Comparative Study on the Breeding of Mainland and Island Subspecies of the Varied Tit, Parus Varius

Abstract

Comparisons on breeding ecology between Parus varius varius in mainland of Japan and P. v. owstoni in Izu Islands were studied using nest boxes from 1972 to 1975. The result obtained was as follows.1. Breeding season. Little difference was found in seasonal distribution of date of first egg laying in two subspecies. In both subspecies, earliest clutch was found in late March, and latest clutch was found in early or middle June. The first large peak in seasonal distribution was in early or middle April, and second rather indistinct peak was in late May (Fig. 2).The brood in which a first egg was laid before May 10 was called the early brood, and brood in which a first egg was laid on and after May 11 was called the late brood.2. Clutch size. The mean of clutch size was 6.2 in mainland subspecies (Fig. 3), and 3.9 in island subspecies (Fig. 4). The dif ference in clutch sizes seems to be closely related to difference of breeding density in two subspecies.3. Egg weight and nestling weight. Marked differences were found in egg and nestling weights, those in island subspecies being larger in correlation with adult body size (Table 2, Fig. 5).4. Incubation period and nestling period. The incubation period reckoned from date of completion of clutch to date of first hatching of young was hardly different in two subspecies, and mean was about 14 days in both subspecies (Table 3). The nestling period reckoned from date of first hatching of egg to date of first young to fly was a little longer in island subspecies. The mean was 18.3 days in mainland subspecies and 19.0 days in island subspecies (Table 4).5. Breeding success. In mainland subspecies, when losses from predation are included, about 75 per cent of eggs hatched successfully and about 80 per cent of them gave rise to flying young (Table 5). When losses from predation are excluded, over 95 per cent of eggs hatched successfully, and also over 95 per cent of them gave rise to young which left nest. In island subspecies, no losses by predation were observed probably because of absence of any snakes and Apodemus argenteus. Percent hatched was over 95%, and percent flying was also over 95% (Table 6). These values were not significantly different from those excluded losses from predation in mainland subspecies.6. Breeding density. The breeding density in island subspecies was remarkably higher than that in mainland subspecies. The number of pairs per 1 km. was five to six in mainland subspecies, and ten to fifteen in island subspecies (Table 7).