Bird density and species richness in suburban Canberra, Australia : relationships with street vegetation, age of suburb and distance from bird source areas of native vegetation

Abstract

1. A total of 99 bird species were recorded from June 1982 to May 1983. Ninety species were recorded in adjacent source areas and 69 species in residential sites. 2. There were more open-forest and woodland bird species recorded during the study than there were grassland and exotic species in the ratio 8:2 but the House Sparrow, Common Starling and the Silvereye were the dominant species in that order (Table 7.2). 3. There were more bird species recorded in the adjacent open-forest/ woodland source areas than there were in the suburban sites, but bird density was higher in the suburban sites than in the adjacent open-forest/woodland source areas. 4. There was a positive relationship between the mean total number of species and the age of the suburbs but only up to 12 year old sites beyond which no increase in species was determined (Figures 4,1 and 4,2). 5. The density of birds increased with the age of the suburbs, but with a higher rate of increase between 1-2 year to 12 year old sites than between 12 year to greater than 30 year old sites (Figure 4,3), 6. The number of open-forest and woodland species increased with the age of the suburbs but the number of grassland and exotic species remained largely unchanged. 7. The relationships observed between the number of species, bird density and the age of the suburbs supported the hypothesis that the increases in the number of species and bird density with increases in age of suburbs represented a response by birds to changes in habitat conditions over time and not necessarily as a response to the age of sites. Such habitat changes reflected the growth of trees and, to a lesser extent, the increased cover of shrubs. 8, Significant positive correlations between the age of the suburbs and eight vegetation habitat attributes suggests that these habitat attributes were interelated with age (Table 5,2). These are as follows: % total foliage cover, % native foliage cover, % foliage cover 2-4m, % foliage cover 4-Bm, % foliage cover 8-12m, % foliage cover >12m, Top height, Foliage height diversity. 9. The relationships between% cover of foliage height classes 1-2 m to >12 m, % total foliage cover, height of the tallest trees and% native foliage cover were positively correlated with the number of open-forest species, woodland species and the total number of species, but not with the number of grassland and exotic species groups (Table 5,4). 10. The lower number of species for open-forest species, woodland and grassland species, and the lower density of birds on 20 year and >30 year old sites with exotic vegetation for the three species groups (Table 4,4) indicated the negative influences of exotic vegetation (most of which was deciduous) on native bird species, but nevertheless enhanced the density of exotics. 11. There were no significant relationships found between the number of grassland species and any of the listed habitat attributes except for % lawn cover. 12. The number of exotic species had significant positive relationships with% lawn cover and foliage height diversity and significant negative relationships with% mulch cover, % foliage cover and % native foliage cover. There was a significant negative relationship with% mulch and the density of exotic species (Tables 5.4 and 5,6). 13. There was a negative relationship between paved surfaces (including the percentage of area under house) and the numbers of open-forest, woodland and grassland species together with their densities but the number of exotic species and their density remained largely unaffected (Tables 5.4 and 5.6 ). 14. Similarly a negative relationship was observed between the numbers of open-forest, woodland and grassland species with respect to distance of suburban sites from source areas. The number of exotic species, however, remained largely unchanged. The hypothesis that the number of species in the suburbs decreased with the increase in distance of the sites from the open-forest/ woodland source areas was supported (Figures 6.1 - 6.4 and Table 6.1). Only the density of individual birds of grassland and exotic species increased with increase in the distance of sites from open-forest/woodland source areas. 15. The list of habitat attributes selected in the step wise regression as being most responsible for variations in the number of species and the density of birds showed that not only were the age of the suburbs, and distance of sites from open-forest/ woodland source areas major factors that affected the number of species and their density in suburban Canberra but also important were attributes related with the vegetation components such as total foliage cover, foliage height diversity and proportion of native vegetation (Tables 7.8 and 7.10).

Date of Award	1985
Original language	English