A comparative study of the Grey-headed Sparrow (Passer griseus L) and the House Sparrow (Passer domesticus L) in Malawi

摘要

The House Sparrow Passer domesticus, an introduced species, and the Grey-headed Sparrow Passer griseus, an indigenous species, are sympatric in Malawi. Their distribution in the country and any possible interactions were studied, principally in southern Malawi. A morphological analysis of museum specimens confirmed that grey-headed sparrows in Malawi belong to the Northern Grey-headed Sparrow Passer griseus as distinct from the Southern Grey-headed Sparrow Passer diffusus. This species was widely distributed in the, country in association with human dwellings, both in rural areas as well as urban centres. In the northern region Greyheaded Sparrows were more abundant in the urban centres than rural areas, but in the central and southern regions numbers in the rural and urban areas were more or less the same. In Blantyre City, where they are in sympatry with the House Sparrow, they were found in the low density and industrial areas and were absent from the high density areas. The House Sparrow, arrived in Malawi in 1967 at Chileka in the southern region. Since then it has spread northwards, moving from the southern to the central and northern regions. House Sparrow numbers were found to be progressively larger in the southern region and lowest in the northern region. House Sparrows were found at sites where food was readily available, as in the immediate vicinity of houses. In the central and northern regions they were restricted mainly to urban areas. In the southern region, they occur both in rural and urban areas, probably as a reflection of the larger period of colonization in the south. In the northern region their movement has apparently been restricted by geographical barriers. In Blantyre City Grey-headed Sparrows preferred areas where tree density was high and house density was low, while House Sparrows preferred areas where house density was high and tree density was low. There was a positive correlation between Greyheaded Sparrow numbers and tree density and a negative correlation with house density. House Sparrow abundance was negatively correlated with tree density and positively correlated with house density. Grey-headed Sparrows bred in the rainy season, whereas House Sparrows bred throughout the year. There were differences in nest site selection: Grey-headed Sparrows used artificial structures such as fencing poles, and wooden telephone or electricity poles. The House Sparrow used mostly buildings and nested in crevices, holes in walls and between the walls and rafters. Nest height also differed- Grey-headed Sparrows nested at heights ranging from 1 - 8 m while House Sparrow nests were at heights of 1 - 5 m. Moult data suggests that although the House Sparrows breed throughout the year, they moult at a particular time of the year when breeding is less common. Grey-headed Sparrows were found to moult mainly from May to September in southern Africa and from June to September in central Africa. In both cases the breeding season extends over a similar period from about October to April/May of the following year. Peak moult periods differed between the House Sparrows and Grey-headed Sparrows. House Sparrows moulted mainly in the first half of the year, and Greyheaded Sparrows in the second six months. The clutch sizes of the two species were similar (mean 3.9 eggs for the House Sparrow and 3.4 for the Grey-headed Sparrow). The clutch size of the House Sparrow varied seasonally and was larger from November to May. The average incubation period for the House Sparrow was 11.5 days and the fledging period 15.4 days. The Grey-headed Sparrow fledging period was 14.7 days. Chick mortality of the House Sparrow at Chikunda farm was attributed to starvation resulting from brood reduction, abandonment, predation, low birth weight, accidental deaths and parasitism by fly larvae. Both Grey-headed and House Sparrows fed their young on insect food. Male House Sparrows fed actively initially, but their contribution declined from about day five onwards. In the Grey-headed Sparrow, both parents fed their young equally throughout the nestling period. House Sparrows fed on the ground near houses; Grey-headed Sparrows fed both on the ground away from houses and in tree canopies. The Grey-headed Sparrow walked as it fed on the ground as opposed to the House sparrow which hopped. Grey-headed Sparrows fed mainly as pairs and singletons while House Sparrows fed as family groups. Larger feeding groups of Grey-headed Sparrows were seen in the northern region at areas where food was plentiful. Where the two sparrows were seen feeding together, there was no direct competition for food. Where individual distance was violated; male House Sparrows displaced Grey-headed Sparrows which landed too close to them. Overall it appears that the distribution of the two species is determined more by their responses to habitat conditions than by interspecific interactions.