Interspecies mating is not the norm but it has happened. But rarely has it been spotted in such graphic detail and among such distinct species as a snow monkey and a deer.
For the first time, scientists have observed and are reporting on an attempted mating between Japanese macaques and sika deer on Yakushima Island. The paper was published this week on Primates.
The two species already cohabitate
The two species have interactions in the past. The snow monkeys drop fruit from trees which are eaten by the deer after foraging. This results in strong cohabitation between deer and macaques. Deer also eat the feces of the snow monkeys specifically and the monkeys have been spotted grooming deer and even trying to ride them.
But until now, there hasn’t been any sign of sexual behaviour between the species. But in November of 2015, scientists on the island studying cultural behaviours among the snow monkeys observed one adult male trying to copulate with at least two different female deer.
One male, two deers
The first female the monkey mounted, some copulation behaviour was observed but no penetration occurred because the male penis was not directed at the genital area. But the monkey did appear to ejaculate because the deer was seen licking seminal liquid after the mount
The second female deer did not accept the sexual behaviour as she attempted to escape/remove the macaque by moving, increasing her speed, turning around and displaying threat.
Interspecies mating ave been widely described and studied in animals. These interactions can be negative for one animal of the two species involved, in prey–predation relationships or positive for both individuals in examples such as mutualism.
Critters can sexually harass other critters
In one study, king penguins were observed being sexually harassed by an Antarctic fur seal. At the end of the mating behaviour, some penguins were killed and eaten.
Unlike the case reported for the Antarctic fur seal and king penguins, the sexual behaviour of the male macaque towards the female deer did not seem to be one of sexual harassment or coercion. In fact, the monkey stayed close to the deer and chased away other male macaques in a behaviour similar to mate guarding.
Moreover, the licking behaviour shown by the deer seems to indicate that the sperm could be a good source of protein. The hormonal surge of the Japanese macaques at the breeding season and the close cooperation between these primates and sika deer may have combined to result in this heterospecific copulation behaviour. Particularly, the behaviour may be a sexual manifestation of the play behaviour already described in Japanese macaques when riding deer. Such proximity or cooperation has also been described as a factor favouring copulation between Atlantic spotted dolphins and bottlenose dolphins.
Why do they do this? They’re juveniles…
One reason why the monkey behaved this way, according to scientists in the paper, is that Japanese snow monkeys are highly social, and it is probable that, if they have to learn to copulate, they could do so by observing others.
But the more realistic reason why the monkey try to hump the deer is even more basic, scientists believe. It’s a theory known as “mate deprivation hypothesis.”
[M]ales with limited access to females are more likely to display this behaviour. Indeed, this heterospecific sexual behaviour is more likely to be observed in species with higher risk of sexual competition (i.e. multi-male, multi-female breeding), as for other sexual behaviour such as masturbation or homosexual behaviour in the Japanese macaque.