Seagulls shit on pregnant women. It's hormones, or pheromones, or the minute change in the timbre of their voices. If you have a pregnant woman in your car, the birds will shit on your car. Even if the pregnant woman has left the car, the birds will still shit on it. If they shit on the pregnant woman, and then the pregnant woman gets in the car, the birds will follow the car, shitting. The shits on the pregnant woman will be small (a smaller target is harder to hit i.e. requires more shots i.e. more shit overall, but also it is out of a sort of respect, though not respect as we could understand it, obviously), but the shits on the car will be huge (bigger target, less attempts required for a direct hit, celebratory exuberance of an easy shot). The shitting on the car and the pregnant woman is a show of sexual prowess. The birds are not attempting to mate with the pregnant woman. The birds understand that the pregnant woman is a pregnant human, but there is a sexual/mating element to the power displayed through the shitting. Needless to day, it is only the males who shit on pregnant woman/cars in which pregnant women are travelling/have travelled.

The shitting increases in incidence at around the start of May, and happens most around seaside towns. It happens in May simply because mating season is over and the birds have more time on their hands (wings? Claws?) and start to go out and look for pregnant women. Also, May is the earliest time that most people, including pregnant woman, will attempt a trip to the seaside. It happens most commonly at the seaside, not only because there are more seagulls near the sea and hence more birds to do the shitting, but also, and more importantly, because this shitting is a collective response, not only to the pregnant woman, but also to the other birds that are shitting on her. So, on recognising the presence of a pregnant woman in the vicinity, there is a small chance that a seagull will begin to follow her from above, and attempt a shit. However, if a seagull recognises that another seagull is following a pregnant woman from above, then the seagull will almost certainly join his fellow seagull, and begin to shit. The group's size increases exponentially and once the size of the group becomes large enough, the birds experience a certain sense of carnival fever; that wild abandon and loss of interest in everyday activities that comes with the excitement and frenzy of group celebration. The birds begin to split in to subsections, divided by imperceptible (to us) differences of body size, skull shape and beak colour that signal their relative position within seagull society. These sub-flocks will now actively seek out pregnant women, and cars that pregnant women are in, and cars that have at one point contained pregnant women, and they will shit on them. There is, needless to say, a masculine competitiveness that defines these shitting competitions, though there is no winner as such. A full day of seeking out pregnant women and cars that have come in to contact with pregnant women will make a seagull incredibly tired (the gulls will not eat during the shitting) and it may well not leave its nest for a day or two after the event. This period of recovery is dangerous for seagulls and some will die through exhaustion and starvation.

Seagulls are revolted and repelled by the smells and sounds produced by newborn human infants. There is no biological evidence that this has anything to do with their attraction to pregnant women, but common sense tells us that there must be a causal link.