You may have noticed that as it gets lighter earlier that the birds are beginning to sing more. What triggers this change in behavior?
A key part of a bird’s brain is affected by seasonal change. When birds are exposed to longer days, the cells start to release a thyroid-stimulating hormone, previously associated only with growth and metabolism. It indirectly stimulates the pituitary gland to secrete further hormones called gonadotrophins, causing male birds' testicles to grow and, results in increased singing during breeding season.
So now is the time to be thinking about providing nesting material and nesting boxes to attract wild birds in your yard because there is nothing like birds’ songs to herald the approach of spring.