Modifiers matching visa:

• valid,
• migrant,
• permanent,
• resident,
• temporary,

Simple categories matching migrant:

• warbler,
• population,
• group,
• shorebird,
• bird,
• organization,
• worker,
• waterbird,
• language,
• fish,
• thrush,
• passerine,
• finch,
• sandpiper,
• songbird,
• sparrow,
• insectivore,
• labourer,
• visa,