PS 32-24 - Environmental drivers of egg size in northern rockhopper penguins

Wednesday, August 9, 2017
Exhibit Hall, Oregon Convention Center
Maggie A. Sawdy1,2, Connie A. Rojas1,2, Tracy M. Montgomery1,2, Eli D. Strauss1,2, Tracy Swem3, Alexander Bond4 and Christie A. Bahlai1,2, (1)Integrative Biology, Michigan State University, East Lansing, MI, (2)Ecology, Evolutionary Biology and Behavior Program, Michigan State University, East Lansing, MI, (3)Fisheries and Wildlife, Michigan State University, East Lansing, MI, (4)RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, Sandy, United Kingdom
Background/Question/Methods

Global change presents a unique threat to marine birds, who rely on both marine and terrestial environments at various points in their life histories. Change can effect these species through multiple biological pathways, both directly through changes to their environments and indirectly via trophic effects. For example, climate change affects sea surface temperatures, which alters prey population densities anddistributions. Egg size is a measure which is largely thought to correlate with maternal health and resource aquisition in birds, and thus provides an ideal metric for examining impacts of change on marine birds. Here, we combined a longitudinal dataset of egg size in the endangered northern rockhopper penguin (Eudyptes moseleyiinhabiting the Tristan da Cunha islands with long-term data on climatic variables (e.g. sea surface temperature, sea level pressure) to investigate changes in penguin reproduction. In penguins, egg size is correlated with offspring size during the week after hatchingwhich may have effects on offspring survival. Contemporary and historical egg measurements from 1873 - presentprovide a viable method for evaluating changes in reproductive success on a large time scale and will allow us to examine observed population declines in this species. We regressed a variety of environmental variables on egg size and used a discriminate function created by Bond et al.(2016) to account for the effects of egg laying order. We used model selection to select the model that best explained the variation in the data. 

Results/Conclusions

Northern rockhopper penguins typically lay two eggs each breeding season. Unusually, the first egg is notably smaller than the second and rarely resultin fledged chicks. We found that first-laid eggs have increased in size over the years while second-laid eggs increased in size throughout the breeding season. Of the four islands studied, Gough Island produced the largest eggs consistently across the years. Periods of warm sea surface temperatures may have changed egg sizepotentially indirectly through decreased prey availability during this time. As an endangered species, understanding the interplay of environmental factors that affect reproductive success in northern rockhopper penguins can support the sucess of conservation efforts.