What characteristics of urban gardens influence the distribution and foraging ecology of Noisy Miners?

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Project Aim

Previous research suggests that the presence of Noisy Miners in gardens is the key factor reducing the abundance of small birds in urban areas. As a first step toward making gardens less suitable to Noisy Miners, the Birds in Backyard Program commissioned a research project to find out more about the characteristics of urban gardens that make them attractive to Noisy Miners. The major aim was to determine whether Noisy Miners were more common in gardens with large-flowered hybrid grevilleas.

Participants

The study was undertaken by Lisa Ashley and Charlotte Taylor from the University of Wollongong, along with Richard Major from the Australian Museum.

Methods

Forty gardens, meeting specific criteria, were selected in the western suburbs of Sydney.

  • 10 gardens contained grevilleas but no eucalypts
  • 10 gardens contained grevilleas but no eucalypts
  • 10 gardens contained both grevilleas and eucalypts
  • 10 gardens contained neither grevilleas or eucalypts

All birds visiting these gardens during four 15 minute surveys were recorded, and the abundance of Noisy Miners was separated out for special analysis.

A total of 560 minutes of foraging activity was also recorded on 45 Noisy Miners in the same suburbs (but not the same gardens), to determine the relative importance of different foods in their diet.

Results

Noisy Miners were significantly more common in gardens that contained eucalypts, but they were no more common in gardens with grevilleas, unless those gardens also contained eucalypts.

Observations of foraging behaviour revealed that in gardens where grevilleas were present, Noisy Miners spent 25 % of their time feeding on grevilleas and 40 % of their time feeding on eucalypts. In gardens without grevilleas, they spent 60 % of their foraging time on eucalypts. They also spent 15 % of their time feeding on the ground and 25 % of their time on other plant species.

Conclusions

This study indicates that Noisy Miners feed on a wide variety of food sources, but that eucalypts provide the most favourable foraging substrate (for nectar, insects and plant sap). Grevilleas are used extensively when they are available, but their presence does not explain the distribution of Noisy Miners at the back yard level. However, it seems that grevillea nectar is a substantial component of the large nectar resource that is present in urban gardens. It is therefore still possible that at the scale of a suburb (rather than a back yard), the abundance of nectar in ornamental gardens might be one of the factors that makes these areas suitable habitat for Noisy Miners.

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