Feeding strategies and food intake of Blackcaps (Sylvia atricapilla) consuming ripe or unripe fruits and insects | Ernährungsstrategien und Nahrungsaufnahme von Mönchsgrasmücken (Sylvia atricapilla) bei reifen oder unreifen Holunderbeeren sowie Insekten
2002
Schaefer, H. Martin (Hinrich Martin) | Schmidtt, Veronika
We compared the feeding behaviour of two groups of captive Blackcaps (Sylvia atricapilla) on a mixed diet consisting of an insect diet and ripe or unripe fruits. Unripe Black Elder (Sambucus nigra) fruits have lower nutritional values, especially for protein, than ripe fruits. We tested the non exclusive hypotheses that birds increase their food intake and/or their digestive efficiencies when feeding on the low quality resource of unripe fruits. Birds fed readily on unripe fruits even when the insect diet was providedad libitum. With respect to food intake, birds consuming unripe fruits always had a lower fruit intake and higher intake of the insect diet than birds feeding on ripe fruits. Thus, the intake of unripe fruits is constrained, probably owing to the accumulation of deterrent fruit compounds. When the insect diet was reduced to 45 % of the birds’ad libitum intake, individuals consuming unripe fruits lost 5 % body mass, while those consuming ripe fruits maintained constant body mass. The mean difference in daily gross caloric intake between the two groups was only 4 kJ. Differences in body mass development are explainable by the different digestibility of ripe and unripe fruits. At the same caloric gross intake, birds feeding for 12 days on unripe fruits lost less body mass (5 %) than birds feeding newly on unripe fruits (16 %). We suggest that an increase in digestive efficiencies of birds being accustomed to this diet causes the difference in body mass development.
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