Picture this if you can. My wife and I are in Rome, standing on a bridge over the river Tiber. The Vatican looms in the background. We watch two ducks wing our way. One appears to be pursuing the other. Soon, I recognize them as drake mallards and, as luck would have it, they land in the water below the bridge and immediately dive. But they quickly resurface and the now obvious pursuit resumes – a mad, flapping, splashing dash over the water. The pursuer grabs the other male, first by the tail feathers and then by the back of the neck. He mounts his victim who is frantically struggling to get free. After a minute of furious thrashing the aggressor convulsively thrusts his tail end several times in a downward motion. His body goes limp as he slides off the other duck. But quickly he recovers and rapidly swims around the other duck in a tight circle, neck outstretched. He then flaps his wings and raises his head in an exaggerated posture, before taking a long drink of water. This is a ritual performed by all drake mallards after they’ve had sex.

A couple of minutes later, the bedraggled victim of the assault is on shore, flapping his wings and preening, trying to dry off and restore his feathers, and probably his composure, too. The aggressor has flown a few hundred yards away and joined a female. She had been sitting on a sand bar during this entire tableau, presumably watching. They greeted each other in the way paired (mated) ducks typically do after a separation.

What had my wife and I just witnessed? She asked, “Were they doing what I think they were doing?”

What we had seen was indeed a rape, not unusual in ducks, especially not mallards. The unusual thing was that this was a homosexual rape and the aggressor apparently was already mated to a female. It seems he had temporarily left her to pursue and rape the male.

Homosexuality is common in animals and it’s been recorded in many species of waterfowl. I’ve frequently seen male black ducks copulate and otherwise behave like any heterosexual pair. However, a prolonged and persistent aerial pursuit culminating in rape like we witnessed in Rome is most unusual. But we know the behavior of ducks can be bizarre.

A European publication recently published the first documented case of homosexual necrophilia in male mallards. The fleeing male crashed into a window and fell dead to the ground. The pursuit drake immediately landed and mounted the still warm, dead drake.

I once did an experiment in which I provided a male mallard with some interesting options. It was the spring of the year and his swollen testes were spilling hormones. When presented with an array of potential mates, he first courted a female mallard. When I removed her, he courted a female black duck. In fact, when deprived of his preference, he courted the females of several different species of ducks. When no females were available, he began courting males, first a mallard, then a black, and so on. When I removed all of the ducks, I was surprised to see him court a hen chicken.

Another bizarre observation of unbridled sex was described to me by a friend who kept chickens. One Christmas she decided to get a male mallard “to add a little colour to her flock.” She got more than she bargained for. When spring arrived the mallard became amorous and, being the only duck on the farm, he acted on the universal male philosophy, “if you can’t be with the one you love, love the one you’re with.” That caused trouble for the hens.

One morning my friend awoke to a commotion in the barnyard. She went out to find a still warm but very dead hen in a large bucket of water. The remaining chickens were clucking and fussing in a highly agitated way. The duck was, however, resting nearby. She awoke the next morning to hear the same ruckus. As she left the house she saw the mallard dragging a hen across the yard. He had her firmly grasped by the back of the neck, the way male ducks hold females when they copulate. When he got to the bucket, he hauled the hen into it and proceeded to mount and then rape her. My friend stood dumbfounded as she watched the hen trying to stay afloat. It was madly treading water with feet that were never meant for swimming.

Once again, she wondered what was going? The answer is fairly straightforward. It was spring and the male’s testosterone motivated him to have sex, but a female mallard was not necessary for him to act on this urge. Why the bucket of water? Well, ducks prefer to have sex in the water. It’s genetically programmed behavior. In fact, the mallard’s genes “made him do it.” He was simply responding to his evolutionary past. He would have raped the hen regardless, but because there was water nearby, he had to do his best to take advantage of it.

Most species of ducks are monogamous, with one male mated to one female. But even so, males of species like mallards are prone to philander. Again, it’s a genetic thing. Females lose interest in sex once they’re incubating their eggs. This is when the still sexually motivated male turns to rape. Indeed, rape is an especially well-developed behavior in pintails. Sometimes each of a hen pintail’s ducklings are fathered by a different male. A dozen or more males may chase a female in spectacular aerial pursuits that last half an hour or more, and climb 500 feet into the sky. Sometimes the birds are barely visible. I’ve seen females land on rooftops and on busy roads to get away from testosterone-driven males. It is not uncommon for females to be gang-raped, resulting sometimes in death.

Unlike the philandering pintail, the highly monogamous drake shoveler is a stay-at-home guy. Rather than rape a strange female that intrudes on his territory, a male will chase her away, pulling her feathers if he catches her. This is clearly hostility and not a sexual advance. However, even the usually faithful shoveler can have “a wandering eye.” I recall a drake that attended to the sexual needs of two females, who both successfully raised broods of ducklings. This male chased all other females away from his territory, but these two were special.

The business of rape works both ways. The universal male paranoia in all animals, including humans, is cuckoldry – having someone impregnate your mate and leaving you to raise his kids. Male mallards, who themselves may be rapists, guard their mates against harassment by other males. They even establish territories and keep other males out. However, sometimes a persistent “stranger” works his way onto a territory and becomes part of a ménage à trois with the pair. When her mate’s temporarily away, possibly chasing another male, the female sometimes will have sex with the “stranger,” who she’s gotten to know well enough. Cheating, too, is common in animals, and it’s not only males who do it.

Interestingly, in such scenarios, if the female’s mate returns to find them “in the act” (flagrante delecto), he immediately interrupts them and chases away the offending male. He then, despite her protestations, forces his mate to have sex with him – he rapes her. Does he do this because he has he been stimulated by what he just saw? Perhaps, but a more likely explanation involves sperm competition. The only way the male can reduce the risk of the other male’s sperm fertilizing his mate’s egg, is to get his own sperm into her reproductive tract and “hope” it gets to the egg first. There’s some evidence to suggest that it may.

And there’s even evidence in some ducks that “size matters.” Waterfowl are one of the few families of birds in which the male has a penis. Most others birds just touch their vents together – a so-called “cloacal kiss” to allow sperm to enter the female. There is no penetration. A duck’s penis is usually hardly big enough to see, except in the breeding season when it can be a couple of inches long. Males of the ruddy duck group display their penises during courtship and apparently this impresses females. The males with larger members get mates while the others don’t. The female who mates with the male she prefers may produce larger eggs which, in turn, produce bigger, healthier ducklings, with obvious benefits to survival.

I’ve frequently received phone calls from perplexed owners of swimming pools. There see two ducks in their pool, they tell me, and the brightly colored one, the one with the green head, sometimes gets onto the back of the brown one. These ducks are invariably mallards and they’re having sex in the pool. But why there, and is this where the female plans to raise her ducklings? The female has no intention of taking her brood there, but she wants to be away from the prying eyes of other males. Neither she nor her mate wants to be interrupted during sex. Disruption is one thing but gang rapes can lead to females being killed. A swimming pool is a good place to find privacy.

Although most frequent and intense during the breeding season, females potentially will submit anytime to a male’s sexual advances. In fact, regardless of the time of year, sex is never far from the minds of ducks, especially the males. The sonorous notes you blow with your duck call may be just the seductive tune a drake mallard is hoping to hear. You may think he’s responding to your “feeding call” but, in reality, he’s coming to your decoy spread hoping for “a little action.”