The red-billed blue magpie at the north gate of Dongshan Lake Park in Guangzhou is invisible.

Does the subject want to ask "the reason why the red-billed blue magpie can't see at the north gate of Dongshan Lake Park in Guangzhou"? Food supply, migration season.

1. Food supply: Food supply is an important factor for birds to choose their habitat. The food resources near the north gate of Dongshan Lake Park decrease or make the red-billed blue magpie unsuitable, and they will choose to forage elsewhere.

2. Migration season: Birds migrate according to seasons and climatic conditions. Red-billed blue magpie is a seasonal migratory bird, so it only appears near the north gate of Dongshan Lake Park in a specific time period or season.