Have we achieved a sustainable balance? Evaluating the effects of regulated guano extraction on an important penguin breeding colony (2008–2019)

Guano extraction in Peru has caused significant impacts on the endangered Humboldt penguin (HUPE, Spheniscus humboldti) colonies. These impacts include HUPE distress, breeding avoidance, and abandonment of nests. Mitigation strategies to minimize the interaction between breeding penguins and guano extraction have been developed and applied since 2001 at Punta San Juan, one of the largest HUPE breeding areas. This study aims to determine the effects of the two most recent guano harvests at Punta San Juan (2012 and 2019) on HUPE breeding. We conducted three analyses to evaluate if such events altered the number of breeding attempts (i.e. nests) or the breeding temporality (i.e. phenology) of the study colony. First, using yearlong nest counts for 11 years (2008–2019), we assessed if extraction years present significant variation in nesting phenology and number of nests compared to non-extraction years. Second, during the 2012 and 2019 guano harvests, we evaluated differences in nesting phenology and the number of nests between sectors of the study colony, given their proximity to extraction activities. Finally, we used a GLM to estimate the relationship between sector distance to extraction areas and the number of active nests on a week-to-week resolution (as nest desertion proxy) during the extraction periods. Results showed no evidence of guano harvest impacts on our study species. However, downward trends in the overall population and irregular variation in HUPE breeding temporality in recent years might be masking possible 2019 harvest effects. While this case exemplifies how a balance between economic and conservation interests can be achieved, it also illustrates the necessity of identifying underlying factors of HUPE population decline and the need for long-term monitoring.