How to Count Parrots: Comparing the Performance of Point and Transect Counts for Surveying Tasman Parakeets (Cyanoramphus cookii)

Abstract

Obtaining precise estimates of population size and trends through time is important for the effective management and conservation of threatened species. For parrots (Psittaciformes: Psittacidae), obtaining such estimates can be challenging, particularly for cryptic species that occur in low densities in complex and/or fragmented habitats. We used a statistical resampling approach with the aim to compare the reliability and precision of counts for the critically endangered Tasman parakeet (Cyanoramphus cookii) that were taken using two methods on Norfolk Island (Pacific Ocean), namely, fixed-point counts and line transect counts. The detections obtained during fixed-point counts had better estimated precision (0.274) than line transect counts (0.476). The fixed-point method was also more efficient, yielding 1.338 parakeet detections per count compared to the 0.642 parakeet detections per count obtained by the line transect method. Although Tasman parakeets can be detected by either of these methods, our research demonstrates that the fixed-point method is more precise and reliable. These findings can help prioritise resources for the long-term monitoring of recovering populations of this species and similar island species.