Modifiers matching passerine:

• passerine,
• small,
• insectivorous,
• european,
• exotic,
• migrant,
• smaller,
• interesting,
• breeding,
• upland,

Simple categories matching migrant:

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