What factor often obscures the slow continental population decline from an observer focused only on local July sightings?

Answer

High local visibility combined with habitat niche shrinkage

A birder seeing dozens locally might be surprised by continental data suggesting decline, because habitat loss is shrinking the specific open-country niche required by the kingbird, even if individuals are healthy in remaining areas.

What factor often obscures the slow continental population decline from an observer focused only on local July sightings?
speciesbirdabundancekingbird