The extinction of the passenger pigeon (Ectopistes migratorius) in the early 20th century is often attributed to human hunting, but recent research suggests that the species’ own biological traits played a more decisive role. First, passenger pigeons had an extremely narrow diet, feeding almost exclusively on mast (acorns and beechnuts) from deciduous forests. This dependency made them vulnerable to natural fluctuations in mast production, leading to periodic population crashes even before human arrival. Second, the species exhibited a highly synchronized breeding strategy, nesting in dense colonies with millions of birds. This behavior, while efficient for predator satiation, meant that any disruption—such as disease or habitat fragmentation—could cause complete reproductive failure across the entire population in a single season. Third, genetic evidence indicates that passenger pigeons had low genetic diversity, as revealed by analysis of mitochondrial DNA from museum specimens. This limited variability reduced their adaptive capacity to environmental changes, such as climate shifts or new pathogens, making them less resilient than other bird species that survived. Therefore, while hunting accelerated the decline, the passenger pigeon’s extinction was inevitable due to its specialized ecology and genetic constraints.
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The reading’s argument that biological traits caused the passenger pigeon’s extinction is misleading. While it’s true that the pigeon depended on mast, historical records show that mast failures occurred regularly, yet the species rebounded each time for thousands of years. What changed in the 19th century was industrial-scale hunting, which removed hundreds of millions of birds annually, far exceeding any natural population recovery. Second, the claim about synchronized breeding being a vulnerability ignores that this strategy had been successful for millennia. The real problem was that hunters exploited these dense colonies, using nets, guns, and even burning trees to kill birds at nesting sites, destroying entire breeding efforts in a single raid. In fact, the last large nesting in 1896 in Ohio was attacked by hunters, resulting in the death of nearly all adults and chicks. Third, low genetic diversity is not a valid explanation because many species with equally low diversity, such as the whooping crane, have survived despite severe bottlenecks. The passenger pigeon’s population was so vast that even a small percentage of survivors could have maintained genetic health if not for relentless human persecution. Thus, the extinction was a direct result of overhunting and habitat destruction, not an inevitable biological failure.
📝 Hướng dẫn viết Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
