A total of 2675 nest record cards of raptors were submitted in 2018 (Appendix 1, handed in up to and including 31 December 2018), covering 12 species. The preceding winter was mild (frost index of 8.3 on a scale of 1-100). The summer was consistently exceedingly warm (summer index 120.9, far exceeding the upper limit of the 0-100 scale). Indices of abundance of prey groups were collected in several nonrandom parts of the country. Voles (Microtus arvalis and Myodes glareolus) and mice (Apodemus sylvaticus) were registered in low numbers. Rabbit Oryctolagus cuniculus numbers were also low. Birds in June-August were relatively abundant, after successful (and early) first broods; however, probably high temperatures in June-September prevented many passerines to start second broods. Social wasps were present in very low numbers (locally higher, though), with near-complete losses during the embryo stage of colonies. However, many combs were found on nests of Honey Buzzards, indicating that in some habitats (villages, farmland) wasp numbers were higher than in woodland (where very few social wasps were found). Honey Buzzard Pernis apivorus: onset of laying averaged 25 May (range 13 May-7 June, n=27). Only four pairs started laying in June. Clutch size was 15x 2 eggs. Brood size was 9x 1 and 17x 2 young. A wide variety of prey species were found on nests, including six wasp species, 1 species of bumblebee, 2 bird species and a frog. Comb size of socal wasps depredated by Honey Buzzards increased over summer. Red Kite Milvus milvus: 11 out of 14 breeding attempts were successful (1x ? number of chicks, 4x 2 and 6x 3 chicks/nest). Black Kite Milvus migrans: a single breeding attempt at Maastricht started 18 April and raised 2 chicks to fledging. White-tailed Eagle Haliaeetus albicilla: 15 nests were occupied, at 11 of which egg laying was commenced (9 successful). Marsh Harrier Circus aeruginosus: mean onset of laying was 25 April (range 7 April-20 May). Clutch size averaged 4.5 (n=51), mean number of fledglings/successful pair 3.19 (n=62, Appendix 3 and 4). 58 complete broods had a sex ratio of 81 males and 68 females. Illegal nest destruction was recorded nine times, nest predation six times; one pair deserted its clutch. Food remains found on nests showed a diverse diet, mostly voles and birds (Appendix 5). Hen Harrier Circus cyaneus: a single pair nested on Terschelling, with another four on Texel. Clutch size was 1x 3, 2x 4, 1x 5 and 1x 6 eggs. Brood size at fledging was 1x 1, 2x 2, 1x3 and 1x 5 chicks. Of individually recognisable breeding birds (colour rings) breeding on Texel five originated from the same island (three males, two females); the natal stite of two more females were on Terschelling and Norderney respectively. On Texel, one pair consisted of a mother-son combination. Montagu’s Harrier Circus pygargus: for details, see www.werkgroepgrauwekiekendief.nl. Goshawk Accipiter gentilis: mean start of laying was 2 April (n=165, of which 42% started in March), clutch size averaged 3.35 eggs (of which 2x C/5 among 165 clutches), brood size (at ringing/fledging) 2.67 (236 nests). Onset of laying varied across regions, most likely related to local food abundance (but unsubstantiated). Sexratio on 127 nests was in favour of males (58%, 336 young). Nest failures were human disturbance (3x), and natural (10x, of which four times a take-over by Alopochen aegyptiaca). The prey list (n=1360) contained almost exclusively birds (96.8%, in 54 species), of which pigeons were numerically by far the most important (40.5% of all prey, mostly racing pigeons and Woodpigeons), followed by corvids (22.3%), woodpeckers (6.8%), thrushes (4.6%) and Starlings (4.4%). Sparrowhawk Accipiter nisus: mean onset of laying was 3 May (range 13 April-31 May, n=46), with 52% of pairs starting in April. Clutch size averaged 4.84 (n=72), the number of fledglings per successful pair 3.75 (n=84). The secondary sex ratio among fledglings was 55.4% (72 males, 58 females, 32 nests). Among nest failures, predation was important: 13x, compared to 1x desertion, 3x Egyptian Goose take-over of nest and 1x human disturbance. Buzzard Buteo buteo: average start of egg laying was calculated at 7 April (range 21 March-2 May, n=249; 15% of all pairs started laying in March). Mean clutch size was 2.41 (n=349, with 16 C/4 and 2 C/5), mean brood size of successful pairs was 1.86 (n=521, with only 3 B/4). Secondary sex ratio in 60 nests with 103 chicks was 69.9% males. Known causes of nest failure included deliberate nest disturbance by humans (16x) and natural causes (21x). Diet was varied, with 43 bird species (37.9% of 763 prey items), 13 mammal species (60.9% of all prey items, lagomorphs and moles being important in terms of biomass), and some snakes, frogs, toads and fish. The relatively high proportion of birds indicated shortage of voles in the breeding season. Osprey Pandion haliaetus: two nests in De Biesbosch fledged 3 and 2 chicks respectively; at two other sites pairs were registered during summer, showing some interest in old stick nests (one of a White-tailed Eagle). Kestrel Falco tinnunculus: onset of laying averaged 21 April (range 6 March-31 May, n=294). Mean clutch size was 5.12 n=437), mean number of fledglings/successful nest 4.28 (n=470). Nest failures included human disturbance (8x) and natural causes (18x, of which 3x take-over by Egyptian Geese and 13x predation). Voles were important among 664 prey found in nestboxes and pellets in the province of Zeeland (67%). A variety of birds (25 species) was also recorded as prey. Hobby Falco subbuteo: mean start of laying was 8 June (range 23 May-6 July, n=30); 6 pairs started egg-laying May. Clutch size was 2x 3, mean number of fledglings/successful nest 8x 1, 25x 2, 25x 3 and 1x 4 (average 2.32). Sex ratio in 2 nests was 3 males and 2 females. Of 80 nests with known outcome, 65 were successful. Most pairs nested on old crow’s nests (69x Corvus corone, 1x C. frugilegus). The proportion of pairs nesting on crow’s nests in electricity pylons was a staggering 60% (n=90 nests), a biased figure given the special attention to finding nests in high tension pylons in the northern Netherlands. Peregrine Falcon Falco peregrinus: all nests were in nestboxes or old crow’s nests, except for a single tree nest (old nest Buzzard, in poplar in Noordoostpolder). Lay date averaged 21 March (range 2 March-23 April, n=35). Clutch size was 2x 1, 1x 2, 7x 3 and 16x 4, brood size averaged 3.06 (n=36). Secondary sex ratio on 31 nests was 57 males and 39 females. Extensive prey lists from breeding sites in Zeeland and Zuid- Holland showed a preponderance of racing/feral pigeons (resp. 34% and 64%).

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Werkgroep Roofvogels Nederland

R.G. Bijlsma. (2019). Trends en broedresultaten van roofvogels in Nederland in 2018. De Takkeling, 27(1), 5–45.