Nesting Biology, Seasonality, and Mating System of Malaysian Fantail Warblers

Abstract

The breeding biology of Fantail Warblers (Cisticola juncidis) in a rice field in northwestern peninsular Malaysia was studied. Data were collected on 38 nests found in rice plants on the 15-ha study area. Clutch size was three or four, incubation lasted 10-14 days, and fledging occurred 14-15 days after hatching. Two breeding seasons occurred annually, January-March and June-September, coinciding with the availability of suitable rice field nesting cover. The presence of several closely spaced, simultaneously active nests on plots occupied by single male birds indicated a polygynous mating system. This was based on the ability of some males to monopolize the limited available nesting habitat early in the rice-growing cycle. These findings differ from those of previous studies, presumably because of differences in the habitat types and mating systems examined. The Fantail Warbler (Cisticola juncidis) is a small sylviid widely distributed in tropical and temperate parts of Europe, Africa, Asia, and Australia. It chiefly inhabits wet grassy areas and rice fields and is rather secretive except during the breeding season when males perform conspicuous aerial displays (Lynes 1930, Givens and Hitchcock 1953). Recent studies in Japan (Motai 1973), France (Robert and Bellard 1975), and Australia (Ey 1977) indicate that the species may be regularly polygynous throughout a substantial part of its range. In this paper, I present results of a study of the nesting biology and mating system of the Fantail Warbler in a Malaysian rice field environment. This research was part of an investigation of the influence of rice cultivation on the breeding seasonality of certain common rice field birds (Avery 1980), and it is the first detailed account of Fantail Warbler breeding biology from the Malayan region since Gibson-Hill's (1950) study, which was conducted on Singapore during the mid-1940's. STUDY AREA AND METHODS The study area consisted of 15 ha of experimental rice fields at the Rice Research Center of the Malaysian Agricultural Research and Development Institute at Bumbong Lima, Northern Province Wellesley (5033'N, 100028'E). The fields were irrigated, and two crops of rice were harvested annually in March-April and September-October. The study period was June 1975-March 1977. Most nests were found by observing the movements of adult birds carrying nest material or food. Other nests were pointed out to me by field workers. I visit6d each nest site every second or third day and recorded the number of eggs or young and the presence or absence of adults. Several nests were observed using a spotting scope in order to monitor the foraging activity of female birds. Boundaries between breeding territories were estimated by observing encounters between males during aerial displays. I distinguished sexes of adult birds by plumage differences (Chasen 1939) and behavioral traits (during the breeding season, males make extended song flights whereas females make brief, low, usually silent flights). Recently fledged birds were easily distinguished from adults by the yellow wash on the pale feathers of the breast and abdomen. Throughout the study, I mist-netted and banded birds, but did ot uniquely mark them for sight identification. Thus, individual recognition in the field was not possible. Field counts of birds on the study area were made an average of three times weekly to obtain an indication of population levels.