Moose mate selection

 

Despite the showy antler displays and asserting of dominance over lesser bulls, the victor of a competition may not do as much of the breeding as has traditionally been thought. In moose, and in a number of other species of the deer family, female choice is an important factor. A bull’s social display can impress a cow to select that bull as her mate. This has the benefit of not depleting his strength by fighting other bulls. However, a cow can reject a bull that does not suit her and remain with a sub-dominant bull of her choosing.

The social structure of a population has considerable bearing on breeding and is comprised of 5 social classes. 1). Calves — young of the year. 2). Yearlings — 2nd year, youngest sub-matures. 3). Teens — 3rd, 4th, and 5th year, older sub-matures. 4). Primes or matures— five years old and older until they become seniors. 5). Seniors— no longer involved, or interested, in breeding. Efficiency of breeding and how it impacts a population can depend on whether the social structure is “organized” or “disorganized”.

An organized social structure has a large number of prime bulls; here female choice of a mate is best seen. Being “chosen” as a mate is different than being “accepted” as a mate when there are too few options available to a cow. Primes come into rut and can breed a week, or more, earlier than do yearling and teen bulls. Therefore, they can successfully breed most cows during the early estrous period. This results in calves being born early enough in the spring that they have adequate time to grow before winter. An additional feature of an organized social structure is that yearling and teen bulls are hunted heavily enough to keep their numbers from being so high that they can be disruptive to breeding, but high enough that there will be an adequate number to replace the present prime bulls.

In a disorganized social structure, there are too few prime bulls, and too many yearling and teen bulls, so only a small portion of cows get bred early. Additional breeding will have to wait until the next estrous period of cows and therefore many calves will be born later in the spring. By then, yearling and teen bulls which outnumber the primes will be in rut and attempting to breed. There is concern that these younger bulls do not have the reproductive stamina to ensure pregnancy of the cow. A bull’s ritualistic courting behavior, which serves to “seduce” a cow, is not completely developed until it is at least three years old. Bulls younger than that are disruptive to efficient breeding of the cows.

Taiga (woodland) moose have about a three-week rut during which to breed. The cow is receptive to breeding for only about six to eighteen hours. She not only decides with which bull she will mate, when, and where; but also, how long the bull will remain with her. She usually separates from him within 18 hours of their first mating bout. During the two or three days that she is with him, she does not allow other cows to compete for him. Therefore, it is desirable to have a rather high number of prime bulls in an area.

Tundra moose gather harems of cows and breeding is completed in eight to ten days. Climatic conditions necessitate a short rut and breeding season to ensure calves are born early in the short growing season for vegetation. Although bulls have their harems, the tundra cows also choose particular bulls with which to mate. Each cow in a harem is unfriendly towards the other cows.

If a sub-mature bull approaches a harem, it is often intimidated by a threat from a cow in heat. These bulls are often sparring near the edge of the harem, but seldom stay long. Yearling bulls are tolerated unless they try to contact a cow.

Cows in a harem watch any contests between the harem bull and another prime bull. If both bulls remain in the vicinity of the cows while recovering from the struggle, the alpha cow will approach both bulls and smell their antlers. Then decide with which bull she, and likely the other cows, will mate.

Large harems may be shared by two or three prime bulls of equal rank. When two or more cows are actively trying to seduce a bull during such a short breeding season, he cannot spend as much time with each as a taiga bull spends with a taiga cow. Therefore, a tundra bull may impregnate as many, or more, cows during eight to ten days as does a taiga bull during three weeks.

Occasionally a bull moose will exhibit abnormal sexual behavior by trying to court, or even mount dairy cows. Such moose are either scared off or killed because it is potentially dangerous to both the cow and the dairy farmer.