Saturday, 29 March 2014

The Behaviour of the Koala. 5. Sex

     In my younger days, when I was giving speeches on the subject, I used to say that the koala's sex life was rather similar to that of humans: the females get jumpy and chase the males, while the males assail every available female and bellow like a bull if they don't get any. Of course, that was spoken in jest, but there was a certain amount of truth in it. The sexual behaviour of koalas contains many interesting features.
     For instance, the vast majority of male mammals are interested in the females only when they are on heat, and they tend to apply at least a modicum of courtship beforehand in order to gain her compliance. That is not how koalas operate. I witnessed nine matings, as well as 97 unsuccessful attempts. In the latter cases, a male resolutely approaches a female, and without any preliminaries, mounts her. She might fight back, and will usually squawk and try to wriggle away, but resistance generally ceases when the male grasps the back of her neck in his mouth. Unfortunately for him, as long as the female holds her rump down in its normal position, like the lady in the photo, he has not hope of achieving intromission, and has to give up. This sort of behaviour has been observed in the wild, so it is not simply an artifact of captivity.
     Although the sample size was not large, it appears that the behaviour is most common among four year old males, but the object of their desire may be any adult female, regardless of reproductive condition. These attempted copulations were frequently quite spontaneous, but also tended to be precipitated by the added excitement present when fighting or an exceptional amount of bellowing had taken place recently. (The same thing applies to penile erections.) I did record the extraordinary case of a male who had been moved to three different pens in the space of half an hour, getting involved in violent affrays with the resident males each time, until he was finally placed in the main pen. After settling down for half and hour, he spent the next two hours making 15 futile attempts at copulation.
     To summarise: all the behaviour patterns of breeding males - bellowing, scent-marking, penile erections, and mating attempts - reach their peak at age four, and can be elicited by the same set of circumstances. The exception, as mentioned before, was Kalba, the albino. Although fully adult, he bellowed only infrequently, and for some unexplained reason, had hardly any sex drive - at least during my period of study. (I've been told he rallied shortly before he died.)
     Koalas appear to be unique among mammals in that the male performs no courtship behaviour at all. It is the ladies who do the courting. Oestrus, or heat as it is known in layman's terms, lasts only a few hours, and only one female was seen to mate more than once in that time, but when it occurs they literally get jumpy and chase the males.
     There are four main features of oestrus. Bellowing is one, and has already been mentioned. The most bizarre are convulsions. The female holds on to the tree, and her whole body jerks forward vigorously at the rate of about once a second, while her head jerks back slightly and her ears flap. In fact, some schoolgirl visitors to the Sanctuary once mistook them for hiccups. It is rather similar to what happens at orgasm. (See below.) Nearly as striking is pseudomale behaviour, in which a female performs male reproductive patterns - mounting, neck-biting, and thrusting - upon another female, although usually briefly and incompletely. Finally, a female on heat displays mild aggression towards the male (though not to other females): chasing him, throwing her arms around him, and giving him love-bites. On two memorable occasions I introduced a male to a penful of females who had displayed the initial features of heat, and before the poor fellow knew what was happening, between two and three amorous females were chasing him around the pen until he got the message and did his duty.
     Once a female is on heat, oestrous behaviour appears to be triggered by the presence of a male, by the sound of a male bellowing (sometimes), aggressive interactions, or the presence of strange individuals. It has the desired effect on males.
     The male's long penis is a wicked forked instrument with knobs on it, which appears only when erect, and emerges behind, rather than in front of the testicles. (Its position is due to the peculiarity of the marsupial interior plumbing,where the tubes from the bladder join the urethra behind, rather than in front of the tubes from the testicles. Similar idiosyncrasies in the female's plumbing mean that marsupial females have a double internal vagina, hence her mate's forked penis. The knobs are to increase sensitivity, and speed up orgasm.) Copulation lasts only about a minute and a half, an advantage for an arboreal mammal, but rather short for a marsupial. I have watched kangaroos mate for a whole 20 minutes, while some marsupial mice can remain linked for hours on end.
     The male mounts the female in a vertical position, clinging to the tree, and grasps the back of her neck in his jaws. She, in turn, stretches her head right back and raises her rump, which allows the male to achieve intromission. The male begins making vigorous pelvic thrusts, about once a second, building up to twice that rate. As soon as thrusting has ceased, the female goes into convulsions again. Intromission remains complete, and ejaculation probably takes place at this stage. Finally, the pair uncouple, but the female may have to squeal to make the male release his neck-grip. When she attempts to depart, the male generally puts an arm around her and gives her a bite, not necessarily hard, and a sudden fight breaks out before the couple separate. Usually a plug of coagulated semen develops in the female's genital opening. This may be the male's insurance policy against another male getting in - although it is unlikely a female would allow it. More to the point, since the animals spend must of their time in a vertical posture, it prevents the semen flowing out. The same thing occurs with kangaroos. (Another vertical species, Homo sapiens gets around it by copulating horizontally.)
     What can we learn from all this? Firstly, the numerous futile attempts to mate when the female in not on heat should remind us why rape is rare to non-existent outside the human species. Apart from the obvious problem ie how can a male, acting on instinct rather than reason, know whether a female is consenting? rape requires the male to be able to immobilise the female. It is hard to see, for instance, how a bull could force himself on an unwilling cow. And even when immobilisation is possible, as with koalas, he still often needs her co-operation to complete the job.
     Secondly, there has been a lot of nonsense written in the press about lesbianism in koalas.  Also, I am rather cheesed off about the fact that most references to it cite a paper by four scientists published in 2007 rather than my own paper of 27 years before. As I pointed out in part 3, if zoologists don't read the earlier papers, they are going to have to discover everything again. In any case, yes, pseudomale behaviour probably is an artifact of captivity. In the wild, the koala's solitary lifestyle would mean there would be few opportunities to practice pseudomale behaviour. However, it is not a form of lesbianism; the female is on heat and wants a male to mate with her. In the same way, artificial inseminators know that when a cow starts mounting other cows, she is on heat, and wants a bull. I suspect that, along with bellowing, it is the result of male hormones released at the time of oestrus.
     Obviously, I am going to have to write another article in due course about the phenomenon [this has now been done], because non-zoologists do not understand that many species of animals use sex in manners not easily referable to human sexuality - or, indeed, to that of other non-human species. Homosexuality as we know it is extremely rare outside of humans.
     Finally, the neck-bite is unusual, because it generally occurs only among predators. A mother cat, for instance, will pick up her kitten by the scruff of the neck, and this induces the kitten to become passive and still. The tom cat therefore grasps the she-cat by the neck during mating, and produces the same effect. Koalas, of course, do not use it with their young, but during mating it does enable the male to steady the female's convulsions. Nevertheless, much of the koala's sexual behaviour is shrouded in mystery.
Go back to
Part 1. Background
Part 2. Basics
Part 3. Bringing Up Baby
Part 4. Communication
or go forward to
Part 6. Fighting
Part 7. Comments and References