The squirrel trap pictured with two captured flying squirrels was taken is a humane double door live trap.  Powered doors, with a panless, push through, panel trigger will sometimes capture more than one animal at a time.  This trap actually made multiple catches several nights in a row.  Even small flying squirrels and mice will fire these cage traps as there is little room for them to avoid the trigger.  It is almost impossible for small rodents to pass through these traps without capture.  
The trigger is light enough to take small birds like chickadees.