Abstract
Grey-faced Petrels (Pterodroma gouldi) are a colonial burrowing seabird predominantly nesting on offshore islands of the upper North Island of New Zealand. We studied their annual breeding biology and the impact of Southern Oscillation Index climatic effects by measuring colony productivity and chick growth rates from 2011 to 2015 on Te Hāwere-a-Maki as unfavorable warmer La Niña conditions changed to favorable cooler El Niño conditions. Across all five years, annual chick hatching consistently occurred within a one-week period at the end of August but fledging variably occurred over a three-week period following Christmas. Because ship rats are pest controlled on Te Hāwere-a-Maki, we found only a slight reduction in breeding success with nearby predator-free islands. However, chick growth and fledging rates were significantly higher under El Niño conditions occurring towards the end of our study, rather than La Niña conditions at the start of our study. Our regular handling of chicks for monitoring had no discernible impact compared to a set of control chicks. The combined impacts of annual variation in predation and climate mean the Grey-faced Petrel colony on Te Hāwere-a-Maki maintains a constant population size of around 100 burrows.
Highlights
For many species, survival and reproduction are affected by climatic variation over the breeding period [1]
We conducted three growth rate investigations: (i) whether growth curves differed across islands in 2011 (‘island effect’); (ii) whether growth curves differed annually from 2011 to 2015 on Te Hāwere-a-Maki (‘annual effect’); and (iii) whether growth curves differed with the monthly Southern Oscillation Index from 2011 to 2015 on Te Hāwere-a-Maki (‘climate effect’)
In our climate effect model, we found no significant differences in growth rates of chick body mass (Figure 3b), but we did find significant differences in wing length (Figure 4b) and tarsus length (Figure 5b), associated with the monthly Southern Oscillation Index
Summary
Survival and reproduction are affected by climatic variation over the breeding period [1]. Variations in climate, and consequent indirect effects on prey, can have broad impacts on species [3]. The outcome of such impacts can be the difference. Colony breeding success is impacted by both short-term local events at their terrestrial breeding sites, such as predation and weather, and long-term regional events at marine foraging grounds, such as oceanic oscillations [10]. The impact of climate variation is further exacerbated during reproduction, when seabirds are anchored to breeding colonies and must tend not just to their own physical condition and that of their offspring and are most sensitive to changes in resource availability [11]
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