The flock now departing

“The flock now departing from the tideline is bound for Beauvais. Curlew can change here for destinations in Germany and Russia”. It’s fascinating to wonder what might be happening when a flock of waders takes to the air, gains height and sets off in a particular migratory direction. With more individuals wearing tracking devices, it was only a matter of time until someone would have data that provides clues as to the association of individuals within flocks – as we see in a 2021 paper in Bird Study by Frédéric Jiguet and colleagues: Joint flight bouts but short-term association in migrating Eurasian Curlews.

Setting off on migration

When we get on a plane to a particular destination, everyone else who is on the same journey has chosen to travel at the same time and we all know where we are going. Each of us has checked that we have what we need for the journey and has a plan of what to do when we land – whether that involves a short shuttle to home or a lay-over before catching another flight.

For waders, planning must be more random? It’s presumably safer and more efficient to be part of a flock but how do you know which flock to join, who organises the schedule and is information shared? We can get some clues from observations of departing migratory flocks. In estuaries, there is often the chatter (which is hard to interpret but tells us that something is about to happen), then the first birds take to the air and start to gain height. A few birds may peel off and return to the tide-line while other birds take off and catch up with the departing flock. As the birds gain height, the direction of travel becomes clearer and more birds may decide to return to the mudflats. There is now a migratory flock of birds that are committed to flying in a particular direction. We have no idea how that direction was chosen, of course, but there is a plausible explanation as to how the flock might have formed.

This is not the last decision that members in a flock might need to make. Tired birds may need to drop out of the flock, to take a break. Perhaps some birds might realise that the direction of travel does not work for them and the flock might break up?

It can be just as chaotic when a flock reaches a destination. Watching Black-tailed Godwits arriving in South Iceland in April is fascinating; a tired flock might come in off the sea, land and start drinking, before either resting or feeding, but this is not always the case. On a clear day with fair winds, the flock may split up, with some birds keen to keep flying and others happy to stop. This reinforces the impression that a flock only maintains its integrity as long as being in a group meets the needs of the individuals it contains.

Tracking Eurasian Curlew

Understanding migration is an important element of Curlew conservation studies in France.

In their Bird Study paper, Frédéric Jiguet and colleagues describe four cases of joint migration by tagged Eurasian Curlews. Their observations were a biproduct of research aimed at a better understanding of the origins and migration patterns of Curlew that spend the winter in France. The species has been a popular target for French hunters, many of whom are keen to resume shooting, as you can read in the WaderTales blog Black-tailed Godwit and Curlew in France. It is estimated that more than 7000 Curlew were shot in France annually prior to 2008, when the first moratorium was put in place.

There is an urgent need to understand links between wintering sites and breeding sites, especially in areas where the species is in rapid decline. How important is France to the Curlew that breed in countries such as Poland and Germany? The current ban on shooting is not perfect (see paper in Forensic Science International: Animals and Environments) but it is better than nothing, given rapid declines in Curlew numbers across Europe.

In winter and spring 2020, the research team deployed 61 GPS tags on Curlews in France and Germany, hoping to learn more about breeding ecology and migratory connectivity. In a separate study, in Poland, four captive-bred juvenile curlews were tagged and released in July 2020. Between them, these tagged birds led to four cases of joint migration bouts. One case concerned two adults leaving their wintering ground for the pre-breeding migration. Two other cases were birds leaving their breeding grounds at the start of migration. The last one was of two juveniles initiating their first flights to the non-breeding grounds.

Spring migration

About 27,500 Curlew spend the winter in France (see French report produced jointly by government and shooting groups), representing about 5% of the European population. Tracking has shown that these birds breed in Belgium, Germany, Sweden, Finland, Austria and Russia (see article published by Bird Guides) but there are reports of ringed birds from many other countries, including the threatened populations in Poland and the UK.

Thousands of Curlew spend most of the year in coastal France – representing 5% of the European population.

Return migration to breeding areas takes place in early April. Frédéric Jiguet reports ‘groups of curlews rising high in the sky at sunset’ from the Moëze-Oléron and Baie de l’Aiguillon Nature Reserves in southwest France.

Back-mounted GPS tag

On 17 April 2020, two individuals wearing tracking devices left their French wintering site at sunset, between 22:37 and 22:40. They became closely associated just ten minutes prior to the start of migration, having typically stood 100 metres apart during the previous hour. They flew together for seven hours before making a stop-over north of Paris, between Creil and Beauvais, in the Thérain Valley.

  • 200185 was on its way again two hours later, flew for six hours, stopped again in the Netherlands and arrived in Norderney, an island of the Wadden Sea in northern Germany, at 18:39 on 19 April.
  • 200187 had a much longer layover in the Thérain Valley, making another evening departure at 20:05 on 18 April. It continued migrating, in stages, for more than a month, crossing the Ural Mountains and reaching the Yamalia municipality, in Asian Russia.

Two birds that had been on the same flight from southwest France ended up in very different locations and at very different times. The German Curlew reached its summer destination five weeks before the Russian bird arrived on territory, the latter having secured places on several different ‘international flights’ as it made its way east and north (see figure below).

Post-breeding migration

After breeding, adult Curlew head towards wintering sites, perhaps stopping to moult en route. Some birds do not travel far; for instance, there are colour-marked birds that winter on the Wash (eastern England) and fly just a few kilometres inland to breed. The Bird Study paper includes reports of two occasions when tagged birds have been spotted migrating together from German and French study areas. Southerly migration of all four birds commenced during the evening of 17 June 2020.

French birds: Two individuals departed simultaneously from Deux-Sèvres (central France) between 19:16 and 19:17 for a non-stop southward flight and arrived together at Ria de Treto estuary, in northern Spain on 18 June at 05:49. The two birds departed separately from this stopover site the same day (18 June).

  • 200201 departed at 18:18, for a non-stop flight to Kenitra (Morocco) where it stopped briefly, before moving a short distance north to Merja Zerga.
  • 200204 departed at 19:46 and flew to the Atlantic coast of Spain, stopping for 2.5 hours on Isla Cristina and then flying to its final destination at Ilha de Tavira, in southern Portugal.

After separation, the two birds travelled at different times but followed quite similar routes and even flew at similar altitudes.

German birds: On 17 June 2020, two individuals departed simultaneously from Dollar Bay, in the Wadden Sea National Park. 201075 began migration between 18:58 and 19:03. After five kilometres, if flew over 201072 at an altitude of about 190m. The latter bird took off and joined 201075. They then flew together for five hours, landing in the Rhine-Meuse-Delta (Netherlands).

201075 departed from the Rhine-Meuse-Delta on 20 June and, after one more stop-over, reached its final destination on the Brittany coast on the evening of the next day.

201072 was also bound for Brittany. It departed on 23 June and flew non-stop for six and a quarter hours.

Migration of juveniles

It will be hard to satellite-tag enough wild juvenile waders to pick up instances of marked individuals migrating in the same flocks. However, head-starting may give some clues as to what might happen when naïve flocks of juvenile waders start their migratory journeys, months after the parents have left them. The full story is told in the paper but a quick summary tells us that two Polish head-started Curlews were released on 1 July, departed together on 5 August and landed in the Baie de l’Aiguillon (France) on 8 August. In between times, they came close to landing in The Netherlands, flew along the English coast from Dover to Poole, flew a long way south and west around the Bay of Biscay and then northeast to the coast of France. They both spent the winter in the Baie de l’Aiguillon but not together.

Although it will be difficult to compare the migratory behaviour of wild-caught and head-started wader chicks using satellite tags, just because of probabilities and costs, researchers are building up datasets using smaller geolocators and GPS tags. Here’s hoping that we will soon know more.

Paper

The nutrient-rich mud of Ile Madame

This paper provides observations of just four instances of joint migration but each story is fascinating. They give us insights as to what might be possible as devices get smaller and when land-based tracking stations collect signals from passing birds. For the moment we can use our imagination to interpret the chattering of pre-migratory flocks of waders, the appearance of a small flock of waders at an inland spot in spring and the noisy arrival of a lone Curlew on an estuary in June.

The paper contains a lot more detail about the methods used to collect and interpret data and a discussion that sets Curlew migration within a much broader conceptual context. Here’s a link:

Joint flight bouts but short-term association in migrating Eurasian curlews.

Frédéric Jiguet, Pierrick Bocher, Helmut Kruckenberg, Steffen Kämpfer, Etienne Debenest, Romain Lorrillière, Pierre Rousseau, Maciej Szajdaand & Heinz Düttmann. Bird Study. DOI/10.1080/00063657.2021.1962805

Wintering Curlew from as far away as Russia and Sweden can be found roosting in these French saltmarshes

WaderTales blogs are written by Graham Appleton (@GrahamFAppleton) to celebrate waders and wader research. Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.

On the beach: breeding shorebirds and visiting tourists

Rising sea levels, stormier weather, coastal development and more people are putting increasing pressures upon shorebirds that nest on beaches. A paper about the breeding waders of Norfolk & Suffolk (UK) coasts illustrates the importance of understanding human behaviour when trying to maintain (or create) space for breeding plovers. This paper will be of particular interest to conservationists trying to support breeding populations of species such as Ringed Plover, Kentish Plover, Piping Plover and Snowy Plover.

The problems of disturbance

Around the globe, nesting plovers are being threatened by human disturbance. Local initiatives to reduce these impacts include the installation of electric fences, recruiting volunteer wardens and changing local bylaws. You can learn more about which interventions work from Conservation Evidencethere’s more about this at the end of this blog.

Panning out, to look at the bigger picture, is it possible to determine where conflicts between breeding birds and tourists are likely to occur, so that one can try to resolve the problems before they start? Can this information help to inform planning decisions?

Oystercatcher with chick

Ringed Plovers and Oystercatchers

The coastline of Norfolk and Suffolk should be an ever-changing environment, dominated by sand and shingle beaches. Coastal defences artificially maintain the barrier between sea and land but sea-level rise is predicted to over-top and destroy sea walls during storm events. How will East Anglia’s beach-nesting waders cope with squeezed beaches at the same time as East Anglia is seeing increasing tourist numbers? In a 2020 paper in Global Ecology & Conservation, Jamie Tratalos and colleagues from the University of East Anglia investigated the distributions of nesting Ringed Plovers and Oystercatchers around the beaches of Norfolk and Suffolk, relating settlement patterns to visitor numbers.

Snettisham beach – sunny weather is not great for the local breeding Ringed Plovers

Ringed Plovers and Oystercatchers breed on sand and shingle beaches that are also attractive to people. They are prone to disturbance, especially by dogs that are allowed to run free, as discussed by Gómez-Serrano (2021). Nests can be trampled, incubation can be interrupted and chicks can be killed. Liley and Sutherland (2006) showed that, over a 9 km stretch of Norfolk coastline, Ringed Plovers bred less successfully when exposed to disturbance by beach visitors, and population declines in this species have been linked to human disturbance (Birds in England by Brown & Grice, 2005). Human recreation has also been shown to be associated with reduced breeding success in Eurasian and other oystercatcher species (Tjørve & Tjørve, 2010), and Ens and Underhill (2014) suggest that increased human use of the coastal zone, combined with increased risk of nest flooding and loss of wetlands, may threaten the conservation of oystercatchers around the world.

Ringed Plovers can have several breeding attempts in the course of a summer

UK breeding populations of Ringed Plover have declined in recent decades, from a conservative estimate of approximately 8400 pairs in 1984 to 4070 in 2007 (Conway et al., 2019) and the species is now red-listed (see the WaderTales blog: Nine red-listed UK waders). Oystercatchers have undergone considerable Europe-wide decline in recent decades and the species has been classified as ‘Near Threatened’ globally (IUCN, 2020).

Counting birds and people

In 2003, when the study at the heart of the Tratalos paper was carried out, East Anglia’s beaches between the Wash and the River Stour held about 3% of the UK’s breeding Ringed Plovers, as well as relatively small numbers of breeding Oystercatchers. As part of a bigger climate change research programme, Tratalos et al were keen to understand what drove the distribution of Ringed Plovers and Oystercatchers, in order to be able to include conservation actions in plans to manage the changing coastline of Norfolk and Suffolk, especially associated the abandonment of outer sea defences. Their research was written up in a 2020 paper in Global Ecology & Conservation.

In the study, the authors examined a 212 km stretch of coastline, mapping all breeding pairs of Ringed Plover and Oystercatcher, as well as the environmental characteristics of beaches. Data on the location of bird territories, and the habitats in which they were found, were collected by Dave Showler in the period between early April and mid-June in 2003. Details of survey methods can be found in the paper.

Map data from Bird Atlas 2007-11 (BTO, BirdWatch Ireland and SOC)

Visitor numbers to different beaches were assessed by filming from a light aircraft, flying at an altitude of 150 metres. 38,634 human visitors were mapped from three flights during sunny weekends in April, June and August, when the tide was at approximately mid phase. There were pronounced peaks in visitor numbers along the coastline, with 19 of the 1003 beach sections experiencing over 10 times the average number of visitors and 231 sections hosting none.

The key findings from surveys and analyses were:

  • Of just over one thousand 200m sections of beach surveyed, 183 beach sections contained Ringed Plover territories (266 breeding pairs) and 117 contained Oystercatcher territories (223 pairs).
  • There were more occupied territories in less-visited areas, for both species. See table relating the visitor index to occupation of sectors. An index of 0.13 means that visitor numbers were 13% of the mean across all sectors.
  • No Oystercatchers were found breeding in sectors where the visitor index was higher than 2.8. No Ringed Plovers were found in sectors where the index was above 5.5.
  • Ringed Plovers territories were more common in sections that had dunes at the back of the beach and where the beaches were broader at low tide.
  • Oystercatchers appeared to need space above the high-water mark, as well as a broad intertidal area.

The associations between territories and habitat enabled the team to predict the number of pairs of waders that might have been present in areas which were highly impacted by visitors. If visitor numbers were reduced to zero across the whole study area, breeding potential could be hugely increased.

Feeding on the mud at low tide – Ringed Plovers and Oystercatchers need a broad intertidal area
  • The authors predict that there would have been an additional 90 beach sections where Ringed Plovers could potentially establish territories, suggesting that tourism and the local use of beaches has already removed 33% of Ringed Plover breeding habitat.
  • There were 96 sections where breeding Oystercatchers might have been expected to be found, so they have already lost 45% of potential habitat.

Practical considerations

These results suggest that human activity on beaches influence the location of breeding territories of Ringed Plovers and Oystercatchers, with both species using territories where the number of human visitors was relatively low, when considered both at the scale of the whole Norfolk and Suffolk coast, and locally within areas of this coastline.

In the absence of people, there appear to be clear features of the areas that determine if sectors are used by both wader species for breeding. This makes it possible to predict places where increased access could cause problems so that, ideally, tourism might be encouraged in areas that are less likely to be used by breeding waders. Unfortunately, the beaches that are great for red-listed Ringed Plover – with a back-drop of sand dunes, a sandy beach to walk along at high tide and a gently-shelving intertidal area – are also ones that attract people. This makes it harder to create discrete ‘people zones’ and ‘wader zones’ than might otherwise be the case.

Access points create issues for breeding wader but the effects of most visitors are localised. Unless birdwatching or exercising a dog, the typical tourist will not stray more than 300 metres from a carpark, as indicated in the graphic above. In less-disturbed beach sections, where Oystercatchers set up territories, chicks can hide in upper-beach vegetation until parents indicate that it is safe to come out to be fed.

When Emma Coombes (Global Environmental Change, 2009) asked visitors to Norfolk’s beaches what they were looking for, there was a remarkable consistency in the responses from dog-walkers, sun-bathers and birdwatchers. They all wanted to be on remote flat, sandy beaches, with sand dunes. They would appreciate a car park and toilets too. As soon as such facilities are provided, of course, visitor numbers increase, the remoteness is lost and so are breeding waders, unless fences and wardens are introduced.

Winterton-on-Sea beach is promoted as a tourist location with access to a national nature reserve

Planners have few tools available to them, when it comes to protecting stretches of coastline. All that they can control is development (e.g. new roads, housing and tourist accommodation) and facilities such as car parks and toilets. This paper clearly shows the need to understand the local features that are needed by nesting waders and the importance of documenting current distributions, so that local and national planning authorities have the information they need when planning for the future.

Paper in Global Ecology & Conservation

Vulnerable Ringed Plover chick

Regional models of the influence of human disturbance and habitat quality on the distribution of breeding territories of common ringed plover Charadrius hiaticula and Eurasian oystercatcher Haematopus ostralegus. Jamie A. Tratalos, Andy P. Jones, David A. Showler, Jennifer A. Gill, Ian J. Bateman, Robert Sugden, Andrew R. Watkinson & William J. Sutherland.

Conservation evidence

Before trying a new conservation technique on a local patch, it is worth checking out what has been tried elsewhere. A quick visit to the Conservation Evidence website and a search on ‘beaches’ and ‘bird conservation’ produced a list of 26 actions that have been written up in papers or grey literature. Although many of these interventions are more appropriate to tern conservation than shorebird conservation, a few seem to be particularly relevant to people who are considering how to help breeding Charadrius plovers. Five potential actions are assessed as ‘likely to be beneficial’

  • Use signs and access restrictions to reduce disturbance at nest sites
  • Physically protect nests with individual exclosures/barriers or provide shelters for chicks of waders
  • Protect bird nests using electric fencing
  • Physically protect nests from predators using non-electric fencing
  • Physically protect nests with individual exclosures/barriers or provide shelters for chicks of ground nesting seabirds
Dogs cannot read ‘no entry’ signs, designed to save space for breeding waders and terns

The Conservation Evidence website aims to make scientific research available to conservation practitioners. Anyone considering any of the interventions listed above can see a quick synopsis of what worked (and what didn’t work) in which circumstances. Anyone who has discovered another successful management technique is urged to write up their study – so that it can be added to the database.


WaderTales blogs are written by Graham Appleton (@GrahamFAppleton) to celebrate waders and wader research. Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.