Vreemde speling van de natuur: een jonge Boomvalk Falco subbuteo met kruisbeksnavel

On 23 July 2001 a Hobby nest was checked to measure, weigh and rmg nestlings. One of the three nestlings had a deformed bill, in which the lower mandible was shifted sideways to the left (Photo). The condition of this nestling was poor compared to its siblings; its body mass was only 125 g (wing length 68 mm) as compared to masses of 255 and 215 g in its siblings (wing lengths 108 and 101 mm). A similar case in a Marsh Harrier Circus aeruginosus some years ago resulted in the death of that particular nestling.