Foerageergedrag van een paartje Grauwe Klauwier Lanius collurio in Noord-Drenthe

During incubation and probably during the early nestling stage, only the male of a pair of Red-Backed Shrikes was recorded hunting. Although its home range covered 26 ha of mixed farmland with hedges and ditches, most of its hunting activities were restricted to only 4.8 ha of linear vegetation strips with a length of 500 and 300 m respectively. The male hunted mainly from poles, with 92.4% of all forays directed towards the ground and only 7.6% being pursuits of flying insects. Most hunting during the incubation took place away from the nest This behaviour changed after 10 July, apparently following nesting failure. After this dale, the male was seen hunting in the vicinity of the nest. When hunting actively, the male on average attempted to catch prey once every 49 seconds (566 catching attempts scored, SD=58 sec, range 4-548 sec), i.e. 122 catching attempts per 100 minutes. Calculated for an observation period of 1518 minutes, the catching attempts averaged 37 per 100 minutes. During 26 June through 10 July, probably coinciding with the incubation period, the male provided his partner on average with one prey item per 19 minutes, i.e. 5.3 preys/100 min. The female was first seen on 11 July; she remained relatively inactive throughout the observation period, and was intermittently fed by the male (instigated by begging behaviour with shivering wings and opened bill). At the end of July, both birds disappeared; the lopsided empty nest was found at a height of 2 m in a Crataegus monogyna. Very few prey items could be identified, partly because many preys were captured out of sight on the slopes of a ditch and probably also because of the small size of the majority of prey items. Identified prey, as observed when brought to the nest, impaled on barbed wire and in a pellet (Table 1), mainly consisted of small beetles, caterpillars and leather]ackets. It is thought that present-day farmland in Drenthe may still provide many suitable breeding sites, but is lacking in a varied and thriving insect life. Therefore, large numbers of breeding pairs (such as in Bargerveen in SE-Drenthe, where up to 125 pairs were located in 1994) only occur in nature reserves with a rich supply of insects.