Holt and Leroux compared the eating habits of northern saw-whet owls to northern pygmy owls and found that they prey on different animals for their main food source, with the saw-whet owl's diet 98% small mammals, while for pygmy owls over one-third of their prey was birds. Their study concluded that these owls could adapt depending on the prey and also with the other predators in the areas where they live. Engel "et al". (2015) in Chain O'Lakes State Park, Illinois, during the winter of 1987–88, compared northern saw-whet owls to long-eared owls. Engel confirmed the saw-whet owl's strong preference for small mammals. Their diet appeared varied in the winter, and was less tied to one mammal than was the long-earred owl; at times, northern saw-whet owls hunted larger prey, such as the meadow vole ("M. pennsylvanicus").