Metabarcoding faecal samples to investigate spatiotemporal variation in the diet of the endangered Westland petrel ( Procellaria westlandica )

As top predators, seabirds are directly impacted by any changes in marine communities, whether they are linked to climate change or caused by commercial fishing activities. However, their high mobility allows them to adapt to changing conditions. For example, seabirds can adapt their foraging behaviour according to the resources available at different seasons. This capacity of adaptation comes to light through the study of their diet. Traditionally, the diet of seabirds is assessed through the morphological identification of prey remains in regurgitates, a method that is invasive for the bird and limited in terms of resolution. However, the recent optimization of DNA-based approaches is now providing a non-invasive and more comprehensive and accurate characterization of animals9 diet. Here, we used a non-invasive metabarcoding approach to characterize the diet of the Westland petrel (Procellaria westlandica), an endangered burrowing species, endemic to the South Island of New Zealand. We collected 99 fresh faecal samples at two different seasons and in two different sub-colonies. Besides from describing the diet of the Westland petrel, our aim was to account for seasonal and geographical variations in the diet of the petrel and assess potential links with the fishery industry in New Zealand. We found that amphipods were the most common prey, or secondary prey, followed by cephalopods and fish, suggesting a close link between the composition of prey items and New Zealand9s commercial fishing activities but, also, some level of natural predation. Our results show significant differences in diet between seasons (before hatching vs chick rearing season) and between sampling sites (two sub-colonies 1.5 km apart), which suggests variability and adaptability in the foraging strategy of the Westland petrel. Due to its non-invasive nature, the method used here can be applied on a great number of samples to draw a comprehensive picture of the diet dynamic in seabirds and unravel their adaptability or ecological requirements. This work demonstrates how environmental DNA can inform the conservation of an endangered species with elusive foraging behaviour, providing, in this case, valuable information regarding the diet preferences of an iconic species within New Zealand9s biodiversity. Introduction