Greenlandic Dunlins on passage in NE Iceland in spring

Short communication Greenlandic Dunlins on passage in NE Iceland in spring Gunnar Thor Hallgrimsson Reykjanes Environmental Research Institute, Gardvegur 1, 245 Sandgerdi, Iceland & Institute of Biology, ASKJA, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland. [email protected] Keywords: Dunlin, Calidris alpina arctica, Iceland, migration stopover Iceland is an important stopover site for large numbers of migrants in Iceland Gudmundsson (2009) concluded that trans-Atlantic migrants. Some of these species also breed in arctica is likely to be present in small flocks in late May but Iceland and this can therefore mask the occurrence of birds evidence for this was lacking. A literature search revealed belonging to breeding populations in Greenland and Canada. no data confirming the existence of arctica Dunlins on pas- This study shows that Dunlins on the shores of NE Iceland sage in Iceland. No arctica Dunlins were found in autumn in late May have biometrics matching breeding birds of catches of 511 individuals in W Iceland in 1972 (Wilson the subspecies Calidris alpina arctica from NE Greenland. 1981). Wilson (1986) and Whitfield & Magnusson (1989) Furthermore, the birds had higher mass compared with birds speculated that autumn migration of arctica through Iceland on the breeding grounds indicating they were accumulating might be negligible. fat reserves. The breeding population size of arctica Dunlins As in many calidrids, female Dunlins have longer bills is small compared to other trans-Atlantic waders known to and wings than males. There is also a difference in bill length stage in Iceland. Knowledge on the distribution, timing and between populations and arctica has a smaller bill than schin- numbers of arctica Dunlins in Iceland is required for the zii, resulting in much overlap in bill length between female conservation of this subspecies. arctica and male schinzii. In spite of significant bill-length Iceland is an important stopover site for a large number differences, wing-length differences for each sex between of waders such as Red Knots Calidris canutus, Sanderlings those subspecies are small (Engelmoer & Roselaar 1998). Calidris alba and Ruddy Turnstones Arenaria interpres that Therefore, a biometrical difference can be used to predict accumulate fat reserves for onward migration to (and in the subspecies. In order to look for the existence and hence some cases also from) the breeding grounds in Greenland the proportion of the subspecies arctica among Dunlins on and Canada (Gudmundsson 1993, Gudmundsson et al. 1991, the shores of Iceland in spring biometrical data was used to Wilson 1981). When on the Icelandic shores, these species predict the origin of Dunlins at a well-known site for migrat- are easily recognized as stopover migrants because they do ing waders. not belong to the Icelandic breeding fauna. The situation is A cannon-net was used to catch Dunlins that were feed- not as straight forward for some other species such as Ringed ing on piles of rotten seaweed at Melrakkaslétta, Iceland Plovers Charadrius hiaticula, Purple Sandpipers Calidris (66°30'N, 16°00'W) between 24 and 28 May 2001. In this maritima and Dunlins Calidris alpina that breed in Iceland area, Sanderlings and Red Knots peak in numbers between as well as in Greenland and Canada. For these species, in- 20 May and 1 June (Benediktsson 2009). Wing-length, bill- dividuals seen on the Icelandic shores could comprise both length (exposed culmen) and mass were measured in a stan- stopover-migrants and local breeding birds. Therefore there dard way using a ruler, a calliper and a 300 g Pesola balance is hardly any information on key areas, timing and numbers respectively. Data on the morphometrics of the subspecies for those populations on passage in Iceland. arctica and schinzii were obtained from Engelmoer & Rose- The Dunlin is a widespread circumpolar wader breeding laar (1998). Ellipses based on the 95% confidence intervals mainly in the low Arctic (Cramp & Simmons 1983). Like for the bills and wings (1.96 SD from their means) of breeding most calidrids, it exhibits a long distance migration between Dunlins from Iceland and NE Greenland were used to show breeding and wintering grounds. Dunlins show geographical where the measurements of the birds caught at ­Melrakkaslétta differences in morphology, moult and migration behaviour would lie in relation to those of the two populations, and and up to ten subspecies have been described (Cramp & thereby determine their likely origin. Simmons 1983, del Hoyo et al. 1996, Engelmoer & Roselaar The biometrics of the birds (n = 56) clustered finely within 1998, Greenwood 1986, Hayman et al.1986). Icelandic Dun- the range of arctica but not schinzii (Fig. 1). Birds having a lins are considered to belong to the subspecies C. a. schinzii bill length ≥28 mm were considered females. The mean mass that breeds in the Faeroes, in the British Isles, in W Europe, of females was 53.3 g (SD±6.8), but birds with a shorter S Scandinavia and in the Baltic, as well as Iceland. On the bill-length, assumed to be males, had a mean mass of 50.7 g other hand, Dunlins breeding in NE Greenland belong to the (SD±4.4). Therefore, the mass of the birds caught on migra- subspecies C. a. artica and these birds winter in W Africa tion in Iceland was higher than that of breeding Dunlins in (Cramp & Simmons 1983). Greenland (Table 1). Given the locations of breeding and wintering grounds of These results indicate that arctica Dunlins stopover in arctica it seems highly likely they will use Iceland as a stop- Iceland in spring even though details of numbers, timing over site on migration and this is generally viewed as a fact and distribution are still largely unknown. The high mass among Icelandic ornithologists. In a review about stopover compared to breeding Dunlins in Greenland further indicates Wader Study Group Bulletin 117(2) 2010: 135 136 Wader Study Group Bulletin 117(2) 2010 38 schinzii schinzii female female 36 34 schinzii male 32 schinzii male Bill length (mm) 30 28 arctica female arctica female 26 24 arctica male arctica male 22 20 105 110 115 120 125 130 Wing length (mm) Fig. 1. Scatter plot of bill-length against wing-length for Dunlin caught at Melrakkaslétta, Iceland, in late May 2001. The ellipses show the 95% confidence intervals for male and female C. a. arctica (solid lines) and C. a. schinzii (dashed lines) from Engelmoer & Roselaar (1998). that these birds are likely to have been accumulating fat re- Table 1. Mean mass (g) of breeding Dunlins of the subspecies serves. However, the masses were not high compared to those ­ rtica in Greenland compared with that of migrant Dunlins captured a of some other stopover waders in Iceland and this might be at Melrakkaslétta, Iceland, in late May 2001. explained by the rather short distance (c.500 km) between Location Sex Mass (SD) N Source Melrakkaslétta and NE Greenland. Greenland Engelmoer & The estimated population size of arctica is 7,000–15,000 male 39.3 (2.4) 4 (breeding) Roselaar 1996 pairs (Meltofte 2004), which is small compared with the estimated 270,000 pairs of schinzii breeding in Iceland Greenland Engelmoer & female 45.5 (1.0) 5 (breeding) Roselaar 1996 (Thorup 2005). This raises the question of the importance of NE Iceland, particularly Melrakkaslétta, for arctica Dunlins. Iceland male 50.7 (4.4) 23 This study The location of Melrakkaslétta appears to be particularly well (migration) situated for stopover migrants en route to breeding areas in Iceland female 53.3 (6.8) 33 This study NE Greenland so the area might be of greater importance for (migration) arctica than other parts of Iceland. However, this has yet to be studied. The mean first arrival date of Dunlin in Iceland during del Hoyo, J., Elliott, A. & Sargatal, J. (eds). 1996. Handbook of the Birds 1998–2010 is 13 April (SD±4 days) (Kolbeinsson 2010). The of the World. Vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona. habitat used by schinzii between arrival and prior to breed- Engelmoer, M. & Roselaar, C.S. 1998. Geographical Variation in Waders. ing is not well known but numbers on the shores seem to be Kluwer Academic Publishers, Dordrecht, The Netherlands. low compared with the population size suggesting that they Greenwood, J.G. 1986. Geographical variation and taxonomy of the Dunlin move inland soon after arrival. Similarly the fact that the Calidris alpina (L.). Bull. B.O.C. 106: 43–56. Gudmundsson, G.A. 1993. The spring migration pattern of arctic birds in Dunlins caught in late May in NE Iceland were apparently southwest Iceland, as recorded by radar. Ibis 135: 166–176. pure arctica suggests that local breeding birds have largely Gudmundsson, G.A. 2009. Fargestir á Íslandi [Arctic birds on passage in disappeared from the shores by that time. If that is the case, Iceland]. Bliki 30: 1–8. [In Icelandic with an English summary]. assessing important areas for arctica in Iceland in spring may Gudmundsson, G.A., Lindström, Å. & Alerstam, T. 1991. Optimal not be difficult. fat loads and long-distance flights by migrating Knots Calidris canu- Dr Aevar Petersen supported the study by providing a ve- tus, Sanderlings C. alba and Turnstones Arenaria interpres. Ibis 133: 140–152. hicle and Adalsteinn Ö. Snaethorsson provided accommoda- Hayman, P., Marchant, J. & Prater, T. 1986. Shorebirds: an Identification tion. Best thanks to Freydis Vigfusdottir, Gudrun Gisladottir, Guide to the Waders of the World. A & C Black Ltd., London. Halfdan H. Helgason, Katla Hardardottir, Olafur Gudmunds- Kolbeinsson, Y. 2010. Icelandic migrant news. The Icelandic Birding Pages: son and Rakel J. Sigursteinsdottir for field work collaboration. http://notendur.hi.is/yannk/migrants.htm. Accessed 16 February 2010. Dr Ron W. Summers and Jannik Hansen commented on the Meltofte, H. 2004. 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