1. Why Pigeons Peck at the Ground: Looking for Plant Seeds
Pigeons walking while pecking at the ground are looking for food. The Osaka Prefecture government explains that feral rock doves eat plant-based items like tree nuts, grass seeds, buds, and leaves. They note a positive side: pigeons help reduce weed seeds [1]. Similarly, Sendai City materials state that these birds primarily eat plant matter [2].
While they are strongly herbivorous, they are technically omnivores. Weather information articles explain that feral rock doves prefer grains the most and do not like fruit or meat [3]. However, since some descriptions mention they may eat insects or earthworms, it is safer not to say they eat "only plants."
One example of what was found in a stomach comes from BioKIDS at the University of Michigan. In a semi-rural area of Kansas, USA, researchers analyzed pigeon stomach contents. The results were 92% corn, 3.2% oats, and 3.7% cherries, totaling 98.9%. The remaining about 1% was small amounts of knotweed or elm [6]. This shows the diet is almost entirely seeds and fruits. However, this is just one example from one location in America, so it does not represent the exact ratios for Japanese pigeons. Food likely changes depending on the land and season.
Seeds are hard food. How do toothless birds break them down?
2. How Pigeons Grind Seeds Without Teeth Using Grit and the Gizzard
Pigeons have no teeth. An explanatory article from Gendai Business explains that they use a special organ called the gizzard. Inside this organ, small stones and muscles work together to grind up food [8]. The same article lists this mechanism as one reason why pigeons peck at the ground so much: they are searching for these stones. The gizzard is an organ found in birds generally, not just pigeons.
Using small stones is a bit like using a stone mill. However, the mill is not turning externally; instead, the stones and muscles move together inside the body to crush the seeds.
Pigeons also drink water differently than many other birds. BioKIDS notes that feral rock doves suck up water with their beaks like a straw [6]. Many birds fill their mouths with water, tilt their heads back, and let it flow down. Pigeons can drink while keeping their heads down. The materials reviewed here do not explain the specific body mechanism that allows this.
So far, we have looked at adult pigeons. Adult pigeons can grind seeds with small stones. Can chicks in the nest grind seeds with stones too?
3. How Pigeon Parents Feed Chicks Crop Milk Made in Their Bodies
Pigeon parents produce "pigeon milk" (crop milk) in an organ called the crop and feed it to their chicks. According to weather information articles, both males and females can produce this [3].
A paper from PubMed Central reports that the pigeon crop reacts to the hormone prolactin to create a nutrient mass. By dry weight, it is about 60% protein, 32–36% fat, and 1–3% carbohydrates [7]. It is not mammalian milk itself. The same paper notes that flamingos and male emperor penguins also produce something similar.
Because of this "milk," pigeons do not need to catch insects to feed their young. Explanatory articles state that they can raise chicks almost independently of seasonal changes in prey availability [3]. Osaka Prefecture lists the breeding season for feral rock doves as early spring to early winter, with eggs hatching in 16–18 days and chicks leaving the nest in about 30 days [1]. Sendai City explains that the breeding period is year-round, but most active from spring to summer [2]. While local governments describe it differently, both agree on the point that they breed repeatedly.
A bird that eats seeds can raise young all year. Is this trait related to why pigeons, originally cliff-dwelling birds, increased in human towns?
4. How Wild Rock Doves That Nested on Cliffs Came to Live in Building Gaps
The ancestor of the feral rock dove, the wild rock dove, originally bred in gaps in cliffs. Canon's Bird Branch notes that their main food is plant-based, and being able to survive on human-provided food likely helped them thrive near human settlements [4].
In cities, buildings serve as substitutes for cliffs. Weather information articles explain that the original wild species nests mainly on rocky cliffs in dry areas. In urban environments, pigeons treat gaps in buildings and apartment balconies as if they were cliffs, using them as roosts [3].
According to materials from the Okayama Prefecture Wildlife Protection Center, feral rock doves in Japan are said to have spread after being brought from overseas as carrier pigeons during the Nara period and then becoming wild. Their original food was tree nuts and grass buds, fruits, and leaves [9]. The specific historical details follow the phrasing of the source materials.
With places resembling rocky cliffs and plant-based food available, what portion of a pigeon's diet comes from human-provided food?
5. How Much of City Pigeons' Food Comes From Humans and How It Affects Their Numbers
A professor at the Percy FitzPatrick Institute in South Africa reportedly stated in news coverage that "about 25% of urban feral rock dove food comes from human-provided sources" [5]. Since this is a news report, the name of the original survey is not clear. This figure applies to South Africa, not Japan. If 25% is one-quarter, then the remaining about 75% is found and eaten by the birds themselves in the wild, such as grass seeds.
Does this mean there is no impact if human food is a minority?
The Okayama Prefecture Wildlife Protection Center materials explain that when getting food becomes routine, pigeons move away from their original way of life. They stop fearing humans and find it easier to breed, which increases their numbers. The fact that they can start breeding about 6 months after leaving the nest also relates to how quickly their population grows [9].
A press release from the Ministry of the Environment states that feeding in parks and temples is considered a main cause of pigeon increases. In a survey from fiscal year 1999, 34% of local governments reported some form of damage [10]. This is not the current percentage.
Chiba City explains that repeated feeding causes locations to become dirty with droppings and feathers. Osaka Prefecture notes that because pigeons have strong reproductive power and few natural enemies, they increase quickly, so they ask people not to feed them [11][1].
The materials seem to suggest that the goal is not to dislike pigeons, but to understand what they naturally eat and watch them from a moderate distance.
6. How to Observe Pigeons for 30 Minutes and Calculate What You See
Try watching pigeons from a distance for about 30 minutes near a park or station. Do not feed them. Do not get too close, do not touch them, and wash your hands after looking.
There are three things to observe. First, count how many times they peck at the ground and note where. Second, watch how they drink from puddles after rain to see if they keep their heads down. Third, look for potential nesting spots. Check gaps in buildings, under bridges, or around balcony pipes to see if pigeons are entering and leaving.
You can also try calculating with the numbers. Using BioKIDS data, 92 + 3.2 + 3.7 equals 98.9. Subtracting this from 100 leaves a remainder of 1.1% [6]. The South African figure of 25% corresponds to about 25 out of 100 if you consider the whole diet as 100. Try writing down in your own words why these numbers might not apply directly to Japanese pigeons.
If you want to read the original sources, pages from Osaka Prefecture and Sendai City briefly summarize pigeon food and breeding seasons. The Ministry of the Environment press release shows the relationship between feeding and population increases through a survey of local governments [1][2][10].