The cli­mate-change clock killing cari­bou

Popular Science - - CONTENTS -

IN THE WILD, TIM­ING IS EV­ERY­THING: MIL­LIONS OF YEARS OF EVO­LU­TION have made species de­pen­dent on sea­sonal cues. In parts of North Amer­ica, fall’s cooler weather sig­nals some birds to fly south and avoid Jack Frost’s chill; mean­while, shifts in both tem­per­a­ture and sun­light tell maple trees to shed their leaves. As Earth warms, some crea­tures are rapidly re­cal­i­brat­ing their clocks. But oth­ers, such as cari­bou in Green­land, have stuck to the same old timetable. For them, the re­sults are cat­a­strophic.

Arc­tic cari­bou herds ar­rive at their far-north calv­ing grounds in early June, when grasses and sedges would be­gin to sprout, pro­vid­ing ten­der, nu­tri­tious meals. Cari­bou, whose in­ter­nal clocks rely on sea­sonal changes in light rather than tem­per­a­ture, still ar­rive at the same time, but global warm­ing has pushed the sprout­ing sched­ule up by as much as 26 days. Lately, herds can find only tough-tochew ma­ture plants. The early ar­rival of Arc­tic mosquitoes makes things worse. In­stead of larva, adult biters now over­whelm and even take down new­borns. These cli­mate-in­duced food and pest prob­lems are killing cari­bou: In years when one Western Green­land herd meets plants and bugs that emerge early, seven times as many calves die.

Big Biter Arc­tic mosquitoes can grow to lengths of nearly half an inch.

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