mrdu madhya adhmatratvat tato’pi visesah

Yoga Sutras of Patanjali, 1.22

mrdu = mild
madhya = medium
adhmatrartvat = intense
tato = from these
‘pi = also
visehah = kinds

The three birds are to represent the three kinds of intensity mentioned in this sutra for the ways to illumination.
Maybe one isn’t better than the other, there are just many ways 🙂