The latest versions of the Empire tech (Dahua) T54IR-ZE-S3 (varifocal), or the T54IR-AS S3 (fixed focal), combined with the latest firmware, do an excellent job of alerting on animals using the internal IVS triggers. Combine that with
Blue Iris (onvif) and it works very well. Mine reliable alert on people, cars, deer, opossum, fox, and depending on minimum size settings, cats, squirrels, groundhogs, and skunks...all of which have dropped by recently. You would need to be able to run ethernet (POE) or have power if recording to an SD card only.