OSIECK ER (1975) Identification of treecreepers Certhia in The Netherlands. LIMOSA 48 (3): 176-187.

Short-toed Treecreeper Certhia brachydactyla In the auturnn of 1972 an unprecedented number of Treecreepers Certhia familiaris were recorded in the Netherlands. In order to judge these records the characteristics of Certhia familiaris and C. brachydactyla both in the hand and in the field, have been tested on their validity. The Short-toed Treecreeper is a common breed[ng bird in most parts of the Netherlands. Only Treecreepers from northern Europe are considered in this study, since descriptions of trappings and birds found dead indicate that the birds involved in the irruption belonged to this form. The extension and colour of the supercilium and the colouration of the underparts and flanks are the most important characters (Table 2). In the hand bill length, length of hind claw and their ratio are useful, but in all these values there is some amount of overlap (Table 3 en Fig. 3). The geographical variation of Certhia familiaris in northern Europe was surveyed, to get an idea of the origin of the birds. A cline of decreasing pigmentation runs from Denmark northwards to north Sweden and eastwards to Siberia. The upperparts become paJler, less brown with larger white spots (Table 4); the flanks, brownish in Denmark, become white (Table 5). The geographical variation in winglength, length of bill and hind claw (Table 6, 7, 8) is less clear. Danish birds seem to have longer wings but shorter bills than birds from central Sweden. Treecreepers from north Sweden have longer wings and hindclaws than their central Swedish relatives. Winglength increases from centml Sweden to Siberia, but the Russian/Siberian birds have shorter bills. It should be emphasi2ied, however, that sample sizes are too small for definite conclusions. The plumages of the Treecreepers obtained during the autumn of 1972 in the Netherlands indicate that they belong to the subspecies familiaris from the area between the transition zone with macrodactyla eastwards into Russia.

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