Guam's forests would indeed resemble Swiss cheese without birds. Birds play a crucial role in maintaining the ecological balance and health of forests. Below are the reasons why the forests of Guam would appear as Swiss cheese if birds were absent:

Seed Dispersal: Birds act as essential agents for seed dispersal, carrying seeds from one place to another, often far from the parent plant. Without birds, many tree and plant species would not have the opportunity to spread and reproduce, leading to fewer diverse plant populations and reduced forest regeneration.

Insect and Pest Control: Birds are natural predators of insects and pests that feed on plants and seeds. Insectivorous birds, such as flycatchers, warblers, and vireos, help regulate the populations of insects that could otherwise cause significant damage to forest plants and trees. In the absence of birds, the insect population would likely increase unchecked, causing considerable damage to the forest's vegetation.

Pollination: Birds are instrumental in pollinating flowers, transferring pollen from one flower to another, allowing plants to reproduce. Numerous plant species, including trees and shrubs, rely on birds for pollination. Without birds, many of these plants would struggle to reproduce, reducing the forest's biodiversity.

Nutrient Distribution: Bird droppings, also known as guano, provide essential nutrients for plant growth. Birds defecate while perching on branches and leaves, distributing vital nutrients throughout the forest. These nutrients are then absorbed by plants, contributing to their growth and health. Without birds, nutrient distribution would be disrupted, affecting the overall health of the forest ecosystem.

Canopy Formation and Structure: The interaction between birds and plants shapes the structure and composition of the forest canopy. Birds can influence tree growth patterns by selectively perching, nesting, and feeding on certain tree species. Over time, this can result in variations in canopy density and plant composition. The absence of birds would disrupt these interactions and could lead to a more uniform and less diverse canopy structure.

Hence, the absence of birds in Guam's forests would have far-reaching consequences, leading to changes in plant diversity, forest structure, and overall ecological stability. The lack of seed dispersal, pest control, pollination, and nutrient distribution would collectively create gaps and holes in the forest ecosystem, resulting in a fragmented and degraded state that resembles Swiss cheese.