Sometime hasa unique “hydrogen isotope signature” – a
Sometime this winter, waterfowl experts from across Canada will gather for theirannual “wing bee.” Their task will be to sort through a small mountainof duck wings obtained from a randomly selected group of hunters, and assign thewings to piles by species, age and sex. Together with statistics from similarshindigs held in the United States, this information will provide a picture ofthe year’s kill and will also offer hints about the ups and downs of duckpopulations. That may seem like a lot to learn from a heap of dried-up remainsbut, to Len Wassenaar of the National Water Research Institute in Saskatoon, aroom full of duck wings is like an archive that can be studied for clues abouteach bird’s life history and movements.
Wassenaar and his colleague Keith Hobsonof the Canadian Wildlife Service have developed a technique for reading afeather’s chemistry and tracing it onto a map. The story begins with rain, whichalways contains a minute percentage of heavy water. That’s regular H2O burdenedwith deuterium, a rare isotope of hydrogen. In North America, the amount ofdeuterium in rainfall is greatest along the Pacic coast and decreases to theeast and south, as weather systems sweep across the continent. Every region hasa unique “hydrogen isotope signature” – a characteristic ratio ofordinary hydrogen to deuterium – imprinted onto the ecosystem, passing from therain into soil, soil into plants, plants into birds and animals.
When thehydrogen is incorporated into hard tissues, it provides a lasting clue to wherethose tissues were made. Last year, Wassenaar and Hobson used this fact toresolve a mystery that has troubled researchers for decades. Since themid-1970s, we’ve known that monarch butterflies congregate for the winter in adozen remote locations in central Mexico. Several hundred million monarchs fromEastern Canada and the U.S. settle onto the hillsides in orange drifts. But oncethe insects have landed, they all look the same to us, and we have no way ofknowing their precise origins.
Which ones came from Ontario? Which from Ohio? Ifone of the wintering sites were logged, how would this affect the breedingstock? The tried-and-true technique of tagging, which has taught us so muchabout the migratory movement of birds, has been disappointing with monarchmigration. Over the past 50 years, hundreds of thousands have been marked withtiny identication stickers, yet fewer than 130 have ever been recovered inMexico. “The tag recoveries are really appalling,” Wassenaar laments.The beauty of the new technique is its directness. By gathering dead butterfliesfrom the wintering sites and analyzing them in the lab, Wassenaar and Hobsonwere able to read each individual’s hydrogen signature. This in turn revealedwhere the butterflies had grown up.
As a result, we now know that the monarchsat the winter roosts are of mixed origins (Ontarians and Ohioans crammed in wingby wing) and that most of the overwintering flocks come from the midwestern U.S.The discovery of the midwest’s crucial importance in maintaining the breedingstock will provide an added focus for conservationists. Gratified by thissuccess, Wassenaar purrs with confidence. “The sky’s the limit with thisnew tool,” he says. Rather than spend years on banding projects, withuncertain results, why not head for the isotope lab and an immediate outcome?Certainly, that prospect appeals to Bob Clark, also of the CWS, who has urgentconcerns about the welfare of the lesser scaup, a diving duck. (That’s “scawp,”an imitation of the bird’s characteristic squawk.
) Cute as a rubber ducky withits upturned blue bill, the scaup has traditionally been among the mostplentiful of waterfowl, with an estimated population of six million. But itsnumbers took a downturn in the mid-1980s, a trend that has recently intensifiedinto a seven-year sequence of record lows. Two-and-a-half million birds havevanished. The losses seem to be worst for scaups that nest in the boreal forestof northern Alberta and the southwest Northwest Territories. Is “somethingfunny going on” in the north woods, as Clark suspects, or does the sourceof the problem lie farther south, along the birds’ migration route or on theirwintering grounds in Mexico and the U.S.
? These perplexities would be easier tocope with if we knew precisely where scaups from the boreal forest go for thewinter. Clark thinks the answers may lie in the scaup wings that are submittedfor the annual bees. Scaups grow new feathers before leaving their breedingrange, so their hydrogen signature should tell him where each bird spent thesummer, be it on the plains or in the forest. By mapping this location and thespot where the duck was shot, he expects to build a detailed picture of scaupmigrations and wintering grounds. Similar information is required for a growingnumber of migratory species, including many of our favourite songbirds.
Sincepopulation declines tend to affect particular subpopulations (like the borealforest scaup), we can no longer get by with a broad-brush sketch of migratorymovements. The hydrogen-isotope technology offers to fill in the details at amoment when this knowledge is urgently needed. Candace Savage is aSaskatoon-based writer and author of 18 books on wildlife, environmental issuesand other subjects.