Regular – almost always observed on given visit; >=90% chance of observation
Frequent – usually observed on a given visit; >=50%<90% chance of observation
Infrequent – observed less than 50% of visits; >=25%<50% chance of observation
Occasional – observed on only on a small minority of visits; >=10%<25% chance of observation
Seldom – not usually seen on visits; <10% chance of observation
These terms refer to visits to appropriate habitats made at appropriate times of the year, making use of common sampling/observation methods. Under those conditions, Frequency refers to the chance of observing at least one individual on a given visit made anywhere within a particular region, or over multiple visits to a single site.