Food Size, Energy Intake and Nutrient Intake of Nestling Tits, Parus varius and Parus major

The feeding rate, food size, energy intake and nutrient intake were studied for nestlings of the Varied Tit (Parus varius) and the Great Tit (Parus major) living in evergreen broad-leaved forest in Minamata, southern Kyushu, Japan. The frequency of daily feeding visit was around 100 times for both species. The diets of the two species were similar in general; feeding on lepidopteran larvae, moths, spiders and Orthoptera. The Varied Tit preferred much smaller prey than the Great Tit. The energy ingested was not so different, but the assimilation rate of the Varied Tit was lower because of feeding on many prey items with hard body parts like moths, spiders and Orthoptera. Assimilated energy was almost the same for the two species. Nutrient analysis revealed that lepidopteran larvae contain less nitrogen than other prey items. The Varied Tit ingested more nitrogen than the Great Tit. The difference in quality of foods may correspond to that of clutch size between the two species.