Your explanation captures the essence of how genetic variation can benefit the bird species, but it could be clearer and more concise. Here's a revised version:
"Genetic variation from sexual reproduction produces offspring with diverse beak sizes and shapes, enabling some individuals to adapt to a seed-based diet and thrive on available food resources. This greater genetic diversity increases the likelihood that some birds will possess traits that allow them to effectively exploit the new food source, helping the species avoid extinction."