Ten percent of the world’s seabirds breed only in New Zealand, making this island archipelago the “seabird capital of the world.” Seabirds act as ecosystem engineers, providing islands with large amounts of marine-derived nutrients through guano deposition, aerating soil by building underground burrows, and affecting all flora from invertebrate communities to endemic tuatara. Furthermore, they hold important cultural significance for indigenous Maori. Consequently, the conservation of seabird populations and habitat is of the utmost importance in New Zealand.
Seabird populations have been devastated by the introduction of non-native predators such as rats (Rattus sp.) by humans. In New Zealand, most seabirds were extirpated from the mainland and restricted in small numbers to offshore predator-free islands. These troubling facts prompted many predator eradication campaigns, and now over 85 islands around New Zealand have been cleared of all non-native predators.
Eradication of predators has not only alleviated pressure on threatened seabird species; it has provided the opportunity to investigate the dynamics involved in natural population recovery. However, long-term studies after eradication are rare and little is known about seabird re-colonization or recovery. In fact, general information about abundance, including baseline counts and breeding habitat, is still poorly known for most seabird species in New Zealand. New Zealand has completed the greatest number of eradication projects in the world, providing a unique opportunity to study a series of islands with large chronosequences since eradication.
The objective of this thesis is to address the lack of seabird research post-eradication by examining the rates and patterns in natural seabird re-colonization and population recovery on northern New Zealand offshore islands.
A conceptual model of seabird recovery after eradication will be built using global (with a focus on New Zealand) post-eradication studies, including any information available regarding seabird response. Factors such as species of predator eradicated, remaining threats, distance to a source seabird population, life history characteristics of each seabird species, availability of nesting habitat, social facilitation, and inter-specific competition will be used to predict where seabirds re-colonize or populations recover. The spatio-temporal nature of seabird colony recovery on Korapuki (predators removed 1987), Moutohora (predators removed 1987), Stanley (predators removed 1991), and Ohinau (predators removed 2005) Islands will be mapped using >10 years of burrow density and distribution data. Furthermore, the role of nest-site preferences, social facilitation, and intra-specific competition or facilitation in affecting the spatial growth of northern seabird colonies will be examined in the predator-eradicated Mercury Islands versus the predator-free (control) Alderman Islands. These findings will be amalgamated into a national framework to guide which islands we can (and should) monitor natural seabird recovery versus which islands may need further management interventions to encourage future recovery.
This research project is being funded by Landcare Research, Department of Conservation, and Natural Sciences & Engineering Research Council of Canada (NSERC).