JUKEMA J & RIJPMA U (1997) Composition of a population of Jackdaws Corvus rnonedula wintering in the northern Friesland. LIMOSA 70 (2): 61-66.

Jackdaws Corvus monedula were trapped, ringed, weighed and measured near Oosterbierum, Friesland province, Netherlands, in January 1985 (N= 170) and February 1996 (N=62). It was relatively easy to trap Jackdaws in cages when, during cold spells, fields were under a cover of snow. A large majority of birds trapped appeared to be C. m. spermologus. Among 232 birds trapped, there were at least five of the Scandinavian nominate subspecies. One of the five was recovered in southern Sweden in April '88. Mean wing length offour Scandinavian birds was 234.5 mm. This is 4.3 mm less than mean wing length of C. m. spermologus: adults 240.2 (N=24) and first year 234.4 (N=72; Tab. 2).
      Mass of birds trapped varied considerable (range 180290 g, Tab. 3b). Retraps showed that during these periods of adverse winter weather, birds hardly lost mass (Tab. 3b).
      Except for the single ring recovery abroad, all recoveries (14) came from within 35 km from the ringing site. Thirteen of these 14 were first year-birds when ringed, and ten were recovered during the breeding season.
      Local breeding birds appear to constitute a very large majority of Jackdaws wintering in Friesland, even during spells of severe winter weather. Our data constitute the first proof of occurrence of the nominate subspecies in Friesland province. Occurrence of the nominate subspecies and of Corvus monedula soemmeringii has been documented previously for the east-central part of the Netherlands.

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