Habitat structure and an introduced predator limit the abundance of an endangered ground-nesting bird

Understanding the factors that limit the abundance of threatened species is critical for the development of effective conservation strategies. However, gaining such knowledge from monitoring programs and using it to inform decision making for rare species can be difficult due to methodological issues posed by the problems of distinguishing true zero counts from false zero counts and analysis of datasets dominated by zero counts. The plains-wanderer (Pedionomus torquatus) is a critically endangered ground-nesting bird that occurs in grasslands of south-eastern Australia. Decline of the plains-wanderer has been attributed to habitat modification but little emphasis has been placed on the role of introduced predators, such as the red fox (Vulpes vulpes), which have had a devastating effect on small ground-dwelling vertebrates in dryland regions of Australia. Here, we use a 9 year-time series of spotlight counts to investigate the impact of vegetation structure and fox presence on plains-wa..., Data from spotlight transects for plains-wanderers. Data were first subject to distance sampling then the dataset was truncated to only include observations of birds within the effective strip-width. metadata in attached excel file., , # Habitat structure and an introduced predator limit the abundance of an endangered ground-nesting bird

[https://doi.org/10.5061/dryad.t1g1jwtb9](https://doi.org/10.5061/dryad.t1g1jwtb9)

Spotlight surveys for plains-wanderers and foxes were conducted 1-3 times per year (Autumn, Winter, Spring) at each site giving a total of 249 surveys. When detected, the perpendicular distance from the survey vehicle to the plains-wanderer or fox was estimated visually.  The total transect length varied between sites dependent on the extent and spatial arrangement of suitable plains-wanderer habitat (mean 15.13 ±SD 3.52 km length: range 7 – 22 km length).

Distance sampling was used to identify the effective strip width within which we had a high (≥75%) probability of sighting plains-wanderers and could be confident that zero counts represented true zeroes. Specifically, we used a detection function with a half-normal distribution to identify the distance from the survey vehicle when plains-wanderer ...