A burrowscope for examining petrel nests in burrows

This report describes the development and refinement of a burrowscope that is reliable and robust enough to withstand arduous field conditions crucial for obtaining accurate data on sooty shearwater (Puffinus griseus) burrow occupancy and breeding success. The burrowscope consists of a miniature camera and infra-red lights mounted on a three metre length of hose through which images are projected on to a screen at the surface. Movement of the camera-head was important to allow burrowscope penetration, adequate inspection of the burrows tunnels and side chambers, and to negotiate corners and obstacles. A hydraulic system for moving the camera-head was not as reliable as a cable system. Occupancy could not be determined for about a third of all burrows on Poutama Island where the deep peaty soils and abundant tree roots are associated with long and complex burrow structures. Ability to determine occupancy declines rapidly once burrows are longer than about 1.5 to 2 m, partly because the burrowscope cannot be manipulated around corners or obstacles once it has penetrated so far into the ground. Weather conditions and especially the temperament of different operators probably affect precision and reliability of the data. Standardisation of the burrowscope design and the way it is used in a study is important for consistency, but even so the burrowscope may be very inaccurate for comparisons between places, or even between different times at the same place. Research is needed to determine whether there are parameters of burrow structure and geometry that can be measured from above ground during burrowscope surveys to predict a "correction factor" to account for eggs or chicks missed by the burrowscope.