Influx of Eurasian Jay in autumn 2019

EichelhäherEurasian Jay (Garrulus glandarius) are not pronounced migratory birds, which can be seen from their flapping flight style and their wide, rounded wings. The Jay´s body is more made to fly from tree to tree, less to cover longer distances. Small migratory movements probably take place annually, but are hardly noticed due to the wide distribution of the species.

Birds from the north and east fly in irregularly, however. In such cases, there are significant migratory movements of thousands of jays that extend far into Central Europe. Extraordinary years of influxes were in 1978, 1983, 1996, 2004 and 2010. Now in autumn 2019 there was another strong jay influx. From the beginning of September, observations of Eurasian Jays migrating in Germany and double-digit flock sizes were reported. It became particularly noticeable from the second decade of September. Not only in Germany, but also in some neighboring countries such as the Netherlands, Belgium, Austria and Switzerland, a strong appearance of Eurasian Jays was registered. Flocks of up to 200 Eurasian Jay and four-digit daily totals were recorded at various points. The maximum was reached in Germany in early October. Some bird watchers, who systematically counted migratory birds at Überlingen on the northern shore of Lake Constance, had an unforgettable day. More than 42,000 jays roaming through were recorded on that day. After that, however, the phenomen quickly calmed down and in mid-October jays were only seen in large numbers in southern Germany, until normal levels were reached again in early November and no more unusual migratory movements were reported. The whereabouts of the birds are unclear. The troops have presumably disbanded and the jays are scattered across the landscape. How many individuals were ultimately involved in the invasion can hardly be estimated. In view of the high daily totals at different observation points, a number in the six-digit range can be assumed in any case. Where did the jays come from? The question of the origin of birds is usually difficult to answer.

In combination with the high number of migratory birds along the southern Baltic coast, there are some indications that the Eurasian Jays may have derived from areas to the east. Additonally, while in 2018 less than 7% of the individuals reported with a direction of migration moved west and a southwesterly direction dominated with more than 67%, this autumn 48% of the reported Eurasian Jays flew mainly west. This can be seen as a further indication of an eastern rather than northern origin. What are the reasons for this impressive Eurasian Jay erruptive migration? The reason for the strong influx into Central Europe is probably the combination of a previous high breeding success in the breeding grounds and lack of food in the current autumn / winter. Fattening years of oak, beech or hazelnut lead to a very good food base for Jays, which often has a positive effect on the breeding success. However, a full mast is often followed by a false mast in the next year. The influxes of Eurasian Jay always seem to correlate with these false masts. Bottlenecks in food supply occur and Eurasian Jay have to migrate in large numbers.

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