Vic Van Ballenberghe, who has worked for both the Alaska Department of Fish and Game and the US Forest Service, is a biologist well known for his work with moose in Alaska. He just returned from six weeks in Denali National Park, where he’s studied moose for more than three decades. And one aspect of his research is looking at why some cows are better at raising calves than others.
“You know we’ve been able to follow some cows during their entire reproductive lifetime, and we found that during that lifetime, some cows only raise one or two calves, while other raise ten or more, ” he says.
He’s been trying to find out why there is such a wide varionation. Diet plays a role, of course. Some moose are more efficient at processing food. And when food is scarce, some cows don’t get pregnant. Van Ballenberghe says maybe some cows are better at avoiding predators, or producing better milk, or finding better feeding areas
“The differences among cows are only part of the story. Maybe Some calves are better able to survive than others. And calves get half of their genes from their fathers, and so it’s important to understand something about the bulls that father these calves. And, if it’s the case that some bulls are more fit than others, and the cows can detect that, maybe the cows are actually selecting which bulls to mate with.” Van Ballenberghe says. He says his recent research in Denali supports this idea.
“And the first thing that we found, is that the mature bulls actually do most of the mating, and they do that by excluding the younger bulls, through either chasing them away from cows or actually fighting. The matures do most of the actual mating, and they do it by controlling groups of cows. ”
He says in the fall, cows get together in groups of 5 or 6 or as many as 20. Most cows remain within the group, and by choosing groups, they choose which bull to mate with.
Van Ballenberghe says mate choice among mammals is a recent focus of researchers. Some mammals mate at random, others mate through some degree of choice. In the case of moose, mating is not a direct choice, since when the cow joins a group, it’s not certain which bull will dominate.
But this brings up the question of killing off mature bulls through hunting, something that concerns biologists.
Van Ballenberghe says he is not a wildlife manager, but his research could be useful to them. The information could become a valuable tool to rebuild moose populations depleted by severe winters.
Hunting and predator control are manipulations of the moose population by humans. And there is a possibility that too much predator control could ultimately weaken the moose population by allowing the weaker bull moose to survive, according to VanBallenberghe.
“Wolf and bear predation on moose over millennia has shaped moose in terms of almost every characteristic that they have. You know, that predation pressure through evolution has created moose that are big and strong and agile and alert and they have extremely good senses of small and hearing and sight. All of those things are the net result of heavy predation by bears and wolves on moose, ” he says.
Van Ballenberghe says, removing predation pressure could allow less able moose to survive, and that would have an impact on the moose population over the long term.
Tony Hollis, a moose biologist with AK Fish and Game in Fairbanks, says management targets a 30 – 100 ratio of bulls to cows. Hollis says it’s true that cows prefer larger bulls with a greater antler spread. Hunting regulations restricting antler size ensure that some mature bulls survive to mate, Hollis says, although it is also true that a cow moose will select a mate with smaller antlers if that is what is available.