The effects of environmental gradients on feather structure and function remain underexplored. We explored how temperature, rainfall, and body size influence feather morphology in 444 neotropical bird species from Colombian sites spanning 600 to 2500 meters in elevation and 732 to 7337 millimeters of rain. We found that temperature is the primary predictor of feather morphology variation, with a significant contribution from rainfall. Birds exposed to high rainfall have a downy region 4.4% larger in area than those under lower rainfall regimes. Birds inhabiting environments with low temperatures have 4% more downy area than those in hotter places. These changes in the area of the downy region of breast, back, and head feathers suggests differences in thermoregulatory demands across body regions. Our study shows that rainfall and temperature shape the general structure of contour feathers in “stable” climatic regions, providing insights into the evolutionary processes driving morphological diversity among birds.