Source - GMAT Test Prep

I don't understand how the answer is related to anything.

In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear radio collars. When, as often happens, a collar slips off, it is put back on. Putting a collar on the rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart. Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. Probably, therefore, some substance in the tranquilizer inhibits fertility.

In evaluating the argument , it would be most useful to determine which of the following

1. whether there are more collared female rhinoceroses than uncollared female rhinoceroses in the park

2. how the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large animals.

3. how often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars

4. whethe male rhinoceroses in the wildlife park lose their collars more often than the park's female rhinoceroses do

5. whether radio collars are the only practical means that park rangers have for trackingthe movemens of rhinoceroses in the park


The answer is 3.

I don't understand how. How is the reason other than attaching radio collars of any significance?