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Predation of artificial ground nests in Australian tropical savannas: inverse edge effects
Fiona J.
Fraser A C,
Peter J.
Whitehead B
A
Tropical Savannas Cooperative Research Centre and Parks and Wildlife Commission of the Northern Territory, Darwin, NT 0900, Australia; and Centre for Resources and Environmental Studies, Australian National University, Canberra, ACT 0200, Australia. Present address: Caring for Country Unit, Northern Land Council, PO Box 42921, Casuarina, NT 0811, Australia.
B
Key Centre for Tropical Wildlife Management, Northern Territory University, Darwin, NT 0909, Australia.
C
Corresponding author.
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Wildlife Research 32(4) 313–319 http://dx.doi.org/10.1071/WR04021
Submitted: 22 March 2004
Accepted: 19 April 2005
Published online: 5 July 2005
Abstract
Depredation of artificial ground nests was examined in tropical savanna in northern Australia to assess potential predation pressures on nests of the partridge pigeon (Geophaps smithii), a declining tropical granivore. Predation rates were examined at two sites, Kakadu National Park (which supported a relatively high density of partridge pigeons) and Berry Springs (which had greater habitat fragmentation and comparatively low partridge pigeon density). The effects of distance from road, understorey structure, topography and nest-microsite concealment on nest predation rates were examined. Artificial-nest predation rates were greater at 150 m from roads than <1 m from the roadside. Predation rates did not vary with understorey structure, topography, or level of nest concealment. There was marked variation between sites, with predation levels at Kakadu more than double those recorded for Berry Springs. Discerning predator identity, or even the size of a predator, from marks left in clay eggs proved difficult and was possible for ~35% of predation events. Of these, 42% of predation events involved predators of a size we considered too small to take a natural partridge pigeon nest. We suggest that extrapolation from artificial to natural ground-nest predation rates be undertaken with caution for landscapes such as Australia’s tropical savanna, which supports a high diversity and abundance of small potential predators of artificial nests. There was no evidence of predation by birds, and the methodology proved inadequate for identifying predation by feral cats (Felis catus).
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