Recent population status and trends of Corncrakes Crex crex in Europe

In the mid-1990s, thriving Corncrake populations were discovered in many eastern European countries, leading also to downlisting the species on the global and European Red Lists. The collapse of collective farming systems provided the species with excellent breeding opportunities, and possibly as a result of movements from these eastern populations, also the relict populations in many western European countries are assumed to have benefited from this development. On the far western and southern fringes of the European breeding range, most populations have continued to decrease until recently, often associated with contraction of the national breeding range. However, in Scotland (UK) numbers increased steadily since the beginning of conservation measures in the mid-1990s, up to a plateau level from 2007 onwards. A review of national breeding bird data shows that between countries distinct patterns exist in trends and annual fluctuations. On one side, Ireland, Scotland and France appear to have small annual changes, probably determined by local breeding conditions. On the other side, many other European countries report highly varying numbers from year to year. Some of them share similar years of peak abundance, e. g. 1998, 2000, 2002, 2003 and 2007, suggesting responses of Corncrakes to synchronous large-scale factors operating at European level. These patterns also suggest that Corncrake abundance in several countries on the European continent depends to a great extent on immigration from the core breeding states in eastern Europe, eventually in combination with fluctuations in productivity. Examples from ringing data, recently added with evidence from satellite-telemetry, show that male Corncrakes may wander considerable distances (up to 1,500 km) over the continent within one breeding season. Such movements partly will be the result of disturbance from mowing, but they may also reflect searches for suitable habitat for second broods. Causes for years with peak abundance are still poorly understood. Ringing data from the British Isles and France show that males in these countries show much smaller withinseason movements, indicating a higher degree of natal and breeding philopatry and different dispersal strategies. This also explains why distinct years of peak abundance in neighbouring countries like The Netherlands, Germany and Denmark are not observed at all on the British Isles or in France. Also the lack of expansion in breeding range in UK, despite a population recovery, is likely to be the result of the lack of dispersal. These phenomena also correspond with subtle differences in genetic population structure, differences in morphological characters and perhaps also different migration routes and wintering areas. Despite the estimated large Corncrake populations occurring in eastern Europe and its secure Red List status, global population assessments and our review of national trends indicate large differences in abundance within the European breeding range, and pronounced annual fluctuations in numbers in many countries, including persistent declines in the west and south. Given the ongoing changes in land-use and the species’ sensitivity to changes in farming practise, it is also not clear if fortunes of Corncrakes, including those in the core breeding range, are secure on the long term. Many of the estimates with 10,000+ Corncrakes come with large uncertainties, and in several of the major countries like Russia a proper monitoring is lacking (but is also challenging), leaving us in the dark when it comes to future prospects of the species. Therefore, we strongly recommend co-ordinated and reinforced survey effort, at least prior to the next overall population assessment.