Bird Populations before and after Wildfire in a Great Lakes Pine Forest

Birds in a 6.25-ha quadrat in a 73-year-old jack pine-black spruce forest (Pinus banksiana-Picea mariana) in Cook Co., Minnesota were intensively studied in June 1976. A wildfire burned through the area in August. The following spring we resurveyed the same quadrat to determine the first-year changes in bird populations. Species and guilds were compared by density, territorial space, existence energy, and importance values. Twelve species had territories in the study grid before the fire; six were not there the following spring, but eight additional species had established territories. Tree-foliage searchers had the greatest importance value before the fire and ground-brush foragers the greatest value afterwards. Density, total biomass, and combined existence energy of birds decreased after the fire by 50, 23, and 41%, respectively, but species using the area after the fire were 63% heavier on the average. Average energy consumption per unit of body weight was calculated to be 23% less after the fire. Fire apparently reduced the total food available for birds, but increased the kinds of food, especially at or near the ground.