Doorbroeden van Buizerd Buteo buteo op onbevruchte eieren

Whilst monitoring parental investment of a Buzzard Buteo buteo pair in the northern Netherlands in 2015 by means of a trap camera (taking a photograph each minute), the birds were found to continue incubation well after the expected hatching date. The first egg was laid around 6 April. Up to and including 9 May, the expected hatching day, the female’s share of incubation amounted to 86% of the recorded incubation time (701.7 h observed), the male’s share 10% (during 4% of the time, the eggs were not covered). The eggs did not hatch, and incubation was prolonged up to and including 8 June; during the extra incubation time between 10 May and 8 June, the female’s share in incubation declined to 73% of the total time observed, the male’s share increased to 20% (especially in the few days prior to desertion); during 7% of the time the eggs were not covered. Over the normal incubation period, only four times the eggs remained uncovered for longer than an hour (range 1.37 h – 4.16 h). It is thought that this cannot have been the cause of non-hatching. Also, four nest visits to retrieve data from the camera, taking 10-16 min each, did not result in long absences of a breeding bird from the nest: returns were camera-recorded 3, 15, 15 and 27 min after the observers had left the nest. The prolonged incubation period of 63 days (+91% compared to an average incubation time of 33 days) falls within the range of similar instances in raptors and other birds (as mentioned in the literature).