In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males.
ɪn dʒˈɛnɚɹəl, ɐ dˈiːpɚ vˈɔɪs ɹˌɛpɹᵻzˈɛnts ɐ hˈɛviɚ ænd mˈoːɹ pˈaʊɚfəl ˌɪndᵻvˈɪdʒuːəl, ænd ðɪs mˈeɪ biː səfˈɪʃənt tə pɹɪvˈɛnt ɪntɹˈuːʒən baɪ smˈɔːlɚ mˈeɪlz.