Two animal behavior words starting with M are mating and migration.
Magic Markers
got married
Mangled umbrella.
mint chocolates
Mischievous rottweiler.
There are no English words that fit that criteria. However, there are two 24-letter words: microelectrophoretically, microspectrophotometries
Moss Moon Moose Midge Mollusk
mount rushmore
miracle
monster
MomMotherMoremagicalmarvelousmagnificentmagical
Magnificent