Local movements, home ranges and body condition of Common Eiders Somateria mollissima wintering in Southwest Greenland Flemming R. Merkel1,2,*, Anders Mosbech2, Christian Sonne2, Annette Flagstad3, Knud Falk4 & Sarah E. Jamieson4 Merkel F.R., Mosbech A., Sonne C., Flagstad A., Falk K. & Jamieson S.E. 2006. Local movements, home ranges and body condition of Common Eiders Somateria mollissima wintering in Southwest Greenland. Ardea 94(3): 639–650. We examined local movements, home ranges and body condition of wintering Northern Common Eiders Somateria mollissima borealis in Southwest Greenland from late winter until spring migration in 2000 and 2001. At key marine habitats at coastal areas and in the inner fjord system of Nuuk, we implanted 33 Eiders with satellite transmitters and collected Eider carcasses for body condition analyses. Most Eiders exhib- ited strong site fidelity during the study period with a mean 95% home range size of 67.8 km2 and a mean core area (50%) of 8.1 km2. Diurnal movements peaked at dawn and dusk when birds presumably moved between feeding areas and roosting sites. Roosting occurred near day- time activity centres, on average 1.7 km apart. Among birds marked at coastal habitats only between 8% and 29% also used the inner fjord habitats, despite high levels of hunting at the coastal area. Birds that did move to the inner fjord system did not return to the coastal area. These findings accentuate the need for managing wintering Common Eiders in Southwest Greenland also at a local scale, taking site fidelity into account. The body condition of adult fjord birds was either equal or superior to that of coastal birds. However, within-years and between- years-variation in body condition were larger for fjord birds, suggesting that they were challenged by a higher unpredictability at the local scale. Observations indicate that differences in habitat characteristics and the behaviour of avian predators may limit the exchange of Eiders between the coastal area and the inner fjord system. Our study suggests that often Eiders build up body reserves for the breeding season elsewhere; in three of four cases adult body condition declined from late winter to early spring. Key words: satellite telemetry, home range, movements, body condition, Northern Common Eider, site fidelity, Southwest Greenland, winter 1Greenland Institute of Natural Resources, P.O. Box 570, 3900, Nuuk, Greenland; 2National Environmental Research Institute, Frederiksborgvej 399, P.O. Box 358, 4000 Roskilde, Denmark; 3The Royal Veterinary and Agricultural University, Bülowsvej 17, 1870 Frederiksberg C, Denmark; 4c/o Greenland Institute of Natural Resources, P.O. Box 570, 3900, Nuuk, Greenland; 5University of New Brunswick, ACWERN, Bag 45111, Fredericton, N.B, E3B 6E1, Canada; *corresponding author ([email protected]) 640 ARDEA 94(3), 2006 INTRODUCTION winter and spring, making the Eiders more prone to search for alternative habitats. We aimed to (1) Migratory arctic birds spend most of their annual determine the home ranges of Common Eiders cycle away from breeding areas; consequently, the and validate the temporal importance of wintering availability and suitability of non-breeding areas areas previously identified as high density areas and their management strongly influence their through aerial surveys (Merkel et al. 2002), (2) population dynamics (Scott 1998). During the quantify the degree of interchange between coastal non-breeding period, birds must restore body and fjord habitats, and (3) to clarify if body condi- reserves lost during the breeding season and must tion of Eiders differed significantly between these maintain sufficient reserves to buffer against two distinct habitats. Coastal and fjord habitats are severe weather and short photoperiods (King & less than 100 km apart, however, hunting intensity Murphy 1985, Blem 1990). Among some large and habitat characteristics differ distinctively migratory arctic birds, body condition at the end of between these two areas. We predicted that the the wintering season has been shown to positively less disturbed inner fjord system would act as a correlate with aspects of breeding performance buffer region, to which Eiders would resort when (Ankney & MacInnes 1978, Ebbinge & Spaans conditions became unfavourable at coastal habi- 1995, Bêty et al. 2003). To optimise individual tats. Common Eiders are considered to be particu- winter survival, birds should select the habitat that larly sensitive to disturbance (Bell & Owen 1990). provides the highest net gain of energy per time Results are discussed in relation to available infor- unit (Werner et al. 1981, Abrahams & Dill 1989). mation about Common Eider distribution and However, factors other than food availability and behaviour in the study area and in relation to man- quality may influence habitat selection in winter, agement perspectives. such as predation risk, human activity, site fidelity and social interactions (Greenwood 1980, Guillemette et al. 1993, Madsen & Fox 1995). A METHODS high degree of site fidelity, for whatever reason, will make birds more sensitive to local environ- Study area mental conditions, including human activities. The study area comprised the coastal waters and We sampled body condition and used satellite fjords surrounding Nuuk, the capital city of telemetry to examine local movements of Greenland (Fig. 1). This is part of the Greenland Northern Common Eiders Somateria mollissima Open Water Area, which is internationally impor- borealis wintering in Southwest Greenland. These tant for wintering seabirds (Boertmann et al. Eiders breed in eastern Arctic Canada and western 2004) and a key wintering area for Common Greenland and migrate to the Southwest Green- Eiders, with c. 25 000 birds in the coastal area and land open water area when Baffin Bay and north 32 000 in adjoining fjord systems based on 1999 and west parts of Davis Strait become ice-covered aerial surveys (Merkel et al. 2002). The coastal (Merkel et al. 2002, Lyngs 2003). We focused on area is an extensive archipelago including exten- the degree of site fidelity from late winter until sive areas of shallow waters, whereas the fjords to spring migration when Eiders have traditionally the east are lined with steep cliffs with little shal- been most intensively harvested in Southwest low water. AVHRR satellite images showed the Greenland. Winter habitats were utilized for innermost fjord system was ice covered throughout approximately five months before the study February, March, and part of April. At peak, in period, making food depletion a possibility during mid-March 2000, c. 53 km (c. 14%) of the inmost late winter. Thus, we assumed that the risk of fjord sections was frozen. In general, less ice birds encountering poor feeding conditions and occurred in 2001 when in mid-March only c. 25 hunting disturbances would be highest during late km of the innermost sections was frozen. Mean Merkel et al.: WINTER MOVEMENTS OF EIDERS 641 anchorage points on shore and deployed with plas- tic Eider decoys. Eiders were also captured at night GREENLAND by means of dazzling. A large and highly elastic net was set up at the stem of the research vessel, CANADA Nuuk and at the base a horizontal mist net was placed to catch and entangle birds sliding down from the 9 vertical frontline net. When approached during 8 low visibility (snowfall or dense fog) Eiders were likely to orientate towards the vessel searchlight. 7 We implanted birds with Satellite Platform Transmitting Terminals (50 g Microwave Teleme- 6 try Inc. PTT 100). Transmitters were programmed to operate at various duty cycles: 4 PTTs transmit- 4 ted 3 h every 7 h, 4 PTTs 4 h every 9 h, 6 PTTs 4 h 3 Nuuk every 14 h, 13 PTTs 4 h every 34 h, and 6 PTTs 2 5 1 transmitted 6 h every 66 h. We marked 21 females and 12 males between 23 February and 6 March in 50 km 2000 and 2001 in the Nuuk study area (Fig. 1), 25 adults, 7 subadults (2nd or 3rd winter), and one Figure 1. The Nuuk study area in Southwest Greenland. juvenile (Baker 1993). External aging of subadult Numbers show locations at which Common Eider carcas- Common Eiders is, however, not accurate (F.R. ses were collected (1–9) and satellite transmitters Merkel, K. Falk, and S.E. Jamieson, unpubl.), and deployed (1–8). it is likely that some of these subadults were adults. We implanted 28 of the 33 transmitters in the temperatures in Nuuk in February, March and abdomen (Korschgen et al. 1996a) and 5 transmit- April were –9.6°, –8.4° and –0.3°C in 2000 and ters were subcutaneously deployed (Korschgen et –7.8°, –5.6° and –1.9°C in 2001, respectively. From al. 1996b). We avoided heat loss on re-exposure to autumn to spring, commercial and recreational seawater by avoiding removal of feathers from the hunters in Nuuk shot on average 11 579 ± 1071 abdominal surgery site by aligning feathers to each Eiders (1993–2001, Dept. of Fishing and Hunting, side of the midline and by making the incision Greenland Home Rule), of which estimated 70% along the linea alba (Mosbech et al., unpubl.). were Common Eiders; the remainder King Eiders Inert eye ointment (80% Vaselin, 20% paraffin oil) Somateria spectabilis (Frich & Falk 1997, Merkel was used for cornea protection during anaesthesia. 2004). Typically, Eider hunting occurs in the Postoperatively, an injection of enrofloxacin coastal zone within 30 km of Nuuk, so hunting (15–25 mg intramuscularly) was given (Baytril, 50 deep in the fjords is rare (Merkel 2004). Up until mg ml–1, Bayer) and 0.02 mg of butorphanol 2002 the hunting season was open from 1 October (Torbugesic, 10 mg ml–1, Forte Dodge) for analge- until 31 May. sia. Birds were kept in boxes and released two hours after surgery. Capture and marking Eiders were captured in mist nets, 21 m long and Movements and home range analyses 3.2 m high (D235/70, mesh size 70x70 mm, Data were received via Argos (DIAG format, Argos Ecotone) supported on aluminium stakes fixed User’s Manual, http://www.cls.fr/manuel).