Mallards are notorious for their unorthodox sexual practices, which include same sex mating and necrophilia (of Ignobel Prize fame, see reference below). This morning, in the apparent absence of a female, four drakes mallards took it on an unfortunate one. I have previously watched apparently consensual male-male copulation in mallard, preceded by courtship, but in this case they behaved exactly like when a gang of males carry out a forced copulation on a female. The series is not very clear, but these are the best I got.
...and the harassed drake eventually flew off!
I do wonder if the many non reproductive pairs and trios that are now found away from water around the verges of the avenues and even on campus, where there is no pond, are actually seeking some peace and quiet from all this pond sexual excitement.
More information
Moeliker, C. W. The first case of homosexual necrophilia in the mallard Anas platyrhynchos (Aves: Anatidae). Deinsea 8 (2001): 243-247. here.
This morning I witnessed a forced gang copulation in mallards. It is a sad thing to watch as the female appears so defenceless, overpowered by a number of males. The female was first pinned down on the ground by three males and a few others joined in later. At least one managed to copulate with her. Forced copulation - as other apparently perplexing behaviours like infanticide - has shifted from being regarded as a pathological behaviour resulting from either captivity, male biased sex ratios or urban bird living, to an sexually selected alternative mating tactic, adaptive for paired males. There are many studies now supporting that forced copulations are more widespread than previously thought amongst some ducks, and are part of their natural behavioural repertoire. (The involvement of many males is probably more likely in urban parks with higher population density than in the wild).
Mallards form new breeding pairs in the autumn, and the couple stays close together, the male guarding the female. Mating within the pair is very ritualised and brief. There is head pumping by both male and female, the female adopts a flat position and the male mounts her. Here is an example from last week.
However, occasionally, other males chase a female - often in groups - grasp her and copulate with her forcefully. A feature of this behaviour that made researchers think this might be an adaptive behaviour for males is that forced copulations tend to happen during the period of egg laying, not before egg laying, and rarely after a clutch has been completed. In addition forced copulations tend to happen in the morning, just after the female leaves the nest after laying an egg. The female lays an egg each day, and ovulates just after laying, and it is during this period that there is a small window of time before the albumen is deposited and blocks entrance for sperm that there is a chance for forced copulation to result in fertilisation. The female does not need to be fertilised at this point as she has stored her mate's sperm and therefore she would have fertilised the egg with his sperm. After all, she has chosen this male to be her mate. But the opportunistic males are after fertilising her eggs in this short time window. There is little the female can do to escape the males's attention, she flies away if she can manage, only to be pursued by the males, its male often trying to intervene. I have noticed that males tend to join in chases and forced copulations if they notice a female being chased.
The number of males increased to six at some point. The
female's bill is just visible towards the right, on the ground.
Although the female cannot always resist forced copulations, she is not so defenceless after all: her vagina comes to the rescue. What! I hear you say, how? Let me introduce first the fact that ducks are amongst the 3% of bird species that have penises (the right term is pseudopenis or phallus) a corkscrew-like eversible organ, that in the case of the mallard is about 13 cm long (by no means the record, a close relative of the Ruddy duck has the dubious honour).
A screen grab of a male that managed to copulate. Its penis still everted as he walks to the water.
Another view of the male with dangling penis, just after he dismounted.
Now to the female side. Some female ducks, including the mallard have evolved long, twisted vaginas with dead ends near the cloacal opening, making it harder for a male trying to copulate with her to achieve a successful intromission and fertilise her eggs if she doesn't collaborate. The female's vagina also twists clockwise, making it harder for the male anticlockwise rotating penis to work. The males of these duck species also have longer penises. This co-evolution might have been spurred by forced copulations, in which the females respond to increased penis length with increased vaginal complexity to thwart the likelihood of successful fertilisation. The little data on extra-pair paternity in ducks appears to support this hypothesis, as the occurrence of extra-pair offsprign appears to be quite low (less than 10%) in the ducks studied. An excellent example of an arms race between the sexes.
More information
Brennan, P. L., Prum, R. O., McCracken, K. G., Sorenson, M. D., Wilson, R. E., & Birkhead, T. R. (2007). Coevolution of male and female genital morphology in waterfowl. PLoS one, 2(5), e418. Cheng, K. M., Burns, J. T., & McKINNEY, F. R. A. N. K. (1982). Forced copulation in captive mallards (Anas platyrhynchos): II. Temporal factors.Animal Behaviour, 30(3), 695-699. McCracken, K. G., Wilson, R. E., McCracken, P. J., &; Johnson, K. P. (2001). Are ducks impressed by drakes' display?. Nature, 413(6852), 128. here.
More often than not there will be a Herring Gull pair by the pond in my local park. I assume it must be the same pair, as seagulls are long-lived birds and they behave in an aggressive way to immature gulls that land near the pond. This pair likes a particular spot which I call "The Rock", a vantage point on a promontory on the edge of the pond, and both individuals often stand there side by side.
Today, a gang of excited Mallard males were giving chase to a female and one of them started mating with her. This behaviour is common in Mallards and is known as forced copulation, where there is no display and the female is corralled by males who are not their partners and forced to mate. The gull, which was very close, saw this, walked to the mating pair, and pecked the male! Not just a gentle peck, no, she even got some feathers out of him. This was a bit too much for the drake, his passion was quickly dispelled, he dismounted the female immediately and walked away a bit ruffled while the other drakes watched. Everything happened fast and I only had time to take a shot of the last part of the scene (below).
Ouch!
The pair of Herring Gulls at the Rock
Some twenty minutes later I noticed the pair were calling noisily with their miaowing calls, they were feeding on something on the ground. An egg! By the look of it it was a duck's egg all cracked and its contents spilled on the path. When I went to check, it had all the looks of an infertile egg. Still, the seagulls took turns feeding on it.
There are just a handful of female mallards in the local park pond. Today I could only see a couple. As for males, there must have been at least two dozen around. This male skewed sex ratio seems to be a general phenomenon in the mallard, possibly due to a higher female mortality during migration and incubation, but given the time of the year, many females in the park are probably already incubating. The remaining females are followed everywhere by their zealous males. Many bird species form monogamous pairs, which help each other in raising the offspring. This is called 'social monogamy' but genetic analysis revealed that it does not follow that the social pair are the parents of the offspring they are raising. First, male cuckolding occurs with some regularity in many species, so that the female mates with other males and a proportion of the offspring is not fathered by her social mate. Secondly, females occasionally carry out 'egg dumping' on other pairs nests.
Mallard pair mounting in the autumn
In the case of the Mallard, our commonest duck, there is social monogamy, with pairing observed at least for six months of the year and lasting at least several years. Pairing starts after the moult in the autumn, when even pair displays and mounting are common, even though breeding cannot occur. Males do not share the parental duties, the female being in charge of incubating, brooding, leading the ducklings and keeping them out of danger. Pairs can be seen carrying out a ritualised courtship, but a different mating strategy is commonly seen, in which one or several males chase a female and force her to copulate.
Group of drakes attempting copulation with a female
Females do try to escape these attempts by flying, diving or hiding and call loudly - presumably for their partner - and they are known to have been injured or even drowned in the process, probably due to the number of males trying to hold onto the females neck to secure copulation. In most cases females are not injured - other than losing some neck feathers - and forced copulations can result in fathered offspring, so it is in the interest of the drake to guard the female against this 'extra-pair' copulations to ensure that he fathers as much offspring as possible. Drakes maintain very close proximity to their mates during a critical period, - up to four days before the beginning of egg laying and up to four days afterwards - following the females everywhere. Males only swam away from their partners to chase other males away or initiate fights when other males approached his partner. Males also attempted to stop forced copulations on their partner with varied success. But it was also during the critical period that both paired and unpaired males initiated approaches to paired females. If the female was on its own, she called loudly if other males approached. Mate guarding also benefits females allowing them to forage more efficiently and possibly, decreasing their mortality due to predation because of their mate's alert state. Males with high testosterone levels in spring are more efficient guarding their females, and females show a preference to pair with such males during the autumn.
More reading
Cunningham, Emma J. A. (2003) Female mate preferences and subsequent resistance to copulation in the mallard. Behav. Ecol. 14: 326-333. here.
Davis, Ellen S. (2002) Female choice and the benefits of mate guarding by male mallards. Animal Behaviour, 64: 619-628. here.
Goodburn, S. F. (1994) Mate Guarding in the Mallard Anas platyrhynchos. Ornis Scandinavica 15: 261-265.here.
