Birds in the heath. (journal extracts).
Interestingly, though, heathlands are patchily distributed in nature, often forming part of a larger mosaic also containing sedgeland, wetlands, open woodland and forest.
Could animals that have evolved in heathlands be pre-adapted for survival in patches of habitat, or are such fragments of habitat a tenuous last foothold for wildlife?
Is there perhaps a progressive change in the bird community as habitat island size decreases or a distinct threshold size marked by an abrupt change in bird fauna?
Ecologists Tara Martin, of CSIRO Sustainable Ecosystems, and Carla Catterall, of Griffith University investigated the effects of fragmentation on heathland birds along the north coast of New South Wales.
They compared abundance and species composition of birds in residential suburbs, sugar cane crops and in four sizes of heathland remnants (1-2 ha, 5-10 ha, 20-50 ha, and more than 500 ha) during both summer and winter.
The overall effect of converting heathland to residential and cane habitat was a distinct change in species composition and reduced species richness.
Heathland remnants smaller than about 5 ha did not provide suitable habitat for many bird species that are known as `natural-vegetation-dependent' species, but they did seem to suit birds that are more characteristic of open or developed lands.
At the other extreme, remnants greater than 500 ha in area, containing several species of nectar-rich banksias, supported many species, and high densities, of typical heathland and bushland birds. The scientists concluded that many heathland bird species manage to persist in habitat fragments as small as 5 ha or so, but that this depends heavily on the state of the surrounding land.
Species such as the white-cheeked honeyeater and little wattle bird may be able to persist in small heathland remnants thanks to their habit of moving between suitable nectar-rich heathland patches, but sufficient remnant patches need to exist in the region for this island hopping to occur.
Residential and agricultural activities in surrounding areas can also lead to altered fire regimes, nutrient influxes from fertiliser use, weed invasions and towering of water tables due to drainage.
These factors are Likely to gradually change the vegetation in smaller heathland remnants and eventually render them unsuitable for heathland birds.
Martin TG and Catterall CP (2001) Do fragmented coastal heathlands have habitat value to birds in eastern Australia? Wildlife Research, 28:17-31.
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|Article Type:||Brief Article|
|Date:||Jul 1, 2001|
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