This is my favorite DIY way to create "birdsavers" (https://www.birdsavers.com/). This method works great for windows up to ~80 inches wide where you have access from outside (ground level or ladder) or from inside through an adjacent window (this case). These expandable tension mount curtain rods come in a variety of lengths from short (18-24") to pretty darn wide (48-84"). For bigger windows I've used simple wooden dowels. I've also experimented with chains and the paracord itself for the topline, but don't love those methods because they tend to sag. Method depends on your access and your mounting options. These tension rods only need a very small lip.