Ecology of the black flying fox, Pteropus alecto, in the seasonal tropics of the Northern Territory: resource tracking in a landscape mosaic and role in seed dispersal

摘要

Radio telemetry was used to investigate roosting and movement patterns of the black flying fox (Pteropus alecto) in the seasonal tropics of the Northern Territory. Sixteen P. alecto were tracked during a 12 month period to 34 roosts and were recorded at 49 foraging sites. Pteropus alecto moved roosts seasonally, from bamboo and mangrove habitats in the dry season to rainforest in the wet season. All radio-collared male and female P. alecto roosted in rainforest during the major part of the wet season. Climatic influences may be responsible for this behaviour with rainforest perhaps providing stable temperatures and shelter from the monsoonal rains. There was a significant seasonal difference in the distances moved by females between successive roosts. There was an association between roosting and foraging habitat: P. alecto roosting in bamboo and mangroves foraged predominantly in woodland, P. alecto roosting in rainforest foraged in Melaleuca spp and rainforest habitat. Females covered greater distances from roosts to foraging locations than did males. Distances from roosts to foraging sites were reduced for males and females during the build-up season (September to November) and wet season (December to April). Seasonally, foraging habitat shifted both floristically and spatially with no significant difference between the sexes. The movements of one female P. alecto were recorded at hourly intervals over three consecutive nights at the beginning of the wet season. Movement patterns were very similar between nights and over these three nights she foraged in at least 7 distinct locations. The total distance moved per night was 15.5 km to 19.9 km including return distance to the roost, assuming straight line movements. Most foraging was done less than 6 km from the roost. The ratio of total distance moved with respect to mean roost to forage site distance was similar between nights (3.8- 4.3), suggesting that a single roost site to forage site distance recorded during this study can provide an index of total foraging distance. Radio-collared animals selected foraging sites that were richer in flower or fruit resources when compared to floristically similar sites. Pteropus alecto moved throughout the landscape in response to the flowering and fruiting of a number of plant species in different habitats. Pteropus alecto foraged only in canopy or emergent trees and foraged on the flowers and fruit from 23 species in 11 families. It appears that P. alecto has sophisticated strategies for tracking the availability of patchy resources that occur in reasonably high densities. The likely probability of ingested seeds being dispersed between rainforest patches was assessed. When gut transit time for seeds, wet season distances and movement patterns for radio-collared P. alecto are incorporated into a seed dispersal model, it becomes evident that P. alecto is an important disperser of seeds between different rainforest patches. Pteropus alecto roosted or foraged in six major habitat types in the study area suggesting a flexible strategy for exploiting patchily distributed resources in the seasonal tropics of northern Australia. Land tenure status identified for foraging and roosting positions recorded for P. alecto emphasises the lack of protection for habitats used by this species. Only 3% of foraging or roosting positions were recorded in any type of conservation reserve. Pteropus alecto requires a range of habitats over a large area for roosting and foraging requirements. No matter how well placed conservation reserves are, P. alecto will be substantially dependent on differing types of off-reserve land. Therefore, we need to develop and implement off-reserve land management practices that take into account P.alectou27s seasonally distinctive and sometimes contrasting requirements for roosting and foraging habitat.