Summary: Abundance of the 16 most common bird species at winter feeding sites in Finnish Lapland

Risto A. Väisänen 2000: Lapin ruokintapaikkojen talvilinnut. Linnut-vuosikirja 2000, pp. 131-140.

• The whole article in Finnish (with tables and figures)

Bird numbers have been monitored at feeding sites during harsh northern winters by the Finnish version of the garden bird survey. Voluntary bird watchers (Table 1) monitored 156 winter feeding sites in Lapland from 1 October to 30 April during 14 half-month periods in winters 1988/1989-1999/2000 (the period 16-30 April was, however, censused during the last three winters only). For each species, the maximum number of individuals observed on the "best day", "the second best day" and median day were reported from each period. Additional data were collected on the counting efficiency (4 categories), as well as on the quantity (3 categories) and the quality of food available (8 categories). Data from ten winters of the 1990s will be used here for South and North Lapland (Fig. 1); results from SW Lapland have been published earlier (Väisänen 2000b).

For presence and general abundance of the 24 most common species see Table 2. Trends of abundance during the winter in 16 species are manifold (Fig. 2): steady decline in mid-winter, apparently indicating winter mortality (e.g., House Sparrow and Great Tit); strong increase in early winter (Yellowhammer in S Lapland) or in the second half of the winter (Redpoll) due to delayed invasion to the feeding sites; decrease in mid-winter caused by partial migration (e.g., Greenfinch and Hooded Crow) or by decline in activity (Siberian Jay); autumn and spring visits by real migratory birds (e.g., Chaffinch and Brambling).

In species-specific diagrams of Figs. 3-6, values of single half-months from one winter are generally based on observations of the "best day" from 8-23 feeding sites (statistical details in Väisänen 1994a). Abundance of the Great Tit has changed rather regularly in South and North Lapland during the study winters (Figs. 3A-B): peak occurrence after the period of autumn movements, decrease by half in settled populations during the winter, resulting on average five birds per site left in the spring. The Blue Tit has increased strongly in SW and S Lapland in the 1990s, and also trends in numbers during October-December have changed (Fig 3C). Population has grown only moderately in N Lapland, where decline in mid-winter may indicate of normal partial migration (Figs. 3D). The decline of the Willow Tit that has been noted in Finnish winter bird censuses in the 1990s, can be seen especially in the data of N Lapland (Fig. 3F). Willow Tit numbers decrease about 30% during November-February in S and N Lapland. Abundance of the Siberian Tit has declined at the feeding sites in the 1990s. The period of peak occurrence of this species has moved to March (Fig. 3H).

Magpie numbers have remained rather stable during the greatest part of the winter, but general abundance has declined during the study years, especially in the North (Figs. 4A-B). Numbers of the Jay drop about 30-40% in South and 60% in North Lapland during the winter, indicating higher mortality in the North (Figs. 4C-D). The Jay has become more common in the 1990s. The same concerns the Siberian Jay in its main area, North Lapland (Fig. 4F). The species is less active in mid-winter and then also visits the feeding sites less often. The Hooded Crow is mainly migratory in Lapland and rare as winter guest from late November to early March (Figs. 4G-H).

The decline of the House Sparrow that has been noted in large European areas, was noted as a crash in SW Lapland in winters 1998-2000. Low abundances have been noted South and North Lapland at the feeding sites in recent winters from January to April (Figs. 5A-B). Sparrow numbers decline about 40% in Lapland during four mid-winter months (Fig. 2), which may be taken to indicate of large winter mortality in the North. The Bullfinch was scarce in Lapland in certain winters (1992/93, 1995/96) and abundant in others (1991/92, 1993/94 and 1997/98) (Figs. 5C-D). Counts along winter bird census routes and at feeding sites have produced mid-winter densities that are correlated (Fig. 7). Rowanberry crop has generally been abundant in winters when Bullfinch numbers have been low. The Greenfinch has become more abundant in Lapland during the study winters (Figs. 5E-F). Mid-winter numbers decline most steeply in North Lapland, apparently indicating that the role of partial migration is strongest there. Abundance of the Yellowhammer has a steep geographical gradient: of numbers found at the feeding sites of SW Lapland about 1/3 are left in South Lapland and 1/10 in North Lapland (Figs. 5G-H). In an average year, numbers increase in SW and South Lapland during the early winter and then slowly decline to late winter (see also Fig. 2); some winters differ, however, notably from the general trend.

The Redpoll prefers to use the seed crop of the birch and the alder during the early winter. It starts to utilize the feeding sites of Lapland more commonly from January to April (Figs. 2, 6A-B). Good Redpoll years became more common towards the end of the 1990s. Annual variation in the seed crop of trees may be at the background, but it is also possible that the bird has learnt to use the new resources offered by man - especially small fragments of sunflower seeds and nuts. Wintertime occurrence of the Great Spotted Woodpecker has been most even among the species studied here (Figs. 2, 6C-D). The monitoring has revealed that the species was more common in winter 1997/98 and moved around in the end of March 1998. The Chaffinch and Brambling are typical migratory birds that visit the feeding sites in the autumn and spring (Figs. 2, 6E-H).

A peak abundance noted in the Great Tit in SW Lapland at the end of November 1992 was caused by local invasion, which coincided with sudden changes in winter weather (Fig. 8). For this kind of more detailed applications of the feeding site data the half-month periods are too crude, but we would need species-specific numbers observed in single days. Starting from the winter 2001/2002, one may gather and send to the Zoological Museum such data by a special internet program (in Finnish at http://www.luomus.fi/linnustonseuranta).