smaller mesh will keep the blackbirds out. Keep them away from the food and water if you can. They carry mites and lice and some diseases too. Sparrows too. Plus they will eat you out of house and home. Squirrels will burrow BIG holes under your coop walls and steal huge amounts of food. They breed like rats and carry fleas, which carry tapeworms. Keep them gone. There is a live trap just for ground squirrels. Works great. Ground squirrels also eat eggs, just warning you. Rats also. Mice mostly just eat your feed, but they carry coccidia and fleas and Salmonella. Poison bait traps work best for rats and mice. I helped a friend with a rat and mouse problem rodent proof his nest box. He hung it on the wall, but screwed a piece of metal flashing to the wall first, then screwed the nest box onto that, and bent the top part so it hung like a slanted roof over the top of his nest box at an angle, out past the next box, steeper than 45 degrees. No rodents could reach his nest boxes (finch and parakeet) and he put the same deal for his feeders. The steep slant to the rin roofing also will keep your hens from perching on them.
