Laura Rayner

Citizen science program shows urban areas have lower occurrence of frog species, but not accelerated declines

Understanding the influence of landscape change on animal populations is critical to inform biodiversity conservation efforts. A particularly important goal is to understand how urban density affects the persistence of animal populations through time, and how these impacts can be mediated by habitat provision; but data on this question are limited for some taxa. Here, we use data from a citizen science monitoring program to investigate the effect of urbanization on patterns of frog species richness and occurrence over 13 years. Sites surrounded by a high proportion of bare ground (a proxy for urbanization) had consistently lower frog occurrence, but we found no evidence that declines were restricted to urban areas. Instead, several frog species showed declines in rural wetlands with low-quality habitat. Our analysis shows that urban wetlands had low but stable species richness; but also that population trajectories are strongly influenced by vegetation provision in both the riparian zone and the wider landscape. Future increases in the extent of urban environments in our study area are likely to negatively impact populations of several frog species. However, existing urban areas are unlikely to lose further frog species in the medium term. We recommend that landscape planning and management focus on the conservation and restoration of rural wetlands to arrest current declines, and the revegetation of urban wetlands to facilitate the re-expansion of urban-sensitive species.

Further knowledge and urgent action required to save Orange-bellied Parrots from extinction

ABSTRACT Only three wild-bred female Orange-bellied Parrots returned from migration in the 2016/17 breeding season, representing the lowest point of a long-term decline. In this context of imminent extinction risk we (i) update knowledge of population parameters, (ii) critically evaluate current recovery actions, and (iii) identify new management options. We present new data from the 2016/17 breeding season. Orange-bellied Parrots were only observed at the last known breeding site where fire suppression may havecaused shortage of natural food. Recently burned habitat elsewhere support abundant food, but no parrots. Fecundity of captive-bred individuals was significantly worse than wild-bred individuals (0.8 vs. 3 fledglings respectively), mostly due to infertility. Bacterial septicemia due to contaminated food caused mortalities of at least four nestlings. Fostering captive-bred nestlings to the wild showed some potential as a recovery tool, with 2 of 4 nests accepting a foster nestling, and one of these fledging successfully. Captive-bred birds had poorer feather condition than wild birds. Addressing food shortages and the addition of new managementactions to improve population recruitment are critical and urgent recovery priorities. We suggest recovery priorities for the species arising from our results, including emergency intervention to prevent imminent extinction.

Effect of nest cavity morphology on reproductive success of a critically endangered bird

ABSTRACT Population limitation is the outcome of cumulative and synergistic processes that act on species over multiple spatial scales. Tree cavity dependent animals are good case studies for exploring processes that potentially limit populations across multiple scales. Fine-scale cavity characteristics have important consequences for predator exclusion and fecundity, while broad-scale processes (food or habitat availability) can determine population viability. We considered the relative importance of cavity morphology in limiting the breeding success of a critically endangered secondary cavity nesting bird that is severely affected at broad scales by nest predation. Swift Parrots (Lathamus discolor) select nest cavities where the minimum entrance diameter is positively associated with cavity depth, floor diameter and maximum entrance diameter. These cavity characteristics are adaptive because they exclude native predators by physically preventing access to the nest chamber; only one introduced nest predator is able to overcome this passive nest defence. Introduced Sugar Gliders (Petaurus breviceps) could prey on Swift Parrot nests irrespective of nest cavity morphology. We found no effect of cavity morphology on the number of eggs laid or fledglings reared by Swift Parrots. This suggests that fine-scale nest cavity characteristics do not influence the nest success of Swift Parrots beyond their effectiveness in excluding native Tasmanian predators.

Undetected Allee effects in Australia’s threatened birds: implications for conservation

ABSTRACT Allee effects occur when survival or reproductive success declines with decreasing population size or density. Species most severely impacted by Allee effects may be the very species for which these effects will be hardest to detect and overcome. This impedes effective conservation through a lack of evidence to drive management actions. We review the literature to identify (1) component Allee effects (components of fitness) which could lead to a demographic Allee effect (effect of all components on the population growth rate) in bird populations; and (2) traits that make species susceptible to component Allee effects. Concurrently, we assess the potential for undetected Allee effects to negatively influence the population growth rate of 14 critically endangered Australian bird species or subspecies. Whilst some (e.g. Helmeted Honeyeater) are unlikely to suffer from a demographic Allee effect, several (e.g. Great Knot, Orange-bellied Parrot) are susceptible to a number of component Allee effects and, hence, a demographic Allee effect. However, traits of the Regent Honeyeater suggests this species’ decline in particular is accelerated by an undetected demographic Allee effect. For this species and others, an inability to detect Allee effects need not preclude efforts to account for their potential presence through precautionary conservation management.