Luke the majestic male lion has apparently had enough male-female lion segregation. Sensing his mate on the other side of the wall (their habitats in the National Zoo are adjacent to one another) he started bellowing loudly as you can hear in the video. Maybe he should be renamed Luke the lonely lion.
The bellowing / mating call was even louder and more impressive in person but I hope you enjoy this little clip. God sure was creative in coming up with so many amazing animals for our plant. May He bless you and yours!