Keep in mind the size of the lungs of the animals you are imitating. As the animal gets smaller, the duration of the call should get shorter.

I hold the call in my thumb and index fingers and cupthe other endwith my hands. As I call, I open my hands to direct and amplify the sound. With each call, I open and close my hands. Get the hang of it, then you can get a little fancier and make it sound like the rabbit is struggling.