Red and black brings on brown study

What's black and red with a tricky bit(e) of white and presents a watcher's brown study?

It's the male Red-backed Fairy-wren - with a grub (the tricky bit(e)).

Two brown birds. No male here? Not so fast. Bird on left shows small black patch under upper breast feathers. Last of moult? New colour emerging?

The big question: why do I never see enough blotchy birds to equal the numbers of black and red males here today and gone tomorrow?