PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 138, Fall 2004: Long-term Data Sets at PRBO


Long-term Data Sets at PRBO--Past, Present, and Future

Time: The Ecology of Change

Nils Warnock, PhD, William J. Sydeman, PhD, and Tom Gardali

The Ecology of Change
Three Long-term Examples
Executive Director's column
The Future of Long-term Data Sets
Long-term Volunteers
Birding for the Record
John and Ricky Warriner
2004 Osher Symposium
Lasting Legacy Campaign

Double-crested Cormorants inhabit a rapidly changing world, as do other wildlife populations and humans. What time scales are needed for the scientific data guiding conservation? ©2003 Suzi Eszterhas
We live in an ever-changing world. The human population in California has grown from 1.49 million in 1900 to 36 million today, and human domination of Earth's ecosystems is almost complete. In the same period, from the late 19th century to the present, Earth's mean surface temperature has increased by 0.3-0.6°C (0.5-1.1°F), with predictions for large increases in the future. It is these kinds of changes--long-term changes--that impact our environment in ways we cannot predict. All biological systems undergo long-term change: some are cyclic in nature, while others may be unidirectional. Some may be due to natural processes, such as climate variation (e.g., colder or warmer seawater cycles) or disturbance regimes (e.g., flooding and fire); others may be due to subtle anthropogenic (human-caused) influences such as global warming.

Some of the most pressing issues of environmental stewardship require long-term data to address. For example, what effect will climate change have on birds and other fauna and flora? Does the interplay of natural environmental cycles with anthropogenic change put wildlife populations at more or less risk? Effective conservation strategies need sound scientific information on the long-term variation in ecosystems. To conserve wildlife populations, the ecological backdrop must be understood.

PRBO has been collecting data at sites in the western U.S. and northeastern Pacific Ocean since the early 1970s, building ecological "time series" rarely matched in duration or depth by other long-term research. Our studies have demonstrated the reliability of this approach for understanding ecosystem variability and the demographic processes (such as annual reproduction and survival) that determine the health of wildlife populations. When surveys reveal increases or declines over time, we evaluate the underlying causes of change, to set conservation priorities and guide conservation actions. This calls for demographic information on the ability of populations to sustain themselves, and understanding how these parameters relate to environmental variability and human-caused change.

Murres and Climate Variation
Common Murres' breeding population on the Farallon Islands responds through the decades to ocean variability. Photo © Jeff Foott

As an example, consider oceanic conditions and seabird populations in the California Current marine ecosystem (British Columbia to Baja California). PRBO studies from 1971-1982 on the Farallon Islands showed that in most years rockfish were a critical component of the Common Murre's diet. In the 1980s, a series of warm-water "El Niño-like" years apparently caused declines in rockfish stocks. Murres continued to feed their young primarily rockfish for a few more years, but as the ocean grew warmer throughout the 1990s, rockfish were less available. The murres compensated by switching their primary prey resource: from the early 1990s until very recently, they fed mostly on anchovies--a great example of how some species are able to respond to natural climate variation.

The murre's dietary shift came with a cost, however. While they produced almost as many fledglings annually when feeding on anchovies as on rockfish, the survival of breeding adults diminished throughout the 1990s. This may be related to demands on murres when they forage for anchovies, which occur farther away from the island than do rockfish. Survival of chicks through the first few years of life was apparently also low during this decade, resulting in limited population growth.

This Farallon finding exemplifies how extending the span of our data sets from years to decades has enhanced our view of climate-ecosystem fluctuations and responses by marine birds. In the 1970s, we learned that pronounced year-to-year variation in oceanographic conditions affects the Gulf of the Farallones food webs that support hundreds of thousands of seabirds. In the 1980s and 1990s, we learned that less frequent environmental variation--the so-called Pacific Decadal Oscillation (or PDO), characterized by warm (less productive) and cool (more productive) ocean water phases--is superimposed on annual variation and can also produce dramatic changes in the coastal marine ecosystem. Now, in the early years of the 2000s, with the onset of what appears to be a new PDO cold-water phase, we are again beginning to sense a corresponding shift in murre food habits and demography. Both juvenile and adult survival appear to be increasing as parent murres are again feeding their young juvenile rockfish. Most importantly, the population is growing exponentially (see page 9) and has reached a level never before seen by PRBO in 34 years of monitoring seabirds of the Farallon Islands.

Of course, human influences also play a role in seabird population change. Consider the seabird mortality caused by oil spills and gill nets in the early to mid- 1980s (see page 8). Only through understanding environmental change on multiple time scales can we properly interpret this human-induced mortality and prescribe appropriate measures to conserve seabirds and the food webs that sustain them--and us.

Landbirds and Habitat Change
The Wrentit is a beneficiary of habitat succession at Palomarin--but for how long? Rich Stallcup photo

At our Palomarin Field Station in western Marin County, we have documented changes in numbers of nesting birds, attributable in part to habitat succession. Without fire in the coastal scrub system, in 20 years we have seen Douglas-firs increase from a few trees averaging less than a foot tall to trees taller than nine feet covering more than 30% of the site. During the same period, the coastal scrub plant community has also thickened, and White-crowned Sparrows, which prefer bare ground and grasses for feeding, have almost disappeared. Wrentits, associated with dense low-growing cover, have increased dramatically, possibly benefiting from the cover supplied by both young Douglas-firs and denser coastal scrub.

Without disturbance such as fire, or direct habitat management (which could include fire), eventually a tall fir forest will replace the coastal scrub, diminishing Wrentit nesting habitat and bringing a community of tree-associated bird species, with most scrub-associated species lost.

Habitat succession is a natural phenomenon that has been unnaturally amplified by the suppression of disturbance cycles across many ecosystems. In the face of added habitat loss, conservationists must ask, Which habitat types and species do we want to manage for over the long run?

Evolving Research Questions

Nearly 35 years of experience have shown us that short-term studies often blossom into long-term research. Questions we can pose become deeper and more challenging as insights are gained over time: long-term data serve not only to test current hypotheses but also to generate important new lines of inquiry. In San Francisco Bay, a study in the mid-1990s, designed simply to ascertain the population size of potentially endangered tidal marsh birds, has continued unabated for close to a decade. With a current emphasis on demography (survival and reproductive performance), the questions of interest have evolved from basic ones (such as "How many sparrows are there?") to complex investigations of habitat influences on population dynamics. Because of its value to the design of tidal marsh habitats, this line of research has found support from habitat managers interested in how to restore San Francisco Bay marshlands for the greatest possible biodiversity within what little space remains.It is often said that the last year of data in a long-term study is the most important. Each year reveals more variability in the natural (and not so natural) world that animals inhabit, adding to our insights into their population cycles and change.

Advancing Conservation

With threats to wildlife and ecosystems increasing, and the critical need to spend conservation dollars effectively, demand for long-term (decadal and longer) ecological information has never been greater. Long-term data sets by themselves, however, do not mean much unless data are collected in a standardized manner, managed well, analyzed, and published where findings and recommendations can be assessed by other researchers, natural resource managers, and state and federal policy makers. We must also use the newest technologies and methodologies, such as Internet-based databases, where answers to queries can be easily shared (see page 7). Spatial long-term data can be illustrated using modern mapping techniques such as geographic information systems (GIS), and dynamic predictive modeling can be used to forecast changes into the future. While consistently funding long-term studies is challenging, it is one of PRBO's highest priorities.

The future of PRBO's conservation science will remain closely tied to our long-term data sets. In the short-term, our data will be used to guide large-scale restoration projects, such as the 12,000 acres of South San Francisco Bay salt ponds that are destined to become tidal marsh, and riparian habitats along hundreds of river miles in California's Central Valley. In the longer-term, we will use these data sets to unravel the mysteries of global warming and how biological communities may respond, and to help address new threats and challenges as they emerge. What will the impact of the West Nile virus be on western bird populations? How will the seemingly uncontrollable spread of non-native species, such as smooth cordgrass (Spartina alterniflora), affect coastal waterbird populations? These questions are approachable only if we have strong background information with which to compare perturbed systems.

It has taken PRBO decades to begin to understand the natural range of variation in western and Pacific bird populations and their ecosystems--and to begin to identify areas for sound conservation investment. We are just beginning to truly comprehend environmental variation in interaction with human-caused change. To understand change at that next level may well take a century or more of ongoing data collection, analysis, and synthesis.

On our small, ever-changing planet, it is PRBO's intention to continue making significant contributions to the ecology of change--applying our long-term studies to provide novel and valuable perspectives in conservation science.

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