Which situation causes birds to become pests?

Birds can be considered pests primarily when they consume seeds that are intended for regeneration projects. This consumption can lead to significant setbacks in efforts to restore or enhance specific plant populations that are critical for ecosystem health or agricultural productivity. When birds feed on these seeds, they can reduce the number of plants that successfully grow, ultimately impacting plant diversity and the broader environment.

The other options, while they might be seen as nuisances or inconveniences, do not typically classify birds as pests in the same way. For instance, birds chirping excessively is usually a natural behavior and part of their communication, but it doesn't impact human activities or resources directly. Migration during winter is a seasonal behavior essential for survival, not a pest-related issue. Similarly, while nesting near human habitation can sometimes be a cause for concern due to potential damage or sanitation issues, it doesn't usually affect the biological objectives of regeneration projects or the ecosystem in the direct manner that seed consumption does.