May 20, 2010

Another Rare Bird: Trumpeter Swan’s Story

Filed under: Adaptation, Animals

Last week, we reported on a truly rare bird—that is, a story in which “global warming” was linked to something good happening to a “good” species, in that case, the grey whale. This week, we have found another rare bird, literally. We report on a findings which suggest that global warming is benefitting another iconic, beloved species, the Trumpeter swan. Maybe there is a growing trend here.

Since it is apparently acceptable practice for Science magazine to accompany an article extolling the evils of anthropogenic climate change (and the need to take action) with an picture of a polar bear (or two) stranded on an ice floe (even though polar bears were not mentioned in the article), perhaps we’ll accompany all of our articles with a photo of a thriving Trumpeter swan. After all, what’s good the goose (or, er, swan)…


Trumpeter swans thriving in a world of enriched CO2.

The Trumpeter Swan Society has been around for over 40 years, and we certainly commend their conservation efforts. On their homepage, they state that “The Trumpeter Swan is North America’s largest waterfowl and one of its rarest native birds. To many people, it is the embodiment of grace, beauty, and unspoiled wildness. It is also an inspiring reminder that we can save some species that have been reduced to near extinction.” Their website also includes statements like “Trumpeter Swans once flourished across much of North America, but by 1900 were nearly extinct due to commercial and subsistence hunting. In recent decades, Trumpeters have begun a wonderful recovery due to the efforts of many people and agencies rebuild healthy and resilient populations that can remain secure amidst our rapidly changing landscape and increasing human impacts”. We knew it wouldn’t be long before the climate change card was played, and sure enough, the Society states “As Trumpeters return, the swans face major problems including climate change, new diseases, lead poisoning, habitat destruction, and the loss of their traditional migration patterns. Their secure restoration requires that we provide adequate long-term habitat, rebuild essential migrations, and create broader distributions that will reduce vulnerability to large-scale die-offs from disease or severe winter weather. Knowledge of the species and its needs, effective advocacy, vision, public involvement, and proper habitat management are essential to success”. Notice that climate change was listed first as a major problem faced by the incredible birds.

A recent article in the Journal of Wildlife Management in which the title includes the words “Evidence of Alaskan Trumpeter Swan Population Growth” – that caught our eye immediately. We are always looking for good news about the trumpeter swans, and we found it in this article produced by five scientists from the states of Alaska and Washington. The work was supported financially by the United States Fish and Wildlife Service division of Migratory Birds Management, the Alaska Department of Fish and Game, Division of Conservation, a State Wildlife Grant, and the University of Alaska Fairbanks, Department of Biology and Wildlife and the Institute of Arctic Biology.” There is no apparent financial link to ExxonMobil, Halliburton, Dick Cheney, or Sarah Palin!

Schmidt et al. begin their article noting that “Trumpeter swans (Cygnus buccinator) declined to near extinction by the early 1900s probably due to overexploitation. The only known breeding pairs at this time occurred in Yellowstone National Park and Red Rock Lakes in the Centennial Valley of Montana, USA, although it was later discovered that populations existed in Alaska, USA. The first breeding pairs in Alaska were positively identified in 1954 in the Copper River Basin. This discovery prompted the initiation of surveys in an area formerly known as the Kenai National Moose Range, where 20 additional breeding pairs were found.” No doubt about it – the trumpeter swans were close to extinction over the past 100 years, and we are all thankful for the efforts to improve the number of these fabulous birds.

The Schmidt et al. team “analyzed aerial survey data collected by the United States Fish and Wildlife Service throughout Alaska between 1968 and 2005. Surveys recorded each swan as a single, pair, pair with a brood, or a flock, and the number of cygnets and number of individuals in each flock were also recorded. Survey coverage increased substantially throughout the study period in response to an apparent increase in distribution of breeding trumpeter swans observed during other waterfowl surveys. Eight total surveys were available for analysis.” By the way, “cygnets” are baby swans, and did you notice the comment here about the increase in the distribution of swans during the 1968 to 2005 period? These four decades are well within the period with a warming earth (and a warming Alaska), and the swans expanded their numbers and range.

Let’s see how the swans are coping with climate change. Figure 1 shows the number of adult swans in Alaska since 1968, and if you notice that the number went from around 3,000 in 1968 to over 20,000 in 2005, then we are indeed looking at the same graph. Schmidt et al. also found that the estimated number of cygnets increased from less than 2,000 in 1968 to approximately 10,000 in 2005.


Figure 1. Estimated annual total abundance of adult trumpeter swans in Alaska, USA, between 1968 and 2005 from the hierarchical analysis including 95% credible intervals (dashed lines). Solid line indicates estimates from the best model. Solid circles indicate raw counts observed during surveys each year (from Schmidt et al., 2009).

Their discussion of these remarkable upward trends is interesting. Schmidt et al. state “We expected lower counts at higher latitudes because the initial population of swans was concentrated in the southern part of Alaska. Only in later years did swans begin breeding in more northern areas, so counts were generally higher at lower latitudes where the population had been growing for years. It is possible that a change in population distribution and growth is due in part to climate warming. Swans are likely limited in the northern part of their range by the number of ice-free days necessary to successfully nest and fledge young”. Furthermore, they note “Many changes associated with climate warming have been observed in the Arctic, including a nearly 12-day increase in the number of ice-free days over the last 100 years. It is feasible that this increase in the number of ice-free days is enough to allow swans to breed in areas that were previously unavailable due to ice cover.”

As we saw at the beginning of the essay, the Trumpeter Swan Society is concerned about how the swans will cope with climate change – the evidence presented here suggests they are doing just fine.

Reference:

Schmidt, J.H., M.S. Lindberg, D.S. Johnson, B. Conant, and J. King. 2009. Evidence of Alaskan Trumpeter Swan Population Growth Using Bayesian Hierarchical Models. Journal of Wildlife Management, 73, 720-727.




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