OSIECK ER (1976) The migration of Goldcrests Regulus regulus and Treecreepers Certhiafamiliaris in 1972. LIMOSA 49 (1): 76-99.

During the autumn migration of 1972 Goldcrests Regulus regulus were unusually numerous in the Netherlands, as shown by the total number of birds ringed (Fig. I). This abundance coincided with about 40 records of Treecreepers Certhia familiaris (Osieck 1975), a species recorded only twice before 1972. This paper gives a survey of the migration of the Goldcrest in the autumn of 1972 in Europe and attempts. to analyse the migratory movements of both Goldcrests and Treecreepers. Data from five Dutch ringing sites were used in this study (Table I). On Schiermonnikoog (Frisian Islands) many Goldcrests were caught in the last week of September, and again in the second decade of October. The numbers ringed at three other sites (Fig. 3, Table 2) show that hardly any migration occurred before 21.9, but it may have continued for some time after 21.10. At these sites few Goldcrests were trapped during the first peak on Schiermonnikoog but in contrast with Schiermonnikoog fair numbers were handled between 1.10 and 10,10. It is argued that the numbers ringed on Schiermonnikoog give a reliable picture of the migration as exceptional falls due to adverse weather could be excluded. The abundance of Goldcrests (and Treecreepers, see Osieck 1975) was also noted at most bird stations in Northern and Northwestern Europe: Finland (alJ' stations: extremely numerous), Sweden (Hammar6: strongest movement ever recorded, for Falsterbo see Fig. 4), Norway (for Revtangen see Fig. 4), Estonia (strong migration), Poland (three bird stations: see Fig. 4), Northern Germany and Belgium (Zwin: invasion). The numberswere, however, rather low in Pape, Latvia (Fig. 4) and not abnormal at Hartso-Enskiir, Sweden (Fig: 4); in Denmark no abnormal numbers of Goldcrests were recorded and the migration was rather light in Scotland in contrast with the British east coast where high numbers were noted. During the autumn migration of 1973 the species was again numerous or even more so, especially in Finland (unprecedently heavy migration), Sweden, Poland (Fig. 4) and England. Recoveries indicate that the influx of Goldcrests in the Netherlands in 1972 came both from the North and East (Fig. 5). In part these birds have wintered in the Low Countries but passage migration has also taken place (see pag. 84). Several recoveries (see pag. 84-85) show that birdsreturned in April 1973. Data on the sex ratio of the Goldcrests can be found in Table 3. Males are often In the majority; exceptions are Schiermonnikoog 1972 (21.9-3.10) and Vlieland 1972. In a sample of 159 birds from Vlieland (1972) 92.5% were first-year birds, bnly one adult was recognised and the remainder could not be aged. Wing lengths Jmaximum chord) and weights are given in Table 4: males have longer wings and are heavier than females. These differences are significant. On the basis of radar observations in Southern Sweden (Table 5) it is suggested that the first groups of migrants at Schiermonnikoog came from the North (Scandinavia), and the sec'ond from the East (Poland). Some data on the sex ratio in Norway and Denmark (males and females in about equal numbers) and Poland (preponderance of males) support this hypothesis. The movements of Goldcrests and Treecreepers cannot be considered as invasions or irruptions in the sense of adaptations to food shortage during a certain year (Sviirdson 1957). The Goldcrest is a partial migrant, of which only part of the northern populations are migratory. The occurrence of large numbers of both species in the autumn of 1972 (and 1973) can be explained by three different hypotheses: (1) change of migration route: a greater than usual part of the population has passed the Netherlands. Although this explanation cannot be excluded, it is unlikely that it accounts for the whole effect, (2) a larger proportion of the population was migratory and (3) the autumn population was bigger. The second explanation has probably played a role in the autumn of 1973. Exceptional low temperatures and snow in August/September in Finland were partly responsible for the release of the mass migration (Hilden 1974b). Goldcrests and Treecreepers are very vulnerable to winters with low temperatures and a prolonged snow cover. Their numbers in the breeding season are to a great extent determined by winter mortality. As the losses apparently were small in the mild winters of 19701'71, 1971/'72 and 19721'73 (see Fig. 6, Table 6 and 7) it is concluded that high population levels were the main cause of the strong migration in the sUbsequent autumns. Goldcrest Regulus regulus Eurasian Treecreeper Certhia familiaris familiaris

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