The Food of Titmice in Oak Woodland

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Abstract
The possible competition for food between the great and blue tit (Parus major and P. caeruleus) in oak woodland, and their relationships with the coal and marsh tit (P. ater and P. palustris), was studied by gizzard analyses. There is little similarity in the diets of the great and blue tits, the great tit taking mainly adult insects, especially weevils, the blue tit mainly scale insects and small larvae and pupae. The coal tit prefers small free-living insects, and scales. The diet of the marsh tit consists of adult insects, scales and some larvae. Spiders form a small proportion of the diet of all four spp. The great and marsh tits feed more on seeds and nuts than do the other spp., and oak bud and gall tissue are found in large quantities only in the blue tit. An analysis of the insect food shows the great tit as largely a ground feeder, except in the breeding season, while the blue tit feeds mainly on oak twigs, buds and leaves. The coal tit prefers insects from trunks and branches, while the marsh tit feeds both on the ground and in the canopy. Beaks of the titmice are adapted to the size and types of foods taken, enabling all four spp. to feed in the same places without necessarily competing for food. Nestling foods of great tits and of blue tits reflect the differences in the type and size of foods selected by the adults. Caterpillars are taken by both spp., but pupae extracted from curled leaves form a much greater proportion of the diet of the blue than of the great tits. Adult insects, forming 19% of the great tit nestling food, are not taken for the young by the blue tit. Both spp. feed spiders, crushed snails and grit to the young. Most of the food items brought to the young blue tits measure under 10 mm, to the great tits over this length. Measurements of the caterpillar and titmouse populations in a nest-boxed area and in an adjoining unboxed control area in 1950 and 1951 showed a predation rate by titmice on all defoliating caterpillars in the boxed area of about 1.4% in 1950, 4.8% in 1951, while in the control area it was 0.9% in 1950, 3.2% in 1951. Winter moth (Operophtera brumata). larvae removed by titmice in the two years in the nest-boxed area was 0.5% in 1950, 2.6% in 1951, and in the control area 0.3% in 1950, 1.7% in 1951. In both years the caterpillar population was relatively low compared with the 1949 population. In the winter of 1950-51 the estimated predation rate by titmice on the female winter moths might have been about 20% in both areas. This predation on the moth population may be affected by climatic conditions, and by the abundance of alternative food spp.

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