BIJLSMA RG, DIJK, J VAN, HUSTINGS F, LENSINK R & POST F (1988) Severe winters and fluctuations in the Woodlark LulluZa arborea population in the Netherlands: a relation?. LIMOSA 61 (2): 91-95.

Wood Lark Lullula arborea After a striking increase from 1000-1200 pairs in 1973-77 to 2500-3000 pairs in 1980-84 (Bij1sma et at. 1985), the Dutch Woodlark population crashed in 1985 and again in 1986. This trend is exemplified with long term censuses in five large plots, showing a decline of 53% in 1985 and of 29% in 1986. The next year showed an increase of 24% (fig. 3). These fluctuations are thought to be typical of the Dutch Woodlark population as a whole. A minority of Woodlarks breeding in The Netherlands winters in the vicinity of the breeding places or elsewhere in NW. Europe. Most birds, however, spend the winter in SW. France or Spain. This migration strategy explains why the severe winter of 1978/79 did not effect the Dutch Woodlarks, because severe winter conditions did not reach south of Paris (fig. 1). On the other hand, the wmters of 1984/85 and 1985/86 extended into SW. France (fig. 2) and Spain, and wiped out a significant portion of Woodlarks. It is thought that the extensive snow cover in South Europe was in particular responsible for this decline. The severe winter of 1986/87 did not adversely effect Dutch Woodlarks, probably because natural selection had favoured long-distance migrants in the partial migratory population (and largely eliminating the strain of residents). Presumably, adaptations to adverse weather also played a part. Furthermore, snow cover in South Europe in the winter of 1986/87 was more discontinuous than in both previous winters, thus allowing evasive flights by Woodlarks. In the Dutch breeding habitats, the decline in 1985 was most pronounced on clear fellings, i. e. the habitat which was only recently occupied (-79%, as compared to -17% in sand dunes and -43% on sandy heather). The increase in 1987 was, on the other hand, largely due to Woodlarks reoccupyingclearfellings (+ 163%, as compared to + 10% in sand dunes and +28% on sandy heather). Apparently, fluctuations in some habitats were much less pronounced, which might be a substantiation of our earlier conclusion (Bij1sma et al. 1985) that clear fellings form a marginal habitat. As a consequence, the ups and downs in the Dutch Woodlark population are not only dependent on the severity of the winter in South Europe (especially snow cover), but also on the presence of sufficient suitable habitat in the breeding areas.

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