Reducing image size for web presentation can sometimes result in resizing artifacts also known as Moiré patterns. These patterns are a form of aliasing resulting from the undersampling of complex patterns. Aliasing refers to the phenomenon of a new pattern arising from the original. In wings, Moiré patterns appear when the parallel barbs in feathers are undersampled when images are reduced in size. The Moiré patterns are not apparent in full resolution or properly resized images and do not naturally occur in the wings. Below are two pictures of a Wilson's Warbler wing: the left photo is affected by Moiré patterning and the right one is properly reduced in size.
Some pictures, such as this warbler, have been saved at a size that exhibits Moié patterns. Images in the database may be thumbnailed at a size that results in Moiré patterning. If you see patterns, use the “zoom and pan” from the top bar to view the image at a different percentage. The patterns often show at 33% and 66% and usually only on the smaller wings.