Grote Bonte Spechten Dendrocopos major in Drentse lariksen in de nawinter van 1996/97
Drentse vogels , Volume 10 - Issue 1 p. 66- 70
In January 1997, habitat choice and feeding ecology of Great Spotted Woodpeckers was studied in Central Drenthe in a woodland consisting mainly of Scots pine and Japanese larch (Table 1). Densities in mixed Scots pine/oak remained stable during February and March, but steeply declined in larch (Table 2). This decline was accompanied by an increasing frequency of drumming (as in Scots pine)(Table 2). Birds collected cones of Scots pine and larch, and took these to anvils for seed extraction. Anvils in larch were mostly c. 20 m high in trees. On average 70 sec elapsed between leaving the anvil and returning with a new larch cone (N=T0, SD=34.5). Larch cones were collected at distances of 5-40 m from the anvil, with an average distance of 13 m (SD=1I.4, N=14). It took on average 228 sec to extract seeds from larch cones (SD=99.0, N=14, range = 125-401 sec). Remarkably, woodpeckers ignored larch trees with a high cone density, presumably because the number of seeds per cone in such trees was less than half the number of seeds in cones of larches with a smaller cone density. This large difference in seeds per cone was thought to have evolved from Siskin predation on seeds in larches with a high cone density (see Larch 1 in Table 3). Cones handled by Siskins could be recognised by the nick on the cone scales. Woodpeckers extracted most or all of the seeds of cones, especially in Scots pine (Table 3). Apparently, only larch experienced an influx of Great Spotted Woodpeckers in winter. This was due to the fact that larches had good cone crop in 1996/97. It is calculated that, in order to satisfy the daily energy intake of 8 grammes of seed, woodpeckers had to forage for 4 hours and 25 minutes in larch (based on 334 larch seeds/gram, 54.7 full seeds per cone, 70 seconds of collecting time/cone and 227 seconds of handling time/cone), against 5 hours and 10 minutes in Scots pine (30.9 full seeds/cone, estimated collecting time of 1-2 minutes, average handling time of 5 minutes/cone; cf Glutz von Blotzheim & Bauer 1980). Foraging in larch was therefore a profitable option for non-territorial woodpeckers in the winter of 1996/97.
|551780.jpg Cover Image , 9kb|