The extinction of the passenger pigeon (Ectopistes migratorius) in the early 20th century is often attributed to overhunting, but a closer examination reveals that the bird's own ecological and behavioral traits made it especially vulnerable. Three key factors beyond human hunting contributed to its demise. First, passenger pigeons bred in massive, dense colonies, sometimes containing millions of birds. This extreme sociality meant that when a colony was disturbed, many birds would abandon their nests simultaneously, leaving eggs and chicks unprotected. Even a single human intrusion could cause a complete breeding failure for an entire season. Second, the species depended on a narrow diet of mast—acorns, beechnuts, and other tree nuts—which themselves fluctuate dramatically in abundance from year to year. When mast crops failed across a region, pigeons faced starvation and were forced to migrate long distances, often into areas where they were more easily hunted or where habitat was already degraded. Third, passenger pigeons had a low reproductive rate: females laid only one egg per breeding attempt, and they typically bred only once per year. Unlike other birds that could quickly recover from population declines by producing multiple broods, the passenger pigeon's slow reproduction meant that even modest losses from hunting or disease could push the population toward collapse. These intrinsic vulnerabilities, combined with human pressure, sealed the species' fate.
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The reading claims that the passenger pigeon's extinction was primarily due to its own biological weaknesses, but this argument overlooks the overwhelming role of human activity. While it is true that passenger pigeons bred in dense colonies, this behavior was actually an advantage for most of their history. Colonial nesting provided protection from predators through sheer numbers and allowed efficient foraging. The vulnerability only became fatal when humans—with guns, nets, and systematic destruction—exploited these colonies. Historical records show that professional hunters targeted nesting sites, killing thousands of birds at once and destroying eggs, which no natural predator could do. The reading's second point about diet is misleading because mast failures were not new; pigeons had survived such fluctuations for millennia by moving to other regions. What changed was that human deforestation and settlement eliminated vast tracts of mature forest, reducing the available mast and fragmenting their habitat. This habitat loss, not the pigeons' dietary preferences, made them unable to find alternative food sources. Finally, the low reproductive rate was not a problem when pigeon populations were healthy. Many long-lived birds with single-egg clutches, such as albatrosses, thrive because adult survival is high. Passenger pigeons were long-lived too, but industrial-scale hunting killed adults faster than they could replace themselves. The cause of extinction was not intrinsic weakness but the unprecedented efficiency of human exploitation.
📝 ライティング指示 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).
