Until relatively recently, and particularly the advent of affordable trailcams, the act of copulation had rarely been observed in the wild and there are some conflicting reports in the literature regarding how the female accommodates the male. Some early authors even assumed, understandably perhaps, that the female rolled onto her back to mate. In recent years, however, we’ve gained a much clearer picture thanks to observations on captive animals and a network of back garden naturalists with remote cameras.
The Art of Woo: Courtship
Maurice Burton was the first to publish an English appraisal of hedgehog courtship, it having previously only been documented in the German literature, based on activity he was alerted to by his gardener on 18th May 1965. Burton wrote a short article for the Illustrated London News during June of the same year in which he described:
“The sequence in hedgehogs starts when the boar approaches the sow, puffing or snuffling loudly. The two meet face to face, stand like this for a while and then the boar may turn and trot away through the herbage. But he seldom goes further than three feet away from the sow. He returns to face her once more, then he begins to walk round her, she pivoting so that her nose is directed towards him, and for most of the time the two are almost nose to nose. She may snap at him from time to time, or strike at him with a front paw; or she may roll up, completely or partially, in which event the boar may try to push his snout under her, as if seeking to unroll her.”
Burton considered that the snuffling served a definite function, with the sow being almost mesmerised by the tempo. This is particularly interesting because, although it is often thought that the snorting/huffing is a mutual exchange, it actually seems entirely the product of the female 'hissing' at the male; males appear to make very little noise during courtship. Snorts are emitted by the female every three seconds or so and many are accompanied by a jerk of the body. It can be difficult to tell from whom the noise is emanating, but my observations make me think it's either exclusively, or at least predominantly, the female huffing. Indeed, we've observed females huffing in apparent frustration or solicitation at a male who got bored (or distracted by food) and wandered off. That said, in his 2018 book Hedgehog, Pat Morris describes huffing coming from males and notes how “both animals snort loudly and persistently”, so it may vary individually. Alternatively, males often sniff rapidly while moving around and this may be mistaken for courtship huffing if a female is coincidentally present.
A female hedgehog shorting during courtship. Hedgehog courtship involves the male persistently circling the female while she turns to face him snorting every second or so. The male's circling, and the female's snorting, can continue uninterrupted for an hour or more. - Credit: Marc Baldwin
Perhaps the most frequently observed part of courtship is the male circling, or attempting to circle, the sow. As Burton noted, however, in some cases they stand face to face. I've observed this in our garden, the two stood (or the female stood/sat and the male crouched) facing one another, the male periodically pulling his forehead spines down to shield his face. To add to Burton's account, I have observed that the male may also spend time sniffing at the sow's rear end, which is presumably an attempt to assess her readiness to mate. Hedgehogs have a well-developed vomeronasal organ in the roof of their mouth and we know that this structure appears to be used to assess hormone information.
My experience and that of others is that courtship can be a relentless and, at times, aggressive affair. (Given the lack of sexual differentiation in hedgehogs, some early naturalists mistook courtship for two males fighting.) In most cases, as Burton described above, the male will circle the female slowly and persistently, periodically changing direction and making attempts to get behind her in order to try and mount her. All the time this is happening, the female is snorting and turning to keep herself facing her suitor. I've seen females aggressively bite and headbutt males and some accounts suggest this is occasionally done with sufficient force to knock an off-guard male off his feet. Certainly in our garden females have shoved boars with sufficient force to push them several centimetres away. Often while approaching or circling, the male will lower his forehead spines, or tilt on one side exposing his spines to shield himself from attack. In some cases, this gives the impression the male is almost slinking his way around the female.
It is not uncommon for several males to vie for the attentions of a single female and in some cases the female wanders off while the males are busy fighting over her! Females are polygamous and males polygynous, meaning each sex will mate with several partners, although it should be remembered that courtship does not always lead to copulation. In a short paper to the Journal of Zoology in 1986, Nigel Reeve and Pat Morris described a total of 27 males courting 20 different females. One female in particular was courted by at least 10 different males, eight of whom also courted at least one other female. Two of the males each courted at least eight different females. Only five (7%) of the courtships Reeve and Morris observed ended in mating. That 93% of courtships didn't end in mating led the authors to suggest:
“Thus, although there may appear to be no selection of partners, it is still possible that some form of exclusivity might operate by sexual selection or inbreeding avoidance. This may in part be the function of the protracted and often inconclusive courtship behaviour.”
A protracted courtship may also help a female judge the vigour of potential suitors, with less tenacious individuals giving up more readily. In Ireland, Amy Haigh and her colleagues documented 39 bouts of courtship between 16 individuals, none of which ended in successful copulation. The average bout of courtship lasted about an hour, although one observation went on for 2 hours and 20 minutes. In our garden, the longest period of courtship circling we've observed lasted for 2 hours and 6 minutes, the male breaking away only briefly to fight with another boar, in July 2020. Kondrad Herter, in his 1963 book Hedgehogs, noted that it frequently took a boar all night and sometimes more than one night to persuade the sow to accept him and this has been our experience, too.
In Haigh's cases, courtship always ended with the male seeming to lose interest and moving away to start foraging, while ours have mostly been either this or the female running away, sometimes while the male is fighting with an interloper. Even in cases where the sow has huffed indignantly at a boar who lost interest and walked away, we've never observed the female to pursue the male. Additionally, in our experience, while we've observed both courtship and mating in the garden (much more of the former than the latter, incidentally), we've witnessed the two in direct succession only once. Interestingly in Haigh's data, the hedgehogs moved into poorer quality pasture habitat (where food was less abundant) to breed, suggesting that less food in the area may mean fewer distractions from mating—at the end of the breeding season they moved back into neighbouring invertebrate-rich habitats.
Haigh and her co-workers also observed promiscuity among the hedgehogs—females were found with up to seven different males and males with up to three different females. While observations of matings remain rare, there are some genetic data to support the idea that females will mate with several partners. A team from the Waterford Institute of Technology in Ireland, led by Siobhan Moran, conducted a small-scale genetic analysis on five litters of hoglets brought into rescue centres, one litter from Devon and four from Jersey; in total, five females and 25 hoglets. Their results, published in the Journal of Zoology in 2009, showed evidence of multiple paternity. The Devon litter and one of the Jersey litters each yielded three paternal alleles, representing the mother and two different males.
In our garden, I have occasionally observed male hedgehogs displaying an interesting chin-wiping behaviour when approaching or circling females. This is not a common behaviour and has also been observed outside of courtship contexts. It's purpose, if it has one, remains unclear at this point. Additionally, we have observed two instances of what appeared to be homosexual behaviour between male hedgehogs. In both cases, a larger male spent a protracted period (in the most recent case, over several days) displaying courtship behaviour towards a smaller boar.
The correct tools
We know a reasonable amount about the internal reproductive anatomy of box sexes of hedgehogs, both being broadly similar to the construction found in most placental mammals. The reproductive structures of the male have, however, been less well studied. Thanks to Sir Richard Owen's nineteenth century opus on vertebrate anatomy, we know that the penis of the hedgehog is what biologists refer to as of “bulbospongiosus-type”. In other words, it has a muscle (the bulbospongiosus) covering the tip that helps sustain an erection as well as help ejaculation. In volume three of his work, published in 1868, Owen described how:
“The penis is long and bent when at rest. There are two 'levatores' which rise from the ischial tuberosities behind the 'erectores'.”
So, as Reeve confirms in Hedgehogs, erection is achieved by engorgement of spongey tissue known as the corpus cavernosum and the muscles running down the length of the penis. This is interesting, because many mammals, and particularly the 'insectivores', have evolved a penis bone called a baculum (sometimes, the “os penis”). This is a special skeletal element that maintains the erection, rather than relying on muscles and hydraulics. Several Internet sites, including WikiPedia, state that hedgehogs possess a baculum but, as far as I can ascertain, this doesn't appear to be the case.
A team of researchers led by Ghasem Akbari at the University of Tabriz investigated the anatomy of seven adult male hedgehogs from the Azerbaijan in Iran. The results of their study, published in Folia Morphologica during 2018, show no evidence of a baculum in any of their subjects. Instead, their analysis confirms that the erection appears to be maintained by blood pressure and muscles. Of particular note was the presence of two small downward-pointing nail-like structures made of keratin at the tip of the penis, which the anatomists suggest may play a role in helping anchor the penis during penetration.
Figures for penis length are more difficult to come by in the literature. In Hedgehogs, Nigel Reeve mentioned that he'd not found any exact measurements, while in their Natural Hedgehog, Lenni Sykes and Jane Durrant wrote that the penis extends from the middle of the abdomen to beyond the nose, which suggests the erect penis is several centimetres long. During their study of Iranian hogs, Akbari and his colleagues found that the average penis length was 7.2cm (2.8 in.). This measurement aligns more or less with the video footage from our garden and a trailcam video captured by Paula Felischmann in 2014 that shows a hedgehog in a nest box cleaning its penis—the full penis is obscured by the bedding material, but it appears to be several centimetres in length.
In her detailed review of hedgehog reproductive anatomy, published in 1934, King's College zoologist Marjorie Allanson noted that the weight of the penis didn't appear to vary according to season, but it was heavier in larger and older animals, ranging from 2.5g to just over 6g (0.09-0.2 oz.). Unlike the penis, the accessory glands do vary seasonally and, during the peak of the rut, Reeve noted that the male reproductive tract may account for 10% of the animal's body weight and the seminal vesicles alone can have increased ten-fold (to 30g/1 oz.) from their regressed hibernation state.
The vagina is in a regressed state during hibernation, enlarging at the beginning of the breeding season and becoming dilated during oestrus, although subsiding a little during pseudo-pregnancy (see: Breeding Biology - Oestrous & Gestation). Located at the rear of the female and close to the border of the spines, the vaginal opening is surrounded by coarse fur and not spines.
Caught in the act
Copulation typically follows protracted courtship that may continue on and off over several days and involves the female stopping, flattening her spines, pressing her stomach to the ground and pushing her back feet out behind her. This position causes her to arch her back and pushes her nose up; a posture referred to as lordosis. At the same time, this position helps present her genitalia to the male who responds by mounting her, sometimes gaining purchase by gripping the female's shoulder spines in his mouth.
It is not uncommon for an over amorous male to attempt to mount an unreceptive female and in such instances the female will walk away with the boar trying to keep up while trying to achieve penetration. In my experience, these 'walking mounts' end in failure and I suspect the same is true in cases where the boar attempts to mount the female while she's feeding or drinking.
Mating may involve the female being mounted for anywhere from about a minute to twenty minutes, with three to six copulations consisting of ten or eleven rapid thrusts. There are some anecdotal observations suggesting hedgehogs may occasionally “squeal” during mating, although I have never heard it or come across empirical data on this. If it does happen, presumably it is the female protesting to having her neck bitten by the male while mounting her, but I'm interested to hear from anyone who has seen or has trailcam footage of this. Once mating has taken place, the male dismounts and the pair separate; there are no records of mate guarding in this species, and males don't play any role in provisioning for the female or her offspring.
Boars do not appear to leave a sphragis (copulatory or vaginal plugs), a gelatinous material excreted by the male after ejaculation to temporarily seal the vagina and give his sperm a competitive advantage, although their large accessory glands do exude a gloopy substance that may have a similar function, albeit apparently much less effective.