Love and courtship

This is just the prelude to the courtship season which continues until the end of July, with May and June as the most feverish months. The males begin re-establishing the hierarchy a few weeks earlier, competing for access to the mating areas, which are the same every year. These are areas particularly rich in food during the springtime, attracting both females without young and their suitors, thus increasing the opportunities for encounters between the two sexes. Once the breeding season is over, the bears’ interest will be focussed exclusively on food. It is very rare for bears to be observed mating during the autumn, even more so in the case of females with yearlings in tow.

On November 3, 2010, park rangers Ezechia Trella and Germano Palozzi witnessed a scene that astonished more than one expert. Still incredulous, here’s their story:

Females are much more selective in their choice of mate, while males aim exclusively for quantity. During a single breeding season, a female may come into heat as many as two to three times. But the phase doesn’t last long. At these latitudes, the follicular activity of female bears (the phase immediately preceding oestrus) decreases drastically from the end of July onwards. As described above, it is very rare for a bear to come into heat in autumn. The surprising thing is that female bears breed “on command”. It is the tactile stimulation of the cervix by the male’s genitals that triggers the neuronal and endocrine response (and thus secretion of specific hormones) that induces ovulation. So by avoiding physical contact with the male, or by assuming a posture that prevents him from completing the sexual act, a female may choose not to be impregnated. Alternatively, a female bear may avoid males altogether, for example, while she is lactating. As we shall see later on, besides the physiologic aspects, social factors may also come into play to inhibit females from breeding. Even after mating, not all females successfully carry the pregnancy through until the following year, but this depends not only on the position of copulation, but also the female’s state of health. The males, on the other hand, enjoy more continuous sexual activity and even though their testicular function decreases after the mating season, a male bear can still impregnate a female with the accumulated sperm. This provides an opportunity for less competitive males to attempt to mate during less intense periods.

While the male is with her, the female is still receptive to other males. So the male must never leave her unattended, as there may always be another suitor lurking nearby. Sometimes a number of males can be seen walking in single file behind a female, or a number of females may be followed by a single male. The male therefore literally “kidnaps” the female, sniffing her genitals to verify the presence of the pheromones which indicate she is on heat. In turn, the female constantly tests the vigour and resistance of the male. In most cases, the females lead the game. They can be very selective, not only in the choice of partner, but also in where and when they mate. During this period, the male neglects eating and loses weight to make sure he never loses sight of the female, defending her from other suitors and also defending himself, and not just from other males. An unwilling female can be very aggressive. If she doesn’t agree, she will sit up on her rump, back away from the male, emit deep, menacing growls or even attack her suitor. On the other hand, if there are no competitors in sight and the male is one of her favourites, the female submits and indulges in lengthy preliminaries before yielding completely. The female usually stands or slides under the male while he bites her hind legs or neck. If the male is slow or not interested enough, the female breaks free, emitting deep growls and baring her teeth. At this point, the male grabs her with his paws and tries to bite her. The female responds by rubbing him with her snout and biting him in turn and the two engage in a playful struggle. This behaviour usually convinces the male and is followed by copulation.

But what are the males’ tactics? Which of them can seduce most females? They are the bears at the peak of their fitness, usually after the first ten years of life, and those able to control their partner, preventing, or at least delaying, her mating with other males. They exercise this control by aggressively chasing away other males, or through prolonged copulations that physically prevent other males from gaining access to the female. But the competition doesn’t end with the act of copulation. When a female mates with many males, the sperm of rival bears also compete in numbers and in their ability to reach and penetrate the available eggs. If that weren’t enough, it also seems the females are able to use an amazing mechanism of control during copulation to ultimately decide who will father their young. The males fight ferociously to breed and when you look at them closely, it’s not uncommon to find wounds and scars left on their heads by the bites of rivals. The males can also impose their dominance in a more ritualised, although no less effective, manner.

In bears, a phenomenon known as “embryonic diapause” occurs. This is also observed in mustelids (otters, martens, stoats, badgers, etc.), many species of seal, marsupials, mice, rats and also roe deer. After fertilisation, the blastocyst remains inactive and attached to the female’s uterus until she enters the den at the beginning of hibernation. The embryo does not continue developing until there are the best conditions for the young to survive. In the case of the bear, the best time is the period of winter torpor, safe from predators. In bears, production of the cascade of hormones that stimulate the uterine mucosa to receive the embryo is triggered by the shorter photoperiod (the number of hours of light) typical of early winter. But if the female lacks sufficient fat reserves or is not in good health, this cascade of effects is interrupted and the pregnancy is not carried to term. The fact that after fertilisation the embryo enters diapause means the female can come into heat again. A female may therefore retain a number of fertilised eggs in her uterus and, given that a female may mate with several males during the same breeding season, it is probable that a single litter may originate from more than one father. This is an effective strategy to increase the quality and variability of the offspring’s genetic heritage, but, as we’ll see later, it also helps protect the young from possible aggression by the males…

A number of adult females in the Apennine population have never been seen to breed successfully, even after ten consecutive years of observations. Furthermore, despite the fact that the cubs leave their mother very early, in their second spring of life, and the females left on their own have been seen mating, none have ever been observed accompanied by offspring the following year. F05 was one of the first females studied by researchers. Already a mother when she was captured, over the following years she gave birth to a full eight cubs. F05 was a very protective mother and managed to raise 88% of her cubs until they were a year and a half old. If you’d like to find out more about her story, continue reading.

Females are at their reproductive peak between the ages of eight and 25 years. Their fertility then begins to decline rapidly. Bears can reproduce as early as three and a half years old, although in high-density populations, such as in the Central Apennines where at the centre of their distribution area there is a density of four bears per 100 km2, different regulatory mechanisms come into play and can delay the first birth until the female is six years old or more. For example, the presence of the mother may act as a natural contraceptive for her daughters. Mechanisms not yet fully understood seem to prevent them from breeding. Female bears are, in fact, governed by the rules of a matriarchy, as the young females are philopatric (closely bound to their place of birth) and therefore tend to establish their own territories within, or near, their mother’s. By combining genetic and remote radio monitoring techniques, researchers have shown that “neighbouring” females compete with each other to breed. The female bears lower in rank may have to wait several years after reaching adulthood before their turn to become mothers. The rule may seem harsh, but it actually serves to ensure the most efficient division of food resources among the bears, thus reducing possible stress between individuals.

Female F05 has had many suitors during her life. The day F05 met with the male M06, also fitted with a tracking collar, was a unique opportunity for the researchers to reconstruct all the stages of their courtship.

As long as a female is accompanied by her offspring, she is not receptive. The cubs remain with their mother for two winters, then when they are about one and a half years old, in the breeding season between April and May, the mother drives them away. Such short intervals have been observed in brown bear populations in northern Europe, but rarely in North America, where the female may remain together with her cubs for as long as three and a half years. In the mountainous areas of southern Asia, poorer in food resources, the cubs may stay with their mother for as long as four and a half years. However, three or more years may be too long for a male to wait to breed again. So in order to get what they want, the males adopt a rather brusque, no-nonsense stratagem, infanticide, killing the female’s young to make her immediately receptive, sometimes even just a few days after the “crime” has been committed. Following this traumatic event, females change their behaviour. While before with their young they were sedentary and elusive, a few days after their loss, they start to move around like other females. Research in Sweden found that 90% of females involved in infanticide during the breeding season reproduced successfully the following spring. Infanticide thus seems to be an effective technique, but for it to be successful, every male must first make sure not to kill his own offspring, then manage to successfully inseminate the female. Based on genetic techniques, Swedish researchers have confirmed that the males somehow recognise the females they mated with the previous season, perhaps by smelling the female and her cubs. Then after committing infanticide, they patiently follow their “victims”, waiting for them to come into heat, thus ensuring they become fathers again.

The females do not, of course, passively accept their offspring being killed. Female bears are proverbially very protective and touchy. They defend their offspring at all costs and aggression by males can sometimes end in the worst of outcomes, namely the death of a mother trying to protect her cubs. In order to minimise the risk of infanticide, females therefore enact their own counter-strategy. The simplest and most effective is obviously to avoid areas frequented by males during the mating season, moving about less, or choosing “shield” areas where they are less likely to meet a male. Some studies carried out in Northern Europe report that in spring, just like prey avoiding a predator, female bears may deliberately choose sites at the edge of built-up areas, usually some one to two kilometres away, as these are rarely frequented by the males, notoriously shyer towards man. Alternatively they may choose marginal, isolated areas, even though poorer in food resources. Females may also decide to invest more in the safety of their young than in the availability of food, waiting to replenish their energy in the summer and autumn. Their other strategy is to confuse potential fathers. Based on remote monitoring and genetic data, females may choose to mate with all males in the vicinity, so each male is convinced he’s the father of the next season’s offspring. Surprisingly, despite the promiscuity, it is always the most powerful male with the best genetic make-up that guarantees transmission of his genes.

The hierarchies established by males during the breeding season may remain in place for several years. In 2007, the male M06 was found poisoned along with two other bears. M06 had a territory of 180 km2, including at least 5 known female bears. The fate of their cubs is unknown, but the possibility that something irreparable occurred cannot be excluded.