As soon as Alex figured out that concealing one's aura made it difficult for the birds to notice them, their journey through the island became much easier. His concealment technique meant that no bird could see him at all. Pearl and Scarlet pulled in their Qi as well, making it so that they would leak as little aura as possible.
They failed to keep it in entirely, but what they had was enough to make them continue on without much danger. They moved slowly, not catching anyone's attention as the birds continued raining down on the various beasts.
Alex noticed that only a handful of beasts had known to conceal their aura, that too only because of his Demon Eyes. Had spiritual sense not been suppressed, they might've had a better chance at figuring it out. As it was, they didn't.
