This is a double shell, solar-vented cool birdhouse for the Birdhouse Challenge, printable in one piece. Your chicks will thank you!
There is a drain at the bottom and a ring of ventilation holes at the bottom and top of the inner shell, and another ring of slots and holes at the bottom and top of the outer shell. Any sunlight on the outer shell sets up a convection cycle with cooler air being drawn in through the lower ring of slots and rising to exit the large holes, so the inner shell and nest remain cooler. A post and ring joins the two shells at the top for a sturdy hanger. The roof, lack of a perch, and gap between shells makes it difficult for a predator to reach the eggs or chicks. There's no bird bath because chicks won't appreciate the resulting disturbance or encouragement of predators, and the opening is high enough that the chicks won't fall out before they are ready.
Please let me know how you do!
I used http://www.drsfostersmith.com/pic/article.cfm?aid=2194 as a guide to design. Sizing - check. Heating and cooling - check, but there's no insulation for winter except to cover exterior holes to trap dead air. Proper drainage - check. Safety - check, while there's no metal plate, there are two openings that would have to be enlarged, and a squirrel would have trouble hanging on anyway. Mounting and access - check/fail. There is no cleanout plug - you'll have to use a hooked wire and fish out all the nesting materials to clean it out.
Print in one piece. Your printer will need to be well tuned. This was printed in one piece on a Solidoodle 3 with 1.75mm ABS at 205C. The walls are 1.5mm, recommend 20% infill and 3-4 shells. The opening (32mm or 1-1/4") can be trimmed for the specific species or the size can be scaled. Critical points to watch are the base, the mid-level vent slots, and the tops of the inner and outer shells. If you can't print the base well, you should probably concentrate on getting this right before continuing. You can see in one of the photos that the top of the inner shell was challenging; I have added some fins to help with closing the inner top (not shown).
160mm dia x 175mm tall - scale to fit your printer.
Sunlight can break down plastic over time through UV exposure so be sure to paint it with a light colored water-based non-toxic acrylic spray paint if you want it to last.
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