Action: Reduce inter-specific competition for nest sites of songbirds by removing competitor species
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- Two studies from Australia found increases in bird populations and species richness after the control of noisy miners Manorina melanocephala – a native but hyper-competitive species.
- A controlled study from Italy found that blue tits Parus caeruleus nested in more nest boxes when hazel dormice Muscardinus avellanarius were excluded from nest boxes over winter.
As humans modify ever-increasing amounts of habitat across the world, the number of nesting sites for many species is becoming limited, potentially increasing competition and reducing reproductive output. Two potential solutions are to increase the number of nesting sites (see separate section in ‘General responses to small/declining populations’) or to reduce competition by removing or controlling competitor species (see below).
Supporting evidence from individual studies
A paired site study of patches of remnant eucalypt woodland in Victoria, Australia (Grey et al. 1997), found a significant increase in bird abundance and species richness after reduction in the numbers of noisy miners Manorina melanocephala in two of three sites. The differences were attributable to an influx of honeyeaters and other small insectivorous birds. In a third site, possibly as the result of the presence of understorey vegetation, there was only a small starting population of noisy miners. The reduction in their numbers influenced the species composition but not bird abundance.
A controlled trial in 2001-2 in beech, holly and oak forests on Sicily, Italy (Sara et al. 2005), found that blue tits Parus caeruleus (also Cyanistes caeruleus) occupied a higher proportion of nest boxes in an experimental area where hazel dormice Muscardinus avellanarius were excluded from nest boxes over winter, compared to a control area where dormice were not excluded, but this difference was not significant. The authors argue that the lack of significance may be due to the small sample size (25 nest boxes in each treatment). Dormice were excluded by blocking nest box entrances between November 2001 and March 2002. This study is also discussed in ‘Provide artificial nesting sites’.
A before-and-after study of bird species in privately owned remnant eucalypt woodland in New South Wales, Australia (Debus 2008), found a decline in small and medium songbirds after a dense colony of noisy miners Manorina melanocephala became established. The number of bird species increased after a cull of the noisy miners, and improved further as new planting of native trees and shrubs became established. The results are consistent with noisy miners causing a decline in small woodland bird diversity by competitive exclusion, released by culling. The restoration of a shrub layer is likely to have played a part in the maintained increase in the diversity of bird species, but the relative contributions of the cull and planting cannot be quantified. The study was not replicated or controlled, and the cull was unofficial and unsanctioned.
- Grey M.J., Clarke M.F. & Loyn R.H. (1997) Initial changes in the avian communities of remnant eucalypt woodlands following reduction in the abundance of Noisy Miners Manorina melanocephala. Wildlife Research, 24, 631-648
- Sarà M., Milazzo A., Falletta W. & Bellia E. (2005) Exploitation competition between hole-nesters (Muscardinus avellanarius, Mammalia and Parus caeruleus, Aves) in Mediterranean woodlands. Journal of Zoology, 265, 347-357
- Debus S.J.S. (2008) The effect of noisy miners on small bush birds: an unofficial cull and its outcome. Pacific Conservation Biology, 14, 185-190