Trends en broedresultaten van roofvogels in Nederland in 2019

A total of 3118 nest record cards of raptors were submitted in 2019 (Appendix 1, handed in up to and including 31 December 2019), covering 13 species (plus two more, i.e. Red Kite and Montagu’s Harrier, which are covered by separate raptor groups). The preceding winter was extremely mild (frost index of 4.5 on a scale of 1-100). The summer was near-permanently warm and tropical (summer index 117.9, for the third time since the year 1706 exceeding the upper limit of the 0-100 scale). Indices of abundance of prey groups were collected in several non-random parts of the country. Voles (Microtus arvalis and Myodes glareolus) and mice (Apodemus sylvaticus) were registered in high numbers, with voles reaching peak numbers especially in the lowlying parts of the country. Rabbit Oryctolagus cuniculus numbers were low in most parts of the country, only locally showing some recovery from the ravages of VHS in the late 1990s. Birds in June-August were relatively abundant, after successful (and early) first broods; (extremely) high temperatures in June-September adversely impacted the fate of second broods. Social wasps were present in low-moderate numbers (locally higher, though), especially Vespula vulgaris (V. germanica is in decline, as is V. rufa). Honey Buzzard Pernis apivorus: onset of laying averaged 26 May (range 14 May-15 June, n=31); 77% of the pairs started laying in May. Clutch size was 12x 2 eggs. Brood size was 6x 1 and 26x 2 young. A wide variety of prey species were found on nests, i.e. combs of Vespula vulgaris (156, plus lots of débris), V. germanica (15), Dolichovespula saxonica (6), D. media (2), Vespa crabro (8) and once remains of a bumblebee Bombus sp. nest. Vertebrate prey consisted of Columba palumbus (1 nestling), 2 Turdus merula, 1 T. philomelos, 1 Fringilla coelebs (nest), 1 Anguis fragilis and 1 Rana temporaria. Red Kite Milvus milvus: 13 breeding pairs were located, of which 12 nests were found. Ten out of 12 pairs were successful (2 pairs refrained from egg-laying), raising 2x 0, 1x 2, 7x 3 and 2x 4 fledglings. Mean start of laying was 16 April (range: 27 March-16 April) (see van Rijn et al. 2019). Black Kite Milvus migrans: a breeding attempt at Maastricht failed to raise chicks. White-tailed Eagle Haliaeetus albicilla: of 16 pairs, at least 12 produced a clutch. Eleven pairs were successful, raising a total of 14 fledglings (van Rijn et al. 2019b). Four chicks received a GPS-sender (for details see: www.werkgroepzeearend.nl). Marsh Harrier Circus aeruginosus: mean onset of laying was 25 April (range 8 April-16 June). Clutch size averaged 4.98 (n=49), mean number of fledglings per successful pair 3.64 (n=78, Appendix 3 and 4). 52 complete broods had a sex ratio of 102 males and 86 females. Food remains found on nests showed a diverse diet, mostly voles and birds (Appendix 5). Hen Harrier Circus cyaneus: two nests were located on Terschelling (both successful), with another four on Texel (2 males with 4 females; only one nest successful) and 7 in Groningen (4 successful). A total of 22 chicks were raised to fledging, i.e. 14 males and 8 females. Mean start of laying was 5 May (range 23 April-11 May), mean clutch size was 4.8, mean brood size 3.14. Montagu’s Harrier Circus pygargus: for details, see www.grauwekiekendief.nl. A total of 53 pairs were recorded in the entire Netherlands, of which 38 pairs raised 142 fledglings (67 males, 60 females, 15 of unknown sex). Pallid Harrier Circus macrourus: a successful pair in Groningen raised 6 fledglings (5 males, 1 female). This is the second successful pair in The Netherlands (in 2017 a pair raised four females, one of which was found breeding in Spain in 2019), with a failed breeding attempt of a mixed male Montagu’s x female Pallid pair in 2018. Goshawk Accipiter gentilis: mean start of laying was 1 April (n=189, of which 44% started in March, range 16 March-23 April), clutch size averaged 3.54 eggs (of which 8x C/5 among 190 clutches), brood size (at ringing/fledging) 2.78 (259 nests). Onset of laying was consistently early throughout the country, except for the Wadden Sea Islands of Vlieland and Schiermonnikoog. Sex ratio on 135 nests was in favour of males (57.3%, 366 young). Nest failures were caused by human disturbance (6x), and natural events (8x, of which twice a take-over by Alopochen aegyptiaca). The prey list (n=1484) contained almost exclusively birds (96.5%, in 56 species), of which pigeons were numerically by far the most important (41.9% of all prey, mostly racing pigeons and Woodpigeons), followed by corvids (21.0%), woodpeckers (5.9%), thrushes (3.3%) and Starlings (4.3%). In cities like Rotterdam and Amsterdam, Ring-necked Parakeets Psittacula krameri are often captured, i.e. respectively amounting to 9.5% (on 21 prey remains) and 6.5% (n=432) of local prey lists. Sparrowhawk Accipiter nisus: mean onset of laying was 26 April (range 15 April-8 May, n=61), with 61% of pairs starting in April. Clutch size averaged 5.25 (n=75), the number of fledglings per successful pair 4.25 (n=86). The secondary sex ratio among fledglings was 51.7% (104 males, 97 females, 47 nests). Among nest failures, predation was important: 37x (8x egg stage, 27x nestling stage, 2x adults), compared to 1x desertion, 1x adverse weather and 1x human disturbance. Buzzard Buteo buteo: mean start of egg laying was calculated at 4 April (range 3 March-11 May, n=314; 31% of all pairs started laying in March). The early laying on 3 March was exceptional (but proven with measurements of the chicks); the second pair to start laying did so on 14 March. Mean clutch size was 2.67 (n=396, with 35 C/4 and 1 C/5; a clutch of 6 eggs was attended by two females and consisted of two C/3), mean brood size of successful pairs was 2.21 (n=647, with 23 B/4 and 1 B/5). Secondary sex ratio in 57 nests with 129 chicks was 55.8% males. Known causes of nest failure included deliberate nest disturbance by humans (19x) and natural causes (27x, including 11x egg predation and 7x chick predation; take-overs by Egyptian Goose were recorded twice). Diet was varied, with 40 bird species (34.5% of 947 prey items), 16 mammal species (64.6% of all prey items, lagomorphs, moles and voles being important in terms of biomass), and some reptiles and frogs/toads. Osprey Pandion haliaetus: two nests in De Biesbosch each fledged a single chick; a pair showed interest in an artificial nest in the southern Netherlands along the Meuse. Kestrel Falco tinnunculus: onset of laying averaged 14 April (range 23 March-8 June, n=419). Mean clutch size was 5.56 n=498), mean number of fledglings/successful nest 4.87 (n=629). Nest failures included human disturbance (7x) and natural causes (17x, all predation). Voles were the single most important prey species, e.g. 89% of 628 preys recorded in nestboxes and pellets in Zeeland. Hobby Falco subbuteo: mean start of laying was 3 June (range 31 May-3 July, n=19); 2 pairs started egg laying in May (on 31st). Clutch size was 1x 2 and 5x 3, mean number of fledglings/successful nest 9x 1, 22x 2, 21x 3 and 1x 4 (average 2.26). Sex ratio in 5 nests was 4 males and 8 females. Most pairs nested on old crow’s nests (50x Corvus corone, 1x C. frugilegus, 4x Buteo buteo, 1x artificial nest). The proportion of pairs nesting on crow’s nests in electricity pylons amounted to 52.8% (n=70 nests), probably biased given the special attention to finding nests in electricity pylons in the northern Netherlands. Peregrine Falcon Falco peregrinus: most nests were in nestboxes, with some pairs using old crow’s nests in electricity pylons. Lay date averaged 11 March (range 26 February-5 April, n=31). Clutch size was 4x 2, 5x 3 and 17x 4, brood size was 6x 1, 7x 2, 14x 3 and 11x 4 (mean 3.06, n=38). Secondary sex ratio on 27 nests was 51 males and 26 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).