The whole point of a forest garden is that you are working with nature to grow edible crops. Birds are a critical part of your ecosystem, eating all sorts of insects (as well as the occasional bit of soft fruit). You can encourage them into your garden by creating nest boxes.
Be sure to site the nest box facing away from the prevailing wind, in as secluded and sheltered spot as possible, out of the reach of cats and other predators.
The plan is adapted from the RSPB, really to help my perforated memory. It’s just a 4½ feet of 6"x1" plan, or 140cm length of 15cm x 2cm in metric. Use untreated Larch, as it’s durable and won’t contain chemicals.
What you do need is a hole saw for drilling the hole. Different species like different sized holes:
Thank you RSPB for all the information.