Climate Change
Implications of Seabird Population Monitoring

Scientific Research on Triangle Island

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Ocean temperatures vary both in the short-term (within and among years), and the long term (over periods of many decades), dramatically affecting marine ecosystem processes. For example, in the California Current, ocean temperatures increased through most of the second half of the 20th century, peaking in the mid-to-late 1990s.

This warming had a marked effect on ecosystem functions, such that production of zooplankton in this oceanographic zone declined by 80% over this period! As events occurring at low trophic levels generally cascade through to upper levels, it is not surprising that populations of some California Current seabirds, notably Cassin's Auklets, declined in the closing decades of the 20th century. These observations pose some interesting questions:

What biological mechanisms link environmental variability (such as warm ocean temperatures) to seabird demographic processes?
And what are the consequences for seabirds in BC?

From the outset, a major focus of the CWE's Triangle Island research program has been to assess the ecological and demographic responses of seabirds to ocean climate variability. This information, which builds on research conducted by CWS in the 1970s and 1980s, will be vital to understanding how seabird populations might respond to long-term, anthropogenic climate change. We also expect that the results will be widely applicable to other areas and to a variety of marine wildlife.
Our approach to this issue has been to monitor inter-annual variation in vital rates (adult survival and breeding success), variation in adult body condition, and variation in nestling diets and growth. In addition, we are investigating whether adult birds feed at different trophic levels in years in which ocean climate differs, using stable isotopes analysis, a relatively new research technique, and investigating the consequences of this variation.
We are also conducting experimental studies on the roles of food availability and adult quality in driving seasonal trends in breeding performance (thought to be a key indicator of environmental conditions), and studies of the responses of important forage fish prey, particularly Pacific sandlance and Pacific saury, to ocean climate variability. Much of the CWE research has been done in association with biological oceanographers from Canada's Department of Fisheries and Oceans. We hope that these studies, and others, will provide us with a novel perspective on ecosystem processes and how they affect marine birds and other wildlife.
What did we find?
During the period 1994-2003, breeding success (here measured as "fledgling production", the mean mass of fledged chick produced per egg laid) of both Cassin's and Rhinoceros auklets was lower in years with higher ocean temperatures (SST, sea surface temperature). The birds were affected at all stages of breeding: in warm years, females were less likely to lay eggs, those that did were less likely to hatch their eggs, fewer of the chicks survived to fledge, and the few chicks that did fledge were light in mass (which does not bode well for subsequent survival).
Ocean climate seems to influence the abundance and availability of important prey such as Neocalanus copepods for Cassin's Auklets, and Pacific sandlance for species such as Common Murres, Tufted Puffins, and Rhinoceros Auklets, that usually feed their chicks on fish.
Not only that, but there was evidence that survival of adult Cassin's Auklets from one year to the next was very low during the second half of the 1990s, which was the warmest period.
Interestingly, we now have evidence that the Cassin's Auklet population at Triangle is recovering since the switch back to a colder ocean regime in 1999. With reproductive success having improved since then, in recent years we have been capturing more birds overall (note that the mean number caught per night banding session in 2003 approached levels from the mid-1990s), and especially more young birds (those with brown eyes), at our night banding stations.
Do these trends reflect normal population fluctuations for the species, perhaps driven by large-scale oceanographic processes like the Pacific Decadal Oscillation, or were the declines in the late 1990s anomalous? To answer questions like that, we need information gathered across many, many years.
While this research mainly focuses on Cassin's and Rhinoceros auklets, we also monitor key demographic parameters for Pelagic Cormorants, Leach's Storm-petrels, Glaucous-winged Gulls, Black Oystercatchers, Tufted Puffins, and Common Murres.
By monitoring the breeding activities of a variety of species, and species that feed at a variety of trophic levels, we hope to obtain a comprehensive understanding of the relationship between seabird biology and the marine environment. To that end, we are also involved in collaborative ventures with other researchers along the Pacific coast.