Species such as Dunlin and Knot are well-served by conservation measures that aim to protect estuaries but the same is not necessarily true for Black-tailed Godwits. In a 2022 paper in the journal Wader Study, Clément Jourdan and colleagues describe the movements of ten tagged Black-tailed Godwits, showing how much time they spend on poorly-protected inland sites and how the species’ use of these habitats changes over the seasons.
Mobile Black-tailed Godwits
Large numbers of Black-tailed Godwits can be found along the Atlantic coast of France, comprising birds from the booming islandica race and others from the struggling limosa race, with proportions varying throughout year. Some limosa breed in France and head to Africa in autumn but the numbers of this subspecies are dwarfed in autumn and spring, when limosa from the Netherlands and neighbouring countries stop off, to top up their fuel supplies for migration. Adult islandica birds from June/July to April/May and some young islandica stay in France during the summer months too.
This mix of the two races, one of which is increasing (islandica: see From local warming to range expansion) and the other of which is in severe decline (limosa: see Dutch Black-tailed Godwits down by nearly 75%) creates conservation challenges. Hunting of waders is still popular in France and decisions as to which species are legally shot need to be evidence based. Do limosa and islandica mix or are there times of year and circumstances when hunters can be pretty sure that they are targeting only islandica? For the moment, there is a temporary suspension of Black-tailed Godwit (and Curlew) from the quarry list (see Black-tailed Godwit and Curlew in France) while more evidence is collected. Set against this background, it is really important to understanding habitat use by both islandica and limosa.
Icelandic Black-tailed Godwits return to France from June onwards and the last birds do not leave again until the start of May. By analysing the movements of 10 wintering islandica Black-tailed Godwits, using GPS-telemetry, Clément Jourdan and colleagues gained insights into the varied ways in which birds spend their time during this non-breeding period. Although it might look as if Black-tailed Godwits have a wide range of sites at their disposal, each individual only made use of a limited number of options during the course of a winter. The tagged birds moved around at both small and large spatial scales, on tidal and/or daily cycles, and changed their patterns with the seasons.
It was already known that islandica Black-tailed Godwits in France use bare mudflats or seagrass during the autumn, with some individuals using grasslands during the winter, and that most birds migrate to The Netherlands or eastern UK in spring, where they forage primarily on grasslands. This northwards movement, especially to The Netherlands, puts birds in pole position for the flight to Iceland (see Overtaking on migration).
Studies of energy intake rates in godwits feeding on mudflats and grasslands in Eastern England suggested that birds move to grasslands when estuarine food supplies are no longer sufficient to fulfil their energy requirements, and that they frequently use both mudflats and grasslands over the winter and spring (buffer effect paper). Colour-ring studies show that birds tend to use the same sites in the same seasons every year (as discussed in Generational Change). The study of tagged birds in France allowed researchers to add daily detail for a small number of Black-tailed Godwits.
The study was carried out on the French Atlantic coast, from the Loire Estuary area, in the north, through the Baie de Bourgneuf and the Vendée Coast, and south to the Pertuis Charentais area. Full details of available habitats are provided in the paper.
Follow those godwits
The tags on the study birds were set to provide locations every thirty minutes. The ten individuals that are the focus of the Jourdan paper provided a mean of 41 locations per day, rather more than can be obtained from colour-ring reading!
At a large spatial scale, the 10 monitored Black-tailed Godwits could be split into two groups:
- Six godwits (BLTG11, 12, 14, 16, 17 and 18) remained within the Pertuis Charentais area throughout their tracked period, exploiting a small number of distinct sites. The average distance travelled in a day varied from 10 km to 31 km, depending on the individual, sometimes exceeding 40 km in one day. These birds were largely coastal, feeding on intertidal areas, but some of them occasionally visited inland habitats around the major roost sites.
- Four godwits (BLTG13, 15, 19 and 20) spent the early and mid-winter period in Pertuis Charentais but then flew north, to the Loire-Bourgneuf area, either directly or with a stop at the Olonne Marshes on the Vendée Coast. These refuelling stations were also used during pre-migration and post-migration periods. BLTG13 and BLTG15 were monitored during two successive years and behaved consistently between years. BLTG19 was tagged as a juvenile and, as expected, stayed in France over the course of a full eighteen-month period.
When it came to habitat use, the authors found it difficult to describe general patterns. This is important; mitigation measures aimed at providing alternative feeding areas tend to focus on the one-size-fits-all principle. In the detail presented in the paper, we see that different birds behave very differently. Wet grassland is not going to be a replacement habitat for a Black-tailed Godwit that specialises on feeding in tidal seagrass beds. Here are a few gems from the paper:
- BLTG13 and 15 showed annual consistencies in their habitat selection but behaved very differently to each other. BLTG15 mainly used bare mudflats between August and February and selected inland marshes just before migration and upon return from Iceland. BLTG13 mainly used inland marshes in the run-up to departure (mid-February to mid-May) and upon return, using other habitats (saltpans, coastal marshes and mudflats) during the wintering period (early August to mid-February).
- Individual birds switched habitat between three and eight times per month, often using multiple habitats during the course of a single day. Several birds spent long periods focusing on intertidal areas but then roosted on marshes or in saltpans, but even here there were exceptions. Having been part of the mud/marshes group, BLTG14 started prospecting inland to marshes and hunting ponds. This bird was one of two that used hunting ponds more intensively, both by day and by night, after the shooting season closed at the end of January.
- Important habitats included inland marshes, hunting ponds and salt pans, with BLTG11 feeding almost exclusively in salt pans and ignoring tidal feeding opportunities. It was also clear that some birds were feeding at night more than had previously been thought.
The movements at both local and large scales underlined the use of multiple habitat types, in both marine areas and freshwater wetlands. Most birds predominantly used intertidal areas from early to mid-winter and then moved to inland marshes just before the spring migration period, but they also showed an ability to shift quickly from natural habitats to artificial wetland habitats such as saltpans or hunting ponds.
Looking at the distribution of Black-tailed Godwits across a wide range of habitats, it may be tempting to think that this is a flexible species. Birds certainly seem able to identify new opportunities that become available as the season progresses, such as switching to grassland feeding when estuaries become less productive and then using hunting ponds once duck shooting is over. However, once a bird has adjusted to its own rhythms, it remains faithful to its own patterns of habitat use between years.
Many of the estuaries of Europe are protected from further development, at least to some extent, thanks to European legislation but rarely do the boundaries of Important Bird Areas extend beyond beaches and sea walls. As Clément Jourdan and his colleagues show, Black-tailed Godwits commonly use feeding areas that lie outside designated areas, especially during the period when they are fattening up for spring migration. As the authors point out, inland pools can also be important roost sites, as described in A place to roost, which highlights the Gilroy ‘godwit field’ near the Dee Estuary of northwest England. This small site can be used by 5% or more of the Icelandic population of Black-tailed Godwits during high spring tides in early autumn.
The boundaries of estuaries have been defined by the sea walls that protect towns, villages and agricultural land but this is an artificial system. Four centuries ago, waders could move freely between estuaries, brackish lagoons and freshwater marshes. These days, waders such as Black-tailed Godwits fly tens of kilometres to find the mix of habitats they need. Studies of these ten birds add rich detail to the picture painted by colour-ring sightings, as discussed in Godwits and Godwiteers.
The ‘near-threatened’ Curlew is even more of a challenge for conservationists. Curlew spend a lot of their time on estuaries but also use nearby fields and grasslands as roosting and feeding sites. Forth Estuary Curlew that can be seen on rugby pitches in Edinburgh are probably not going to be disturbed more than a few times a week but a new £150 million distribution centre at West Melton in Hull is permanently removing fields used by Humber Estuary birds.
We know that other wader species, such as Golden Plover and Oystercatcher flip backwards and forwards between marine and terrestrial feeding/roosting areas but tracking may well show that such behaviour is more widespread than we thought across species of wader.
Godwits in France
This paper provides fascinating insights into the lives of individual Black-tailed Godwits. There are too few tracked birds for formal analyses of habitat preferences but there are enough differences within the ten individuals to show that the removal of one site from a winter network can have wider implications than might have been expected. The full Wader Study paper is available here:
Combination of marine and freshwater artificial habitats provide wintering Black-tailed Godwits with landscape supplementation. Clément Jourdan, Jérôme Fort, Frédéric Robin, David Pinaud, Philippe Delaporte, Didier Desmots, Alain Gentric, Pamela Lagrange, Julien Gernigon, Loïc Jomat, Pierre Rousseau & Pierrick Bocher. Wader Study. DOI 10.18194/ws.00271
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.