How many common cranes (Grus grus) winter in Spain and Portugal?

The Iberian Peninsula, i.e., Spain and Portugal, is one of the most important wintering areas of common cranes (Grus grus), accounting for 50% of the European winter population. Historical winter censuses have never managed to provide a complete picture, and in 2015 a striking difference of almost 100.000 birds has been found between the winter census and an unprecedented census of migrating birds crossing the Pyrenees in spring after overwintering in the Iberian Peninsula. This infers that the Iberian wintering population is dramatically higher than annual winter censuses suggest. What lies behind this discrepancy in common crane numbers and how can we improve their population estimates? These underestimations of population size in winter censuses may be due to two reasons. Firstly, not all potential common crane winter areas have been covered, especially in the “dehesas” where access is often restricted. Secondly, a combination of different census methods (area counts vs. roost counts; and roost counts at dusk or at dawn) makes it difficult to achieve reliable results. In order to find those “missing” cranes and obtain a more realistic count of common cranes during winter, it would be necessary to make an additional effort, covering more areas and paying more attention to the census method. If these results fail to provide satisfactory results, attention should be shifted to key areas in order to monitor the demography of this emblematic species indirectly.