Monitoring environmental change and ecosystem health using seabird guano chemistry

Abstract

One of the first studies to investigate the use of stable isotopes from seabird guano and extracted uric acid for monitoring environmental changes in diet and trophic relationships of seabirds and anthropogenic pollutant levels, this study supported the hypothesis that guano and uric acid offer an alternative non-invasive sampling technique. The study found strong evidence of inter- and intra-specific differences in δ¹³ C and δ¹⁵ N signatures across species and breeding locations, which were primarily attributed to the feeding ecology of each species. Patterns of intra-and inter-specific variation were also seen in kittiwakes from the east coast of Scotland where samples were collected within and between years, with considerable isotopic overlap observed in the results suggesting that individuals from these colonies were consuming isotopically similar prey, taken largely from similar regions. For most species the δ¹³ C and δ¹⁵ N signatures of uric acid were not significantly different from that of guano (<1‰ for δ¹³ C and 1.2‰ for δ¹⁵ N) with a highly linear relationship, suggesting that either tissue could be used when studying the short- term (in the order of days) foraging behaviour of seabirds. When considering the heavy metal burden of seabirds, the present study showed that there are both similarities and differences in trace element concentrations both within and between species that can largely be attributed to dietary variation, although other factors including anthropogenic activities can potentially contribute to this variability in specific locations. With knowledge of the sources and controls on metal variability in diets and bodily accumulation such data derived from seabird guano can provide a potentially useful bio-monitor of trace element concentrations in the wider marine environment. Stable isotope analysis of seabird guano and uric acid can be used to document changes in diet and trophic relationships that may be associated with environmental change. Using multiple species and sampling locations, such studies can provide an alternative monitoring tool at a range of temporal and spatial scales.