Red-breasted nuthatches coat the edges of their nests in sap, keeping out pesky squirrels or other birds! By @rheisman.bsky.social But wow can you imagine getting all this resin and spreading it and then trying to get it off your BILL with no HANDS. URGH. https://www.allaboutbirds.org/news/why-nuthatches-coat-nest-entrances-sap/