Look for" Pet immune PIR/Microwave dual technology motion detector"
"The pet motions that I have found work well in most situations are the Paradox Digiguard 75 dual lense infrared device (for animals up to 70 lbs), and the Detection System DT500, dual technology motion (for animals up to 100 lbs). I use the Paradox motion for ALL installations, and substitute the DT500 "moose proof" motion only when problems occur. Most companies make pet immune motions that work very well within their stated limits. These two just happen to be the two devices I have had the best luck with."
you can use ultrasound transmiter and receiver to do that it'sraidly avialable and easy to use i use it in my graduation project to detect the presence of human in front of access control system
Added after 4 minutes:
to differnitiate between human and animal you can use two sensors fixed in different hights