Yes, that is definitely true :)

Sorry HSC......If you look at the definition of 'defy'    you will see that birds DO defy gravity:

de·fy

dəˈfī/

verb

openly resist or refuse to obey.

"a woman who defies convention"

synonyms:disobey, go against, flout, fly in the face of, disregard, ignore;

LOL

I think that birds only TRY to defy gravity.

They do not really succeed or else they would fly into space and leave the earth's gravitational field.

Although,

I suppose they do TRY to resist gravity.....  Maybe you do too when you walk or jump ://    

It is more accurate to describe them as "overcoming" gravity, temporarily, through the sheer effort of flapping the muscles of their wings, which takes a lot of energy to do so.