Birdhouse Builder · The Helper Hub — a bit of the right size just fills the circle, inside edge to inside edge
📱 On a phone screen these circles are not actual size. Print the sheet at 100% first, then hold the drill bit to the paper.
Every bird here is a cavity nester: it raises its young inside a hole. Only the Downy Woodpecker really digs its own, and it will take a box packed with wood chips to dig out. The chickadee and the nuthatch sometimes dig into soft, rotten wood; the rest take what they can find. So will two birds brought over from Europe: the House Sparrow and the European Starling. Both will take over an occupied box and destroy the eggs or young already inside. You cannot lock them out — you keep them out with the size of the hole, and the margin is small enough that a bit one step too big undoes it.
Two numbers do all the work.
1½ inch is the largest hole a European Starling cannot get through. Every box in this app is at or below it, so none of them can be taken by a starling.
1⅛ inch is the largest hole a House Sparrow cannot get through. Only the chickadee and Brown-headed Nuthatch boxes are that small. A House Sparrow can pass through 1¼ inch and anything larger — so the titmouse, nuthatch, woodpecker, bluebird, wren and swallow boxes are all open to them. That is not a flaw in the plan; there is no hole size that admits a bluebird and excludes a House Sparrow. It is why those boxes need watching, not just building.
Hole sizes are NestWatch’s (Cornell Lab of Ornithology), except two that come from an Audubon chapter chart: the Downy Woodpecker’s, which NestWatch does not list, and the Tree Swallow’s 1½ inch, where NestWatch gives 1⅜. Exclusion sizes follow NestWatch (Cornell Lab of Ornithology), “Managing House Sparrows and European Starlings”. Verified 2026-09-10.
Take this to your counselor · requirements as published for 2026
⚠️ “Plans approved by your counselor.” Building this box does not by itself satisfy 9d — show these plans to your counselor and get their approval first. Merit badge requirements also change; check the current ones with your counselor before you rely on this sheet.
Only one of the three is the box. Answer in your own words — the app can give you the facts, but the describing is the part that is yours.
Hint: which of these birds actually live near where the box will hang? A box for a bird that is not in your area is an empty box.
Hint: the entrance hole’s size and its height above the floor were chosen for your species. The floor is the same for every bird on your roof style, so the app’s nest-box table (Guidelines, then View Detailed Specs) shows how it compares with the published charts for yours — tap “Why this number?” on any row.
Hint: on the flat roof the front swings aside on one screw; on the gable the floor swings down on two pivot screws. Ask yourself why a nest box has to be opened at all, what happens if nobody ever does, and what time of year it is safe to do it.
Scout: Troop: Date:
Counselor approval of plans: Date: