Watership Down (1978)

Plot hole: Perhaps the biggest plot hole in the movie is centered about the reappearance of the Owsla officer Holly. Even if the warren was destroyed right after Hazel's band had departed, Holly would not have caught up with them right before the new warren at Watership Down - even with the delay at Cowslip's warren - with the additional detour in Efrafa, considering that acquiring the amount of information he got from its organization would take more than just one or two days. In addition, Richard Adam's novel, on which this movie is based, features the location of Efrafa some distance away from the down, nowhere between it and the Sandlefort warren (Hazel's and Fiver's home). In fact, Holly went to Efrafa (along with a missionary group of Hazel's band) some time after they had settled down in the new warren.

Hazel: Lord Frith, I know you've looked after us well, and it's wrong to ask even more of you. But my people are in terrible danger, and so I would like to make a bargain with you. My life in return for theirs.
Frith: There is not a day or night that a doe offers her life for her kittens, or some honest captain of Owsla, his life for his chief. But there is no bargain: what is, is what must be.

Trivia: Occasionally the rabbits use terms which are not explained in the movie, but which are featured in Richard Adam's novel, along with their meanings. For interest, some of these are: "owsla"=a term for a selected band of rabbits responsible for both security and raiding parties (for vegetables, mostly; organization varies with the warren); "hraka"=rabbit droppings or something similarly offensive; "tharn"=mad or paralyzed with fear; "elil"=any rabbit-killing/-eating enemy; "hrududu"=generic term for motorized vehicles; "zorn" (which Holly cries out right before he joins the others near the new warren)=catastrophe; "Frith"=the sun; "Inle"=the moon, or death; "hlessi"=a wandering rabbit.

Question: I'm trying to remember the song that was made famous by this film. Can anyone help me?