Pectoral Calidris acuminata and Sharp-tailed Sandpipers C. melanotos are phenotypically and ecologically similar high-latitude-breeding Holarctic shorebirds with long-distance migrations to South America and Australasia, respectively. Pectoral Sandpiper has two separate breeding areas, in the Arctic tundra of Siberia from the Yamal Peninsula (70oE) east to the Bering Sea, and along the north coasts of Alaska and Canada east to Hudson Bay (Cramp & Simmons 1983, Zockler & Lysenko 2000, Lappo et al. 2012). Sharp-tailed Sandpiper breeds solely in eastern Arctic Siberia from the Taimyr Peninsula (132oE) to Chaun Bay in Chukotka (170oE), and its entire breeding range is overlapped by that of Pectoral Sandpiper (Lappo et al. 2012). There is recent evidence that its breeding range may be expanding west (Lappo et al. 2012).

Sharp-tailed Sandpiper has a complex migration. Post-breeding, adults move south from Siberia on a broad front in early August, mostly passing east of Lake Baikal, and east to the Pacific coast of Russia and the Yellow Sea coasts of China (Barter 2002) and Korea, from where most apparently fly directly to Micronesia and New Guinea in late August (Higgins & Davies 1996). It is uncommon on the Asian coastal flyway south and west of the Yellow Sea, being reported only as a straggler in Vietnam, Cambodia, Peninsular Malaysia, Pakistan (Roberts 1990), India (Ali & Ripley 1969) and Sri Lanka (Roberts 1990, Henkanaththegedara 2002, van Gils et al. 2018). Migrants depart Papua New Guinea at the onset of the wet season, travelling south-west and arriving in north-west Australia mainly in mid September, then moving slowly south to south-east Australia, some crossing the continent en route, where the majority of the world population overwinters, with numbers peaking in December–early February (Higgins & Davies 1996). However, most juveniles, and a few adults, have a remarkably different strategy, migrating east from the breeding grounds across the Bering Strait to Alaska, where they fatten between mid August and late October (Tomkovich 1982, Handel & Gill 2010, Lindstrom et al. 2011). It is presumed that these birds fly from Alaska across central and western Oceania to reach Australia and New Zealand in a non-stop trans-Pacific flight of more than 10,000 km (Grönroos et al. 2010, Lindstrom et al. 2011). Some continue south along the Pacific coast of North America south to Washington state, less frequently to California, and there is a scatter of records east in North America where the species is considered ‘possible anywhere' (Mlodinow 2001). Prior to 2001 there were 32 records in the interior USA and 19 records on the Atlantic coast (Mlodinow 2001). It is possible that small numbers continue south on the west coast to Latin America, but to date there are only two records in the region, both recent, from Panama (Anon. 2016) and Bolivia (Knowlton 2016).

Sharp-tailed Sandpiper is a rare vagrant to Europe, with records in 11 countries (most in the UK, with 32 records by 2012: Hudson & the Rarities Committee 2013) of both juveniles and adults, mostly in August–October (Britton 1980, Cramp & Simmons 1983, van Gils et al. 2018). There are records in the Middle East and Central Asia, six from Kazakhstan (Wassink 2014) and singles in Oman (Eriksen & Victor 2013) and Yemen (Brooks et al. 1987).

In the Indian Ocean, the easternmost records are on Christmas Island (Australia), where there are four sets of records totalling 16 birds between 15 October and 10 December (James & McAllan 2014), with at least three records on Cocos (Keeling) Island in November–December 2016 (eBird). Further west there are five records from the Chagos archipelago in September–December (Carr 2015) and also five in the Seychelles, one in July, two overwintering in September / October–February and two on passage in November (Skerrett et al. 2017). There is one record from Madagascar in November 1999 (Patient 2003, Safford & Hawkins 2013).

There is also a remarkable specimen from Tristan da Cunha, collected on 16 June 1950, identified by Elliott (1957) as Sharp-tailed Sandpiper. This was followed by Cramp & Simmons (1983) and Higgins & Davies (1996), but the identity was questioned by Hockey et al. (1986). Mackworth-Praed & Grant (1962) referred to it as a Pectoral Sandpiper and Hockey et al. (1986) presumed that this was based on examination of the specimen at what is now the Natural History Museum, Tring (NHMUK). As this is an important record, the specimen was re-examined by A. J. Bond and the identity confirmed as a Sharp-tailed Sandpiper in breeding plumage (Fig. 1.). A. J. Prater (in litt. 2018) had also examined the specimen and noted that it was in suspended inner primary moult and probably therefore not fully adult (Hayman et al. 1996).

Pectoral Sandpiper also has a complex migration and vagrancy pattern. Siberian breeders are believed to depart south across the Arctic Ocean and travel along the east coast of the Pacific (Lees & Gilroy 2004), but the majority—an estimated 90%—migrates south in short hops (Piersma 1987, Farmer & Wiens 1999) via a narrow overland corridor through North America, not concentrating at particular wetlands (Skagen et al. 1999). It is surprising therefore that it is the most frequently recorded of the Nearctic vagrants to Europe (Lees & Gilroy 2004) with a regular annual influx in September–October mainly of juveniles, some of them clearly displaced by transatlantic weather systems. However, it is also possibly a ‘pseudo-vagrant' (Gilroy & Lees 2003) with relatively small numbers from both North America and Siberia apparently on intentional, regular passage via Europe to wintering quarters in Africa (Lees & Gilroy 2004). This pattern is also mirrored in Australia and New Zealand, where small numbers of presumably Siberian breeders follow the west coast of the Pacific, joining groups of Sharp-tailed Sandpipers to overwinter mainly in Australia (Higgins & Davies 1996).

Pectoral Sandpiper is a regular vagrant to Africa, with records in 23 countries from northern, western, eastern and southern Africa (Hockey et al. 1986, Urban et al. 1986, van Gils et al. 2018b) as well as the Atlantic islands (Cramp & Simmons 1983, Hockey et al. 1986), Madagascar and the Indian Ocean islands (Hawkins & Safford 2013) as far south as the subantarctic (Viet et al. 2007). Up to five birds per annum are recorded in the southern African region (136 records 1965–2018; 36 records 1970–90) between September and May, but most arrive in December (peak) and remain until April. Peak arrival date is later than most other migrant waders in the region and suggests that they slowly trickle south through the continent (Hockey et al. 1986). Records are mostly coastal and in the east of the region, especially Gauteng Province, South Africa, probably reflecting observer coverage (Hockey et al. 1986). It is surprising, therefore, that the first record in Mozambique was as recently as January 2017 (Allport 2018a).

Figure 1.

Specimen of female Pectoral Sandpiper Calidris melanotos (below) compared to female specimen NHMUK 1953.55.113, collected on Tristan da Cunha, 16 June 1950 (above), confirmed as a Sharp-tailed Sandpiper C. acuminata, the identity of which had been questioned; see main text (Harry Taylor, © Natural History Museum, London)

Both species select similar habitats on passage and in winter, the muddy edges of shallow fresh or brackish wetlands with inundated or emergent sedges, grass, saltmarsh or other low vegetation including lagoons, swamps, lakes and pools near coasts, dams, waterholes, saltpans and hypersaline salt lakes inland (Higgins & Davies 1996). However, Sharp-tailed Sandpiper prefers coastal graminoid meadows in Alaska (Lindstrom et al. 2011) and particularly favours saltmarsh and brackish lagoons where Salicornia and Cotula provide cover in Australia, less often using similar inland habitats such as wet fields of short grass. In Australia it is thought to occupy coastal mudflats mainly once ephemeral terrestrial wetlands have dried out (Higgins & Davies 1996).

The identification of this species pair was an early challenge to modern field ornithologists. Britton (1980) presented the first analyses of the identification characters of Sharp-tailed Sandpiper based on field experience of an adult and a juvenile, the written descriptions of all 16 British and Irish sight records at the time, and an examination of three specimens, along with many records of Pectoral Sandpiper. Harrop (1993) later revisited their identification adding more plumage detail. Both papers encompassed identification issues for juveniles and adults in summer or transitional plumages in the boreal autumn. As vagrancy in the non-breeding season and on spring migration is relatively uncommon, identification of winter-plumaged birds and those in transition into breeding plumage is scantily covered in the main Eurasian field guides. These plumages are, however, covered in Australasia (Higgins & Davies 1996, Pizzey et al. 2010), albeit not in great depth, perhaps because Sharp-tailed Sandpiper is a relatively common bird there with which most birdwatchers are very familiar.

Recent records in Mozambique

Regular bird observations were undertaken by GA while based in Maputo, Mozambique, between October 2010 and April 2018. Casual, low-effort, opportunistic observations were made at sites ranging from Ponta d'Ouro and Maputo Special Reserve, in Maputo province in the south, north through Gaza Province to the Bazaruto archipelago in Inhambane province (see Allport 2018b for map). Sightings were recorded in eBird. Coastal and inland wetlands were visited at all times of year. Beaches and mangrove-fringed mudflats in Maputo Bay, Inhambane and Barra were frequently visited, but freshwater and brackish swamps were mostly inaccessible. In 2017 the construction of a new bridge at Marracuene gave access to an area of tidal, tall brackish marsh in the Incomati estuary, the northern part of Maputo Bay, permitting regular coverage of these habitats for the first time.

On 4 February 2018 GA, M. Costeira da Rocha & B. Briggs visited Macaneta wetlands. At 09.10 h an area of tall saltmarsh with scattered reeds, sedges and Salicornia was searched on a rising spring tide where Curlew Sandpipers C. ferruginea and Little Stints C. minuta were feeding (25o44′05.83″S, 32o43′20.49″E). A bird that looked like a Pectoral Sandpiper was found at c.50 m range. It walked purposefully away from the observers and within two minutes started to roost on a bank. Some low-quality photographs were taken as the bird was walking. It was then flushed by an overflying Peregrine Falco peregrinus, along with all of the other waders, and settled distantly out of sight preventing further observations. The photographs (e.g. Fig. 2) suggested that the bird had an unusually ginger crown and a wellmarked supercilium, but the pectoral band appeared well defined, the flanks not heavily or clearly marked, and its behaviour matched Pectoral Sandpiper. The photographs were widely shared as a Pectoral Sandpiper on social media without any queries being raised.

At 07.00 h on 18 February 2018, GA revisited the area on a rising spring tide and, in poor weather conditions, found a very different-looking Calidris at c.70 m range. It was feeding in Salicornia, skulking and clambering on and amongst the vegetation, displaying a strongly marked face and head pattern. Based on previous experience (very similar behaviour to a UK bird; see Catley 1984), GA quickly identified it as a Sharp-tailed Sandpiper and fortunately the bird stayed in the same area for two hours as weather conditions improved, permitting better-quality photographs (Fig. 3; see  https://vimeo.com/256275383). This was clearly the same bird as seen on 4 February 2018, but looked and behaved differently. Further inspection of images confirmed the identification, based on the following characters: similar to Pectoral Sandpiper but with bright ginger crown, dark ear-coverts contrasting with supercilium extending and broadening behind the eye, white eye-ring, shorter dark bill with limited pale flesh (not yellow) base, longer legged and with a small number of chevrons on the left flank, although these were only visible in some photographs (Hayman et al. 1986).

Figure 2.

Sharp-tailed Sandpiper Calidris acuminata, Macaneta, Mozambique, 4 February 2018 (M. Costeira da Rocha / Gary Allport)

Figure 3.

Sharp-tailed Sandpiper Calidris acuminata, Macaneta, Mozambique 18 February 2018 (Gary Allport)

The sighting aroused considerable interest and birders from the region visited the site the next day, but the bird was not relocated. On 20 February a very similar bird in exactly the same area was photographed in poor weather and identified as a Sharp-tailed Sandpiper, and the same bird was seen again the following day. However, a close check of the photographs revealed differences from the original bird, and on 22 February it was seen well by GA and identified as a Pectoral Sandpiper (see images at  https://ebird.org/view/checklist/S43106332).

On the next spring tide, on 2 March 2018, GA, R. Lindsay-Rae, J. R. Nicolau, D. Pitzalis & D. Snow awaited the rising water, and rather surprisingly at 06.15 h a Sharp-tailed Sandpiper that was clearly not the original bird was found by JRN; it was then joined a few minutes later by the bird seen on 4 and 18 February. The two birds roosted over the high tide and were seen and photographed well (Fig. 4). On 3 March the same area again held two Sharp-tailed Sandpipers but on this occasion they were joined by two Pectoral Sandpipers, and the four birds formed a small flock for two hours over the high tide (Fig. 5).

The two Sharp-tailed Sandpipers remained, usually together, until 6 March when the tidal range ebbed and the feeding area quickly dried out. One Pectoral Sandpiper was also seen but usually not with the Sharp-tailed Sandpipers. The three birds reappeared on the new moon tides on 18–21 March, and singles of both species were seen foraging separately on 31 March. A single Sharp-tailed Sandpiper was last seen on the spring tide on 16 April (Table 1).

Figure 4.

Two adult Sharp-tailed Sandpipers Calidris acuminata, 2 March 2018; the original bird (front) showing bright fringes to the tertials and a single well-marked chevron on the flanks (© J. R. Nicolau / Unearth Safaris)

Figure 5.

Two adult Sharp-tailed Sandpipers Calidris acuminata (below and right) and two Pectoral Sandpipers C. melanotos (above and left), Macaneta, Mozambique, 3 March 2018 (© Michael Mason)

Figure 6.

The second Sharp-tailed Sandpiper Calidris acuminata, Macaneta, Mozambique, March 2018, showing two old outermost primaries, indicating that it is an adult; this bird was mostly in winter plumage when initially found on 2 March 2018 (© David Hoddinott)

TABLE 1

Summary of observations of Sharp-tailed Sandpiper Calidris acuminata (STS) and Pectoral Sandpiper C. melanotos (PS) at Macaneta, Mozambique, February–April 2018.

Both Sharp-tailed Sandpipers showed evidence of having recently completed outer primary moult (cf. Fig. 6.) and were therefore aged as adults (see Prater et al. 1977). It was impossible to determine gender as they were similar in size.

Identification

The multiple misidentification of both species by experienced observers reported herein is salutary and warrants comment. Whilst the treatment of both species in boreal autumn plumages is thoroughly covered by the main identification texts (see above), they are not well covered during spring moult into breeding plumage. It is worth flagging the following features.

Head pattern.—The combination of rufous crown, darker ear-coverts, paler supercilium widening behind the eye and pale eye-ring provide an excellent suite of features for distinguishing Sharp-tailed Sandpiper from Pectoral Sandpiper in winter / spring plumages. However, note that the supercilium is illustrated as being broader behind the eye in Pectoral Sandpiper in some references (e.g. Snow & Perrins 1998). Use of this feature is also made more complex as the supercilium in Sharp-tailed Sandpiper becomes less well defined as summer plumage is attained, when dark-centred feathers speckle the face, breaking-up the superciliary pattern. In contrast the eye-ring emerges as even more distinct during this transition. The dark ear-coverts add contrast to the definition of the supercilium in winter plumage, when they represent a strong feature, but also become less discernible in summer plumage. The two Pectoral Sandpipers also showed quite bright ginger crowns in certain lights, more so than illustrated in major field guides, although much less well marked than the adjacent Sharp-tailed Sandpipers.

Breast and underparts pattern.—Underparts pattern is cited as an important feature in separating these two species, but it is clear that as Sharp-tailed Sandpiper moults into summer plumage this can be very similar to Pectoral Sandpiper (Fig. 1). Pectoral Sandpiper can also show dark-centred feathers on the flanks in summer plumage, so it is only the dark chevrons on the flanks that make the identification of Sharp-tailed Sandpiper obvious at this time (February–May). It is also unclear how much streaking Pectoral Sandpiper can show on the rear flanks and undertail-coverts, making identification using this feature a question of degree and difficult to assess in lone individuals.

Bill colour.—Pectoral Sandpiper usually shows a clear yellow basal third to the bill, and the two Sharp-tailed Sandpipers had a pale flesh-coloured base to the mandible (Fig. 4). However, review of images of summer-plumaged Sharp-tailed Sandpipers revealed birds with clear yellow coloration over up to 50% of the mandible, ‘bleeding' onto the maxilla (e.g. Lundquist 2011 in April). Therefore, bill colour can be used to positively identify a Sharp-tailed Sandpiper only if it is mostly dark and does not show yellow tones.

Thus the combination of facial pattern and to a lesser extent bill characters are critical for separating these two species in late winter / early spring. Underparts pattern may be conclusive but only if clear chevrons are evident.

Records and vagrancy

A literature search demonstrated that the Sharp-tailed Sandpipers reported herein are the first and second records for Mozambique, for the southern Africa region (T. Hardaker in litt. 2018) and for continental Africa (R. J. Dowsett in litt. 2018). Based on the pattern of records in Europe, Central Asia, the Middle East and on Indian Ocean islands, the possibility of vagrancy by this species to mainland Africa, and the southern Africa region in particular, had been anticipated (Hardaker 2008, Peacock 2016). However, it is remarkable that two were found together with relatively limited effort in suitable habitat in Mozambique. Indeed, several visiting birders commented that the species might prove to be regular at the site in small numbers as a pseudo-vagrant (Gilroy & Lees 2003), as is true for a few other shorebirds at specific wintering localities in the region, such as infrequent but regularly occurring Great Knot C. tenuirostris at Barra, Mozambique (Peacock 2016), Steppe Whimbrels Numenius phaeopus alboaxillaris at four localities in southern Mozambique and South Africa (Allport 2017), and, further afield, Pacific Golden Plover Pluvialis fulva in Gabon (Christy 1990).

There are two possible routes of vagrancy for these birds. The first is the Central Asian–East African corridor, possibly via the Rift Valley. The first conclusive evidence of the use of the Rift Valley overland migratory route by coastal waders was shown by a satellite-tagged Steppe Whimbrel in 2016 (Allport et al. in press) but there is strong circumstantial evidence that this route is used by a wide range of shorebirds wintering in southern Africa (Dowsett 1980). Use of this overland flyway, potentially with no continental stopovers, might explain the lack of records of Sharp-tailed Sandpiper further north in Africa. Southern coastal Mozambique lies on a natural route where migrants following the Rift southbound would reach the coast of the Indian Ocean (a similar explanation for coastal records of Baltic Gull Larus f. fuscus in southern Mozambique has been postulated: Allport 2018b). Two records of Sharp-tailed Sandpiper in the Middle East support this idea, and the possibility that the species breeds further west in Siberia (Lappo et al. 2012) increases the likelihood of vagrancy via this route.

The cluster of records on Indian Ocean islands points to a second, possible, transoceanic route. The frequency of records on Christmas Island suggests that Sharp-tailed Sandpipers regularly wander to the eastern Indian Ocean on southbound migration in September–December, probably from the major migratory crossing, Micronesia / Papua New Guinea to north-west Australia, a movement with a strong westerly component and likely to result in overshoots. There is a general decrease in the frequency of records south and west across the Indian Ocean, with none from the relatively well-watched islands of Mauritius and Réunion (Safford & Hawkins 2013), a pattern which again suggests that the origin of vagrancy lies to the east, and only a few stragglers might reach coasts of East Africa. It should also be considered that Sharp-tailed Sandpipers might enter the Indian Ocean via the Indian Subcontinent, but there are only two records in Pakistan / India (Roberts 1990) and five from Sri Lanka (Henkanaththegedara 2002), making this unlikely to be a major route for transoceanic vagrants. One other, even more unlikely, but intriguing possibility is overshooting by juveniles leaving Alaska intent on reaching their Australian wintering grounds for the first time. Grönroos et al. (2010) postulated that the potential single-haul, 12,000 km migratory flight of juveniles from Alaska to Australia would cross Papua New Guinea potentially on a broad front, meaning some might easily overshoot into the Indian Ocean. Most of the birds recorded in the Indian Ocean were not aged, but all those photographed on the Chagos archipelago were adults (P. Carr pers. comm.) with just one record from the Cocos (Keeling) Islands of a juvenile (19 November 2016,  https://ebird.org/view/checklist/S32777999). Both birds in Mozambique were adults.

Both the Rift Valley and Indian Ocean transoceanic routes therefore seem plausible for the birds recorded in Mozambique. Only further records in the region might enable the route of vagrancy to be better understood.

Turning to Pectoral Sandpiper, Hockey et al. (1986) concluded that those found in southern Africa enter the continent solely via the Nearctic–Europe route rather than the Asia–East Africa flyway. In drawing this conclusion, the more easterly distribution of Pectoral Sandpiper records in southern Africa was considered to reflect probable observer bias, and the lack of records of Sharp-tailed Sandpiper—which it was presumed would have arrived via the Central Asia–East Africa flyway—was noted in support of this hypothesis, as was the questionable validity of the Tristan da Cunha record. Both latter suppositions are now invalid, and the notion that Pectoral Sandpiper has a range of inter-African migratory strategies including southerly migration from the western Siberian breeding range via the Asia–East Africa flyway to eastern Africa acquires greater support (Hockey & Douie 1995, Lees & Gilroy 2004, Hjort 2005). This not to say that Pectoral Sandpipers of a Nearctic, rather than Palearctic origin, do not enter the region too, as held by Curry-Lindahl (1981), and implied by Feare & Watson (1984) for the Indian Ocean islands; both entry routes to the continent appear likely.

The distribution of records in the region must, to some extent, reflect both observer coverage and ability to identify the species (as in Australia and New Zealand: Higgins & Davies 1996), but the number of records strongly supports Lees & Gilroy's (2004) idea that a small population regularly overwinters in Africa and many of these are probably intentional migrants.