A couple of opposite sex moose twins!
It has been suggested the ratio should be 50:50!
Are moose twins always the same sex?
Great question Peter!
There has not been a lot of research into the sex ratio of newborn moose twins but there is some information that I can tell you.
First, to answer your question: no all twins are not necessarily the same sex.
Quite a few moose investigators have found differences in moose calf ratios.
Trivers and Willard (1973) have suggested that a higher maternal investment is required to sire male calves.
Williams (1979) further suggested that where there are two offspring it requires slightly more energy to produce males than females.
According to his model, the sex ratio and liter size would could or would compromise of the following: one female, one male, to two females, to mixed twins and finally twin males.
Schwartz and Hundertmark (1993)have suggested the ratios suggested by Tivers and Williard (1973)do not conform to records from the Moose Research Center in Alaska.
None of the data has been verified and further study would be needed to verify the various hypothesis.