Timescales of response by pelagic seabirds to global climate change

Background/Question/Methods

Global climate fluctuates on several timescales.  We have characterized some of these scales as “cycles”, “trends” and “regime shifts”, in order of increasingly large period, and asked how these environmental changes have impacted populations of pelagic birds.  We have drawn a broad diversity of examples of seabirds from all the world’s major ocean basins to characterize and compare variation at each of these three scales.  We draw on abundance data from shipboard surveys as well as demographic data collected in nesting colonies. 

Results/Conclusions

Cycles: There are many examples of seabird response to cyclic variation in climate, especially ENSO.   The most dramatic responses to cyclic variation are from the Pacific and include Sooty Shearwaters, alcids and pelicans.   Indications so far are that, by virtue of their longevity and consequent ability to breed in many years, seabirds recover quickly from declines related to these short-term cycles.  Trends:  Some longer term (decadal or more) declines and increases in seabird populations have occurred that are correlated with longer-term changes in oceanic climate.  These include shearwaters and murres in the Pacific, penguins and petrels in the Antarctic and kittiwakes and alcids in the North Atlantic.  Regime Shifts:  There are clear examples of regime shifts in marine ecosystems of the North Pacific, North Atlantic and Antarctic Oceans, but these shifts have apparently not caused changes to the dominance structure of seabird communities.   For all of these examples, the climate impacts are mediated through oceanic productivity and seabird prey resources, in direct contrast to results known from terrestrial systems.