One for sorrow, two for joy, three for a girl, four for a boy, five for a letter, six for something better.

This rhyme is often quoted when there are magpies about.  It is too superstitious for my liking.

One swallow does not make a summer.
Just because the first few birds have flown in from their migration does not mean that the weather will be warm.  There are other metaphorical meanings too.

All our geese are swans.GeeseWe think our own children are wonderful, when other people may not agree.

Swans

Swans

Duck or grouse.
This is a popular sign above a low doorway.  If you are tall and forget to duck, you may have cause to complain.  Like many words in English, grouse has to be taken in context;  as well as being a game bird, it is a slang word for grumble.

A rare bird may turn out to be a person with unusual skills.

A wily old bird is an astute person.

A bird’s eye view,
not surprisingly, is the view from above.

Watch the birdie.
I can’t see a bird!  This is a standard instruction from a photographer asking everyone to look in the direction of the camera.

She would fetch ducks off water is a comment about a pretty little girl.

Packed like sardines (in a tin).
Overcrowded.

Set a sprat to catch a mackerel.
A fishing expression concerning the bait used to catch larger fish.  It could be used about other inducements.

Fishing for something.
Something is likely to be information.

There are plenty more fish in the sea.
An expression, which is intended to help someone whose boyfriend or girlfriend has just broken up with them.

Catch as catch can.
The alliteration here is very appealing.  It sounds like a game of tag in a quotation from Samuel Foote (Penguin Dictionary of Quotations).

What’s the catch?
Something sounds like a bargain, but it is as well to make sure that it really is.

Having a whale of a time.
A whale isn’t really a fish, but in the story of Jonah “a big fish”, may well have been a whale.  The story is only four Chapters long and makes up The Book of Jonah.

Jonah didn’t have a whale of a time in the story, as it means having lots of fun.