter in Ireland are likely site-faithful, and those that make the Irish Sea shuttle do so regularly 

Red Knot colour -ringed in the UK. Photo credit: Richard Smith.

There was evidence that other species of wader colour-ringed in the Dublin area returned to Dublin, as we read 37 Oystercatchers, 24 Bar-tailed Godwits and 8 Redshank ringed there in previous seasons by the Dublin Bay Birds Project. These colour-ring resightings are consistent with information gathered by the Dublin Bay team and volunteers over the years. These collective resightings have shown that these three wading species, colour-ringed in Dublin Bay, typically return to the Bay each winter.   

Oystercatchers colour-ringed by the Dublin Bay Birds Project. Photo credit: John Fox.

In addition, we saw waders colour-ringed elsewhere that had been seen in Dublin in previous seasons. These included a Turnstone ringed in August 2018 in the West Frisian Islands of the Netherlands and a Dunlin ringed in September 2018 on the Yorkshire coast. Both of these birds were seen just north of the wooden bridge at North Bull Island where we had also seen them in February 2019. A Dutch-ringed Bar-tailed Godwit ringed in August 2015 was near there too, having been spotted in the same place in February 2017 and 2019.  

Bar-tailed Godwit colour-ringed by the Royal Dutch Institute for Sea Research. Photo credit: Peter Knight.

Another Bar-tailed Godwit, dear to our hearts as it is one of the few we had ringed on Merseyside in March 2018, was near the wooden bridge for its second winter season. That we had ringed it in March suggests it crosses the Irish Sea in early spring before heading further northeast to breed. Interestingly, in March, July and August of 2018 we had spotted three of the Dublin Bay colour-ringed Bar-tailed Godwits at Merseyside, confirming the links between these two sites. It was a nice surprise that we spotted two of those three wintering as usual at North Bull Island in 2020. However as we have made only these three sightings we think that Irish-wintering Bar-tailed Godwits pause only briefly on Merseyside. 

So, like many humans who have seaside holidaysindividual waders of many species find a wintering site they like and come back to the same site every year. How they discover that favoured site is still an open question.