The researchers had previously collared 15 bears. They tracked them to learn where the bears were instead of massacring thousands of salmon as usual and discovered the bears were upslope. On the hills far above the streams red elderberry bushes flourished and the bears were gorging on carbs. All the bear droppings seen that summer were full of elderberry skins. (Amazing that these aren’t digested!)
Normally, the salmon run doesn’t overlap with the ripe elderberries so the bears feast first on fish and then later move upslope to eat the ripe fruits. But through examining historical data, the researchers saw that this timing had shifted.
That grizzly bears would abandon the calorie-rich salmon in favor of berries didn’t make sense. Because bears are preparing for winter hibernation, the men thought the animals would choose the highest calorie food and that they only ate the elderberries because the salmon run was over. To help make sense of this, they talked to Charles Robbins who oversees the Bear Center at Washington State University. Robbins told them that bears need to get 17 percent of their energy from protein and if they ate more protein than that, the bears lose weight.
Salmon are far too rich in protein—it accounts for about 84 percent of the energy in their flesh. But elderberries, by astonishing coincidence, comprise around 13 percent protein—far more than your typical berry, but almost exactly the optimal amount for a grizzly bear. By focusing on that single food, the bears can gain weight as fast as possible.
Now, in years with unusually warm spring weather, the elderberries flower earlier and the fruits are ripe earlier, coinciding with the salmon runs. Elderberries are ripening 2.5 days earlier every decade, on average. And if this continues, by 2070 the elderberries will regularly ripen at the same time the salmon swim into the island streams to spawn.
Scientists have assumed that generalists like bears “will fare better under climate change because they have more dietary options,” says Stephanie Carlson, an ecologist from the University of California, Berkeley. That might not be the case. The bears, Carlson says, are used to “riding different resources waves,” bouncing from one high-quality foraging option to the next. If the berries ripen earlier, that might be a good thing, but once they’re done, the bears will have missed out on the earlier salmon pulse.
Of course the situation is more complex than this. Other animals depend on the bears leaving behind dead salmon. Plants depend on the bears’ feast because the decaying salmon replenish soil nutrients. These sockeye salmon are wild and not all fish spawn at the same time, so some are swimming in later, unlike fisheries dependent on hatcheries. Thus, after eating the earlier ripening berries, the bears could switch to the late-spawning salmon, although their numbers are much less than the primary run. Perhaps there are other nutrient needs the bears obtain from salmon that elderberries won’t provide, such as fats?
The case of the Kodiak bears represents “an under-recognized phenomenon—that of increasing synchrony of [natural] events due to climate change,” says Nicole Rafferty, from the University of California, Riverside. “And the consequences of this shift in foraging behavior could be large with knock-on effects for the ecosystem as a whole.”
“Species that never lived together can now interact because we’re removing the barrier of time,” says Armstrong. “We’ll see these new combinations that we never thought about, and we’ll get strong responses that no one could have ever predicted.”
Most stories of climate change consequences on ecosystems deal with plants and animals being out of sync. Flowers mature before the pollinators arrive. Birds migrate in to nest to find their food plants already fruited. Animals shift their habitats upslope to cooler sites but the plants don’t move as fast.
Now we hear that climate change can remove the barrier of time and allow species to intermingle that time had kept apart! What strong response might we see next?
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