Penguins Shown to Be Poor Indicators of Global Warming
Saraux, C., Le Bohec, C., Durant, J.M., Viblanc, V.A., Gauthier-Clerc, M., Beaune, D., Park, Y-H., Yoccoz, N.G., Stenseth, N.C., and Le Maho, Y. 2011. Reliability of flipper-banded penguins as indicators of climate change. Nature 469: 203-206.
Introducing their study of the subject, Saraux et al. (2011) note that "in 2007, the Intergovernmental Panel on Climate Change highlighted an urgent need to assess the responses of marine ecosystems to climate change. Because they lie in a high-latitude region, the Southern Ocean ecosystems are expected to be strongly affected by global warming. Using top predators of this highly productive ocean (such as penguins) as integrative indicators may help us assess the impacts of climate change on marine ecosystems."
Following that charge from the IPCC, several recent reports have used data collected from penguins marked with flipper bands (Barbraud and Weimerskirch 2001; Jenouvrier et al., 2009) to predict impacts on the entire population from climate change scenarios modeled for the future. Flipper bands are metal markers attached to the upper part of the front flipper, where they are easily visible on land or in the water. Since penguins are birds that fly through the water, these "flippers" are actually wings and thus the sole source of a penguin's swimming power. Banding involves a single loop slipped over the upper, muscular section of one wing (equivalent to the human upper arm) and is meant to remain there for the life of the bird. But might these bands have an influence on the data being collected on these penguins?
In an attempte to answer this question, research was conducted over a decade, in part to test the assumption that birds would adapt within a year at most to any negative effects of the metal flipper band (Barbraud and Weimerskirch 2001). Specifically, Saraux et al. (2011) analyzed differences in reproduction and survival on 50 banded and 50 unbanded penguins over ten years. Types of data evaluated by the researchers included annual and overall survival, arrival time at the breeding colony, laying dates, breeding success, success in chick rearing, duration of feeding trips ("foraging") and population growth.
Results indicated that the "banding of free-ranging king penguins (Aptenodytes patagonicus) impairs both survival and reproduction, ultimately affecting population growth rate." Over the course of the 10 year period, banded birds were found to produce 39% fewer chicks and had a survival rate 16% lower than non-banded birds. Much of this effect appeared to be due to an increased time banded birds required to find sufficient food (both before and during the summer breeding season) and to their relatively late arrival at the breeding colony.
With respect to the implications of their findings, Saraux and colleagues write that "one of our major findings is that responses of flipper-banded penguins to climate variability (that is, changes in sea surface temperature and in the Southern Oscillation index) differ from those of non-banded birds. We show that only long-term investigations may allow an evaluation of the impact of flipper bands and that every major life-history trait can be affected, calling into question the banding schemes still going on. In addition, our understanding of the effects of climate change on marine ecosystems based on flipper-band data should be reconsidered."
IPCC authors take note!
Barbraud, C. and Weimerskirch, H. 2001. Emperor penguins and climate change. Nature 411: 183-186.
Croxall, J. P., Trathan, P. N. and Murphy, E. J. 2002. Environmental change and Antarctic seabird populations. Science 297: 1510-1514.
Jenouvrier, S., Caswell, H., Barbraud, C., Holland, M., Stroeve, J. and Weimerskirch, H. 2009. Demographic models and IPCC climate projections predict the decline of an emperor penguin population. Proceedings of the National Academy of Sciences USA 106: 1844-1847.
Tynan, C. T. 1998. Ecological importance of the southern boundary of the Antarctic Circumpolar current. Nature 392: 708-710.