Urban Planning, Ecological Transition, Urban Services and Housing

Pigeon overpopulations can pose a danger to public health as some birds may suffer from illnesses or carry pathogens that can be transmitted to humans (zoonosis).

Furthermore, pigeons are harmful to our architectural heritage, street furniture and vegetation. They also cause problems in particular buildings and housing blocks, in grain storage sites and gardens (they spot planted seeds and eat them).

They can give rise to agricultural problems in some areas, where crops are very close to cities, as some birds can move to these places for feeding.

When a city's pigeon density exceeds its tolerable limit (300-400 pigeons/km2, on average, although this can vary according to the city’s features), measures need to be established to control their population numbers.

There are several ways of reducing pigeon numbers in a particular place, which we can group under:

- Change of habitat (by reducing the amount of food resources, water availability and number of places for resting and nesting).

- Increasing the rate of mortality (capturing and elimination, increasing the number of predators etc.)

- Reducing fertility (eliminating nests and/or eggs, sterilisation, etc.)

There are numerous control methods, but studies have to be made before we choose one or another, in the first place, on the population to know its variables, especially those that refer to density, reproduction and migration, as well as to determine the area used, movements and zones for feeding, rearing and resting.

This is the only way we can establish effective control measures. Several measures will have to be established depending on whether we are dealing with a local (very localised problems) or a general control (problems present in most of the city).

Pigeons are a species whose survival strategy is based on compensating their high juvenile mortality rate with an even higher reproductive rate.

Changes in habitats shift the problem to other areas where increasing mortality rates proves ineffective, given that the remaining individuals exploit food and space resources to increase their rates of reproduction.

Reducing fertility by sterilisation cuts down considerably the number of new individuals and this, along with the species’ high mortality rate, causes a drop in the population number.

Nicarbazin is part of the carbanilide group belonging to anticoccidial drugs. It is an equimolecular complex of 4,4'-dinitrocarbanilide (DNC) and 2-hydroxy-4,6-dimethylpyrimidine (HDP).

This is a flavourless, odourless, pale yellow powder that is insoluble in water but dissolves in alcohol and some organic solvents.

Nicarbazin is a substance that has been used for a long time to control coccidiosis in chicken meat.

Its use in egg-laying chickens as a coccidiostatic agent has highlighted its totally reversible inhibiting effect on the productive and reproductive function, by reducing egg production.

The first scientific study on the effect of nicarbazin on the reproductive activity of pigeons came from an experiment conducted at the Institute of Clinical Veterinary Medicine and the Institute of Veterinary Pathological Anatomy at the University of Parma by Martelli et al., in 1993.

This compound produces a hormonal imbalance that has a very serious effect on egg production (reduced laying) and quality.

It causes:

- Reduced weight.

- Thinning of the egg shell.

- Depigmentation of the brown egg shells of egg-laying hens.

- Speckled yokes. White spots also appear, due to the leakage of liquid from the albumen (white of the egg) into the yoke, as the latter's membrane becomes increasingly permeable.

The rupturing of the yoke's membrane causes it to mix with the albumen, changing the conditions needed for the embryo’s viable development. It affects the growth of chicks and their metabolism too, by raising their rectal temperature, which reduces their fertility.  Hypoplasia in spermatogenic cells and absent spermatid cells have also been observed.

The toxic effects on birds disappear once the drug has been removed from their diet. Therefore, nicarbazin only has an inhibitory reproductive effect on birds, and as a result of a side effect caused by the daily administration of a specific dose and which disappears after 4 days.

Nicarbazin’s two components are absorbed separately into the birds’ digestive system. DNC is absorbed faster although it disappears from tissues more slowly than HDP. DNC is basically excreted in faeces, which is why it is used as a marker for studies on waste.

A medicine has to be shown to be safe, effective and of established quality and purity before its use can be registered and authorised in a European country. And it will have to be properly identified and accompanied by suitable information (Directive 2004/28/EC of the European Parliament and of the Council of 31 March 2004).

This product is already registered in Italy and Belgium and complies with European regulations. Nicarbazin has also been registered and marketed in the USA for controlling Canadian geese and pigeon numbers since 2005. It had to pass exhaustive EPA controls in the USA before it was approved and its toxicity has been classed as equal to that of sugar (see EPA Fact Sheet, Nicarbazin Conditional Registration, Nov 2005).

Nicarbazin is marketed under the commercial name of OVISTOP and its generic versions. This is a special Veterinary-use medicine distributed by the ACME DRUGS S.R.L. Laboratory (Cavriago, Italy).

The product has a European patent and is registered in Italy and Belgium where the competent authorities have classed it as a special Veterinary-use medicine according to the provisions set out in European regulatory legislation as no biocidal action has been observed for it.

The only express indication for which it has been approved is as a contraceptive for pigeons and its target species are urban pigeons. While the registration process is being completed before the Spanish Agency for Medicines and Healthcare Products (AEMPS), its use falls within the Exceptional Prescription Procedure for Therapeutic Gaps established in Spain's Royal Decree RD 109/1995 of 27 January. This procedure is used after consultation with AEMPS (Spanish Agency for Medicines and Healthcare Products) and receipt of its approval.

Nicarbazin was first used 15 years ago in Italy. It underwent a pilot trial in Catalonia in 2004, funded by the Barcelona Provincial Council in the localities of Granollers and Calella with very satisfactory results.

It is currently being used in Arenys de Mar, Artés, Badia del Vallés, Capellades, Cardona, Cassà de la Selva, Cardona, Castellar del Vallès, Guissona, Igualada, Molins de Rei, Olesa, La Pobla de Claramunt, Puigpelat, Puig-reig, Ripoll, Sant Quirze de Besora, La Seu d’Urgell, Solsona, Sant Vicenç de Castellet, Vilafranca del Penedès, Alicante and Valencia.

According to the approved registered product's instructions, the daily dose for nicarbazin to have its desired effect on reducing fertility and acting as a control method is 10 g of product per pigeon present at the administration point.

Pigeons will be treated through an automated dispensing device which comes in two models depending on the place it is to be put up in: public roads or high up (roofs).

The dispensers have a deposit for the product, with a 30 kg capacity, roughly, and a motor that disperses the treatment some 2-3 metres away at the time set.

The dispensers’ installation places were chosen in areas with a higher concentration of pigeons, which means that the pigeons’ feeding and breeding places are in the vicinity (under 300 metros away).

No. While the product's nicarbazin concentration is the amount necessary for its inhibitory effect on reproduction, it is physically impossible for pigeons to consume the quantity required for intoxication. It disappears from a pigeon’s body after it has stopped consuming food with nicarbazin for a few days.

Treatment with Nicarbazin lasts for 8 months a year, from 15 March to 15 November. It will be distributed for 5 days a week, Monday to Friday, early in the morning, when pigeons are most in need of feeding.

The first year of treatment is expected to see a reduction of around 20%-30% (though there can be fluctuations according to area) and after 4-5 years the reduction rises to 80% of the original population.

When pigeons ingest nicarbazin, they metabolise it quickly, unlike progesterone, and it breaks up into two components, DCN, the active part, and HDP, which enables its absorption into bird intestines.

When it is not in complex with HDP, the DNC aggregates form particles that are too large for absorption into the intestine, so they have no effect on animals that consume DNC.  This also happens when nicarbazin dissolves in water or goes to the surface of the ground.

In addition, the quantity of nicarbazin and its metabolites excreted into the environment by a population of pigeons treated with the stated dose proves to be 100 times less than the limit provided for under current European regulations on “Environmental Risk Assessment (E.R.A.)”, which sets this limit for this substance at 10 µg per kg of earth. Persistence in the environment is limited, owing to the product's sensitivity to ultraviolet rays.

If a bird of prey eats a pigeon treated with nicarbazin, it ingests the broken-up, inactive form of that product which cannot be absorbed.

The nicarbazin, what is more, is absorbed into the caecum of the large intestine, which is missing or rudimentary in diurnal birds of prey.

Even so, the inactive nicarbazin residues that can be consumed are insignificant due to the scant quantity remaining in the pigeon's tissues and organs (see United Nations World Health Organization (WHO), Food & Agriculture Organization (FAO), Joint Expert Committee on Food Additives (JECFA). Evaluation of Certain Veterinary Drug Residues in Food (Nicarbazin). Series 888, pp.66-72. 2000). 

The following concentrations of nicarbazin are found in pigeons treated with the product:

A bird-eating predator would therefore consume 0.30-0.45 mg of nicarbazin, a dose that is 20 times less than the minimum required for having any effect.

Product consumption through undigested content from the prey's crop and intestines could be considered a means of exposure. However, consuming a pigeon with an undigested product, in contrast to a toxin, does would not even constitute a single dose for a bird of prey. A suitable dose and duration are required before any contraceptive effects would be produced.

So a female peregrine falcon weighing 1500 g would require 5 times the dose of a 300 g pigeon and would have to consume 5 pigeons a day.

In addition, the dose would have to be given out every day, for a minimum of 5 days, before contraceptive levels could be reached in the blood. In other words, falcons would have to consume the undigested product in the intestines of 25 pigeons in 5 days before the contraceptive levels could be reached in the blood. This is an extremely unlikely scenario.

Periodic checks will be made during the treatment period to determine the number of pigeons treated at each administration point and gather information on the variations that may arise, to adjust the doses that are distributed and optimise the product's use.

The product dose represents 30% of the pigeons’ daily diet. Having the distribution programmed for the early morning ensures all the dispensed treated maize is consumed and that none of it is left in the environment.

The trials that nicarbazin had to go through before its approval by the United States’ Environmental Protection Agency (EPA) show that the effects on land and aquatic organisms are in the lowest category, even in larger concentrations than the ones used for controlling reproduction.

When it comes to granivorous birds, the calibre of the maize grain prevents it from being ingested by species that are smaller than pigeons.

As for birds that are the same size as pigeons, by adapting doses to the number of pigeons in a place, the latter’s voracity and aggressiveness only allow the occasional ingestion of the product by other species, which would result in de-infestation of coccidia rather than sterilisation.

Nicarbazin can only have a sterilising effect if it is continually ingested and at a certain daily dose.

Studies on toxicity in mammals and birds receiving short- and long-term doses of nicarbazin have shown minimal effects. Adverse effects in animals have generally been observed only after a year or more of treatment, which would not apply here as the treatment lasts approximately 8 months.

In any case, treatment involves a monitoring and control of dispensation points for studying possible use by other species. These species in any case have a period of reproduction limited to a couple of months, during which, where a risk is confirmed, the pigeons’ treatment may be temporarily interrupted.

Studies from the World Health Organisation (WHO) suggest that mammals (including humans) would have to consume enormously high quantities of the product before it could have toxic effects on them.

According to the EPA (the US Environment Protection Agency), based on acute oral toxicity data on rat LD50 values and for the American product (2500 ppm) with a concentration of nicarbazin three times higher than the European product's (800ppm), a single acute ingestion for a child (15 kg) would have to exceed 60 kg of the product and for a dog (10 kg) 40 kg of the product before it could cause lethal effects in 50% of people or dogs that consumed it.

The product used in Barcelona involves practically no risk as it only has toxic effects based on 12 kg of product for every kg of weight. A person would have to ingest 750 kg a day of the product before it could be toxic. As a result, daily consumption of the product is impossible, as is ingesting a dangerous quantity of the product.

On the other hand, a person who consumed 100 g of liver containing 670 µg/kg of nicarbazin would receive a 67 µg dose, which is below the Recommended Ingested Dose of 24,000 µg for a person weighing 60 kg.

No, seeing as maize grain treated with nicarbazin is covered by an edible silicone layer that is water-repellent so that even when the grain is wet the nicarbazin stays in it.

In the hypothetical case of powdered nicarbazin coming into direct contact with a person’s eyes, all the person needs to do is wash their eyes out with water.

Yes. Public collaboration is important for the following reasons:

- Controlling the running of the dispensers.

- Taking part in the register of incidents and their possible solutions.

- Reducing direct feeding and controlling indirect feeding by eliminating food leftovers on the ground.

- Informing the authorities of the locations of abandoned and open buildings that enable nesting.