My tribe has 8 wyverns currently growing, and we found that the easiest way to get milk is to carry someone on an argy and get a female to chase you, just stay out of its attack range and it should remain aggroed on you as long as you continue to hit it with tranqs. Avoid Lightning wyverns as their projectile travels faster and in a straight line. Poison is the easiest to avoid. Works much better and is easier to us than the trap we built from a youtube vid about it.
I got a level 150 lightning egg and I was so excited to hatch the egg...that when I went to put the egg down I accidentally ate it instead. :( ps4 users: R2 ISN'T GONNA DROP THE EGG YOU'RE GONNA EAT IT LIKE ANY OTHER EGG. REMEMBER THIS. LOGIC BEFORE EXCITMENT.