Yes, chia seeds are generally safe for birds to eat. While they expand after absorbing moisture, this isn't a major concern for birds as they have digestive systems different from those of humans.
Here's a tip: If you're worried about the expansion, sprinkle the chia seeds on a flat surface like a bird feeder or a piece of bread so they don't clump together.
Sunflower seeds are also a great choice for birds, as they are a popular and nutritious food source.
So, feel free to offer both chia seeds and sunflower seeds to your feathered friends. They'll appreciate the variety!