Apart from the natural phenomenon, there are some factors which decide how long a sparrow can stay alive:
This is common to every animal, even human beings. When a sparrow is prone to attack by predators, it can start counting out its days as it will almost be under attack every day, and sooner or later, the predator will succeed in its goal.
However, where there are no predators, a sparrow will be able to live its life peacefully and probably live its full life in tandem with its body system. Illegal hunting and poaching also pose a threat to the lives of sparrows.
The environment also plays a big part in determining how long a sparrow will be able to stay alive. A sparrow living in a habitat where it is able to get sufficient food, where it can breed successfully, will tend to live out its full years. Where there abound sufficient resources necessary for its survival, sparrows will be able to thrive and survive successfully.