Glad you like them! I think the combination of shallow depth of field (these were shot almost wide open at f/6.3) & long focal length is giving the '3D' effect as only the subject is in focus & the background is thrown out of focus. The Cat Bird was shot at 356mm (570mm, 35mm equiv) & the Robin at 800mm (1280mm, 35mm equiv). You can use the 'Gaussian Blur' filter along with the History Brush, to selectively blur backgrounds, in Photoshop to 'fake' this effect on your images (not used here!).