Plain backgrounds bring attention to the bird you’re photographing. There are definitely cases where background elements add to the photo, but there are also many in which busy backgrounds crowd and overwhelm the subject. For bird photos, especially in the Caribbean, sky and water are probably two of the most common plain backgrounds, but there are plenty of others if you look out for them.
A blue sky is visually pleasing, offers superb contrast, and, even when the subject is perching, reminds us that birds are creatures of the sky.
Cloudy skies, on the other hand, are usually not nearly as pleasing. They can also make it harder to get a good exposure when a dark bird is backed by a bright, white cloud. Sometimes it is possible to shoot from a different position so there is some blue sky behind the subject.
Water can be a fantastic background. Up close, it may be mostly plain, but with ripples that convey a sense of movement.
Water in the far background can blur into washes of color that give the background some texture.
Very still water can also provide a reflection of the subject, surrounded by otherwise empty space.
Vegetation can be relatively plain as well. In this example, much of the vegetation is out of focus, creating a soft green background. Even the parts that are in focus have a relatively consistent yellow-green color that contrasts well with the bird.
Solid stone backgrounds probably aren’t as easy to come by, but they can do a great job highlighting a subject.
Manmade backgrounds can work, too. This dove was walking along with a yellow building in the background. Urban settings often make for busy, distracting backgrounds, but there are exceptions, and they may include colors that aren’t so easy to find in the wild.