A particular case and a general pattern: hyperaggressive behaviour by one species may mediate avifaunal decreases in fragmented Australian forests

Abstract

2003. A particular case and a general pattern: hyperaggressive behaviour by one species may mediate avifaunal decreases in fragmented Australian forests. -Oikos 101: 602-614.We quantitatively assessed edge effects associated with elevated abundance of a hyper aggressive bird species, the noisy miner Manorina melanocephala, in fragmented eucalypt forest adjoining developed land. Long-term data from Toohey Forest, subtropical Australia, show that noisy miner colonies intensively occupy a zone of 20 m from the forest edge, with frequent use occurring up to 100 m from the edge, but little beyond 200 m. Within noisy miner colonies, the abundance and species richness of other birds were both about half those recorded at nearby transects which were outside the colonies' main activity area. Bird species smaller than noisy miners, which are also those with similar diets, were collectively 20 -25 times more abundant, and their species richness tenfold greater, outside miner colonies than within them, whereas larger species, which have less dietary overlap, did not differ. Exclusion of small insectivorous birds has been hypothesised to cause elevated insect herbivore density, but we found no difference between tree crown defoliation or dieback rates within versus outside miner colonies.Aggression by noisy miners can be viewed as a mechanism of interspecific competition, since miners have a relatively large body size for their diet and are hence able to exclude virtually all potential competitors at relatively little cost. We examine evidence indicating that reduced bird diversity in eucalypt forest fragments of eastern Australia is often simply the effect of noisy miner occupancy of edges, acting directly on the densities of other species through their aggressive behaviour. With an edge effect 200 m deep, a remnant 10 ha in size is likely to become entirely occupied by noisy miners, and this is a size threshold that has been commonly reported in association with area-standardised avian diversity reductions. Convergent patterns of species loss from small forest fragments in different continents are the result of different underlying ecological processes.

What is the role of trees and remnant vegetation in attracting people to urban parks?

“…Native ecosystems commonly remain or have been rehabilitated within and around Australian cities (Newton et al 2001;Bekessy et al 2012), and while many fauna species have declined or become extinct within these areas (Piper and Catterall 2003;Catterall 2009), many populations of native forest birds, mammals and plants still persist (Brady et al 2011;Moxham and Turner 2011;Shanahan et al 2011a, b;Daniels and Kirkpatrick 2012;Stagoll et al 2012). Thus, tree cover and remnant vegetation cover provide measures respectively of the greenness and the ecological value of parks.…”

Is landscape context important for riparian conservation? Birds in grassy woodland

“…3. With increasing intensity of the use of the wider landscape, the riparian bird assemblage will become less rich, the abundance of 'edge specialist' bird species such as noisy miners, Manorina melanocephala (Piper and Catterall, 2003), members of the family Corvidae and Artamidae , exotic birds and native generalist foragers will increase as will overall mean bird body size (Wiens et al, 1985). Conversely the abundance of small-bodied woodland/forest species will decline.…”

Abundance patterns across months and locations, and their differences between migrant and resident landbirds in lowland subtropical eucalypt forest

“…Furthermore, in the present study, the avoidance of Noisy Miner densities was a criterion used in site selection. Small fragments and thinned or partly cleared areas of lowland eucalypt forest are at high risk of being occupied by Noisy Miners, which results in the exclusion of the smaller-bodied winter migrant species (Catterall et al 1991(Catterall et al , 2002Piper and Catterall 2003;Catterall 2004). Therefore, the winter habitat of a wide range of common Australian migrant landbird species is at risk of disappearing before its significance for within-or between-year sustenance of the eastern Australian populations of these birds is understood.…”

“…1991: Catterall et al . , 2002Piper and Catterall 2003). Sites were located using aerial photography and 1:25000 topographic maps, followed by ground-truthing for ease of access, and agreement with the selection criteria.…”