There are features in the frequency ranges of bird calls that suggest this. Alarm calls are usually on frequencies that have better propagation (this also depen

There are features in the frequency ranges of bird calls that suggest this. Alarm calls are usually on frequencies that have better propagation (this also depends on the habitat that birds occupy - ground living birds have much lower frequency calls because the sound spreads better close to the ground. Calls that go to chicks tend to be on higher, less propagating frequencies. On the other side, the calls that hunting birds make tend to look like an all frequency sweep - possibly they are trying to get a response from other species to locate them.