As a biologist and a birder, I especially like watching the edges when I am out in the field. In ecology, the word ecotone refers to a transitional area between two biomes or patches of the landscape. The ecotone, or transitional boundary, may be wide or narrow, appearing as a gradual blending of the two communities across a broad area, or it may show as a sharp boundary line. Examples of the gradual blending type of ecotone would be that found between the forest and grassland ecosystems, or between a lake and the reeds and shrubs along its edge. An example of a narrow ecotone would be that between a forest an agricultural field. I suppose that the ecotone shown adjacent to my back yard is a broad and wider ecotone originating in a pond, through a wet and moist woodland which finally forms a sharp boundary with our grass; if we didn't keep fighting back the blackberries, salal, and ferns, the yard would form a broader, mixed ecotone, eventually converting to mixed woodland like that found on the other side of the fence.
Another type of edge is that represented by the seashore. Here the boundary transition can be broad or sharp, depending on the specific nature of the shore and land interface, as well as tidal level. I have often thought that the main reason I became a marine biologist goes back to reading Rachel Carson's "The Edge of the Sea" when I was in high school in the late 1950s, and to the great amount of time I spent exploring the the shores of Puget Sound south of Seattle.
Ecotones tend to be biologically rich in that they can contain not only species common to the communities on both side of the edge, but they may include species that tend to colonize such transitional areas. This increased variety of plants and animals in an ecotone is called the edge effect and is what makes these areas so rewarding to birders hoping to maximize the species that they may find.
So what, you ask, does all this have to do with bird carving? Simply, it is this: carved and painted birds also have edges, and those of us wanting to make realistic birds need to watch the edges. Spend time making the edges where feathers lie over each other so that they appear to stack softly onto the feather below. In your painting, take special care to paint the transitional edges where different colors meet blend into each other in a pleasing and realistic fashion. Mastering the techniques of doing these tasks will greatly improve your carvings.