A TWELVE‐MONTH FIELD STUDY OF THE ALDABRAN FODY FOUDIA EMINENTISSIMA ALDABRANA

Abstract

SummaryThe Aldabran Fody Foudia eminentissima aldabrana was studied for 12 months on West Island, Aldabra atoll. A complete annual cycle was followed in detail in a small population of marked birds, and observations were made on feeding, courtship, breeding and other behaviour. The breeding season coincided closely with the wet season, when insect abundance was highest.Although coconut palms and casuarina trees are both thought to have been introduced into Aldabra by man, the fodies preferred both of these trees as nest‐sites to the native vegetation. It is suggested that this may be a recent preference, resulting from excessive predation by introduced rats Rattas rattus on nests in other sites.In addition to insects and seeds, the Aldabran Fody feeds partly on nectar, and its tongue shows some degree of adaptation to a nectar diet. It is argued that the diversity in bill shape in Foudia cannot be interpreted simply in terms of adaptation for feeding on insects or seeds, but that all three elements in the diet must be considered, in conjunction with the presence or absence of possible competitors.Adult males defend and maintain nesting territories for most of the year. After breeding, they undergo a full moult and assume an eclipse (female‐type) plumage for a variable length of time, regaining the male breeding plumage after a partial prenuptial moult. A small number of males were found to be aberrant, the red in the plumage being replaced by golden yellow. One such bird showed defective territorial behaviour, and four that were dissected Jacked gonads.In almost all ways the behaviour and reproductive patterns of the Aldabran Fody are very similar to those of the Madagascar Fody F. madagascariensis. The latter has been introduced onto many Indian Ocean islands, and in view of its similarities to the Aldabran Fody might well be a serious competitor if it were to be introduced onto Aldabra.