Invasion of the nutcracker, Nucifraga caryocatactes, in Schleswig-Holstein and Hamburg in 1968/69

Abstract

1. The nutcracker invasion of 1968 was characterized by its intensity (28 July to 30 November 1968, approx. 13,300 individuals) and early onset (mid-July). It peaked in the second half of the first ten days of August (6 August, approx. 1,300 individuals). Fig. 1 shows the other peaks of the wave-like influx. The curve flattens out significantly in the first ten days of October. The increase (with swarms) at the end of December 1968 / beginning of January 1969 is striking (Fig. 2). The significant reduction in the total number of individuals in late January and February indicates that they left our area.

2. Approximately 110 reports from different locations indicate varying resting periods. In one case, the duration of stay verified by ringing was 26 days.

3. More of the spotted nutcrackers reported in the spring and summer months of 1969 may have bred than was determined. There are two breeding records from the Hamburg area (without breed specification).

4. During the peak period, the west coast region (including islands) can be considered the main migration route (Fig. 3). The second wave of migration in the last third of August seems to have mainly affected eastern Holstein. From September onwards, the occurrence in geest and young moraine areas increased significantly. In the forest and field biotopes of this zone, including the ecologically similar habitats of gardens, parks, etc., the species occurred almost exclusively from December 1968 to September 1969, namely in the central and southern parts of the reporting area.

5. For information on biotopes, please refer to the summary above.

6. In general, the migration was relatively stormy. Of the 720 specimens reported as migrating or flying, about 70% flew in a W-S direction and about 30% in a NWSE direction. Two reports of ringed nutcrackers from Jutland on Sylt confirm migration to the north (as a secondary direction). Corresponding observations of NNW-N-E migration directions have been made in Finland, Sweden, Denmark, and the GDR. There is only one report of a return migration. 

7. Information from Finland, Sweden, Norway, Denmark, the USSR, and the GDR suggests that the flight took place along the northwestern and southeastern Baltic Sea coast. The main migration route continued along the coasts to Holland, Belgium, France, and England, as there are relatively few reports from the southern GDR, the CSSR, and the southern FRG (Baden-Württemberg, Bavaria). The migration was scattered, at least in the central part of the FRG.

8. Forty-one nutcrackers were examined according to the information in the manuals. In addition to the problem of species analysis, the results show that members of N. c. macrorhynchos (estimated proportion 70-80%) and N. c. caryocatactes (probably to a very small extent), as well as specimens from the mixed area northwest of the Urals, were definitely involved in the invasion. Weight data indicate the very different nutritional status of the birds.

9. The moulting findings on 11 pelts essentially correspond to the descriptions in the manuals. In addition to information on the temporal course of moulting, the results of age determination are also included. According to these, it can be assumed that at least the first flights of nutcrackers in August 1968 consisted of (at least yearling) adult birds. Taking into account the possible causes of invasions, the question arises as to whether the adult birds that flew in at the beginning of August could have been non-breeders.

10. Of 38 stomachs examined, 25 contained mainly animal matter and 8 contained mainly plant matter. This raises the question of whether the natural losses of spotted nutcrackers due to starvation are a consequence of their specialization in eating Swiss stone pine fruit.

11. Information on behavior.