The Pigeon Poop Probability Calculator estimates the chance that a pigeon dropping lands on you while you stay in one place for a set time. It combines published counts of feral pigeons, laboratory measurements of how much pigeons excrete, and the area an adult takes up seen from above. It is meant for fun. Nobody has measured how often people are actually hit, and real pigeons do not spread their droppings evenly.
How the calculation works
- Droppings per pigeon. A pigeon passes 11 to 26 g of droppings in 24 hours, and a single dropping weighs 0.5 to 1.5 g (Spennemann & Watson (2017) (opens in new tab), citing Laurila et al. 2003 and other feeding trials). The middle values give 18.5 g ÷ 1 g = 18.5 droppings a day. The low setting uses 11 ÷ 1.5 = 7.3 and the high setting 26 ÷ 0.5 = 52. For comparison, a widely quoted yearly figure is about 12 kg per pigeon, or roughly 33 g a day (Haag-Wackernagel & Geigenfeind (2008) (opens in new tab), citing Kösters et al. 1991).
- Pigeons per square metre. Each place uses a published count (see the table below) or the number of pigeons you count around you.
- Your target area. Seen from above, an adult covers about 0.14 m², the “body ellipse” used by pedestrian planners (Fruin, Pedestrian Planning and Design, 1971). Buchmüller & Weidmann (2006) (opens in new tab) gives 0.10 to 0.17 m² for the same thing.
- Expected hits. Pigeons per m² × droppings per pigeon per hour × 0.14 m² × hours = expected hits (λ).
- Chance of at least one hit. 1 − e−λ, the Poisson formula for rare, independent events.
Worked example: one hour in Trafalgar Square at its 2003 lunchtime peak. 4,000 pigeons on 0.93 hectares is 0.43 pigeons per m². 0.43 × (18.5 ÷ 24) × 0.14 × 1 = 0.046 expected hits, so the chance is about 4.5%, or 1 in 22. The same hour on an average Barcelona street (4,242 pigeons per km²) comes out at about 1 in 2,200.
Figures used for each place
| Place | Pigeons | Source |
|---|---|---|
| City square with feeding | Up to 4,000 at lunchtime in Trafalgar Square (0.93 ha) before 2003: 0.43 per m² | BBC News, 17 November 2003 (opens in new tab); area GiGL (opens in new tab) |
| Busy city square | An average of 2,000 in Trafalgar Square before control: 0.22 per m² | Mayor of London, answer to an Assembly question (opens in new tab) |
| City square with pigeon control | About 200 after feeding was stopped: 0.02 per m² | BBC News, 17 November 2003 (opens in new tab) |
| City streets, pigeon-heavy city | 4,242 per km² in Barcelona | Senar et al. (2016) (opens in new tab) |
| City streets, ordinary city | 840 per km² in Basel before its pigeon programme | Senar et al. (2016) (opens in new tab), citing Haag-Wackernagel |
| Park bench, café, station, elsewhere | Your own count within 10 m (314 m²) | Your eyes |
| Under a ledge or bridge | Your own count of birds perched over you | Your eyes; see the assumption below |
Two numbers are our own choices, not measurements, and we say so here. The 10 m counting radius is just a distance most people can judge. For ledges and bridges we assume each perched pigeon’s droppings land somewhere in the square metre below it, so if you stand in that patch, 0.14 of its droppings could hit you. We could not find a published measurement for either.
Why the answer is only rough
- Pigeons on the ground cannot hit your head, and the model counts them anyway. Pigeons digest much of the day’s food overnight at their roosts (Spennemann & Watson (2017) (opens in new tab)), so the open-square figures are on the high side.
- Pigeons bunch up where food is. Standing next to someone throwing bread is very different from standing at the edge of the same square.
- The Trafalgar Square counts are from 2003. Feeding there was banned in November 2003 (BBC News, 17 November 2003 (opens in new tab)), and the square now has far fewer birds.
- City-wide densities are averages over whole districts, including roofs and courtyards where nobody stands.
If the worst happens, our guide on whether pigeon poop is good luck has the folklore and what to do next.
Questions
Is anything I enter saved?
No. The sums run in your browser. A shared link carries your answers in the web address after the # sign, so whoever opens it sees the same result.
Why is my city not on the list?
Few cities publish a pigeon census, and the ones that do count in different ways. If yours is missing, pick the park bench or “somewhere else” option and count the pigeons around you.
Sources
- Spennemann & Watson (2017) (opens in new tab): Dietary habits of urban pigeons (Columba livia) and implications of excreta pH, a review. European Journal of Ecology 3(1).
- Haag-Wackernagel & Geigenfeind (2008) (opens in new tab): Protecting buildings against feral pigeons. European Journal of Wildlife Research.
- Senar et al. (2016) (opens in new tab): Reducing the availability of food to control feral pigeons: changes in population size and composition. Pest Management Science.
- BBC News, 17 November 2003 (opens in new tab): Feeding Trafalgar’s pigeons illegal.
- Mayor of London, answer to an Assembly question (opens in new tab): Trafalgar Square Pigeons.
- GiGL (opens in new tab) (Greenspace Information for Greater London): Trafalgar Square, 0.93 ha.
- Fruin, J. J. (1971). Pedestrian Planning and Design. Body ellipse of 0.14 m².
- Buchmüller & Weidmann (2006) (opens in new tab): Parameters of pedestrians, pedestrian traffic and walking facilities. ETH Zürich, IVT Report 132.