De postduif Columba livia als prooi van de Havik Accipiter gentilis in de duinen van Noord-Holland

During 1995 through 2001, Northern Goshawks more than doubled in breeding numbers (5 in 1995, 11 in 2001; Table 1) in the study area of 7400 ha in the dunes between Egmond aan Zee and Camperduin (province of Noord-Holland, cf. Figure 1 for location of study site). The trend showed a tendency to level off in later years. Nest sites and roosts were regularly visited during the breeding season to monitor breeding success, and to collect prey remains. A qualitative overview of prey species found in the study area is given in Table 2. Goshawks mostly preyed upon birds varying in weight between 70 and 500 g, especially woodpigeons, racing pigeons, jays and carrion crows. Special attention was paid to find rings of racing pigeons (and other birds) underneath nests and roosting sites, and in pellets (Table 1). In August 2001, all Goshawk nest sites and roosts in the study area were also systematically checked with a metal detector. The information on the rings was used to identify and age the pigeons, and to trace their origin. In 1999, almost 1.7 million rings were distributed among pigeon fanciers in The Netherlands to band newborn nestlings. One Goshawk pair apparently did not capture racing pigeons; the other pairs did with varying frequency. Over 1995-2001, 465 rings of racing pigeons found as Goshawk prey in the dunes of Noord-Holland showed a clear pattern: 81 % of the birds had overflown their destination and could therefore be categorised as “lost” (Fig. 1). The remaining birds were probably captured while still heading for the loft. The origin of the killed pigeons is depicted in Table 3 (Dutch birds) and Table 4 (foreign birds). The most distant pigeon, from Northern Ireland, was about 1000 km away from home. Very few pigeons originated from fanciers in the nearby villages of Bergen and Egmond aan de Hoef/Zee, where 908 respectively 1378 rings were distributed among fanciers in 1999. Only 24 pigeons from these villages were found among the pigeons captured by Goshawks in the nearby dunes, which is on average less than 0.1% of the annual numbers available (Table 5). It is concluded that during the breeding season Goshawks are only a minor threat to pigeons in nearby lofts, and that mostly pigeons astray are taken. Of 436 age-identified racing pigeons, 56% was in their first year of life, 24% in their second year, and 20% in their third year or older (Table 6). The oldest pigeon killed was in its thirteenth year of life. This age-distribution is consistent with findings in several other studies in The Netherlands and abroad, although some outliers were recorded (Table 7). A local pigeon fancier estimated the age-distribution of pigeons used for racing at 50% in their first year of life, 40% in their second year and 10% in their third year. It is unknown whether this ratio is applicable to racing strategies of pigeon fanciers in general. It remains therefore to be seen whether Goshawks preferentially select first-year, relatively inexperienced racing pigeons as prey.