Abstract for presentation at Biodiversity Extinction Crisis Conference - A Pacific Response

In recent decades many species of seed-eating birds have declined across the tropical savannas. This is puzzling, because the dominant land use in the savannas is relatively low intensity pastoralism, and the landscape looks superficially intact. However, seed-eaters rely on a succession of different grass species throughout the year, and the grazing, feral animals, weeds and altered fire patterns that accompany pastoralism have the potential to change the overall grass species composition of savannas as well as seed yields in key grass species.

To help design better land management strategies for this guild, we investigated how pastoralism affects seed-eating birds by monitoring the seasonal health patterns of several finch species in areas of Mornington Wildlife Sanctuary (Central Kimberley) with different fire and grazing histories. We also used telemetry to follow the ranging behaviour of two species – Gouldian finches and Long-tailed finches - to determine which grasses they feed on and how far they flew to find them.

We found that spinifex seed was a crucial food resource for finches in the early wet season, a time when few other grasses are seeding. However, since spinifex typically needs 3 fire-free years before it sets seed, finch populations living in areas with frequent fires may face a period of severe food shortage. In support of this, the haematocrit and haemoglobin concentrations of finches living in areas with frequent extensive fires was significantly lower during the early wet than that of finches living in areas with infrequent, small fires. Large areas of northern Australia are burning at 2-3 year intervals. This may reduce the availability of spinifex seed across the landscape and explain the widespread declines of seed–eating birds. These results have implications for fire management across the tropical savannas, stressing the importance of maintaining areas of old-growth spinifex across the landscape.