Using¹³⁷Cs and²¹⁰Pb to characterise soil mixing by burrowing petrels: an exploratory study

Abstract

This exploratory study tested the hypothesis that petrels (Aves: Procellaridae) actively plough the soil of their entire breeding colonies, as implied by their well-known burrowing capabilities but contra-indicated by widespread horizonation in colony soil. Two profiles to lithic contact were excavated within a forested Westland petrel (Procellaria westlandica) colony; one, a ridgeline control without nearby petrel burrows, and the other from a steep slope among petrel burrows. On the ridgeline, 137 Cs activities (estimated per volume) steadily decreased with depth as expected. At the burrowed site, a subsurface maximum at 12Á16 cm depth indicated a post-1963 burrowing or landslip event. Both 210 Pb profiles were successfully modelled (r 2 c. 0.9) using a simple first-order model usually applicable only to undisturbed soils. In this model, mixing is accounted for by radioactive decay and first-order, mm-scale biodiffusion. The results therefore indicated that soil mixing was not dominated by petrel burrowing; rather, petrels confine their burrowing activities to maintenance of their burrows as semi-permanent (decades to centuries) structures. However, further sampling is recommended to confirm this view.

The biogeochemistry and ecological impact of Westland petrels (Procellaria westlandica) on terrestrial ecosystems

“…These descriptions of the impact of major storms (Waugh et al 2015a) fit well with the nature of the side-slope of the Study Colony as a concave erosion surface, a caesium-137 depth profile consistent with minor post-1963 soil movement (Hawke 2010b), and reports of localised land slips carrying away burrows (Hawke & Powell 1995). Conversely, lead-210 depth profiles indicate overall slope stability on a decadescentury timescale (Hawke 2010b).…”

“…Burrow construction by burrowing seabirds typically extends over several seasons (Furness 1991), and burrows at the Study Colony are long-lived (decades-century) structures (Hawke 2010b). Nevertheless, the terrain across the entire region is steep and comparatively unstable, experiencing frequent high-rainfall storms and recurrent earthquakes.…”

Breeding Westland petrels as providers of detrital carbon and nitrogen for soil arthropods: a stable isotope study

“…obs.). The soil is an Orthic Brown Soil (New Zealand Soil Classification), equivalent to a Dystrudept in USDA Soil Taxonomy; a complete soil description is given in Hawke (2010). Vegetation is dominated by tree ferns (Cyathea spp.)…”