can u dig a 3/4ft wide hole around your loft? if so dig a trench a few feet deep an cover it with cardboard or old carpet and some dirt, put broken bricks and sharp/spikey metal down there, if they go near ur loft, they will be hurt, unless they know its there and jump over it. might seem a bit extreme but, im sure if some1 falls down, they will flee b4 they light any fire. hope your birds stay safe mate.