Why do snowy owls lay more eggs when lemmings are abundant?

Snowy owls adjust their reproductive output based on the availability of their primary food source. In years when lemmings are abundant, snowy owls are able to attain higher nesting densities, begin nesting earlier, and produce larger clutches of eggs compared to years when prey is scarce.1

This behavior is linked to the owl's survival strategy: egg laying is timed to ensure that young become independent when prey populations are at their peak. Because snowy owls can lay up to 12 eggs, they require significant resources to support a large brood. If prey populations prove inadequate during the season, the younger, less aggressive nestlings may starve, while the older, stronger nestlings continue to thrive. Thus, the increased egg production during high-lemming years is a direct response to the increased capacity of the environment to support a larger number of offspring.1