Avian

• birds of a feather flock together 
• eat like a bird
• wise owl
• eagle eye
• sing like a canary
• head in the sand
• jail bird
• the early bird gets the worm
• eat crow
• naked as a jaybird
• snow birds
• hen party
• pigeon toed
• crow's feet
• duck tail
• nest egg
• mother hen
• chick
• chicken-shit
• bird brained
• swan dive
• ugly duckling
• chicken little
• kill two birds with one stone
• free as a bird
• flew the coop
• bird's eye view
• a bird in the hand is worth two in the bush
• which came first; the chicken or the egg?
• a little bird told me
• as the crow flies
• lord love a duck
• what's good for the goose is good for the gander
• lovey dovey
• bird on a wire
• big cock on the block
• pigeonhole 
• the birds and the bees

Canine

• a wolf in sheep's clothing
• wolf down your meal
• foxhole
• foxy lady
• out fox
• coyote ugly 
• dog eat dog world
• doggy style
• sly dog
• in the doghouse
• his bark's worse than his bite
• every dog has it's day
• dog days of summer
• can't teach an old dog new tricks
• dog's dinner
• dog-eared
• puppy love
• hot dog
• bull dog
• hound dog
• dogfight
• hair of the dog that bit you
• sick as a dog
• dirty dog
• dog tired
• bright eyed and bushy tailed
• it's raining cats and dogs

Feline

• cat nap
• cat fight
• smitten kitten
• cat got your tongue?
• cat and mouse game
• cat burglar
• he's the cat's meow
• she's the cat's pyjamas
• cat scratch fever
• kittenish
• the cat's out of the bag
• curiousity killed the cat 
• nine lives
• the lion's share
• eye of the tiger
• have a tiger by the tail

Aquatic

• swim with the fishes
• swim like a fish
• drink like a fish
• lookin' like a beached whale
• crab walk
• crabby
• card shark
• loan shark
• fish tail
• fish tale
• red herring
• packed in like sardines
• clam up
• clammy
• crying crocodile tears
• crabby pants
• shrimpy

Rodentia

• eager beaver
• hung like fieldmouse
• I smell a rat
• rat race
• mousey
• ferret out
• squirell away
• getting squirrelly
• quiet as a mouse
• ratting someone out
• when the cat's away, mice will play
• rat tail
• porcupine ball
• weasel word

Ungulate

• happier than a pig in shit
• pig-headed
• pig out
• piggy back
• piggy bank
• cast pearls before swine
• war pig
• lipstick on a pig
• when pigs fly
• pig pen
• hog tied
• I'm so hungry I could eat a horse
• horsing around
• putting the horse before the cart
• ponytail
• horse play
• hung like a horse
• going through life with blinders on
• buck wild
• hungry as a horse
• you can lead a horse to water, but you can't make it drink
• beating a dead horse
• stud muffin
• wild horses couldn't drag me away
• get off your high horse
• Italian stallion
• rockabilly filly
• stubborn as a mule
• what a jackass
• cock and bull story
• bullshit
• bull's eye
• bull headed
• don't have a cow
• holy cow
• elephant ears
• ignoring the elephant in the room
• elephant in a china shop
• gentle as a lamb
• in two shakes of a lamb's tail
• the black sheep of the family
• sheepish
• put out to pasture
• that's how the zebra got it's stripes
• doe eyed
• caught like a deer in the headlights 
• goatee
• got my goat

Arthropod

• butterflies in your stomach 
• float like butterfly, sting like a bee
• the birds and the bees
• you're the bee's knees
• beehive hairdo
• don't want to mess with that hornet's nest
• wasp-waisted
• got a bee in your bonnet
• black widow
• shoo fly
• bug off
• flea bag
• got ants in your pants
• getting antsy
• he's such a parasite

Squishy

• going at a snail's pace
• snail mail
• book worm
• opening up a can of worms
• worm your way in
• leap frog
• frog in your throat
• feeling sluggish
• feeling froggy
• toadyish
• leeching off of __
• leech onto them