Untersuchungen zum Nahrungseintrag von Kohlmeisen in einem Gradationsgebiet der Kleinen Fichtenblattwespe (Pristiphora abietina Christ)

Using a modern data survey system combined with a videocamera for observation, it was possible to determine the percentage of sawfly larvac in breeding food of titmouse (Parus major) without disturbing the birds. The activities of a titmouse pair in a spruce stand, located in southeast Bavaria and seriously damaged by spruce sawfly, were observed during the whole breeding period. Spruce sawfly larvae were used as breeding food preferably at 4th larvae instar or later. Since larvae of this instar were available, they dominated the insects used as breeding food with more than 70%. During the most intensive feeding period nearly 500 sawfly larvae per day were used as food. The consumption of sawfly larvae during the whole feeding period added up to a total of more than 5000 larvae. The birds can not significantly reduce the sawfly density in heavily attacked stands. This can be shown in a simple calculation: there had been 11 titmouse pairs per hectar. They used appr. 55000 old larvae for breeding food. This represents appr. 15% of the estimated number of old sawfly larvae per hectar. But in a low density area an insect-feeding songbird population may possibly hinder a serious increase in the sawfly population.