Pigeons are very adaptive birds and fit perfectly into urban environments where they have no natural predators. Despite their homing ability, they are sedentary and resident (i.e., non-migratory) birds. They move when they need to feed, roost or nest and they like to be able to follow spatial as well as temporal patterns. They are also surprisingly able to memorize places, people and timetables to keep hunger at bay.
Pigeons have a high reproductive potential. They mate all year round and raise their young in two months. They are capable of breeding five times a year, although not all of their clutches come to term. The number of pigeons can, theoretically, double in a year. But in practice their population stabilizes at a given moment and, although the number of individuals remains constant, their health is affected. This is why, even though if pigeons are well taken care of they may live to be 17 years old, it is estimated that city pigeons are subject to such wear and tear that they only live an average of five years.
How many pigeons there are is determined by how much food is available and by whether there are buildings where they can nest and roost. These are the basic conditions for the increase in pigeon populations.
Pigeons are allowed to entertain society as long as their numbers are tolerable and they do not cause any damage. It is true that the demographic explosion of city pigeons in the last few years has turned into a real problem in city locations where they have a high population density. This has forced local authorities to put pigeon control programmes into effect. Although they are more vulnerable to habitat control than to direct control of their populations, it is often necessary to capture them to bring the situation back to normal.
Pigeons have turned into controversial animals due to their population density, their habits and their interactions with people. Citizens have contradictory opinions about them that go from sympathy because they are symbolic and tame animals, to a generalized aversion.
In many Spanish cities the population of pigeons has increased excessively. This biomass, concentrated in reduced spaces, causes certain problems:
In the first place, constant exposure to their droppings damages buildings, monuments and parks because of the corrosive substances they contain.
Also, many citizens complain about pigeons roosting in certain areas such as balconies, attics or abandoned houses, mainly because of the accumulated debris and because they are noisy.
On the other hand, an excessive number of pigeons entails a rise in their own health problems because they transmit diseases more easily. Added to poor and inadequate food and to the physical deterioration brought on by continuous and uncontrolled breeding under unfavourable weather conditions, the result is that their life expectancy is much lower than anticipated.
Pigeons usually harbour many parasites in these situations, although most of their external parasites only affect humans accidentally. In the same way, the risk of pigeons transmitting diseases to humans is low because they interact only marginally with each other. Despite this, you should keep in mind two things. One, that the most important diseases that pigeons may transmit to humans are salmonella, toxoplasmosis and psittacosis. The other, that children, because of how they play and because they use open-air public spaces more frequently, are more likely to have contact with them and their droppings.
Control programmes for these birds must be comprehensive and continuous to be successful. Their final aim should be to maintain populations only in certain areas and create the necessary infrastructures to do this. As to preventing the nuisance they cause in certain other areas and the problem with their droppings, the best option is using physical exclusion systems.
It may be necessary to use different methods to trap pigeons and even to discourage people from feeding them. This is difficult to understand for those who do it with the best intentions, but it is really the origin of pigeon overpopulation.
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