The theory of island biogeography is a central tenet of ecology, explaining that biological communities are modulated by area and isolation. While island biogeographical principles have been used post hoc to explain distributions of taxa, opportunities to observe biogeographic forcing on faunal community assembly in situ are scarce, as the generation of novel island community assemblages is rare and requires extensive timeframes to study. However, recovery of islands after invasive species eradication offers a unique opportunity to observe biogeographic forcing on community assembly at realistic spatiotemporal scales. Using data from Aotearoa New Zealand, the world's leader in invasive species eradications, my coauthors and I sought to understand the relative role of abiotic (geography) and biotic (invasive species depredation) factors in shaping seabird community assemblages. We amassed one of the largest long-term invasive mammal datasets, documenting seabird breeding presence, invasive species arrival and subsequent eradications, and restoration programs for >500 islands, with observations from 1664 – 2020. We found strong evidence that seabird assemblages are consistent with patterns of island biogeography, but these trends were disrupted by invasive mammals, with legacy effects detectable long after mammal eradication.

Following invasive mammal eradications, seabirds slowly return to establish breeding colonies during a passive island recovery period. Understanding resource use, particularly as it relates to reproductive output, can help explain individual species recruitment rates and population growth. We monitored five species of sympatrically breeding Procellariiformes on a recovering island in Aotearoa New Zealand by collecting dietary samples and measuring chick growth. Our analysis of diet revealed that adults provision chicks differently than for their own means, with chick diets of lower trophic levels and possibly more lipid-rich. However, we detected little effect of diet on measures of chick growth and survival. Our results suggest quality of forage may not be limiting seabird productivity during passive island recovery.

We examine seabird and vegetative changes at Pokohinu (Burgess) Island, predator-free for almost 30 years, of the Mokohinau Islands. In 2009, we documented seabird distributions, plant diversity, and soil depth across the island and performed smaller surveys in 2014 and 2019. We found an overall 62.5% increase in seabird burrow densities with a strong spatial overlap of species distributions. Diversity of plant species also significantly increased, possibly due to the increased abundance of seed-dispersing birds and the simultaneous expansion of invasive plant species. In addition, we performed burrow and vegetation surveys at other Mokohinau Islands that lack same extent of past human disturbance as Pokohinu, which is a retired lighthouse and farm. Seabird densities between islands were comparable but plant communities lacked many of the invasive species found at Pokohinu. Overall, our results suggest that vegetative cover might not be limiting nesting habitat availability within the Mokohinaus, as seabirds are able to utilize areas dominated by dense vegetation. We emphasize the importance of understanding vegetative succession during recovery periods which may help explain recolonization rates for more specialist species.