Actually, I don’t know if they really are brothers, but they are roughly the same size and look to be similar in age judging by the size of their antlers, and seem to like to hang out together as they roam the back yard.
So, that got me to wondering if they were, in fact, brothers — twins that grew up together and have stayed together, even during and after the rut when they should have been competitive for the same does.
And then I began to wonder if they could be identical twins, the product of a single, fertilized egg, or do white-tailed deer even have identical twins? Are all twin fawns fraternal twins?
Antler growth is strongly influenced by nutrition, however, which could account for the difference in their pattern. If they truly are brothers, what is the likelihood that they are identical, or are all twin fawns fraternal?
Unlike humans, deer have a two-horned uterus, and typically, each ovary contributes an egg which is fertilized in one of the horns, giving rise to an embryo that develops in that horn — thus, most twin fawns are likely fraternal. The incidence of identical twins is very small, as it is in humans.
However, that doesn’t mean that they are full brothers, the result of eggs fertilized by the same sperm. Using a molecular genetic analysis, studies on deer herds in Michigan found that 22-26% of twin fawns actually had different fathers (the percentage is higher in penned deer herds than free-ranging), and that the largest, oldest bucks in the herd do not always father all of the offspring. In these herds, 18% of yearlings, and 50% of 2 year-old bucks were also successful in fathering offspring.