Are Urban Populations of a Gliding Mammal Vulnerable to Decline?

Small populations are at high risk of extinction, and they are likely to need management intervention. Successful management, however, relies on sufficient long-term demographic data in order to determine whether apparent declines are natural fluctuations or the product of threatening processes. In this study, we monitored a small urban population of squirrel gliders (Petaurus norfolcensis) in Queensland, Australia, over a 16 year period. A reference population in a larger forest patch was also studied in order to investigate whether its demographic trends were similar. Using mark-recapture data to generate estimates of apparent survival and population size, we found evidence of a decline within the small population but not in the reference population over the monitoring period. We suggest that the influence of multiple factors may have led to the decline, but, ultimately, that the genetic condition of the small population may be responsible. Understanding demographic trends is an important context for management interventions of small populations, although causes of decline need to be identified for successful management. The squirrel glider provides a useful case study for small urban populations and particularly for arboreal mammals.

The influence of urban encroachment on squirrel gliders (Petaurus norfolcensis): effects of road density, light and noise pollution

Context Loss and degradation of habitat from urban development is a key threat to the squirrel glider (Petaurus norfolcensis), because its distribution coincides where most people live in Australia. Squirrel gliders are known to occur in or around urban fringes where native vegetation is retained; however, little is known about specific anthropogenic factors that may affect their persistence. Aims We investigated the relative influence of biophysical and urban factors on the use of large hollow-bearing Eucalyptus trees, which are a key resource for squirrel gliders. The study was located in a typical urban growth area located in southern New South Wales. Methods A stratified random sampling approach was used to survey squirrel gliders in urban and rural areas. Infrared, motion-sensor cameras were placed in 34 selected trees for 17 nights to record squirrel glider occupancy and activity. Data on urban (e.g. light and noise pollution levels, road and housing density) and biophysical (e.g. tree height, hollow-bearing tree density, vegetation cover) variables were recorded at each survey tree. Data were statistically analysed using general linear modelling approaches. Key results Squirrel gliders were detected more frequently in the rural matrix (23.4% of camera trap-nights) than in urban areas (9.5%). Model results showed that tree height, and the distance to neighbouring trees, had a significant influence on the occurrence and activity of squirrel gliders. Road density and light pollution were included in ‘best’ models to explain glider activity (a negative influence), and noise pollution negatively influenced glider occurrence. Although gliders used large trees in both urban and rural areas, activity generally decreased as levels of urbanisation increased. Conclusions and implications Access to and availability of key resources such as tall, hollow-bearing trees is critical for gliders to persist in urban environments. Squirrel gliders will tolerate human stressors such as roads, noise and light pollution to a certain extent, but impacts on population viability remain largely unknown. Novel solutions need to be developed to lessen the effects of anthropogenic factors (such as light and noise) on patches of native vegetation retained in urban areas for conservation purposes.

The value of countryside elements in the conservation of a threatened arboreal marsupial Petaurus norfolcensis in agricultural landscapes of south-eastern Australia--the disproportional value of scattered trees

Human activities, particularly agriculture, have transformed much of the world's terrestrial environment. Within these anthropogenic landscapes, a variety of relictual and semi-natural habitats exist, which we term countryside elements. The habitat value of countryside elements (hereafter termed ‘elements’) is increasingly recognised. We quantify the relative value of four kinds of such ‘elements’ (linear roadside remnants, native vegetation patches, scattered trees and tree plantings) used by a threatened Australian arboreal marsupial, the squirrel glider (Petaurus norfolcensis). We examined relationships between home range size and the availability of each ‘element’ and whether the usage was relative to predicted levels of use. The use of ‘elements’ by gliders was largely explained by their availability, but there was a preference for native vegetation patches and scattered trees. We found home range size was significantly smaller with increasing area of scattered trees and a contrasting effect with increasing area of linear roadside remnants or native vegetation patches. Our work showed that each ‘element’ was used and as such had a role in the conservation of the squirrel glider, but their relative value varied. We illustrate the need to assess the conservation value of countryside elements so they can be incorporated into the holistic management of agricultural landscapes. This work demonstrates the disproportional value of scattered trees, underscoring the need to specifically incorporate and/or enhance the protection and recruitment of scattered trees in biodiversity conservation policy and management.