Brood size decreases with (adult) body mass, so that an elephant has fewer young (usually just one) per brood than a mouse.
bɹˈuːd sˈaɪz dˈiːkɹiːsᵻz wɪð ɐdˈʌlt bˈɑːdi mˈæs, sˌoʊ ðæt ɐn ˈɛlɪfənt hɐz fjˈuːɚ jˈʌŋ jˈuːʒuːəli dʒˈʌst wˈʌn pɜː bɹˈuːd ðˌænə mˈaʊs.