If we think of Venice, we can imagine ourselves in Saint Mark’s Square surrounded by architecture that excites us and transports us to other times. But in the square we are not alone. Among the tourists and the Venetians there are also pigeons.

They do not look at the monuments and, in fact, do not respect them. They live in the holes in the stones of the buildings and perch on the sculptures excreting their depositions without regard.

A problem in the conservation of cultural heritage is the presence of birds and the consequences of this are high budgets for restoration campaigns.

But how can we explain to the pigeons that they must respect the monuments?

Heritage attacks

We cannot reason with pigeons and their attacks on heritage can be quantified in very high numbers. In 2008, Venice came to calculate a cost of €275 per inhabitant per year or an average of €16 to €23 for each Venetian pigeon. Among the main conservation problems derived from their presence we can mention the accumulation of excrement, but also the wear of stones and the corrosion of metal surfaces.

The works of art that we find outdoors in our cities and towns can be seen covered by palomina and guano, the droppings of pigeons. The acid component of these depositions causes corrosion in materials such as bronze. Some recent studies, for example the 2022 study focused on Nepal, have analyzed specific cases to find solutions to an international problem. The droppings also become a breeding ground for bacteria and fungi, a place for the growth of lichens and mosses.

The consequences are the deterioration of the surfaces, the alteration of the colors or the disintegration of the parts that can cause breaks, cracks, detachments or other injuries. These depositions are also a possible route of contagion of zoonotic diseases, those of animal origin that can affect humans.

In addition, the pigeons wear away the monumental stones to better cling to the surfaces. Noses and shoulders of the sculptures can be damaged to ensure stability when they land tired from flying. With these erosion actions, the beak is also filed down.

The most surprising thing is that they even ingest the stones. The idea that pigeons can eat our cultural assets seems like science fiction, but it is. Like other birds, the intake of stones helps them in their digestion processes. Many monuments were built with sandstone that is very easily eroded by inclement weather, by air pollution or by the presence of our birds.

What solutions can we apply in cities by heritage protection agencies?

Animal respect above all

The spikes, the sonic repellents or the toxic gels have been some of the proposals that have been tested. These remedies have been more or less effective in curbing this problem, but not definitive. They can sometimes be harmful to animals and, after all, the most important thing is to avoid hurting them.

For this reason, the skewers that began to populate the cornices a few years ago have fallen into disuse. Over time it has been seen that this system caused injuries to the birds without avoiding the problems of accumulation of defecation, to which we must add leaves or other materials that get trapped between the spikes and cause clogging in downspouts or gutters.

New experiences have opted for plastic mesh, usually high-density polyethylene, which can be made in the color of the monument they protect, isolating it from birds that cannot nest on the ledges or access the existing holes. In Córdoba it has been a few years since they have been installed on the facades of some of its churches.

Some contraceptive measures have also been implemented for population control, such as the Barcelona experience that has reduced its presence by 60%. These may include surveillance of the dovecotes to reduce the number of young, the extraction of eggs or offering food with products that reduce the reproductive capacity, as well as the capture and transfer of specimens to other areas outside the heritage nuclei. .

These actions are discouraged due to the traumatic effect they can have on birds and the need to make their existence compatible with our heritage. It is better to resort to programs based on ecological and sustainable systems at an economic level, but also long-lasting and ethical, which require previous studies adapted to the needs of each specific case.

An example is the use of falconry in the Alhambra. This World Heritage art with birds of prey intimidates pigeons, which move to other settlements.

And if we turn the traditional scarecrow into a figure that reproduces one of these birds that scare them, they themselves will look for other places to nest. Since we cannot explain to them why they should respect the monuments, we must look for different ways to deal with our neighbors, the pigeons.

José A. Ortiz, Professor of the Department of Art History, Barcelona University

This article was originally published on The Conversation. Read the original.