After consuming choice morsels(一口, 少量), bears abandon the carcass and return to the stream to spear another fish. Thus, bears kill far more salmon than they eat. At a small stream in southeastern Alaska, for instance, we observed a 200-kilogram female brown bear capture more than 40 chum salmon during several feeding periods over the course of eight hours. She removed over 143 kilograms of salmon from the stream but consumed only a small fraction of it.
Why is this unusual feeding behavior important for the vitality of the ecosystem? After all, in the absence of bears, the salmon would still die following spawning, and their carcasses would be eaten by birds, fishes and insects in the streams, decomposed by microbes and flushed out to the ocean. By killing many of the fatter salmon, carrying the nutrient-loaded fish to the forest, and abandoning the carcass with most of the species remaining, bears make a tremendous amount of food and nutrients available to streamside plants and animals that would not otherwise have access to this resource. The bears are truly ecosystem engineers: they deliver marine-derived nutrients to the river side system.
The spread occurs because many different animals make use of the protein and fat in the abandoned fish. Flies, beetles, and other insects colonize the carcasses almost immediately and deposit their eggs there. Gulls, ravens, crows, jays, magpies, mink, marten, and other species of birds and mammals readily and often quickly make a meal of the carcasses.
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