Trends en broedresultaten van roofvogels in Nederland in 2022

A total of 2959 nest record cards of raptors were submitted in 2022 (Appendix 1, up to and including 31 December 2022), for 13 species (not including Montagu’s Harrier which is covered separately; www.grauwekiekendief.nl). The winter preceding the breeding season was extremely mild (frost index of 3.0 on a scale of 0-100), the summer itself was extremely warm (summer index 88.9, on a scale of 0-100). Food abundance on various trophic levels was moderate at best. Voles (especially Microtus arvalis) and mice (Apodemus sylvaticus) were at a low ebb but not as low as in 2021. Bird numbers in June-August were again small, a long-term trend which is particularly evident among birds in the weight classes of 200-500 g. Social wasps were moderately abundant (but rather low compared to a longer run of decades). Honey Buzzard Pernis apivorus: onset of laying averaged 24 May (range 14-31 May, n=24, excluding a possible repeat laying on 22 June). Within the period of 1996-2022, mean onset of laying was earliest in 2022 (and 2015). Clutch size was 11x 2 eggs. Brood size was 2x 1 and 25x 2 young. Chick condition, as illustrated by body mass corrected for age, was good. In 10 nests, prey remains constituted Vespula vulgaris (59, combs), V. germanica (17), unidentified combs (33, of grey texture), Dolichovespula media (6), D. saxonica (2), Vespa crabro (4), Woodpigeon Columba palumbus (2, squabs), Song Thrush Turdus philomelos (1, nestling) and Rana temporaria (2). Comb diameter increased from 60 mm on 8 July to 120-130 mm in mid-August. A wide variety of tree species was used as a nesting tree (10x deciduous in 5 species, 24x coniferous in 7 species), with an average nesting height of 16.1 ± 4.5 m (range 9-24 m). At least 55% of 27 nests were built by Honey Buzzards (possibly 74%, when old nests were included, some of which had been occupied by Honey Buzzards in previous years), with a scattering of nests of Goshawk (3), Buzzard (2), Red Kite (1) and Carrion Crow (1). Red Kite Milvus milvus: 30 nests were located (-14% compared to 2021), in 20 of which egg-laying commenced (resulting in 6x 0, 6x 1, 4x 2 and 4x 3 fledglings). Black Kite Milvus migrans: two breeding pairs in the southeastern Netherlands (poosibly two more, but no details), raising respectively 2 and 1 fledgling(s). White-tailed Eagle Haliaeetus albicilla: of 30 pairs, 22 produced a clutch. Fifteen successful pairs raised 9x 1, 5x 2 and 1x 3 fledglings. Marsh Harrier Circus aeruginosus: mean onset of laying was 27 April (range 11 April-25 May, n=93), i.e. similar to the long-term average (no change, apart from annual fluctuations, over 1996-2022). Clutch size averaged 5.03 (n=85), mean number of fledglings per successful pair was 3.12 (n=109). 55 broods had a secondary sex ratio of 96 males and 82 females (53.9% male). Out of 183 pairs that started egg-laying, 66 failed in either egg or nestling stage (64% was successful in raising at least one young). Causes of nest failure were 6x human-related and 6x caused by natural events (egg and nestling predation, each 3x). Food remains found on nests consisted of 30 birds (many young of Pheasants, ducks and geese, with a scattering of passerines) and 45 mammals (mostly rodents and hares). Hen Harrier Circus cyaneus: six nests on Wadden Sea Islands (3 Terschelling, 3 Texel, respectively 2 and 1 successful). A nest in Groningen failed during the eggs stage. A juvenile female with sender dispersed from Texel to Veluwe, with short trips in between, up to Belgium. A fledgling male with sender was found dead by late August on Texel, at some distance from the nest. Montagu’s Harrier Circus pygargus: for details, see www.grauwekiekendief.nl. Pallid Harrier Circus macrourus: a male (born nearby in 2019) helped with food provisioning at the nest of a Marsh Harrier in a field of wheat in Groningen. Goshawk Accipiter gentilis: mean start of laying was 1 April (n=158, of which 50% started in March, range 17 March-24 April), clutch size averaged 3.28 eggs (of which 4x C/5 among 177 clutches), brood size (at ringing/fledgling age) 2.53 (218 nests, none containing 5 chicks). Sex ratio in 137 nests showed 180 males and 175 females (50.7% male). Causes of failure were 2x human-related and 10x natural (mostly egg desertion, and predation of eggs or nestlings). Out of 364 nests with full details on breeding performance, 107 failed to raise fledglings (29%). Two cases of avian influenza (H5N1) were recorded. Prey remains collected near nests showed 96.6% birds in 45 species (especially pigeons and corvids including Jay, with respectively 32% and 29% of all prey, and with Starling, woodpeckers and thrushes in much smaller numbers), as well as some mammals in 3 species (mostly rabbits, some hares and red squirrels). Sparrowhawk Accipiter nisus: mean onset of laying was 28 April (range 12 April-14 May, n=104), with 72% of pairs starting in April (following an extremely mild winter). Clutch size averaged 5.08 (n=99), the number of fledglings per successful pair 4.25 (n=115). The secondary sex ratio among fledglings was 169 males and 148 females on 72 fully sexed nests. Among 244 nests, 76 failed to produce fledglings; predation is by far the most common cause of failure (31 out of 38 failures with known natural cause of failure, occurring throughout the breeding cycle and affecting adults, eggs and nestlings. Buzzard Buteo buteo: mean start of egg laying was calculated at 8 April (range 16 March-12 May, n=241; only 14.1% of all pairs started laying in March). Mean clutch size was 2.31 (n=316, with 10x C/4), mean brood size of successful pairs was 1.88 (n=437, with 4 B/4). For nests with both clutch size and number of fledglings recorded, the number of fledglings per nest started increased from 0.52 in C1 (n=21) to 1.25 in C2 (n=181), 1.77 in C3 (n=95) and 2.64 in C4 (n=11). Secondary sex ratio in 73 nests was 74 males and 53 females. Of 779 pairs with know reproductive outcome, 258 failed to raise chicks. Of the 258 failures, 127 could be attributd to non-laying (49.2%). Deliberate disturbances caused by humans accounted for 33.3% of all failures (out of 33 with know cause), the rest was attributed to desertion (2x), egg predation (5x), chick predation (5x), death of parent bird (2x) and adverse weather causing nest destruction (6x). Diet included 38 bird species (43.0% of 446 prey items) and 10 mammal species (53.8% of all prey items, lagomorphs, moles and voles most important in terms of biomass), plus some reptiles, frogs/toads and fishes. Among mammalian prey, voles accounted for 16.6% in numbers (i.e. poor vole season). Osprey Pandion haliaetus: the Dutch population comprised of four pairs, of which three nested in De Biesbosch (each pair fledged 3 chicks) and another on the northern Veluwe (1 chick raised). Another male in De Biesbosch occupied a nest but remained without mate. Kestrel Falco tinnunculus: onset of laying averaged 27 April (range 26 March-7 June, n=423). Mean clutch size was 5.03 (n=553), mean number of fledglings/successful nest 4.34 (n=640). Out of 946 nest boxes with attending pairs, 212 remained without eggs (22%). Almost all pairs nested in nest boxes, i.e. 946 compared to only 6 on nests of Carrion Crow in electricity pylons. Voles were the single most important prey species, e.g. 69% of 701 preys recorded in nestboxes and in pellets in several parts of the country. Hobby Falco subbuteo: mean start of laying was 8 June (range 26 May-21 June, N=66). Clutch size was 2x 2 and 4x 3, the number of fledglings/successful nest 10x 1, 34x 2, 46x 3 and 5x 4. Sex ratio in 3 nests was 3 males and 2 females. All pairs used old nests of crows (n=146 nests). The proportion of pairs nesting on old nests in electricity pylons amounted to 67% (n=98 nests), confirmation of the steady increase from 0% in the 1970s-1980s to consistently >50% recently. Mean nest height in tree nests was 19.4 m (SD=6.3, n=41, mostly poplars but covering a wide range of other tree species of which only 5 in coniferous trees), compared to 40.7 m in pylons (SD=11.8, n=78). Peregrine Falcon Falco peregrinus: most nests were in nestboxes, but breeding on crow’s nests in electricity pylons in farmland and niches in industrial buildings is increasingly recorded. Lay date averaged 14 March (range 28 February-16 April, n=80). Clutch size was 1x 1, 2x 2, 24x 3 and 42x 4, brood size was 11x 1, 24x 2, 32x 3 and 26x 4 (mean 2.78). Secondary sex ratio on 68 nests was 101 males and 96 females. Extensive prey lists from breeding sites in Zeeland, Zuid-Holland and Noord- Brabant showed a preponderance of racing/feral pigeons (45-60% of all prey items), complemented with a wide variety of small avian prey (usually <150 g).