Bird Sudoku Level 138 Hint
Pick a row, column, or habitat with a low remaining count, then check which of its perch cells are blocked by open diagonal flight lines.
Bird Sudoku Level 138 Strategy
Hard Level 138 uses a 9x9 board with 29 perch cells, 11 blockers, and 8 habitats. Use the row and column counts first, then test each open diagonal flight line.
Bird Sudoku Level 138 Solution
Bird positions in the solution: R1C4, R2C2, R2C8, R3C4, R3C8, R4C1, R5C3, R7C2, R7C9, R8C6, R9C8.