Establishing accurate baseline estimates of breeding populations of a burrowing seabird, the grey-faced petrel (Pterodroma macroptera gouldi) in New Zealand

• Published in: Biological conservation Vol. 169; pp. 109 - 116
• Main Authors: Whitehead, Amy L., Lyver, Philip O’B., Jones, Christopher J., Bellingham, Peter J., MacLeod, Catriona J., Coleman, Morgan, Karl, Brian J., Drew, Keven, Pairman, David, Gormley, Andrew M., Duncan, Richard P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-01-2014; Elsevier
• Subjects: Abundance estimation; Animal, plant and microbial ecology; Applied ecology; Aves; Biological and medical sciences; Breeding distribution; Conservation; Conservation, protection and management of environment and wildlife; Construction; Density; Estimates; Forests; Fundamental and applied biological sciences. Psychology; General aspects; General aspects. Techniques; Grey-faced petrel; Habitats; Hierarchical Bayesian model; Islands; Mathematical models; Methods and techniques (sampling, tagging, trapping, modelling...); Metrosideros excelsa; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Populations; Pterodroma macroptera gouldi; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; New Zealand; Oceania; PSE, New Zealand; Abundance estimation; Breeding distribution; Grey-faced petrel; Pterodroma macroptera gouldi; Hierarchical Bayesian model; Marine animal; Burrower; Abundance; Marine environment; Vertebrata; Reproduction; Aves; Environmental protection
• ISSN: 0006-3207; 1873-2917
• DOI: 10.1016/j.biocon.2013.11.002

•We used field surveys and predictive habitat models to estimate grey-faced petrel abundances.•Breeding burrow densities increased with elevation and decreased with taller forest and denser canopy cover.•We estimated 72,410 breeding pairs across the four Ruamaahua Islands and 69,330 on Moutohorā.•Habitat variables and spatial variation in burrow density and occupancy are important in estimating breeding populations.•Accurate baseline abundance estimates are important in managing species’ responses to perturbations.
Accurate estimates of breeding population size are essential for detecting change and guiding conservation management and sustainable use. In New Zealand, the grey-faced petrel (Pterodroma macroptera gouldi) now breeds predominantly on offshore islands, but is also subject to customary harvest of chicks by northern tribes of Māori (New Zealand’s indigenous peoples). We used island-wide surveys of 3186 breeding burrows, corrected for detection error, and associated habitat variables on two island systems (Ruamaahua Islands and Moutohorā), combined with data from geographic information systems, to build hierarchical Bayesian models to predict the distribution and abundance of breeding pairs. Burrow densities increased with elevation on all islands and, on Moutohorā, were lesser in gullies and on terraces. On the Ruamaahua Islands, burrow densities were associated positively with deeper soils and forests dominated by pōhutukawa (Metrosideros excelsa), and negatively with taller forest, denser canopy cover, and northern and western aspects. Predicted breeding-pair densities for each island group provided breeding-pair population estimates of 72,410 (95% credible interval 14,280–138,400) across the Ruamaahua Islands and 69,330 (10,590–128,300) on Moutohorā. Estimating burrow densities using habitat characteristics provided greater precision and accuracy than simpler models that extrapolate sampling data over larger areas. The methods used to estimate population size are applicable to other cryptic seabird species, especially those that live or breed in burrows. It is important to establish accurate baseline estimates of the populations of common seabird species against which to determine responses to perturbations and management interventions.