Capture Bonus
From Pokemon Go Wiki
Capture Bonus grants a catch bonus when you earn medals based on catching certain types of Pokemon. These new bonuses will give you a better chance of capturing Pokemon with a related type. For example as you reach a higher tier for Bird Keeper medal, your bonus to catch Flying type Pokemon increases.
Trainers can work their way to a new tier by catching many Pokémon of the same type. If a Pokémon has multiple types, your bonus will be the average of your bonuses for each type. For example, Pidgey is both Normal and Flying type. Your bonus in this case would be the average of your Normal-type and Flying-type bonuses.