托福综合写作

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The extinction of the Passenger Pigeon, once the most abundant bird in North America, is often attributed solely to overhunting by humans in the 19th century. However, a closer examination reveals that a combination of ecological and biological factors, not just hunting, led to its demise. First, the species had an extremely narrow diet, relying almost exclusively on mast (acorns and beechnuts) from specific forest types. This dietary specialization made them vulnerable to natural fluctuations in mast production, which could lead to massive die-offs in years of poor nut yields. Second, passenger pigeons nested in densely packed colonies, sometimes containing millions of birds. This colonial nesting behavior, while effective for predator swamping, created ideal conditions for the rapid spread of infectious diseases, such as avian trichomoniasis, which could decimate entire breeding populations in a single season. Third, the pigeons' reproductive strategy was highly dependent on synchronous, large-scale breeding events. If the population fell below a certain threshold, as it did due to habitat fragmentation, the birds failed to breed successfully because they required large numbers to stimulate courtship and nesting. Thus, even without hunting, these intrinsic weaknesses would have likely driven the species to extinction.

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The reading’s argument that factors other than hunting caused the passenger pigeon’s extinction is not convincing. First, while the pigeons did prefer mast, they were not strictly limited to it. Historical records show they also fed on a wide variety of fruits, seeds, and even invertebrates, especially when mast was scarce. So, occasional poor mast years would not have caused population collapses. Second, the claim about disease is speculative. No historical evidence documents any major epidemic among passenger pigeons. In fact, their dense colonies would have facilitated disease, but the birds thrived for millennia in these conditions. The sudden disappearance in the late 1800s coincides precisely with the peak of commercial hunting, not with any known outbreak. Third, the reproductive threshold argument misunderstands the species’ adaptability. Passenger pigeons did not require immense flocks to breed; smaller groups did nest successfully when undisturbed. The real reason breeding ceased was that hunters deliberately targeted nesting colonies, destroying eggs and adults. Therefore, the most parsimonious explanation remains that systematic, industrial-scale hunting by humans was the primary cause of extinction, and the other factors were minor or unsubstantiated.