Too Many Ender Dragons

Sorry for my poor English skill

 

There are so many Ender dragons in The End.

I used /locate and found stronghold.

When I entered End at the first time, there's only one Ender dragon.

But I died in End several times and got back to End instantly.

4~5 Ender dragons have flown in the sky.

I changed my gamemode and used tp, are they the reason of this problem?