If a birder misses the brief period when Grosbeaks pass through during migration, what might they miss entirely for the year?

Answer

The species' local availability

Because their local availability is highly ephemeral, missing the brief window of arrival in spring or departure in fall means missing the species entirely for that year in that specific location.

If a birder misses the brief period when Grosbeaks pass through during migration, what might they miss entirely for the year?
raritybirdfaunaobservationGrosbeak