KOFFIJBERG K, & DIJK AJ VAN (2001) Influx of Corncrakes Crex crex in the Netherlands in 1998. LIMOSA 74 (4): 147-159.

Like in most parts of its breeding range, the Corncrake in the Netherlands has experienced a long-term decline (Fig. 4) During the 1990s, the population did not exceed 60 territories and was expected to become extinct on a short term. However, in 1997 more than 250 singing males were recorded, not only in well-known core areas like the forelands of the rivers Rijn, Waal and Ijssel and in the Oldambt area in the province of Groningen, but also in many small-scaled river valleys in e.g. the provinces of Drenthe and Overijssel. An even more pronounced influx occurred in 1998. 586 singing males were counted, and the number present was estimated at 640 700. Highest numbers were found in the NE part of the Netherlands (Fig. 1). Strongholds were the Oldambt area (156), the forelands of the river Ijssel (75) and the southwestern part of Drenthe (41). Densities in the most important areas ranged from 0.3 to 2.4 singing males/km?(Tab. 1). After some arrivals in the first half of May, large numbers settled between 8-20 June. Preferred habitats were hay meadows managed for nature conservation (mowing dates from 15 June onwards). Large numbers also established territories in arable land and nature reserves along the rivers Rijn, Waal and Ijssel (Tab. 2, Fig. 3) Breeding in crops on arable land was almost entirely confined to the Oldambt area and other parts of Groningen (Fig. 3), where Corncrakes prefer alfalfa and autumn-sown cereals. In Groningen and Drenthe, three observations of a female with chicks were recorded, one of them in winter-wheat. Based on indirect evidence (criteria by Schäffer 1994), at least part of the population was thought to be paired and perhaps successful breeders. However, there are no country-wide data on the productivity of Corncrakes during the influx in 1998.
     The sudden recovery of Corncrakes in the Netherlands in 1997 and 1998 contrasts strongly with the ongoing declines recorded since the 1960s. High numbers like in 1998 have only once been recorded before , in 1968 (Fig. 4). Moreover, the influx in the Netherlands can be regarded as part of a major influx of Corncrakes in NW Europe in 1998 . The large numbers in the NE Netherlands coincided with large numbers recorded in northern Germany and the Scandinavian countries. and also peak numbers in Poland. It is hypothesized that this influx might have been triggered by prolonged heavy rainfall in Belarus and the northwestern regions of Russia in May and June 1998 (Fig. 5). These regions have large breeding populations of Corncrakes, which were probably forced to leave flood plain meadows because of rising water tables. On the other hand, extremely wet conditions in the Netherlands (and neighbouring countries) enhanced settlement of Corncrakes (see Fig. 5). Since many meadows in river valleys were not accessible for machinery until July. As a result mowing occurred late or was abandoned at all. Hence, Corncrakes were provided with an unusual large area of suitable breeding habitat, and were probably also able to breed undisturbed.
      Unlike previous influxes in e.g. 1979, the Dutch Corncrake population did not show a subsequent decline again, but is still subject to a major recovery (Fig. 4). Between 1997 and 2001, at least 200 singing males were recorded annually and large numbers were recorded again in 2000 (preliminary estimate 500). This recovery coincides with an increase in conservation action and an extension of suitable breeding habitat. The first large-scale conservation action was undertaken in 1998 along the river Ijssel and in small river valleys in Drenthe. Protective measures include late mowing (from August 1" onwards) and stimulating nature conservation bodies to manage their areas in a suitable way for Corncrakes. Besides , farmers were offered financial compensation if they contribute to the late mowing scheme. In 2000, these measures were expanded to the forelands of the river Rijn and Waal , and from 2002 onwards they will be included in a special conservation action plan. Besides these conservation programmes, Corncrakes probably benefit from the current expansion of hay-.meadows with late mowing, of ten established to protect other meadow birds or for conservation of botanical values. In various parts of the country, the number of fields with a mowing data of 15 June or later has increased considerably in the 1990s. Moreover, establishment of new nature reserves and ecological restoration schemes in the forelands of the large rivers have contributed to a more extensive breeding habitat. Both factors might finally result in re-establishing a sustainable breeding population of Corncrakes in the Netherlands. Corn Crake Crex crex

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