Webcam-observatie bij een nest Torenvalken Falco tinnunculus

In 2007 Birdlife Netherlands placed several webcams at nests of Kestrel Falco tinnunculus, Barn Owl Tyto alba and Little Owl Athene noctua. A group of volunteers decided to watch a full breeding cycle of the Kestrel pair, coordinating dawn-to-dusk observations (even at night) and making systematic notes on parental care, food choice, food deliveries and behaviour in general. The Kestrel produced six eggs, the first being laid on 30 March, with following eggs produced on respectively 1, 3, 5, 7 and 9 April. Incubation started from the 3rd egg onwards, at first haphazardly but uninterrupted after the clutch was completed. The first 3 eggs hatched on 5 May, two more eggs on 6 and 7 May; one egg didn’t hatch. The incubation period for the first-laid egg lasted 36 days. Both parents took part in incubation, but the female was responsible for 74% of the daytime incubation (and exclusively for the night shift). Breeding shifts were frequent, on average some 15 times/day-1 with incubation bouts lasting between 30-115 minutes for the female (mean 70 min) and 10-33 minutes for the male (mean 21 min). On six days between 12 April and 2 May the female’s shifts were normally between 2.8 and 3.6 times longer than the male’s (Table 2). Up to 12 days of age the chicks were hardly ever left alone in the nestbox. From then on parents were absent from the nest for 11-15 hours per day, when also the female stopped roosting in the nestbox. Chicks increasingly fed independently from day 12 onwards. The first chick fledged 32 days after the first egg had hatched, later that day followed by two more chicks. Eleven days after fledging, the nestbox was visited by a fledgling for the last time; the day before a pair of Stock Doves had started nest building in the same nestbox. Food mainly consisted of voles, i.e. mostly Common Voles Microtus arvalis (89% including unidentified Microtus, out of 553 food items), with much smaller numbers of mice, birds, frogs, insects and earthworms (Table 3). Food delivery increased steadily during the first 12 days of the nestling period, reaching 20-25 voles per day (400 g) at day 12-15, and then levelled off at some 15-20 voles per day (300 g) with some outliers throughout the nestling cycle (Fig. 2). The male disappeared when the chicks were 14-16 days old, resulting in a steep drop in prey delivery that day. However, rate of prey delivery returned almost to previous levels from then on, despite the fact that the female alone was responsible for food provisioning. The nestbox proved to be a magnet for cavity-nesting bird species. A Bam Owl was repeatedly filmed at night when observing or entering the nestbox in the presence of the incubating female Kestrel. Once this resulted in a fight, during which the birds locked talons for a prolonged period of time and scattered the eggs; the Bam Owl eventually left. Jackdaws Corvus monedula and Stock Doves also showed interest in the nestbox, but were chased by the male Kestrel.