Comparative Feeding Ecology of Two Geographical Forms of the Varied Tit, Parus varius varius in Southern Izu Peninsula and P. v. owstoni in Miyake I. of the Izu Is

Abstract

Comparative feeding ecology of two geographical forms of the Varied Tit, P. v. varius in southern Izu Peninsula and P. v. owstoni in Miyake I. of the Izu Is. was studied during April 1972 to March 1975. The main method of the observation was as follows. Feeding sites, foods, and feeding methods were divided into several types respectively, and the number of observations in each type was recorded while walking a regular course in a constant speed. The nature of the feeding activity recorded was that first seen. The observation was carried out in the same frequency every month. Then the observation rate (%) in each type was calculated and was tabulated later. The followings are the results.
1. Feeding sites. Both of P. v. varius in S. Izu and P. v. owstoni in Miyake tend to feed most often in the twigs and leaves at all seasons except winter. However, varius in S. Izu fed often in the uppermiddle layers of the forest, while owstoni in Miyake fed often in the middle-lower layers. Furthermore, owstoni in Miyake fed much more often on the ground, especially in winter, than did varius in S. Izu (Table 1, Table 2). These differences were thought to be partly due to the difference of the environments investigated (this was also based on the difference of the habitat preference), and partly to the difference of the food habits.
2. Feeding methods. Both of them used most often the hanging method and the flycatchings in getting nuts and berries, and used most often the hanging method in catching insects (Table 3). While eating, in both of them, nuts were held by both feet, and insects were held by one foot. Furthermore, the foot predominantly used in holding insects was almost determined in each bird in both subspecies. Therefore, in the feeding method, they showed the resembrances rather than the differences, and so this habit may be common to all populations of the species.
3. Foods. Foods of both forms were composed mainly of animals, such as insect larvae, in the breeding season. In winter, however, they fed more often on nuts and berries (Table 4 and Table 6). This disposition was remarkable in P. v. owstoni in Miyake I., and the form fed especially on the nuts of Castanopsis cuspidata. This higher dependence on that nuts in owstoni in Miyake I. was thought to be based on the ecological poverty of the island.
4. Storage of foods. This habit was observed in both form, but the frequency of observations was higher in P. v. owstoni in Miyake I., partly because of the easiness of observations. In owstoni in Miyake I., the store of foods could be observed during August to February, and the main foods stored were the nuts of Castanopsis cuspidata, and also Styrax japonica (Table 8). It was thought that almost all of the nuts of Castanopsis cuspidata ate in winter to spring were those stored in earlier periods. The storing behaviour was observed under capitivity in both forms, and this behaviour may be innate, because it could be seen in the hand-reared birds which were brought within a week after hatching and were kept in isolation from the adult birds.