But was the cat in question unusually soft-hearted, or just uncommonly forward-thinking?
I believe the theory forwarded was that the lioness had lost her cub (cub?) and "out of grief" (!) adopted another species' young as replacement. The lioness was starving herself watching and guarding the wildebeast, while the wildebeast was starving being cut off from its mother. Apparently this has happened several times and was not a one-off freak accident.
So the cat didn't reason that the bird would be a good tool for catching other birds?
I wonder whether there have been any instances of predators reasoning that, in some cases, it may be better to adopt a prey animal and use it as a lure than to eat it.
Saw a documentary once where a lioness adopted a young wildebeast. Two different instincts fighting it out. So much for eat or be eaten...?