Extent and quality of habitat for the endangered forty-spotted pardalote (Pardalotus quadragintus) at Howden, Tasmania

In 2009-2010 a survey of Pardalotus quadragintus (forty-spotted pardalote) found that there had been a 60 % decline in the species population size over the last 25 years. In some bird colonies, Eucalyptus viminalis (white gum) decline and dieback was considered to be the primary cause of this population decline. In contrast, one of the smallest P. quadragintus colonies, located at Howden (approximately 3 km south of the town of Kingston in Tasmania) declined from 20 to 10 birds over the last 10 years, despite E. viminalis in the area appearing to maintain sufficient quality to support the previous population size. The Howden habitat is located in a sub-urban landscape, in which the surrounding area has been extensively cleared over the last 10 years. Therefore, human related disturbances might be a causal factor for this declining bird population. However, a comprehensive habitat survey has not been undertaken to test this possibility. This study attempts to identify the potential causes of the decline in the Howden population and determine the key habitat characteristics that influence the habitat preferences of this species. Recommendations for implementation of specific conservation actions are provided based upon the results of this study. A survey of habitat quality and occurrence of P. quadragintus was conducted between March and September 2010 in the Peter Murrell Reserve and Conservation Area (the Reserve) and adjacent land. The survey identified 32 forest patches containing E. viminalis, which were separated into three groups based upon geographical position ‚ÄövÑvÆ Coffee Creek (29 ha), Mid-eastern (4.3 ha) and Channel Highway (6.5 ha). All of eight patches in the Mid-eastern and the Channel Highway groups were newly identified as potential habitat for P quadragintus. Habitat attribute variables were surveyed at both patch and group levels. One result of this study was to increase the total estimated habitat size of P. quadragintus from 12 ha to 40 ha. Identification of this additional habitat potentially increases the local estimated population size of this species (previous estimations based on a habitat of 12 ha suggested that 10 birds occupy the area). However, the extremely small number of birds detected during the study period suggests that the estimated population size of 10 birds is likely to be correct. The tree health of E. viminalis in the Coffee Creek habitat was examined by comparing the tree crown condition with that of trees from the 'Township' habitat on nearby Bruny Island. The result identified that the Coffee Creek habitat provided better habitat quality (e.g. crown condition, abundance of large E. viminalis trees and canopy coverage of E. viminalis) than that provided by the 'Township' habitat. Different environmental and land management factors (e.g. soil/rock types, topography and grazing history) between these two habitats were considered to differentially affect water holding capacity, altering the availability of water to plant species. Better tree health and habitat quality in Howden are consistent with a previous study and suggest that the decline of the P quadragintus population at Howden may not be linked with habitat quality, rather human disturbances may be important. The P quadragintus detection rate did not show any strong association with the measured habitat characteristics believed to be favourable for P quadragintus. This result suggests that the birds are not able to establish their natural ecological behaviour due to pressures from human related disturbances, rather they are forced to use lower quality habitat. A 50 % increase in the number of buildings adjacent to the Reserve between 1990 and 2005 was confirmed, and has likely brought more visitors to the Reserve and increased interspecific competition and predation of nestlings as a result of elevated edge effects. Increased levels of habitat isolation may also be partially attributable to the negative effects of human disturbance. The central finding of this study is that even in situations where stands of E. viminalis forest have been reserved and sufficient habitat quality has been maintained, P quadragintus may well not be saved from extinction if significant levels of human related disturbance occur in and around these habitats. Hence, it is essential that land managers consider both the immediate habitat of P. quadragintus and the surrounding landscape in order to protect the population in the Howden area. Monitoring of the population also needs to be undertaken to evaluate the impacts of any actions adopted and to increase our understanding of P. quadragintus ecology.