Its easy, just have a argentavis with good health and 200℅ speed. If they come after you fly away of their nest they will not agro you anymore. Make a trap to get easy Wyvern Milk. Dont worry dont come close to lightning.
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.