Table 2.

Potential mechanisms underpinning the ENSO–pandemic influenza association

	Potential mechanisms
1	Changes in bird number in SE Asia during La Niña
2	Changes in bird fitness/viral shedding in SE Asia during La Niña
3	Changes in bird stopover time in SE Asia during La Niña (more time in residence to mix with local population)
4	Changes in bird species composition in SE Asia during La Niña caused by migration changes that bring new virus segments to the region (testable by both bird species composition and virus diversity in bird-exploited waters)
5	Changes in water habitat type and abundance in SE Asia during La Niña that facilitate fecal–oral avian and swine infections, multiple infections, and reassortments

These changes would likely differ from region to region. As an example, we focus on southeast Asia. SE, southeast.