Ardea
Official journal of the Netherlands Ornithologists' Union

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Solheim R. (2009) Age, sex and size of dead Tawny Owls Strix aluco found during a winter famine in 2006. ARDEA 97 (4): 597-601
From January to May 2006, 130 Tawny Owls were reported dead along the coastal areas of southern Norway. Of these, 79 were collected for a museum collection, most from the counties Vest-Agder (27), Aust-Agder (37), Telemark (9) and Vestfold (4). One owl was found starving, and was nurtured back to life. Of 67 sexable specimens, there were 34 males and 33 females. Nine of the birds were ringed, 5 females, 3 males and one unsexed bird. Five ringed owls were juveniles (in their second calendar year), while four ringed were old adults (calendar year 612). Of 79 aged owls, 51 (65%) were juveniles, while 28 (35%) were adults (third calendar year or older). Weight and body measurements were taken from all individuals as far as the carcasses allowed. The famine followed a very good breeding year of Tawny Owls along the southern coast of Norway in 2005, with high numbers of wood mice Apodemus sylvaticus until frost and snowfall in November. The following winter was cold, followed by heavy snowfall on 2021 January 2006. Snow depth increased steadily through February and March, reaching about 1 m in the coastal areas of Agder around 10 March. Tawny Owls started dying in February (n = 7), but most owls were found in March (n = 52). Many owls found in April (n = 17) were more or less decomposed, many probably having died in March. Young and old birds seemed to die at a similar pattern through spring. Neither was there any sex difference of mortality patterns.


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