What's wrong with the blue song?

The blue song's buttocks sticky is because it is thin, indicating that there is a problem with diet or health.It mainly eats insects. It can eat leaf bee, elephant nose, golden flower worm, hoe, and ants. In addition, spiders, mussel shells, and other small vertebrates can be eaten.This kind of bird is usually active, and there are also pairs of activities. They are more good at hiding and have the characteristics of migration. Birds in different regions often migrate differently.