The activities surrounding, and use of, four summer nests of Honey Buzzards (nests built in summer but without egg laying, called ‘Spielnest’ in the past by German authors) and a Buzzard nest refurbished by Honey Buzzard were continuously tracked by means of Reconyx HC 600 cameras. The cameras were either used with timelapse (each minute one photograph taken), or via motion-trigger (or both). Nest visits were registered, sex and identity noted, and material brought to the nest identified (if possible). Summer nests were also tracked in the following years, by putting up cameras prior to arrival and recording subsequent activities. Individual recognition was also possible via photographs taken of flying birds observed from tree tops or from the ground. All data were collected in southeastern Friesland in the northern Netherlands, where farmland dominates and woodland is fragmented and of small acreage. The first summer nest was detected on 23 July 2013 in a Douglas Fir Pseudotsuga menziesii in Oranjewoud This nest fell down in autumn, was rebuilt in 2014 at almost the same spot but egg-laying did not occur. In 2015, a dark intermediate male arrived on 21 May, at 5.50 h, and almost immediately commenced nest-building (nest already refurbished when camera was installed on 20 May). The dark female was first recorded on 24 May, the first egg was laid on 1 June. In the intermediate time the nest was at least visited 68 times by the female and 132 times by the male (4x by unknown sex), often bringing twigs or prey (5 birds, 1 thrush, 9 unidentified vertebrate preys, 11 frogs and 1 unknown prey item). Both adults were captured and (colour)ringed when the chicks were some 10 days old. The chicks were depredated by a Pine marten Martes martes when 26 and 28 days old. The female continued bringing wasp combs to the nest up to five days after the predation event. The next year, 2016, a light adult male arrived at the nest on 9 June, and immediately commenced nest-building; between 9 and 18 June (except on 13-15 June) he visited the nest 98 times, mostly in the early morning hours till 10 o’clock. Nesting material was provided on at least 38 of those visits. On three images the bird is visible with open bill, possibly calling. However, a female was not recorded on the nest. At a distance of 4.2 km, near Katlijker Schar, another Honey Buzzard nest was found in a Picea sitchensis on 22 June 2016. This nest must have been built in 2015 (and held a latrine of Pine Marten); the nest contained two eggs. Installation of a camera proved that the pair was the same as the Oranjewoud-pair of 2015, but it remained uncertain whether the Picea-nest had been built by that pair (but possible; in May 2015 the Picea did not yet have a nest). The single chick fledged (other egg did not hatch). Remarkably, this nest was visited by the light adult male (i.e. not the breeding male of this nest but a visitor from the 2016-Oranjewoud-nest) when the surviving chick was 40 days old, then again 30 minutes later. The chick did not react. This light male paid two more visits on 26 August, at least once bringing a twig. In 2017, the nest at Katlijker Schar was again occupied by the same pair as in 2016. The male and female arrived together on 15 May at 10.19 h, i.e. 6 days earlier than in 2016 for the male, and three days earlier for the female (at least as recorded by the camera at the nest). The nest was delapidated following occupation by Egyptian Goose Alopochen aegyptiaca, and despite repair with fresh coniferous twigs, the Honey Buzzard pair left after three days. On 28 May, the light adult male arrived at this nest but was recorded the next day at the Oranjewoud nest (12 days earlier than in 2016). A very dark female showed up at Oranjewoud on 31 May. Between 28 May and 10 June (when first egg was laid) male and female visited the nest resp. 160 and 80 times. The male was almost solely responsible for bringing nesting material (31 times, female only once). Six copulations took place on a branch close to the nest. Both eggs hatched, and both chicks fledged (but the youngest was killed shortly after fledging by a Goshawk Accipiter gentilis). A nest at Delleboersterheide had been occupied in 2014, and again – successfully – by the same pair in 2015. In 2016 the male returned (according to images of the camera) as late as 21 May (11 days later than in 2015), but only shortly (with another visit on 24 May). No nest-building occurred during both visits. The female of 2014 and 2015 was not recorded at this nest in 2016, but instead showed up at another nest (newly built) 16 km away (where she was captured on 21 July, and data-loggered); here, she raised two young. It remained unknown whether she shifted because of the late arrival of her 2014/2015-male. Her erstwhile partner also shifted in 2016, and was found some km away with a newly built nest in a Scots pine Pinus sylvestris while carrying a prey (presumably a tit Parus sp.) and followed by a female. This male was seen to share his territory with three different females, but a brood did not commence. In 2017, a camera was used to detect activities at the nest, but due to failure did not result in pinpointing the arrival date. On 20 May the nest contained fresh greenery. The female turned out to be a new one (unringed); egg-laying started on 24 May. The last observation of his female was registered by camera on 19 June, the fourth week of incubation. The male continued incubation for another 6.5 days but deserted on 25 June (2 days prior to expected hatching); on 27 June, when the eggs should have hatched, he once more returned to incubate for 70 min, then departed not to return. His female (of 2014-2015) showed up in 2017 at her 2016-nest, unfortunately too short to read the data from the logger. She stayed in the general vicinity, also visiting the nest site of her erstwhile partner at Diaconieveen on 17 May (where he may have been present, given the fresh greenery on the nest on 20 May). She probably did not nest in 2017, as her widely dispersed fixes indicated. On 15 July 2017 a Buzzard nest was located near Wolvega, decorated with fresh leaves of Alnus glutinosa. After setting up a camera it became clear that these Honey Buzzards were unknown in our database. The male shared the nest with two females, which visited the nest on the same date (18 July, but not simultaneously). The male had been ringed as nestling in 2014, at a distance of 154 km. Especially the male frequently visited the nest (32x) between 18 July and 5 August, bringing nesting material and some frogs; the females visited the nest resp. 3x and 6x. Egg-laying did not commence. The above observations showed a case of natal dispersal (154 km, of a male which presumably settled as a breeding bird when 3 years old), and a likely case of natal dispersal (20 km for a female, ringed as nestling in 2009, found killed in 2014 and known to have bred there in 2013; probably her nesting attempt in 2013 was her first breeding season in life, and hence a likely case of natal dispersal; Bijlsma 2014) and several cases of breeding dispersal (26 km for an adult male, ringed as nestling in 1996 and recaptured as breeding bird in 2012, then seen annually up to and including 2016) and 20 km for another male (ringed as nestling in 2000, captured as a breeding bird in 2017 at his nest with two chicks, and found killed by a Goshawk in summer 2018). It seems that summer nests are important in the life of Honey Buzzards, given the high frequency of occupation (and breeding) in the following year (four out of five summer nests). It remains to be seen whether building and refurbishing of summer nests (mostly by males, who also bring prey) is used as a way to advertise quality as a breeding bird. Interestingly, non-breeding males and males that lost their nest/partner sometime during the breeding season also may make prolonged above-canopy flights (often high) whilst carrying a clearly visible prey.

De Takkeling

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Werkgroep Roofvogels Nederland

R. Riem Vis, V.S. van Bergen, & J. Brinkgreve. (2019). Transitie van zomernest naar broednest bij Wespendieven Pernis apivorus, en aantekeningen over broed- en natale dispersie. De Takkeling, 27(2), 100–116.