Symbols of happiness and joy, birds are regarded as a necessity on the Christmas Tree. The male cardinal, with his bright red coloring, is popular at Christmastime. The female s feathers are lighter and yellow-tinged. Birds are symbols of happiness and joy, so they are regarded as a necessity on the Christmas tree. Glassblowers often kept wild birds during the winter months since the sound of the gas flame in the workshop prompted the birds to sing. Then when spring arrived, the birds returned to freedom.