Summary Settlement date, mating status, and breeding success of individually marked great reed warblers, Acrocephalus arundinaceus, were studied during the 1980–84 breeding seasons in Kahokugata, Ishikawa Prefecture, Japan. Twenty‐five per cent of the territorial males were polygynous, of which the majority were bigamous. The settling periods of both sexes were long, extending for 65 days in males and 49 days in females. About 80% of males and females settled in the first half of the settling period, and the settlement date of 28–54% males overlapped with that of females. Many of the late settlers were bachelors and the males which mated earlier tended to be polygynous. The timing of a male's settlement is important in acquiring mates. Fifty‐five per cent of eggs laid were lost before fledging, mainly due to predation. The mean number of fledglings was 3.19 per primary female, 2.41 per secondary female, and 2.80 per monogamous female. Comparison of the number of fledglings of females which mated during the same period showed that the presence of another female in the same territory did not adversely affect the breeding success of either of the polygynous females. Polygynous males have the advantage of decreasing the risk of breeding failure under high predation pressure.

The social system of the Rufous Vanga Schetba rufa was studied in a deciduous dry forest in Ampijoroa, western Madagascar. The species lived in groups of two to four individuals. Groups typically contained one adult female, one or two adult males and sometimes a (presumed) immature. All group members appeared to defend the territory. The presumed immatures had spotted throats and were smaller than adults in body size. They helped feed young and guard the nest but did not incubate or brood.

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ku. Osak(4 j j X . ltiptiri In a population of'the Great Reed Warbler Arroc~~pliirius arirrrilirirrc.c~irs in central Japan 3 3 cascs of m a t e desertion by males were recorded during eight breeding seasons. Thirty of these occurred at the e n d of the breeding season. The absence of t h e male parent during t h e nestling period affected neither the frequency of'nestling starvation nor the return of I'emales. Eight deserters were confirnied to have begun moulting prior to the fledging o f their young. Males which had abandoned their territory relatively early in t h e s u m m e r tended to settle earlier a n d to be polygynous t h e following spring. As earlier settling is an important factor influencing polygyny i n males. a n increased chance of early scttling the following season c a n be regarded as a long-term benefit of m a t e desertion.Mate desertion is defined as the termination of care by one parent of the offspring in a breeding attempt before the offspring are capable of independent living (after Fujioka I 989). In the Great Reed Warbler Acrur~pphulus trrurrdinuc.t,us. mate desertion takes the form of abandonment ofthe territory by the male. and occurs late in the breeding season when no opportunity exists for additional mating (Kzaki I y88). Based on a record that one deserting male had begun moulting while his mate was still feeding his nestlings. Ezaki ( I y 8 8 j speculated that an improved survival rate through early moulting might be the primary benefit promoting mate desertion. However. the survival of males was not followed and the study failed to demonstrate any effects of mate desertion or early moulting.In the course o f an 8-year study of the polygynous mating of the Great Reed Warbler (IJrano 1985. r y y o a . b). mate desertion by males was observed every breeding season. In this paper, I describe the seasonal pattern of the occurrence of mate desertion. I compare the breeding success of females whose mates disappeared with those whose mates were present, and examine whether the difference in the timing of' territory abandonment among males affects their survival or the timing of settlement the following spring.

This study compares the habitat use by three species of couas, the Crested Coua Coua cristata, Coquerel's Coua C. coquereli and the Red‐capped Coua C. rujiceps, in a dry forest at Ampijoroa, western Madagascar. The Crested Coua used higher layers (> 5 m) exclusively. Both Coquerel's and the Red‐capped Coua stayed mainly on the ground, but the former used middle layers (1–5 m) for inactive behaviour (including resting, preening and basking) and whistling more frequently than did the Red‐capped Coua. Both Coquerel's and the Red‐capped Coua foraged almost exclusively on the ground but differed slightly in feeding technique. The Red‐capped Coua took food on trails, relatively open areas in the forest, more frequently and more efficiently than Coquerel's Coua.

The male's role in feeding young and his effect on the mortality of eggs and nestlings of the Great Reed Warbler Acrocephalus arundinaceus were studied in Kahokugata, central Japan, during eight breeding seasons. Three potential costs of polygynous breeding for females were examined:(i) a reduction of male parental care per brood, (ii) an attraction of predators due to concentration of nests, and (iii) an increase of unfertilized eggs due to the reduced frequency of copulation per female. Only the first cost was found to occur:polygynous males fed their young, especially of their second broods, less frequently than monogamous ones. The lowered paternal feeding frequency, however, did not increase the mortality by starvation in second‐hatched broods. This was because the warm climate emancipated females from brooding and enabled them to compensate for the deficiency of feeding by males. The paper discusses possible roles of the staggering of the time of laying among harem mates and the shift of breeding status of females caused by nesting failure, in reducing potential costs of polygynous breeding for females.

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