How does the four happy birds breed?

Si Xixi Birds breeds in April-July. Because the males are fighting, in order to compete for spouse, they often fight with similar campaigns for 1-2 hours.This bird will built the nest in the tree hole, and it is mostly composed of dry grass, grass roots and fine branches.Female birds will spawn in the nest. Each nest will produce 4-6 pieces. The eggs are pale green, green brown, yellow or gray, and dense brown or brown spots on it.