Trends en broedresultaten van roofvogels in Nederland in 2020

A total of 3199 nest record cards of raptors were submitted in 2020 (Appendix 1, handed in up to and including 15 January 2021), covering 14 species (not including Montagu’s Harrier which is covered separately; www.grauwekiekendief.nl). The preceding winter was extremely mild (frost index of 2.1 on a scale of 1-100), the summer extremely warm (summer index 90.7, on a scale of 0-100). Voles (Microtus arvalis and Myodes glareolus) and mice (Apodemus sylvaticus) declined to low numbers during spring and summer. Bird numbers in June-August were average, but mostly belonged to weight classes <100 g. Social wasps were present in low numbers, mostly referring to Vespula vulgaris. Honey Buzzard Pernis apivorus: onset of laying averaged 29 May (range 11 May-14 June, n=27); 77% of the pairs started laying in May. Clutch size was 12x 2 eggs (in one C/2 a third egg was laid 10 days after the second egg was laid, but its origin remained unknown). Brood size was 6x 1 and 22x 2 young. A wide variety of prey species were found on nests, i.e. combs of Vespula vulgaris (133, plus lots of débris), V. germanica (11), V. rufa (2), Dolichovespula saxonica (14), D. media (4), Vespa crabro (32) and unidentified social wasps (grey combs, 67). Vertebrate prey consisted of Columba palumbus (1 squab), 2 Turdus philomelos, 1 young Coccothraustes coccothraustes and 1 Rana temporaria. Red Kite Milvus milvus: 22 breeding pairs were located, of which 18 commenced egg-laying (resulting in 9x 0, 1x 1, 3x 2 and 5x 3 fledglings). Start of laying averaged 9 April (range 25 March-25 April). Breeding success was poorest in regions where novel breeding pairs had settled (presumably first-time breeders). Black Kite Milvus migrans: two breeding pairs in the southeastern Netherlands raised 2 and 3 fledglings. White-tailed Eagle Haliaeetus albicilla: of 20 pairs, 18 produced a clutch. Fourteen successful pairs raised a total of 22 fledglings. The Dutch population is still increasing (14 pairs in 2019), and since 2006 – the first breeding case – produced already >100 fledglings. Of the breeding birds in 2019 and 2020, five had been ringed in Germany and nine were recruits from Dutch origin. Marsh Harrier Circus aeruginosus: mean onset of laying was 26 April (range 7 April-20 May, n=66). Clutch size averaged 4.56 (n=63), mean number of fledglings per successful pair 3.07 (n=68), i.e. slightly below the long-term averages. 48 complete broods had a sex ratio of 74 males and 65 females (53.2% male, very similar to the long-term average for 1996-2019 of 53.3% based on 1736 nests with 2964 males and 2599 females. Food remains found on nests showed a diverse diet, mostly hares (important in terms of biomass), voles and birds (148 prey remains collected). Hen Harrier Circus cyaneus: six nests were found in cereals in mainland Groningen (4 successful, producing 15 fledglings), two nests on Terschelling (both successful, one of these raised 4 fledglings), and three on Texel (two successful, raising only 5 fledglings). Mean start of laying was 28 April (range 24 April-5 May, n=3), mean clutch size was 4.0 (n=3), mean brood size 3.4 (n=7). Montagu’s Harrier Circus pygargus: for details, see www.grauwekiekendief.nl. A total of 80 pairs were recorded in the entire Netherlands (compared to 53 in 2019), of which 41 pairs raised 102 fledglings (48 males, 38 females, rest of unknown sex). Two pairs consisted of 2nd-calender-year breedings birds (male ánd female), one of which was successful. Breeding habitat largely consisted of winter cereals (86% of 76 pairs), with another 7 in alfalfa and 4 in grassland. One female was found shot on the nest, of another all three chicks were deliberately killed by man. Pallid Harrier Circus macrourus: a female Pallid was mated to an adult male Montagu’s Harrrier of Danish origin, but the latter switched to a female Montagu’s Harrier and commenced breeding nearby. The female Pallid produced a nest but it remained unknown whether she laid eggs (although seen in flight with ‘full belly’). Goshawk Accipiter gentilis: mean start of laying was 2 April (n=167, of which 45% started in March, range 12 March-22 April), clutch size averaged 3.24 eggs (of which 4x C/5 among 183 clutches), brood size (at ringing/fledging age) 2.53 (236 nests). Over 1974-2019, onset of laying remained constant (mean 2 April, n=6437 pairs), although annual outliers were more common in the 1970s-1990s when severe winters were still part of the scene. Lay date of Goshawks is strongly correlated with severity of the preceding winter. Mean clutch size in 2020 was 3.24 (n=183), mean brood size 2.53 (n=236). Sex ratio in 151 nests showed 219 males and 168 females (56.4% male), slightly more male-skewed than evident from 5365 nsts with 14.299 young in 1996- 2019 (55.2% male). Prey remains collected near nests showed 97% birds in 57 species (especially pigeons and corvids, with respectively 40% and 18% of all prey), and some mammals in 6 species (mostly rabbits). Sparrowhawk Accipiter nisus: mean onset of laying was 27 April (range 13 April-19 May, n=89), with 64% of pairs starting in April. Clutch size averaged 4.89 (n=101), the number of fledglings per successful pair 4.07 (n=107). The secondary sex ratio among fledglings was 148 males and 132 females on 69 nests. In the longer run, i.e. 1996-2019, males accounted for 51.2% among 13.923 young on 3639 nests. Among 238 nests, 80 failed to produce fledglings, but the failed proportion should be higher because many nests are depredated at an early stage of the breeding cycle (and are therefore not found by raptorphiles). Buzzard Buteo buteo: mean start of egg laying was calculated at 6 April (range 11 March-7 May, n=259; 26% of all pairs started laying in March). Mean clutch size was 2.45 (n=333, with 12 C/4, 1 C/5 and 1 C/6), mean brood size of successful pairs was 1.94 (n=485, with 3 B/4 and 2 B/5). Secondary sex ratio in 64 nests was 57 males and 62 females (47.9%). In the long run secondary sex ratio is male-skewed: 54.8% for 4295 nests in 1996-2019 with 4401 males and 3764 females. Of 50 nest failures, 40% were deliberate disturbances caused by humans. Diet was varied, with 34 bird species (33.8% of 714 prey items), 16 mammal species (64.7% of all prey items, lagomorphs, moles and voles most important in terms of biomass), and some reptiles, frogs/toads and a single fish. Osprey Pandion haliaetus: three pairs in De Biesbosch each fledged 3 chicks; two other pairs were present but did not commence breeding. Kestrel Falco tinnunculus: onset of laying averaged 19 April (range 18 March- 2 June, n=526). Mean clutch size was 5.22 n=705), mean number of fledglings/successful nest 4.49 (n=816). Almost all pairs nested in nest boxes, i.e. 984 compared to 6 nests in trees and electricity pylons (stick nests) and 1 in a building. Voles were the single most important prey species, e.g. 75% of 826 preys recorded in nestboxes and pellets in several parts of the country. Hobby Falco subbuteo: mean start of laying was 5 June (range 12 May-21 June, n=21); 3 pairs started egg-laying in May. Clutch size was 7x 2 and 13x 3, the number of fledglings/successful nest 7x 1, 22x 2, 26x 3 and 1x 4 (average 2.32). Sex ratio in 4 nests was 6 males and 4 females (compare 1996-2019: 229 males and 276 females on 211 nests). Most pairs nested on old nests of crows (96% of 71 nests). The proportion of pairs nesting on old nests in electricity pylons amounted to 56% (n=88 nests), in line with a steady increase from 0% in the 1970s-1980s to >50% recently. This change in nest site choice partly reflects biased interest of raptorphiles for electricity pylons in farmland but also a habitat shift (away from forests, increasingly nesting in farmland). Peregrine Falcon Falco peregrinus: most nests were in nestboxes, but with an increasing number using old stick nests in electricity pylons and niches in industrial buildings. Lay date averaged 14 March (range 2 March-3 April, n=28, with a repeat laying on 3 May not included in mean lay date). Clutch size was 2x 2, 9x 3 and 17x 4, brood size was 7x 1, 11x 2, 15x 3 and 8x 4 (mean 2.58, n=41). Secondary sex ratio on 27 nests was 39 males and 34 females. Extensive prey lists from breeding sites in Zeeland, Zuid-Holland and Noord-Brabant showed a preponderance of racing/feral pigeons (52% of 561 prey items) complemented with small avian prey (of species <150 g).