Ervaringen met een cameraval bij een sperwernest Accipiter nisus, of: de schijn van een super-territorium

Noordlaarderbos (110 ha) in the province of Groningen annually housed several pairs of Sparrowhawks since at least the late 1970s. Chick production per successful pair averaged 4.6 in the 1980s (14 nests), better than the average of 3.9 young per successful pair for the entire province in the 2010s. In 2015 and 2016, two pairs in Noordlaarderbos failed. Several rings of nestlings were recovered from pellets collected at a nearby Goshawk Accipiter gentilis nest, suggesting predation as the main cause of failure. A trap camera was installed at the only nest in 2017 to register events leading to nest failure. The camera was installed on 4 June, when four chicks were a few days old (start of laying back-calculated at 23 April). Three female chicks were ringed and measured on 14 June. The camera was retrieved on 3 July, when the nest was found empty. Analysis of 885 photos (in 295 series of three photos within 1 sec each) revealed that the adult female (the same as in 2016, based on comparison of moulted feathers) covered the chicks till 9 June (when chicks 8-9 days old). A total of 69 incoming flights of the female were recorded (not always clear whether or not with prey), between 2 and 8 times a day (usually early morning and evening). The nest still contained four chicks on 12 June at 16.01 h but was visited one minute later by a Goshawk. The next day, only three chicks were recorded on the nest. Three chicks were still present at 19.14 h on 16 June, but only one chick remained by 20.35 h. The cause of the disappearance of two of the chicks was not registered (event too fast?). On 17 June, at 15.51 h, the remaining chick was still present, but had disappeared after a Goshawk visit at 21.31 h. The adulte female Sparrowhawk visited the empty nest that same day on 21.37 h, the presumed male on 22.42 h. The last visit to the nest was paid by the female on 18 June at 5.22 h. The camera was a success, showing that the nest was raided on three separate days in the course of five days; it was impossible to tell whether one or more Goshawks were involved in the predation events.