DIJK AJ VAN & SWART MJ (1979) The occurrence of the Crossbill Loxia curvirostra in Drenthe in 1974 - 1977. LIMOSA 52 (3): 161-175.

Surveys of breeding birds in the years 1974 - 1977 have shown that the Crossbill Loxia curvirostra has started to breed in the province of Drenthe (fig; I and 2). In 1975 there were five confirmed breeding cases and in 1977 two (fig, 4). In.1975 we noticed, after a small invasion, a relation between the occurrence of breeding birds and the abundance of sprucecones. In 1977 also a connection with the invasion of 1976 could be possible (fig. 3). Though it is rather difficult to prove all cases of breeding of the Crossbill, there are at least 25 cases in which breeding is possible or even probable (fig. 4). The forests of Drenthe seem to becomegradually a good breeding habitat for the Crossbill. In these woody areas there is food enough for Crossbills throughout the year (tabel I) which may imply that the bird is becoming a resident. Recent observations point that way. Before 1974 three confirmed and about fifteen possible breeding caseswere known in the Netherlands, especially in the central part and on the coast (tabel 3). Since 1974 however, the Crossbill proved to be a breeding bird especially in the eastern part of the country, mainly in Drenthe and in the province of Gelderland (on the veluwe). In consequence of the large differences in observation intensity it is rather difficult to compare all the previous observations with the recent ones. Nearly all the probable and confirmed breeding cases were recorded in the year after an invasion took place; this occured in the adjacent areas of Western Germany and Belgium as well. Inthe seventies, however, there is a reason to believe that the Crossbill is a breeding bird in this area evenwithout the occurence of an invasion. This situation bears resemblance to what was established in England. The irregular and irruptive migration behaviour of Crossbills is a serious obstacle in theinvestigation into the background of breeding cases Common Crossbill Loxia curvirostra

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