Trends en broedresultaten van roofvogels in Nederland in 2009

A total of 2912 nest cards of raptors were submitted in 2009 (Appendix 1, up to and including 31 December, not complete yet), covering 12 species. The preceding winter was rather mild (frost index of 14.2 on a scale of 1-100), spring extremely dry and warm through early May. The summer was warm (summer index 72.8, on a scale of 1-100). Food supply varied from very poor (voles, mice, rabbits, hares) to normal (birds) and poor (social wasps, after a promising start in May, with German and Common wasp Vespula germanica and V. vulgaris showing heavy mortality among embryo nests in May/June). European Honey-buzzard Pernis apivorus: onset of laying averaged 23 May (range 11 May-2 June), with a unimodal distribution peaking in 21-30 May. Only clutches with 2 eggs were recorded (N=21), and mean brood size was 1.68 (SD=0.47, N=48). Out of 35 nests, 24 were built by Honey-buzzards, the other nests were made by Buzzard (4), Goshawk (6) and Carrion Crow (1). Mean nest height was 13.8 m (SD=5.25, N=25). Black Kite Milvus migrans: a single nest in the southern Netherlands (poplar) fledged two chicks. White-tailed Eagle Haliaeetus albicilla: the breeding pair in Oostvaardersplassen, the only one in The Netherlands, laid two eggs and raised one chick. In the winter of 2009/10 three colour-ringed birds stayed in the SW-Netherlands, presumably the young raised in 2008 and 2009. Marsh Harrier Circus aeruginosas: mean onset of laying was 24 April (range 4 April-16 June; Appendix 2). Clutch size averaged 4.55 (SD=0.82, N=76; Appendix 3), mean number of fledglings/successful pair 2.96 (SD=1.04, N=95; Appendix 4). All surviving nestlings in 81 nests were sexed: 141 males and 101 females. Over the years 1996-2009, a biased secondary sex ratio has been prevalent (53.1% males in 1122 nests with 3601 nestlings). Illegal nest destruction was rife, especially in the province of Friesland. The poor breeding performance was due to an extreme low in vole populations. Hen Harrier Circus cyaneus: the decline of the Dutch population is gaining momentum, with only 19 pairs registered in 2009 (2 in Oostvaardersplassen, rest on the Wadden Sea Islands, where Ameland was devoid of breeding pairs for the first time since its colonisation in 1940). Mean start of laying averaged 29 April (range 18 April-1 May; Appendix 2), clutch size 4.00 eggs (range 3-5; Appendix 3), brood size of successful nests 2.60 (range 2-3; Appendix 4). The decline is now so steep, and allencompassing, that there is little hope of recovery. Montagu’s Harrier Circus pygargus: see www.grauwekiekendief.nl for details of breeding results and satellite tracking data. Goshawk Accipiter gentilis: start of laying was on average 2 April (range 13 March-25 April, Appendix 2), clutch size 3.15 eggs (SD=0.74, N=242, range 1-5; Appendix 3), and brood size (at ringing/fledging) of 2.52 (Appendix 4, SD=0.84, N=331, range 1-4). Secondary sex ratio on 221 nests was in favour of males (55.0%), and in line with the long-term mean for 1996-2009 (55.2% male in 3735 nests with 10,030 nestlings). Among identified causes of nest failure, illegal human activities were important (12 out of 29), with natural causes being desertion (8x), egg predation (2x), chick predation (4x), adverse weather (2x) and take-over/disturbance by Egyptian Geese Alopochen aegyptiacus (1x). Food remains found near nests showed a preponderance of pigeons (top 3: Racing Pigeon Columba livia, Woodpigeon C. palumbus and Jay Garrulus glandarius; together 44.9% of 1044 prey remains). Among age-identified Racing Pigeons, 1 -yr old birds were rather scarce (32.6% of 45 rings found on nests and in pellets). Sparrowhawk Accipiter nisus: mean onset of laying was 1 May (range 16 April-30 May, N=l28; Appendix 2), a rather late start that was recorded throughout The Netherlands. Clutch size averaged 4.76 eggs (N=l28, Appendix 3), number of fledglings/successful pair 3.85 (N= 161, Appendix 4). Predation of eggs, nestlings and breeding birds accounted for 92% of the recorded nest failures (N=52). Secondary sex ratio was almost fifty-fifty (232 males, 221 females, 112 nests). Among breeding birds, first-years were scarce: 12.5% in males (N=8) and 11.5% in females (N=52). Buzzard Buteo buteo: average start of egg laying was late, i.e. 8 April (range 21 March-1 May, N=45B; Appendix 2). Mean clutch size was 2.18 (N=269, with only 4 C/4), mean brood size of successful pairs was 1.73 (N=728, only one B/4; Appendix 4). Late start of laying, and small clutch and brood sizes, were consistent with very low vole numbers. Many pairs refrained from breeding. The secondary sex ratio in 117 nests was strongly male-biased: 59.0% of 188 young. Food choice was varied, with 48 bird species (53% in prey numbers), 15 mammal species (43% in prey numbers), 6 species of reptiles and amphibians, and 2 fishes (Appendix 6, N=964). Out of 74 identified causes of failure, 43 could be attributed to deliberate human action (mostly in the province of Friesland). Kestrel Falco tinnunculus: onset of laying averaged 1 May (range 2 April-2 June, N=409; Appendix 2), later than ever before since 1996. Mean clutch size was 4.68 (N=364; Appendix 3), mean number of fledglings/successful nest 3,92 (N=512, Appendix 4). Late starts and small clutch and brood sizes were recorded throughout The Netherlands, consistent with an overall low in vole numbers. Causes of failure were mostly natural (35 out of 38), i.e. desertion and predation. Hobby Falco subbuteo: mean start of laying was 10 June (range 30 May-25 June, N=36; Appendix 2). Mean clutch size was 2.81 (N=16), mean number of fledglings/ successful nest 2.41 (N=66). Secondary sex ratio in 6 nests was 10 males and 6 females (sexes identified by body mass and vocalisations). The proportion of pairs nesting on crow’s nests in electricity pylons in 2009 was 30% (N=85 nests). Peregrine Falcon Falco peregrinus: a minimum of 65 pairs were registered in 2009. Details will be published by the Peregrine Working Group.