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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Corncrakes Crex crex in crops - population dynamics, habitat use and conservation strategy in two intensively managed arable farming areas in The Netherlands and Germany (2016)
Auteurs :	Ralf Joest, Auteur ; Kees Koffijberg, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (136(2-3, Sp. Iss.) 2016)
Article en page(s) :	163-174
Résumé :	Breeding Corncrakes are usually associated with herbaceous meadows and floodplain habitats whereas breeding in crops is often considered to be of secondary importance. Here, we present data for two regions where nationally relevant breeding populations of Corncrakes are found in crop-dominated, intensively managed agricultural landscapes: Oldambt in the Netherlands (2007-2015 3-70 calling males, up to 188 in 2003) and Hellwegborde in North-Rhine Westphalia, Germany (2007-2015 4-60 calling males). Calling Corncrakes were present annually, but abundance was subject to large annual fluctuations. For Oldambt, no overall significant I trend in numbers could be detected for the period 1984-2015; in Hellwegborde a significant positive trend was found in a sample plot counted since 1991. The majority of males arrived in the second half of May and first decade of June, with influxes of late-arriving birds in some years. In Oldambt, more than 80 % of all Corncrakes were found in winter wheat and alfalfa. In Hellwegborde, more than 80 % of all calling sites were situated in winter wheat, winter barley, triticale and spring cereals. Highest densities occurred in alfalfa (either in commercial use in Oldambt, or used as set aside in Hellwegborde). All these crop types have in common that they provide suitable vegetation structure and cover by the time Corncrakes arrive in May and early June. Alfalfa and set aside are also assumed to have highest food abundance.Abundance, aggregations of calling males, patterns of seasonal occurrence, as well as direct I observations of chicks all point out that in both study areas Corncrakes do breed successfully, although data to quantify the amount of successful breeders is absent. Corncrakes in crops I generally benefit from much later harvest dates compared to mowing of grassland. Birds settling in late May and even through June (winter wheat until late June) still have good opportunities to breed undisturbed and raise chicks to independence. Commercial cultivations of alfalfa, however, do attract many Corncrakes but do not allow successful breeding due to early and frequent mowing. The main arrival period, in combination with the general harvest regime (peaking in August), suggest that Corncrakes in crops will be hardly able to raise two broods in order to sustain a stable population. Therefore, it is likely that numbers observed also result from immigration from elsewhere, for instance birds that have lost a clutch in early mown meadows and/or birds that are in search for suitable habitat for a second clutch after leaving a first brood earlier in the season.In order to protect chicks of late broods and moulting adults it is necessary to promote agri-environment schemes that include corncrake-friendly harvesting techniques (harvesting from one side to another), or leave refuge strips unmown. Additional conservation measures include provision of suitable forms of set aside, either to offer suitable breeding habitat that is left undisturbed during the entire season, or to provide refuge cover during or after harvest. Land use changes due to the increase of intensive cattle farms (Oldambt) or agricultural biogas plants (Hellwegborde), as well as cumulative effects of infrastructural developments like commercial areas, motorways and wind turbines (Hellwegborde) may affect both Corncrake populations on the longer term. Conservation strategies should therefore also focus on maintaining sufficient large areas of suitable habitat.

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