Ask Mr. Smarty Plants

At the Lady Bird Johnson Wildflower Center, we work at the preservation and protection of plants native to North America, but we're interested in birds, too. They, and mice, however, are a little out of our line. We'll see if we can find some material that might be of use to you. We had a similar situation in an apartment with a porch and a couple of large lovely trees for shelter. We put in bird feeders and water and for about two days, enjoyed all sorts of beautiful little birds. And then, the pigeons discovered the loot. They drove away the little birds, were noisy and very messy, and gobbled up everything in sight. So, guess what? We don't feed the birds any more. But the pigeons are still out there, and turning off the food supply is not the solution, although it's necessary, because they will come back. It would appear that you will also have to turn off the food supply for at least a period of time, and then take other measures to evict the mice.

Here are three articles we found on the subject. First, from Talk About Wildlife, an article entitled Of Mice and Feeders. From the Hungry Owl Project: Rodenticides and Raptors, a Deadly Relationship. From The Ornithology Website: Clean Your Bird House to Prevent Disease.

So, once again, we remind you this is not our field of expertise, but you seem to have a real problem. If you poison the mice, you'll be in trouble for possibly poisoning some of the raptors that feed on mice, and then die if the mouse was poisoned. To get rid of the mice in the elm tree, you are either going to have to establish a colony of rat snakes in that tree, or take out the tree. Of course, mice are adaptable, they'll find somwhere else to squat. A couple of cats might help out, but they like birds, too. If you take the line of least resistance, the mice and birds will continue to share the seeds, along with various diseases, some of them pretty scary. And while we're sitting here talking about it, those mice are reproducing like you wouldn't believe. So, we would suggest you shut down the bird feeding, at least for a period. Clean up thoroughly under the feeder, clean up the feeder, and put it away in a non-mice accessible container. Then, talk to an exterminator, or research the possibility of putting some sort of pepper-based additive in the seed, that the birds can't taste but the rodents can, and find some way to condemn the mouse apartment house in your elm tree.