Signaling and detecting estrus

A female elephant in estrus signals her condition through auditory and chemical signals. An estrous cow may also show one or more distinctive behaviors during this period. Cynthia Moss has described in detail estrous behavior in African elephants at Amboseli in Kenya.

Wariness: A cow is noticeably alert and wary of approaching bulls, quickly moving out of their way and not tolerating attempts to test her estrous condition.

Estrous walk: In response to approaching bulls, an estrous female may walk away briskly from her group with head held high and turned to one side as she watches the bull following her; she makes an arc before returning to her group.

The chase: An estrous cow may increase her pace to a run and may be pursued by one or more bulls. The cow usually describes a wide arc before returning to her group. However, she may stop if a bull succeeds in touching her.

Consortship: An individual cow and a large bull may maintain physical proximity for a short period. The large bull threatens or chases away other bulls that approach the pair, while the cow avoids other bulls by moving toward her partner.

A female elephant in estrus also advertises her condition through chemical signals released through urine or vaginal secretions. The nature of chemical compounds used in communicating estrus and behavioral responses by bulls have been studied in detail by L.E.L. (Bets) Rasmussen and several collaborators, in particular Michael Schmidt at Washington Park Zoo, where captive Asian ele-

phants were studied (also see chapter 4). They carried out extensive tests of responses by bull elephants to urine, organic compounds extracted from urine, and various synthetic compounds. Urine was collected from cows during the preovulatory period, the period of peak interest by the bull, and when they were anestrus. The response of bulls was tested using whole urine and extracts from urine placed in a suitable solution. Behaviors recorded included sniffing, flehmen, blowing, avoidance, and penile erections.

Flehmen behavior in elephants refers to testing a chemical signal using the trunk and the vomeronasal organ. A typical flehmen consists of placing the tip of the trunk on the part or substance of interest (the urogenital orifice of the female, urine on the ground, or temporal gland secretion [TGS], for instance) and bringing a sample of the chemical substance to the pair of vomeronasal organs located on the roof of the mouth (fig. 3.3). The tip of the trunk is curled, inserted into the mouth, and pressed against the twin orifices of the vomeronasal organ, which assays the chemical substances. A flehmen lasts for 3-8 seconds and may be repeated several times.

While a bull elephant may regularly test the urogenital orifice or the urine of a female, the frequency of flehmen responses increases about 10-fold when the cow is in estrus. In one set of experiments, the flehmenlike responses by captive bulls averaged 5.9 responses per 1-hour test with estrous urine, 3.8 per test when estrous urine extracts were resuspended in nonestrous urine, and less than 1.0 response per test when presented with nonestrous urine extracts, nonestrous urine, or other controls, such as organic solvents used in urine extraction.

Naturalist M. Krishnan, several years earlier, described an advertising behavior by a female elephant in which she slapped the tip of her bristly tail against the urogenital region and held it aloft for some moments. This behavior

Figure 3.3

Detecting estrous in elephants: (left) a bull tests a cow for estrus and (right) performs a typical flehmen. (Photo courtesy of R. Rasmussen.)

Figure 3.3

Detecting estrous in elephants: (left) a bull tests a cow for estrus and (right) performs a typical flehmen. (Photo courtesy of R. Rasmussen.)

may be a signal to males or, as other observations indicate, a signal to other females. Maximal tail flicking in captive cows occurs a few weeks prior to ovulation. In the wild, the males seem to bypass such tail-flicking females, but other females check them and perform flehmen.

Bets Rasmussen and coworkers recently identified the chemical compound released in urine by female Asian elephants to signal their estrous state as (Z)-7-dodecen-1-yl acetate, the same volatile compound used by many female insects to attract mates.

Even if courtship in elephants may last for several hours or days, mating itself is a short affair, lasting no more than a couple of minutes. The bull places his trunk lengthways on the cow's back and mounts her by rearing up on his hind legs. Intromission occurs by locking the tip of the S-curved erect penis into the cow's vagina, located in front of her hind legs. Some observers have remarked that the anatomy of the elephants' genitalia demands absolute cooperation by the female if intromission is to be successful. A pair may also mate several times over the period of 1 or more days.

0 0

Post a comment