Introduction Common etiologies of hypersensitivity pneumonitis (HP) include avian, bacterial, fungal, occupational, and agricultural exposures. We present a case of HP to an external avian antigen that became present in the home. Case description A 69-year-old non-smoking retired teacher with adult-onset asthma presented with an 18-month history of dry cough without improvement with ICS/LABA or H2 antagonists. She had been treated with prednisone 10mg daily for four months with difficulty tapering due to cough. She denied fevers or weight loss. She had no pets although previously had a bird feeder in her yard but denied pigeon exposure. Exam was notable for diffuse rhonchi. Chest CT showed patchy ground glass densities. Spirometry demonstrated FEV1 1.70 (74%), FVC 2.41 (80%), FEV1/FVC 0.71. An initial HP panel was negative, but IgG sent later for pigeon droppings was positive. Due to high suspicion for HP, patient's home furnace filter was analyzed which showed a precipitin band to pigeon droppings. After changing home filters and avoiding pigeons, her cough resolved, and prednisone was tapered to 1mg. Discussion Organic material from pigeon droppings outdoors can become aerosolized and compromise indoor air quality. The diagnosis of chronic HP may be difficult to confer in patients with persistent asthma. Our patient's refractory cough, CT findings, serum IgG and filter pigeon precipitins, and symptom resolution with avoidance met criteria for HP. Despite not owning or working with birds and a negative commercial lab HP panel, a high suspicion allowed for identification of an unsuspecting outdoor source within the home.