What happened to the bird without breeding

There are many reasons for crashes that do not reproduce. It may be that the sex of two birds is the same, or it may be caused by mature or environmental problems.The breeding period of this bird is usually built in the birch, fir tree, and pine trees, and its nest is cup-shaped.After building it, it will lay eggs. Each nest can produce about 5-7 pieces. The eggs are green, and there are red-purple spots on it.