We don’t really think of antlers as being practical weapons. No species of deer that has them has them year round, and in only one species, caribou/reindeer, do both sexes have antlers.
We tend to think of antlers as being used to attract the opposite sex and for ritualized combat between conspecifics, usually just competing males during the rut in all species but caribou/reindeer. In that species, the females retain antlers well into the winter, which they use fight for preferential feeding areas, a great asset in feeding the calves they carry through the long northern winters.
But we don’t normally think of them as weapons to be used against predators. After all, predators are a problem that plagues deer all year, not just during the rut, and if they were widely used in fighting off predators, one would think they would evolve to hold onto them permanently or at least for longer periods of the year.
The authors found that bull elk that lose their antlers relatively early tend to be in better physical condition than those that retain them, and those that lose their antlers early tend to grow larger antlers than those that retain them, simply because they have more time to grow their new antlers in the coming year.
The authors found that there is a massive trade-off for how long elk hold onto their antlers. Those bull elk that lose their antlers are preferentially targeted by wolves. Yes, even though they are in better physical condition than those that retain them, the wolves go for elk that lack antlers as weapons.
Predation from wolves could be driving elk in Yellowstone to hold onto their antlers longer, and it could explain why elk in general hold onto their antlers long after their breeding season.
This study has some interesting implications, because wolves could indirectly be selecting for smaller antler size in elk, simply because the elk that lose their antlers sooner tend to have bigger racks in the following year. Further, because the elk hold onto their antlers longer when they are in poorer physical condition, the wolves could be selecting for weaker elk that are much poorer foragers than they might otherwise be.
These questions were not addressed in the paper, but I’m sure the questions did arise as the researchers looked at their data. More work is going to have to be done, but it is clear that wolf predation is a lot more complex in how it selects for fitness in the elk population than we might have assumed.