BIJLSMA RG (1980) The influence of predation on the breeding results of the Woodpigeon Columba palumbus on the Southwest-. LIMOSA 53 (1): 11-19.

This paper contains supplementary information to an earlier publication on the breeding biology of the Woodpigeon on the Southwest-Veluwe (Bijlsma 1978). During 1978 information was gathered in three woodland-plots and one gardencity-plot (totalling 3.99 ha) with regards to the extent of predation and its influence on the breeding results of Woodpigeons.
      The plots were systematically checked from March up to and including November. Extensive information is given on how to recognize and identify different predators by means of damaged eggs (fig. 1), remains of nestlings, excrements, moulted fealthers and so on. Some difficulties are pointed out.
      Egg-laying lasted from the end of March to the middle of November and was bimodal in occurrence (fig. 2). The late egg-production in October and November probably resulted from the predominantly cold and wet summer of 1978. Hatching success was very low (x=38.7%) and so was breeding success (x=27.6%) (tab. 1). Most nestlings fledged during September and October (68.8%, n=90).
      Breeding Woodpigeons were exposed to severe predation. Of 162 clutches started only 45 resulted in fledglings. Of 99 cases in which the cause of failure could be established, 82.8% was due to predation. The major part of breeding attempts failed during the egg-stage (tab. 1, 3). Jay, Magpie and Squirrel were responsible for most destruction (tab. 3).
      Predation was heaviest during May to August and coincided with the period during which unguarded nests were most often found, probably a result of foodshortage (tab. 4). High densities of breeding Woodpigeons resulted in the development of a searching image among predators. On average twice an hour Jays purposeful searched breeding places of Woodpigeons (tab. 5). The method used during these visits is visualized in figure 3. From a fixed starting point the Jay followed a more or less fixed, anti-clockwise route. If a nest was robbed, the immediate vicinity was carefully checked after which the usual route was taken up again (see 10.42 u in fig. 3). The next visit the Jay flew straight to the place where the previous visit the nest was robbed. The mean distance covered during a visit was 40 m (n=4, variation= 25-47). At regular intervals (x=2.6 m, n=4, variation = 1-7) stops were inserted (x= 16 stops, n=4, variation= 12-19). The stopping places were used to search for unguarded nests. The searching height fluctuated between 6-9 m (fig. 3) and corresponded exactly with the height of most Woodpigeon nests in coniferous woodland (x=7.5 m, n=647, sd=2.66; Bijlsma 1978).
      Breeding success was inversily related to breeding density, especially as a result of increasing predation (tab. 6). Low breeding success was compensated by more breeding attempts and consequently the average number of fledglings per pair per year hardly differed between Woodpigeons breeding at high or low densities. In all, average annual production (2.2 fledglings per pair) was amply sufficient to replace adult mortality (tab. 7). Mortality through predation of eggs and nestlings is evidently unimportant as a factor regulating population size. In fact, high breeding densities of Woodpigeons on the Southwest Veluwe (4792 territories on II 780 ha) coincided with a dense and variable predatory population (tab. 2). After House Sparrow and Blackbird, the Woodpigeon is the most common breeding bird on the Southwest-Veluwe and much more common in woodland (x= 88.0 territories per 100 ha) than in built-up areas (x= 39.4 territories per 100 ha)despite the fact that by far the most predators are found in woodland. Common Wood Pigeon Columba palumbus

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