Can starlings or pigeons clog vents or drains?

European starlings, house sparrows, and rock (feral) pigeons are cavity-and-ledge nesters that treat a dryer, bathroom, or kitchen vent opening as a ready-made nest cavity — dark, sheltered, and often warm. They build with grass, twigs, feathers, and debris, packing the material densely enough to significantly restrict or fully block the duct behind the vent hood. This is routine, well-documented behavior for these species around buildings generally, not an unusual or rare event.

A packed nest restricts exhaust airflow. In a dryer vent, that means heat and moisture that should be venting outside instead build up in the duct, which raises the appliance's operating temperature and can cause a foil or thin flexible duct to rupture under pressure. NFPA's research on home fires involving clothes dryers found that failure to clean the vent — predominantly lint accumulation — is the single leading contributing factor in dryer fires, at roughly a third of incidents, ahead of mechanical failure and electrical failure. A bird nest is a real, physically identical blockage mechanism to lint buildup, but it isn't the dominant documented cause of dryer fires; it's one of several ways the same vent can become dangerously restricted.

This is the point competitors routinely blur: not all birds carry the same legal status. Under the U.S. Fish and Wildlife Service's federal list of species the Migratory Bird Treaty Act does not apply to, European starlings, house sparrows, and rock pigeons are explicitly named as non-native species outside that law's coverage. Practically, that means their nests can be removed once you've confirmed the species — no federal permit or special timing is required the way it is for a native bird. That is a materially different situation from a woodpecker or a chimney swift, whose active nests generally cannot be disturbed at all. Confirming which bird you actually have, before removing anything, is the step that keeps you on the right side of that distinction.