to tuck in a tail - with his/her tail tucked in
with his/her tail between her legs

e.g.

I fully agree with Andi's 'einziehen' ! -

Man 'kneift' vor einer Aufgabe, bei einem Problem / bei/vor Rückzug 'zieht' man jedoch
(aus Angst/Furcht) den Schwanz 'ein' . . .

I'm not so sure I'd use "to show the white feather." Is that BE? As for a nice picture, having someone come in "with his or her tail tucked between his/her legs..." seems much more apt than the white feather, to me at least.

@ #4: I was wondering about LEO's suggestion for it's translation . . .

(but who am I anyway ?!?) . . . ;-))

I think the expression is "he put his tail between his legs" (and took off in a hurry). I think the image is that of a dog tucking its tail between its hind legs when it is trying to escape a situation it fears. But I haven't researched it.

I haven't reasearched it, either, but the way I've always understood it is that someone has his/her tail tucked) between his/her legs when they've done something wrong or when they feel shame, regret, fear, etc.

Dude, yes, I believe I've heard that, too: "He put his tail between his legs and slunk away" (don't quote me on the past tense of "slink," however!).