The ecology of a temperate bird introduced to a tropical environment : the house sparrow, Passer domesticus (L.) in Townsville, North Queensland

Abstract

The ecology of the house sparrow Passer domesticus (L.) was studied in Townsville in order to examine behavioural, population and morphological changes in temperate bird species adapting to tropical climates. A study of geographic variation in Australian house sparrows was also conducted. House sparrows in Townsville used communal roosts for the full period of study rather than deserting them in autumn and winter. Roosts in Townsville contained smaller numbers of birds than those in temperate areas. Birds left the roost at sunrise and flew to feeding areas for the day, returning just before sunset. The times of departure and return varied seasonally. The proportion of juvenile ( "snco") birds in the population was similar to that in temperate locations in May and decreased over the year because of mortality, dispersal and ossification of the skull. The sex ratio did not differ from parity over the study period, though males always made up 50 to 60 per cent of the population. The population under study decreased in size by two-thirds from March to October. The diet of house sparrows in Townsville included animal food for a longer period of the year than it does in temperate areas because of the longer availability of insects. Insects were captured by active searching of leaves, by flycatching and by collection from cobwebs. Testicular recrudescence occurred from March to May and nest-sites were established and nests built at this time. In June, regression of the testes occurred as temperatures reached their minimum levels. Reproductive activity commenced again in July and the breeding season began in September. Because of the timing of the project, insufficient breeding data could be obtained to allow breeding parameters to be calculated for Townsville populations. Temperate Australian populations breed from October to January; their average clutch-size is 4, of which 3 survive to fledgling stage. Relative to that in house sparrows of temperate localities, seasonal variation in body weight in Australian house sparrows was reduced, as was seasonal variation in bill length. Significant geographic variation was found in body weight, male wing length and male tail length. Intrapopulation variability was similar to that in European and North American populations. Interpopulation variability in Australia was similar to that found in North America, though it was less than that found in England. Sexual dimorphism in size increased from south to north in the samples collected. There was no geographic variation in variance of bill length. Show more