AbstractsBiology & Animal Science

Eradication of introduced mammalian predators to restore island ecosystems has become increasingly common, with over 800 successful projects around the world. Historically, introduced predators depleted populations of many native species, leading some, especially seabirds, to extinction or local extirpation. Island restoration is dependent on seabird population recovery, due to these birds’ indispensible role as ecosystem engineers. However, natural population responses are rarely documented and recovery dynamics are poorly understood. New Zealand holds the world’s highest diversity of seabirds and has completed more introduced predator eradication projects than any other country, making it an ideal location to study seabird population processes and island restoration. In this thesis I outline a model of seabird population growth, test the importance of key ecological variables in driving the recovery of burrow-nesting seabirds (order: Procellariiformes) on islands in New Zealand, and examine a possible method of enhancing population recovery. Finally, I summarize an effective post-eradication monitoring scheme that could provide information to improve the model of seabird population growth and facilitate priority setting for New Zealand’s seabirds. My thesis begins by constructing a generic conceptual model of seabird colony growth to identify key predictor variables relevant to recovery and re-colonization (Chapter 2). I tested the importance of these variables in driving seabird population responses after introduced-predator eradication on islands around New Zealand. The most influential variable affecting re-colonization of seabirds was the distance to a source population, with few cases of re-colonization without a source population ≤ 25 km away. Colony growth was most affected by metapopulation status; there was little colony growth in species with a declining metapopulation. I conclude that these characteristics can help guide the prioritization of newly predator-free islands for active management. The distribution of burrow-nesting seabird colonies is thought to be partly regulated by the availability and quality of suitable breeding habitat, which may limit colony growth after predator removal. I used a Bayesian hierarchical modelling approach to examine how nest-site selection differs among recovering procellariiform seabird communities after eradication of Pacific rats (Rattus exulans; Chapter 3). I found that soil depth was the most important predictor of burrow presence, abundance, and occupancy in plots among islands, with more burrows found in deeper soil. There was a striking linear relationship between burrow density and time since rat eradication (P < 0.01, R2 = 0.37) and birds showed weaker nest-habitat selectivity with increasing time since rat eradication (P = 0.02, R2 = 0.47). Results suggested that selection of particular nesting habitat may be more important in small recovering populations. Thus, colony expansion immediately after introduced-predator removal may be limited by…