While the bird dog exercise mainly works the core muscles, improving stability and strength, it also targets the lower back, shoulders, hamstrings, and glutes, making it one of the better full-body exercises you can do.
Over the years, I've done plank after plank and seen few benefits. It's just not the exercise for me. I can hold the position for about a minute before everything starts shaking and my forehead starts sweating. Even with practice, it feels torturous.