if gravity pulls us down what keeps bird (and things that fly) up?

Question: if gravity pulls us down what keeps bird (and things that fly) up?
- Keywords:
  gravity,
  how science works,
  physiscs
Asked by emilyshearsmith to Nick on 11 Mar 2014.
- Nick Wright answered on 11 Mar 2014:
  
  Well birds fly partly by flapping their wings (which allows them to push down on the air around them) and also by gliding on currents of air (kind of like a kite does). Other things fly in other ways, for example aeroplanes fly by a combination of their engines and by creating uplift due to air passing over their wings.

Question: if gravity pulls us down what keeps bird (and things that fly) up?