Large suburban and bush Tasmanian blue gums (Eucalyptus globulus) and black gums (Eucalyptus ovata) in Mount Nelson, Tasmania, as foraging resources for the endangered swift parrot (Lathanzus discolor)

Remnant trees in suburban areas constitute potential habitat for vertebrates by providing food and nesting sites. Trees, including the Tasmanian Blue Gum (Eucalyptus globulus) and Black Gum (E. ovata), are known to supply nectar and pollen to the endangered Swift Parrot (Lathamus discolor), whose breeding success depends on flowering of these two eucalypt species. The outer Hobart suburb of Mount Nelson, Tasmania, is one of the foraging grounds that the Swift Parrot utilises during its breeding season. The aim of the project was to investigate the relative value of large E. globulus and E. ovata in the bush and suburban areas of Mount Nelson as foraging habitat for Swift Parrots, and to examine which characteristics of the trees and their location affected flower production. In addition, the study investigated the recent and current trends of tree removal from private properties, as well as future plans for tree felling, in order to determine whether the forage sources for the Swift Parrot are declining within the suburb. From a sample of 261 randomly selected large E. globulus and E. ovata trees ( greater than 60 cm in diameter at breast height) in Mount Nelson, it was found that suburban trees produced more flowers than their edge or bush counterparts. Hence, the former are more reliable nectar and pollen sources for a range of nectarivorous birds, including the Swift Parrot. It is thus argued that suburban trees do not just provide a secondary (to bushland) food supply for Swift Parrots, but constitute an important foraging habitat in their own right outside bush areas. Bush trees, however, despite being less important in providing food to the Swift Parrot, were more likely to support a greater number of nesting hollows for the species. The study found that the abundance of flowers produced was significantly related to a number of tree variables. Trees with denser canopies, of better health, with no or a low percentage of branches in the canopy that were dead, and no fire damage were likely to support more flowers. The impact of fire was at least partially mediated via its effect on increasing tree dieback and the percentage of branches that were dead, and to a lesser degree, reducing canopy density. A survey of Mount Nelson residents suggests that many large E. globulus and E. ovata occur on private unprotected land of Mount Nelson. However, they are rapidly being removed. An estimated 28.8% of all large E. globulus declared in the survey and 29.9% of E. ovata have either been removed in the past five to ten years, or will be removed in the near future. Hence, the amount of food available to Swift Parrots in Mount Nelson is being reduced. There is thus a need to retain these valuable tree resources. Maintaining trees in the suburbs as foraging habitat, as well as trees in the bush as nesting habitat, could be important for the long-term survival of the Swift Parrot.