Does variation in garden characteristics influence the conservation of birds in suburbia?

Published source details Daniels G.D. & Kirkpatrick J.B. (2006) Does variation in garden characteristics influence the conservation of birds in suburbia?. Biological Conservation, 133, 326-335.
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Summary

A study was undertaken in suburbs of the city of Hobart, Tasmania (Australia) to assess if enhancement of garden habitat for native birds has conservation benefits. The influence of vegetation structure, flora and other garden attributes, and environmental and landscape controls, on the abundance and richness of bird species in gardens, were investigated.

Study sites: Ten suburbs in Hobart, representing a range of environments (annual precipitation and altitude) and distances from the city (1 km to 16 km from the General Post Office) and natural habitat (<5 m to >3 km) were selected. Hobart is a coastal, city of 190,000 people, mostly surrounded inland by forested hills and mountains. Most people live in self-contained houses, with both front and back gardens. These gardens vary markedly in their structural characteristics and floristic composition. The total number of properties from which data were collected was 107. Front and back gardens were treated as independent locations, giving a total of 214 sites. The gardens ranged between 50 and 1,600 mÂ² in area.

Bird counts, resource use and garden characteristics: Point counts (20 min duration) were undertaken between sunrise and 11:00 h, 11:00 to14:00 h, or 14:00 h to sunset. Pilot surveys identified 20 min as a sufficiently long to record all individuals in a garden on any one occasion. Each garden was sampled four times during the project, twice in winter 2004 and twice in spring 2004.

Birds were counted in each garden and the resources they utilized noted. Vascular plant species and other attributes of the garden were recorded, along with rainfall, altitude, distance from natural vegetation, distance from the city and garden size. Garden floristics and bird assemblages were anaylsed, to assess if garden groups could be characterized by particular bird assemblages.

In total 40 bird species were recorded in the gardens, including six Tasmanian endemics and six non-native species. Bird species richness ranged from 0 to 18 (average 5.2). Native bird species richness ranged from 0 to 16 (average 2.9). Garden bird abundance ranged from 0 to 119 (average 21.6). Native bird abundance ranged from 0 to 45 (average 9.2).

The non-native blackbird Turdus merula was the most frequently recorded species (412 records); the non-native house sparrow Passer domesticus was by far the most abundant (1,458 individual records). The most frequent native bird was the New Holland honeyeater Phylidonyris novaehollandiae (194 records); the most abundant was the silvereye Zosterops lateralis (534 individual records). Other frequently recorded natives were eastern spinebill Acanthorhynchus tenuirostris and crescent honeyeater P.pyrrhoptera.

Native birds showed a preference for native plants, but also utilized many exotic plants. Non native birds tended to largely use exotics. Variation in garden characteristics substantially affected the nature of bird assemblages in those gardens surveyed, with weaker environmental and landscape influences, e.g. the percentage cover of shrubs, proved a very important influence on garden birds; shrubs favoured the small woodland birds, the woodland assemblage, and the New Holland honeyeater; Supplementary feeding strongly enhanced exotic bird abundance and richness, but also increased native bird abundance, and numbers of black-headed honeyeater Melithreptus affinis and silvereye.

Dog presence positively influenced the ‘lawn’ bird assemblage and the superb fairy-wren Malurus cyaneus. This appears due to these birds foraging predominantly on the ground, and being thus vulnerable to cat predation. Dogs tend to chase cats off or spoil their predatory attempts.

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