MANEN W VAN (2012) Breeding biology of Black Woodpecker Dryocopus martius in The Netherlands. LIMOSA 85 (4): 161-170.

In 1995-2010, during territory mapping of birds in large woodland areas or during special surveys for the species, 176 breeding attempts of Black Woodpecker were monitored in The Netherlands (Fig. 1). Young were measured (maximum wing chord), weighed and ringed. Nestlings were sexed by the quantity of red on the head. Onset of laying was calculated by estimating the age of oldest chicks based on their wing length (Fig. 3). Although the monitored nests were concentrated in the northern and central parts of The Netherlands (Fig. 1), the data may be regarded as representative for the entire country. Woodland covers nearly 11% of The Netherlands. The larger woodland areas (which host most of the woodpecker pairs) have been planted after 1900 with mainly coniferous trees. Important tree species are Scots Pine Pinus sylvestris, Pedunculate Oak Quercus robur, Douglas Fir Pseudotsuga menziesii, Japanese Larch Larix kaempferi, Norway Spruce Picea abies and Beech Fagus sylvatica. Most stands are intensively managed and thinned every five years. Mean distance between territories in continuous habitat averaged 1498 m (SD=892, N=110). Minimum distances between occupied nests were 270-472 m. Densities varied between 0.1 and 0.5 pairs per 100 ha woodland. Nests were found mainly in Beech trees (89% of N=175). Calculated laying date in 149 nests varied between 27 March and 21 May (Fig. 2), mean onset of laying was 15 April (SD=10.5). Probably most clutches that were started in May were repeat clutches. Complete clutches contained on average 3.82 eggs (SD=0.75, N=106). Clutch size decreased with laying date. In most cases the number of chicks was lower than clutch size, but it remained unclear whether this was a result of mortality of embryos or mortality of young. Successful nests fledged on average 2.92 young (SD=0.74, N=128). A negative correlation between laying date and number of fledglings per successful nest was partly explained by the seasonal decline in clutch size. The secondary sex ratio (10 or more days after birth) among chicks was 49.6% males (N=383) and not significantly different from 1. Sex ratio was not related to laying date, clutch size or brood size. Age differences between chicks within a brood, estimated from wing length, were limited (for the first four chicks, 0.4, 0.9 and 1.8 days respectively), hardly increased with age (Fig. 3) and were not influenced by laying date. Male nestlings were heavier than females, on average 30 g (12%) at fledging (Fig. 4). When corrected for sex and age, weight differences among chicks were larger between than within broods, but first-born chicks were up to 5% heavier than their later born siblings. In broods from which no or only one young fledged, young were in poorer condition than in broods fledging 2-4 chicks . Chicks in early-laid clutches were heavier than those in late ones (Fig. 5). In 103 breeding attempts, mean daily survival rate was 0.9943 (SE=0.0015), resulting in a nest success over 43 days of 78% (69-89%). Failures during incubation were due to usurpation by Jackdaw Corvus monedula (1×), hatching failure (1×), and (probable) predation (8×). In one fresh nest in a live Douglas Fir, the eggs probably were inadvertently removed by the inhabitants after becoming stuck to its plumage due to raisin leaking from the nest entrance. During the breeding stage chicks were deserted, possibly due to death of one or both parents (4×), became hypothermal by incoming rainwater (2×), drowned in the cavity after severe rainfall (7×), or were (probably) predated (7×). With on average 69-89% successful breeding attempts and 2.8-3.0 young per successful attempt, Dutch Black Woodpeckers produced 2.0-2.6 young per pair annually (95%- c.l.). This resulted in a stable population during the study period. The reproduction figures and density of breeding pairs from The Netherlands are not in contrast with figures from other European countries. Apparently the Black Woodpecker has not been hampered by the young age of trees, the plantation of exotic tree species and intensive harvesting of timber in Dutch forests.

[pdf only for members] [dutch summary]