SocLap sap – working draft

1.2.3. N. a. orientalis population

Considerable uncertainty remains over the population size of N. a. orientalis, partly due to no information being available on breeding numbers in western Siberia. A previous estimate of 90,000-350,000 individuals, based on transect counts, in the Yamalo-Nenets Autonomous Area in Western Siberia (Tertitsky et al. 1999) is most certainly an overestimate (Lappo et al. 2012). Perennou et al. (1994) estimated the wintering population at 28,000, including almost 25,000 South West Asian birds, but acknowledged this figure was likely to be a considerable underestimate (Delany et al. 2009). Stroud et al.’s 2004 estimate of 44,600, based on 1990s midwinter counts and estimates, was also considered an underestimate due to incomplete coverage in parts of the Arabian Peninsula and Northeast Africa. Included was an old estimate of 20,000 birds in Iran. This figure was based upon 1970s aerial surveys of the north coast of the Persian Gulf and the coast of Persian Baluchestan (Perennou et al. 1994, Scott 1995). These birds have been unrecorded since. More recently, the population estimate for the population using the East-Asian Australasian Flyway (EAAF) was increased to 100,000. This revised estimate followed non-breeding counts in coastal China of 82,000 birds in 2008 (Cao et al. 2009) and was increased to 100,000 to account for birds that winter inland. This recent estimate is more than twice the previous estimate of 40,000 for this flyway (Bamford et al. 2008).

1.2.4. N. a. suschkini population

There is little information available on the population size of N. a. suschkini. Thorup (2006) assigned 1,220-2,170 breeding pairs in south and southeast Russia to N. a. suschkini whilst Delany et al. (2009) concluded that the numbers breeding in Southwest Asia were unknown but likely to be very low. A population estimate of 1-10,000 has been adopted.

1.3. Distribution throughout the annual cycle

January. Birds are on their wintering grounds. Whilst breeding pairs are monogamous, there is little evidence that the pair bond is maintained outside the breeding season (Cramp & Simmons 1983). The largest wintering populations occur in northwest Europe, West Africa, the Middle East and East Asia. The first birds start their northbound migration towards the end of the month.

February. An increasing number of birds that breed in northwest and central Europe start their northbound migration. Birds at more northerly and easterly latitudes remain on their wintering grounds (Delany et al. 2009). The first adults arrive back on their breeding grounds in France (Fouquet et al. 2013). Males typically arrive a few days before females (Delany et al. 2009).

March. The main passage of birds during the northbound migration. Birds start to leave Tunisia (Feltrup-Azafzaf pers. comm.). At estuaries in northern Scotland, resident birds depart for their breeding grounds; those that breed in Scandinavia will remain for a further month (Wernham et al. 2002, Dennis et al. 2011).

April. The main passage of birds continues. Mating and egg-laying commences in southern and western regions of the breeding range. Most birds form solitary territorial pairs. Occasionally, small colonies are formed. Birds breeding at more northerly latitudes - such as Fennoscandia and Russia - depart their wintering grounds and start to arrive back on breeding grounds (Delany et al. 2009). Some birds make stopovers en route to breeding grounds (Dennis et al. 2011).

May. Early clutches hatch with the first chicks fledging towards the end of the month. Breeding starts in Fennoscandia (Valkama et al. 1999). Both sexes contribute equally to incubation (Currie et al. 2001) but the level of subsequent parental care varies: males stay with chicks during the entire brood-rearing period whilst females depart approximately halfway through. Females depart earlier at north-easterly latitudes. They also depart sooner when they have late clutches (Currie et al. 2001).

June. Breeding continues whilst the first southbound migrations begin (Delany et al. 2009). Some females in central Europe depart their breeding grounds at the beginning of the month and arrive at their non-breeding grounds. Unsuccessful females typically depart first, followed by breeding adults, and lastly by juveniles. The wing moult starts towards the end of the month (Delany et al. 2009) and moulting flocks beginning to assemble at sites such as the Wadden Sea and the north coast of the Caspian Sea (Lebedeva & Butiev 1999). In Fennoscandia, females depart breeding grounds during the second half of the month, leaving successful males to guard their young (Adriaan de Jong, pers. comm.).

July. Breeding continues at northerly latitudes. Most British chicks fledge. Increasing numbers of west European birds gather on the coast as the post-breeding moult continues (Delany et al. 2009). During the moult birds are fairly sedentary (Sach 1968). There is little evidence of further movements following the moult: many birds, particularly in Europe, will spend the rest of the non-breeding season at their moulting sites (del Hoyo et al. 1996). Birds arrive in Tunisia (Claudia Feltrup-Azafzaf pers. comm.).

August. Final month of breeding at northern latitudes. Moult flocks increase in size as increasing numbers of birds undertake their autumn migration. The first migrants arrive in southern Africa (Underhill 1997). There is some overland passage in eastern & southern Africa, as birds move southwest towards wintering sites on the Atlantic Coast (Urban et al. 1986, del Hoyo et al. 1996).

September. Juveniles from continental Europe begin to arrive at their coastal wintering sites.

October. Eastern European birds continue moving south and west.

November. The last birds complete their southbound migration (Delany et al. 2009). During the winter the species usually forages singly or in small groups, occasionally aggregating into flocks of several thousand individuals, especially at roosting sites.

December. Birds remain on their non-breeding grounds. Last moults finish in northern Scotland (Simon Foster, pers. comm.). Many first-year birds spend the whole of the following year on their wintering grounds (Bainbridge and Minton 1978) including in southern Africa (Delany et al. 2009).

1.4. Migration routes

Most Eurasian Curlew populations are fully migratory (del Hoyo et al. 1996) although there can be considerable variation in the migratory behaviour between populations.

Irish birds appear to be largely resident and Ireland sees an influx of birds arriving from northern Britain, which also overwinter on the British coast of the Irish Sea. Birds from southern Britain winter mostly in southwest Britain, France and occasionally Spain (Bainbridge and Minton 1978). Bainbridge and Minton’s study discussed variation in the timing of migration by fledged juveniles. Whilst some had travelled long distances by early August, the movement of many was slow: 70% were within 100 km of their natal site in August. This was reduced to 55% in September, and down to 6% in October.

Breeding populations in Fennoscandia, the Baltic states and north-west Russia winter in the British Isles, the Netherlands, Germany and western France. A small population also winters in the coastal north of Norway (Strann 1993). Some may extend into Iberia and beyond.

Breeding populations in Germany, Belgium, Denmark and the Netherlands mostly winter in the Wadden Sea and the British Isles, although some birds winter inland in Germany (Trösch, 2003). The arrival of birds into Britain swells the wintering population, and internationally important numbers (i.e. over 1% of the global N. a. arquata population) can be found at Morecambe Bay and the Wash (Austin et al. 2014). Similarly, the vast numbers arriving into German, Dutch and Danish stretches of the Wadden Sea results in 4 sites holding internationally important numbers. The Rhine-Maas-Schelde Delta and Friesland Province in the Netherlands also host internationally important numbers, as too does Baie des Veys at Marais du Cotentin, France.

Ringing recoveries have shown that whilst birds from southern Finland winter in western France, those from northern Finland largely winter in Britain (Jensen & Lutz 2006). Birds from southern Germany and France also winter in western France, and into Iberia. Many migrate beyond the Iberian peninsula, extending into the Atlantic coast of West Africa, where internationally important numbers winter in the Banc d'Arguin National Park, Mauritania and the Bijagos Archipelago, Guinea-Bissau. The exact range limits of arquata and orientalis in West Africa, whilst poorly understood, are thought to overlap to an unknown degree. However, the majority of birds in Guinea and Mauritania are thought to be orientalis (Trolliet & Fouquet 2004, Isenmann et al. 2010). There have been no definitive records of N. a. arquata in southern Africa (Underhill 1997).

Birds breeding in central and southeast Europe, including southern Russia, are thought to winter around the Mediterranean coast (Smit & Piersma 1989, Boschert 2001). As large populations migrate south-westerly from Russia, large concentrations gather at important stopover sites including the Danube Plain and Hortobagy in Hungary. Whilst birds can be found around the Mediterranean coastline, large numbers concentrate in particular at one site: the Gulf of Gabès, Tunisia.

Birds breeding in the western region of the N. a. orientalis range appear to migrate in a south-westerly direction, which sees them pass through parts of eastern Europe (including large numbers in Ukraine, where they possibly mix with arquata birds) and southeast Europe (Greece, Turkey, Bulgaria) before migrating further into Africa. Large numbers are known to pass through parts of Central Asia during migration, including at Rogatoe Lake in Uzbekistan. Birds using this flyway also migrate in large numbers through the Middle East, and several sites hosting internationally important numbers (i.e. over 1% of the global N. a. orientalis population exist in Iran (Khouran Straits, Rud-i-Gaz and Rud-i-Hara Deltas, Rud-i-Shur, Rud-i-Shirin and Rud-i-Minab deltas), Iraq (Khawr Al Zubair), Oman (Barr Al Hikman), Saudi Arabia (Tarut Bay), the United Arab Emirates (Khor al Beideh). Flocks of several hundred birds have also been observed at sites in Yemen (Midi-Al-Luhayyah) and Kuwait (Sulaibikhat Bay).

suschkini arquata orientalis Figure 4: Global range of the Eurasian Curlew including the approximate distribution of the three subspecies. The map includes the breeding range (yellow), passage range (pink), wintering range (blue) and areas where it is resident all year round (green). Maps adapted from original maps (BirdLife International and NatureServe. 2013) using information from Delany et al. 2009. Note that the area of overlap between N. a. arquata and N. a. orientalis in West Africa is likely to be further north than indicated on the map; the majority of birds in Guinea (Trolliet & Fouquet 2004) and Mauritania (Isenmann et al. 2010) are thought to be N. a. orientalis.

A large number of N. a. orientalis birds migrate to the coasts of East and South East Asia. A portion of the population also spends the non-breeding season in South Asia. The geographical zones that separate the different migration routes are not known. As these regions are outwith the scope of AEWA, they are not described here in detail.

Lastly, little is known about the migration routes and non-breeding grounds of N. a. suschkini. They are thought to winter mainly in Africa (Delany et al. 2009) although have been recorded as far afield as Sri Lanka (Oriental Bird Club) and the Netherlands (Foundation Voorne Bird Observatory).

1.5. Site Fidelity

1.5.1. Natal philopatry

Bainbridge and Minton’s 1978 study reported that of 287 Eurasian Curlew ringed as chicks in Britain, 94% of birds aged 2 years or more were recovered within 100km of their birthplace between April and June, showing that most birds return to the vicinity of their natal area to breed.

1.5.2. Winter site fidelity

Adults and first winter birds show a high degree of site fidelity to their wintering sites both within and between years. Of British & Irish Eurasian Curlew ringed as fully grown birds during the non-breeding season (including both first winter birds and adult birds), 81% were recovered within 30km of the original ringing site in subsequent winters. Virtually all were recovered within the same estuary system (Bainbridge & Minton 1978). Of recoveries within the same winter, 83% of adults were recovered within 30km of the ringing site. The percentage was slightly less for first winter birds, with 67% within 30km and 22% within 31-100km; juveniles appear to travel further during the non-breeding season.

At one study site in Wales, UK of 3000 captures over 36 years, only 1 bird has been recovered elsewhere (Taylor & Dodd 2013).

1.5.3. Breeding dispersal

Eurasian Curlew exhibit a high degree of breeding site fidelity, rarely nesting more than 250 m from previous nesting attempts. Kipp (1982) investigated breeding dispersal (the extent of movement between years) in Germany by colour-ringing 142 adults and found that a large proportion (77.5%) remained in their territories in subsequent years, even if breeding sites were subsequently degraded. Valkama et al. (1998) also investigated breeding dispersal both between successful and unsuccessful pairs across two study sites of varying landscape characteristics: the ‘fragmented’ Vammala, which comprised 5 small agricultural units separated by woodland, farms and small villages; and the ‘continuous’ Kauhava, which comprised a larger area of continuous farmland of long, narrow fields separated by ditches.

In Vammala, a statistically significant difference (p=0.034) was found between pairs that had failed in their previous breeding attempt compared to successful pairs. Mean dispersal distance amongst failed breeding pairs was 281m (±40.5m, n=24) whilst mean dispersal of successful pairs was only 143m (± 43.2m, n=12). There were too few failed nests at Kauhava to quantify breeding dispersal between successful and failed breeding attempts.

Breeding dispersal was significantly higher (p=0.004) in Vammala (mean dispersal distance=236±32, n=36) compared to Kauhava (mean dispersal distance=102±23, n=18). The differences were attributed to lower breeding densities in Vammala (allowing birds to move over larger areas) and higher nest predation rates in Vammala compared to Kauhava (70% compared to 10%), i.e. Eurasian Curlew avoid breeding close to sites where they have previously failed due to nest predation.

Breeding dispersal is highest amongst pairs that have failed in previous breeding attempts, and some evidence suggests pairs may seek new territories after continually unsuccessful breeding years (Berg 1994, Valkama & Currie 1999).

1.6. Habitat requirements

1.6.1. Breeding habitat selection and use

Eurasian Curlew breed in the boreal, temperate and steppe regions of Europe and Asia (Delany et al. 2009), occasionally extending as far north as the subarctic (Cramp & Simmons 1983). The altitudinal range for breeding varies from sea level to 750m (Cramp & Simmons 1983) and a variety of coastal, lowland and upland habitats are used. There are some common features of breeding habitats: the availability of wet features, a suitably long sward structure for nesting and good visibility (Berg 1992a, Valkama et al. 1998). As such, territories are typically in ‘open’ landscapes away from woodland, although patchy low-lying shrub and tall herbage are tolerated (Boschert 2001, Cramp & Simmons 1983).

They mostly breed in solitary territorial pairs (Johnsgard 1981) although small colonies are occasionally formed (Flint et al. 1984) including with other wader species, where they may benefit from communal nest defence against predators; the so-called ‘protective umbrella’ (Valkama et al. 1999). The nest is a shallow scrape on the ground, or on a hummock if on wet ground (Flint et al. 1984). Nests are sometimes in the open but more often protected on one side by tussocks of grass, heather, etc. (del Hoyo et al. 1996). They may also be in uniform habitat e.g. in dense swards such as those typical of leys in Sweden (de Jong, 2014) or in sparse swards e.g. spring cropping.

In upland areas, they breed in wet and dry heathlands, peat-bogs, fens, acid grassland and steppe. In the UK they often breed in moorland (unenclosed farmed land) containing Calluna vulgaris (Stillman & Brown 1994) and Molinia caerulea (Haworth & Thomson 1990). Structural heterogeneity within these moorland habitats is important; abundance typically increases with varied vegetation height and the presence of plants indicative of wet ground including rushes Juncus spp. (Pearce-Higgins & Grant 2006). Enclosed agricultural grasslands adjacent to moorlands can be an important component of these moorland territories (see later). In the steppes of southern Russia and western Kazakhstan, birds breed in dry meadows within lake depressions, amidst large sandy expanses (Belik 1998). They have also successfully adapted to breeding in a variety of lowland agricultural systems, such as permanent pastures, meadows, grass leys and extensive farmland in large swampy river valleys (Hayman et al. 1986). In many regions, farmland supports substantial proportions of the population: two-thirds of the Swedish and Norwegian population and 90-95% of the Finnish population breeds in farmland. Arable fields are utilised as well, for example in Germany (Boschert 2004), the Netherlands and Finland, where they breed in spring-sown cereals and potato crops (Jensen & Lutz 2006, Valkama et al. 1998). However, within these arable landscapes, the availability and proportion of grassland as brood-rearing habitat is important: tall grasslands occur more frequently in territories than would be expected by its availability (Valkama et al. 1998, Berg 1992a). Arable fields and improved grasslands comprise preferred foraging habitats for adults during the breeding season (Berg 1992a, de Jong 2012). The temporal usage of both habitats has been found to vary in different study areas, but both habitats are probably preferred due to higher invertebrate densities (especially earthworms), higher foraging success rates due to more open swards and prey being more conspicuous on tillage (Valkama et al. 1998, Berg 1992a, Galbraith et al. 1993).

Coastal marshes and dune valley systems are also used for breeding (del Hoyo et al. 1996), including grazed shore meadows in Finland. Grassy or moss-dominated bog habitats within forests have also been reported in certain parts of their range (del Hoyo et al. 1996) and birds nest on large open aapa mires in Northern Scandinavia (Adriaan de Jong, pers. comm.).

As the range of nesting habitats suggests, Eurasian Curlew adapt to new breeding habitats in response to modification by man. One German study (Peitzmeier 1952) observed how nests at one study site were confined to an area of boggy ground, with no nests in the surrounding arable land. The boggy ground was subsequently drained and cultivated, yet the birds remained site faithful and bred on the same ground despite the transition to arable cropping. In subsequent years, nest sites expanded into the previously avoided cultivated land; the expansion was attributed to the imprinting of young birds reared on the new habitat (Cotter 1990). There is evidence from the UK and Germany that populations traditionally nested in upland moorland and raised bog respectively, before expanding into surrounding farmland (Hötker pers. comm.). Conversely, birds started breeding in Estonian farmland in 1956 in areas not close to mires (Jaanus Elts, pers. comm.). In Sweden, birds started breeding in arable fields (cereals and leys) when they replaced natural damp grasslands as a result of drainage and cultivation (Adriaan de Jong, pers. comm.).

In Berg’s Swedish study, there was evidence that the most important factor when selecting a territory was good foraging habitat. This is probably a necessity for the energy-demanding acts of territory establishment and egg production (Berg 1992a). Nest sites in close proximity to good foraging habitat may allow feeding adults to quickly come to the aid of the incubating adult during acts of nest defence (Berg 1992a).

Berg (1993) showed that foraging behaviour changed as the breeding season progressed. Earthworms are an important part of the diet during the pre-breeding period due to their large biomass compared to other invertebrates. Berg found that birds preferred to forage in habitats where earthworms were readily available, namely sown grasslands. Here, they enjoyed higher foraging success compared to tillage - despite both habitats containing similar earthworm biomass - because cultivation destroys earthworm burrows and therefore reduces prey availability. Whilst surface-living invertebrates are not a particularly important prey source during the pre-breeding period, Berg found them to be more important during the breeding season, as their biomass increased.

1.6.2. Breeding Density

Breeding density can vary considerably between different habitats. Densities may range from 5-7 breeding pairs/km² on parts of mainland Northern Ireland, UK (Grant et al. 1999) to 16-17 breeding pairs/km² on the Orkney Isles, UK (Andy Knight, pers. comm.). In moorland sites in the UK, densities were 1.85 breeding pairs/km² in upland plots where dwarf shrubs (e.g. Calluna vulgaris) comprised 0-33% of vegetation cover. This increased to 2.77 in plots containing 33-66% dwarf shrub cover but reduced to 2.45 in plots with 66-100% dwarf shrub; densities peak where vegetation structure is relatively heterogeneous in terms of height (Pearce-Higgins & Grant 1996). At Swedish study sites breeding density varied from 0.1-0.68 breeding pairs/km² (Berg 1992b). In 700 ha of open farmland interspersed with forestry and settlements in northeast Sweden, densities have fallen from ~ 5 breeding pairs/km² in the 1990s (de Jong 1990) to ~3 breeding pairs/km² (Adriaan de Jong, pers. comm.). In Finland, nesting density varied from 1.6 breeding pairs/km² on arable ground interspersed with towns and forests, compared to 6.7 breeding pairs/km² in a similar arable setting without woodlands and towns (Valkama et al. 1999).