You don't say where you are, but if they were mine, it would be winter burn. The leaves that are exposed to sun and wind rather than covered by snow or shaded by other leaves are often damaged by freeze-thaw cycles and dry winds and by the lower levels of moisture in the soil even when it isn't frozen. IME they will fall off when the new leaves open or a bit sooner, and if you look closely you can see new little buds waiting to open.