A Contribution to the Breeding Ecology of Two Species of Euplectes (Bishop‐birds) in Tanganyika Territory

Abstract

Summary.Observations on the inter‐relationship of two species of Bishop‐bird (Euplectes hordeacea and E. nigroventris), breeding in association in Morogoro, eastern‐central Tanganyika Territory, are described, with particular reference to previous work by Lack (1) and the Moreaus (2) on the same species when nesting in different localities in N.E. Tanganyika. E. nigroventris began nesting about three weeks earlier than E. hordeacea, and both had a breeding season of about 3 1/2 months in 1938. The earlier breeding of E. nigroventris may be due to its readiness to use shorter herbage and poorer cover than E. hordeacea, but where both species nested in the same, though foreign, conditions of a patch of Ramie, E. hordeacea was still some three weeks later. The use of the Ramie by both species is inexplicable, as there were adjacent areas of suitable grasses which neither species used for nesting. The strong, almost shrubby growth of the Ramie, with its heavy foliage, formed a much denser and more impenetrable cover than the types of grasses generally used by Euplectes spp. It was useless for food, and provided no nesting material. In two cases where territories covered a part of the Ramie, but were largely in the pasture, the males abandoned the Ramie, in one case after having reared young there.Territories of E. nigroventris were variable and at first large, from 120 to 510 square yards, but the largest was later reduced to 300 square yards. Those of E. hordeacea were, with one exception, rather smaller than the smallest found by the Moreaus (2), but sufficiently constant and sufficiently near their figure to support their view that size of territory in this species is specific. Boundaries were generally rigidly kept between territories of the same species and between contiguous territories of the two species, particularly when near to nests. Parts of E. nigroventris territories were appropriated by male E. hordeacea about two‐thirds the way through the breeding season of the former. This agrees with the Moreaus' (2) observations on E. nigroventris. The size and the selection of the territory would appear to have no relation to the food supply (cf. (1) and (2)); this refers in particular to the area of foodless Ramie. In certain cases where territories were bounded by topographical features which separated them from ground useless for food or nesting, those features appeared to form a boundary to the territory.Although males drove off from their territories intruding males of either species, later in the season E. hordeacea appeared to show some tolerance towards intruding male E. nigroventris. Coliuspasser albonotatus nested in a territory of E. nigroventris and was generally tolerated by both species, as was C. ardens. Other species tolerated or attacked are mentioned. E. hordeacea. showed a marked preference for the tall‐growing Pennisetum purpureum, practically all of which was in E. hordeacea territories. The smaller E. nigroventris was content to use low‐growing shrubs and shorter, weaker grasses. It is considered that this characteristic of E. hordeacea is specific, notwithstanding that, in common with E. nigroventris, it nested for a time in a patch of Ramie introduced to the area, and unlike any local natural nesting habitat of Euplectes spp. E. nigroventris had an average incubation period of 19 days and fledging period of 13 1/2 days, compared with 18 and 11 days respectively for E. hordeacea. Twenty‐five per cent, of known nests with eggs were destroyed by unknown predators.