Dunlin Calidris alpina alpina moulting on nest in Swedish Lapland

On 3 July 1997 a 2c (calendar year) female Dunlin was caught on four eggs near Snannaviejgiera (68.07 N, 19.30 E), 870 m a.s.l., on the high plain N of Rautasjaure, Torne Lappmark, Swedish Lapland. The bird had shed primaries 1 and 2; the new first primary had grown to 50 % of full length, the second was still not to be seen. One egg showed small cracks and was hatching. (On 8 July there was heavy snowfall followed by 50 mm rain in the same area).

In his pioneering study of moult strategies in the Dunlin, Greenwood (1983) bluntly states: No Dunlin examined from the west of the Ural mountains had commenced moult while on breeding site. Only those Dunlin from east of the Urals in Russia, and from North America were moulting while on their breeding grounds. In contrast Gromadzka (1989), studying skin collections from breeding grounds in Russia, found at least two birds from the breeding area of the subspecies alpina, which had just started their moult, and the same author quotes Danilov et al. (1984) as stating that ...on the Yamal Peninsula, it is known that some Dunlins may start their moult while breeding, but that this is not usual. So, at least a minor fraction of the alpina population will shed remiges while still breeding. If this means shedding primaries while still actually brooding or shedding them while conducting the young is of less importance, given the present state of inadequate knowledge; at any rate some birds start "while on breeding site". There is no other way to explain how Dunlins can occur on migration in the Baltic with moult scores 25 - 30 already by the end of July (Gromadzka 1989, Holmgren et al. 1993). "Both initiating and completing the moult during migration" (a possibility quoted by Gromadzka 1989) can not be a viable strategy in regard of the compressed breeding season and the pace of adult bird migration.

One year earlier, on 27 June 1996, I had caught another brooding 2c female at Gearggevuomus (68.02 N, 19.10 E), 770 m a.s.l., in the same area, but south of Rautasjaure; so females in their second calendar year will breed in Swedish Lapland. (I forgot to look particularly for moult in this bird). At both sites lakes were still covered by ice, and the permafrost floor lay at most 10 cm below the average ground level; there was no visible prey in the wetland surrounding the nests, no Diptera larvae, few mosquitoes in the air. Nor were breeding partners visible, but this is the rule at high altidudes in Lapland; the "free" bird feeds at lower altitudes, where nutrients and energy for egg-laying were probably collected as well. The reason for this recent pauperization of the breeding habitat of waders at high altitudes in Lapland is extreme snowfall in winter and consecutive prolonged melt of snow in spring (high acidity of the melt-water probably being as injurious to the habitat as prolonged snow-cover). In the 90's many well-documented breeding sites, visited and described by renowned Swedish ornithologists as early as the 30's and 40's have lain quite hostile and abandoned by breeding birds when visited in early July. (Wind-swept grass plains at 1000 m altitude in S. Lapland seem to be the exception.) A vacuum has been created by adverse climate in the whole area, creating an immigrant situation, where first-time breeders are forerunners. Food supply or even: "a peak of food at hatching time", as suggested by Greenwood (1983), cannot be the proximate factor triggering moult in the birds involved. Rather, poor quality of remiges in first-time breeders is the principal reason, as suggested by Gromadzka (1989).

This note was written by Christer Persson, published on the web on 29.10.98