Maybe try a lower wattage bulb to provide just a small area of heat. The ducks can avoid it if they feel to hot.
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
either of those wattage should work to provide a warm area that is easily moved away from....but sufficient since they probably are close to being feathered by now. Plus they feather faster if they are not kept too warm.