| Summary: | Abstract I studied the rare and threatened lesser white-fronted goose (Anser erythropus), abbreviated LWfG in 1989–1996 in sub-arctic Finnish Lapland (I). The studied subpopulation consisted of 2–15 breeding pairs annually. A total of 30 broods were observed with an average of 2.9 goslings per brood. The 1st year survival of tagged 10 geese was low. Satellite locations, recoveries and re-sightings were received from NW Russia, Kazakhstan and the Azov Sea area. Cold spells had a negative, and the sum of effective temperatures by 5 July a positive influence on reproduction. Habitat selection (II) was studied in the same area. LWfG preferred the vicinity of water, flat close-range landscape, low forest height and intermediate relative altitudes. LWfG aggregated in the vicinity of conspecifics within the preferred habitats. The averaged RSF model assigned observation and random points correctly with 83.4% success. Locations of historical observations of LWfG matched the predicted distribution of breeding sites. (III) Spring migration patterns on the Bothnian Bay coast of LWfG were examined in 1907–1916 and 1949–2014 and the taiga bean goose (Anser fabalis fabalis) in 1975–2014. Arrival of the short-distance migrant A. fabalis advanced more and earlier than the long-distance migrant A. erythropus, 10.9 days since late 1980’s vs. 5.3 days since the beginning of the 2000’s. In the LWfG, the best model for explaining variation in timing included global and local temperatures, in A. fabalis global and local temperatures and winter NAO. Increasing global temperatures seem to explain trends in both. In the spring staging places of the Bothnian Bay almost all dietary items of the LWfG were Monocotyledons, mostly grasses growing in extensive sea-shore meadows (IV). Only Phragmites, Festuca and possibly Triglochin palustris were preferred. Lesser White-fronts preferred extensive natural meadows. Mowing and grazing benefit the restoration of habitats. Genetic structuring of the LWfG was examined in its whole distribution area ...
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