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Difficulty: HardCommand of Evidence: Textual

Ecologist Dr. Amina Yusuf and colleagues investigated the nesting habits of the red-billed oxpecker (*Buphagus erythrorynchus*) in South African savannas. Because these birds are secondary cavity nesters—meaning they rely on existing cavities in trees to build their nests—their breeding distribution is thought to be limited by the availability of these shelters. Some biologists hypothesize that oxpeckers depend almost entirely on cavities excavated by primary cavity nesters, such as woodpeckers. Yusuf and colleagues, however, contend that oxpeckers primarily utilize cavities formed by natural wood decay and branch breakage, suggesting that oxpecker populations can persist in environments even when woodpeckers are absent. Which choice, if true, would most directly support Yusuf and colleagues' contention?

  1. In a survey of red-billed oxpecker nests across multiple savannas, the researchers found that over 80 percent of the occupied cavities had irregular, fractured borders and internal wood rot, whereas fewer than 15 percent had the clean, symmetrical edges characteristic of woodpecker excavations.Answer
  2. B
    Savannas with high densities of red-billed oxpeckers also tend to support larger populations of large herbivores, whose hides provide the ticks and insects that constitute the primary food source for the birds.
  3. C
    In savannas where woodpeckers are scarce, red-billed oxpeckers were observed actively excavating new nesting cavities in healthy, decay-free trees.
  4. D
    As global temperatures rise, the rate of natural wood decay in South African savannas is projected to increase, which will likely lead to a corresponding expansion of the red-billed oxpecker's geographic range.

Answer

In a survey of red-billed oxpecker nests across multiple savannas, the researchers found that over 80 percent of the occupied cavities had irregular, fractured borders and internal wood rot, whereas fewer than 15 percent had the clean, symmetrical edges characteristic of woodpecker excavations.
The correct answer shows that the vast majority of occupied oxpecker nesting cavities exhibit physical characteristics of natural decay and fracture, while only a small percentage show signs of woodpecker excavation. This directly supports the contention that oxpeckers primarily use decay- and breakage-formed cavities rather than relying on woodpeckers.

Step-by-Step Solution

1
Identify the core contention of Yusuf and colleagues in the passage.
The researchers contend that red-billed oxpeckers primarily nest in cavities formed by natural wood decay and branch breakage, rather than depending on cavities excavated by woodpeckers.
To determine what evidence would support this contention, we must first clearly define the claim being made.
2
Evaluate what findings would directly demonstrate that oxpeckers use natural decay cavities instead of woodpecker-excavated ones.
Direct physical evidence showing that actual oxpecker nests are located in cavities with decay/fracture features rather than woodpecker-excavation features would support the claim.
Connecting the physical characteristics of the occupied cavities to natural decay processes directly validates the hypothesis.
3
Assess the options to find the one that provides this empirical support while eliminating distractors that are speculative, contradict passage details, or support unrelated claims.
The option showing that over 80 percent of nests have decay features while under 15 percent have woodpecker features is the only choice that directly supports the contention.
This option provides quantitative, empirical proof of the primary nesting cavity origin, directly matching Yusuf's contention.

Key Concept

Identifying textual evidence that directly supports a specific scientific claim.
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Topics

Command of Evidence: Textual

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