This page can help with Requirement 5 of the Mammal Study merit badge.
We have seen that the number of mammals a given area of land or water will support is called its carrying capacity. To influence that number, we must improve the habitat in some way.
If, for example, you would like to see more cottontails around your home, you might plant shrubs for food, and you might build a brush pile for cover. On the other hand, if you live in a city and your building is overrun with mice and rate, you would want to eliminate them. The best way is to clean up trash piles and keep a tight lid on garbage cans.
All mammals need food, water, shelter, and living space. Without all four they cannot survive. And so, if you want to influence their numbers, you must adjust the environment to their needs.
Here are a few possible projects: