I personally have a theory. Unseen illness,?
Wind farms, Constant harassment from avian raptors ,If loins and leopards were running loose all over the country .? I can guaranty you'd have a very fast pair of training shoes. And if they gave Chase you'd probably do something silly like knock your self out in the process of trying to get away .Or in blind panic find yourself somewhere not familiar to you and helplessly lost . Exactly the same predicament face pigeons every single time they are racing .
Chased out to sea or dying in the process to evade them . It would probably explain why none are reported.