Bird migration is a common frustration when it comes to managing tunnel-ventilated houses. Why do birds migrate towards the inlet end of tunnel-ventilated houses? It is not due to the fact that the incoming air is cooler, because birds will migrate in a tunnel-fog house where the air is typically hotter at the inlet end than at the fan end. It is not because it is darker or lighter at the inlet end, because birds will migrate in clear curtain houses with evaporative cooling pads where it is darker at the inlet and in a tunnel-fogging house equipped with dark curtains where it is brighter at the inlet end. Migration is simply the result of a bird’s response to the consistent breeze that is generated in a tunnel house. The fact of the matter is that birds will also migrate in curtain-ventilated houses if there are a large number of circulation fans blowing air in one direction.