BIJLSMA RG (1984) On the breeding association between Woodpigeons Columba palumbus and Hobbies Falco subbuteo. LIMOSA 57 (4): 133-139.

Eurasian Hobby Falco subbuteo Common Wood Pigeon Columba palumbus Breeding association between Woodpigeons and Hobbies is well known. It is widely thought that as a consequence of the fierceness of Hobbies, predators are kept away from the nesting area, thus enabling Woodpigeons to rear young in a relatively safe environment. However, neither the extent of the phenomenon nor a quantification of the breeding success has ever been given. Both questions are tackled in this paper, based on observations on Hobbies and Woodpigeons on the SW. Veluwe during 1975-78 (see also Bijlsma 1978, 1980a-c). In the study area Woodpigeons usually breed in den- 138 se stands of c. 20-40 years old Douglas Fir and Norway Spruce (tab. 1), with densities varying from 9.1 to 38.0 pairs/IO ha, and locally up to 180 pairs/lO ha. Breeding densities in Scots Pine are much lower (0.8-2.7 pairs/IO ha). Mean nest height is on an average 7.5 m (fig. 3). The breeding period extends from March to November, during which two peaks in egg production are found. Most Woodpigeons have nests with eggs during August and September (fig. 6a-c), when spilled grain provides an abundant food supply. In these months breeding success is highest (tab. 2). Hobbies prefer to breed in old nests of Carrion Crows in the upper third of Scots Pines in old, open stands (fig. 1, 2), with a mean nest height of 16.2 m (fig. 3). Egg-laying takes mainly place during the second half of May and the first decade of June (fig. 6e). In a radius of 50 m around the nests of 82 pairs of Hobbies I searched for occupied nests of Woodpigeons. In sum, 441 nests were found, giving a mean density of 68.5 pairs/l0 ha, which is extremely high for woods consisting mainly of mature Scots Pine. Nests were situated at considerable heights (x = 14 m), which sharply contrasted with the choice of non-associated Woodpigeons (fig. 3). As compared to the nests of Woodpigeons nesting in spruce, those of Woodpigeons associated with Hobbies appeared to be flimsy, hurriedly built structures. Nine out of 82 pairs of Hobbies were not surrounded by Woodpigeons, suggesting individual differences in the tolerance of Hobbies with respect to Woodpigeons. The number of nests sharply decreased with increasing distances from the nests of Hobbies (fig. 4). Eleven nests (2.5%) were situated in the same tree as the eyrie of the Hobby, with a minimum inter-nest distance of one metre. The number of nests of Woodpigeons per Hobby varied from 0-15 (fig. 5). On an average, 5.4 nests of Woodpigeons were found per Hobby nest. The Woodpigeons synchronized the onset of breeding with that of the Hobbies (fig. 6d-e). Woodpigeons waited with nestbuilding and laying until the Hobbies had definitely chosen their nest site and had started egg-laying. The time lapse between egg-laying of Hobbies and associated Woodpigeons was sometimes only a few days. The laying period of Woodpigeons nesting close to Hobbies was very restricted; repeat layings did not occur at the same breeding place when a brood failed half-way the breeding cycle. Association with Hobbies resulted in an improved breeding success as compared to that of Woodpigeons nesting under usual circumstances (72.8% and 36.3% respectively, tab. 2). Improvement of breeding success was due to reduced predation, which can be attributed to the aggressiveness of Hobbies towards predators. The most important cause of failure among Woodpigeons nesting close to Hobbies appeared to be strong winds, which may be disastrous for the unstable nests (tab. 3). It is evident that Woodpigeons benefit from the protection of Hobbies. On the contrary, there are no indications that Hobbies profit from the presence of breeding Woodpigeons

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