Long-tailed acrobat

Watching Blue Planet of a Sunday evening you can only marvel at the differences and adaptations in species, and the avian ones in our elder tree are no exception.

Thankfully I already had the window opening, enjoying the starlings falling out in heaps, otherwise I would have had to enjoy the long-tailed tits through the glass as they are so skittish.  They arrive in a mini flock, one second they are there, blink, a dog barks, a door slams, a camera clicks and they are gone in that same instant.  But why do they hang off the branch to eat their seeds?? Is it the length and fragility of their legs or the balance with their beautiful long tails?  Hopefully gladders or intothehills or another of our blipexperts will have an answer for me...