There is a lot to learn about casting and bird nests happen due to a problem in your cast. Usually, it is where there is too much spool coming off the line. Quite simply, you want the spool to stop with the lure and you will learn this with experience.
Here are 3 ways that you can improve your casts to prevent this;
1. Use your thumb to control the spool Learning how to control the spool is a big part of casting. You can practice casting in a field or other large area and dont need to be where there is water. You should start by making sure that the tension is set so that when the lure hits the ground, the spool turns no more than a quarter turn. Keep on casting to learn how to control your spool - use your thumb to stop it feeding the line by pressing down on rim once the lure has stopped.
2. Buy a reel to fit your hands As above, If you have good thumb control then your casting will be much better, so get a reel that fits right. A higher price doesnt always mean better and ergonomics will play an important part in your decision. Once you master how to cast, you can then look into other features that are available.
3. Make sure the rod tip follows the lure After casting, you should keep the rod tip pointing in the trajectory that the lure is following; if you drop the tip before or when the lure hits the water then you might find that extra line is being spooled off, even though the lure has stopped. This will also cause bird nests. It can also happen if you have too much movement in your wrist after casting.
You should find that a baitcasting reel is great fun and very rewarding although you will have to get some practive in first With a some practice, you can easily overcome the problem of backlash when casting. Don't be put off by it and if you are still having problems, practice some more and re-read these 3 tips.
