Urban Planning, Ecological Transition, Urban Services and Housing

Nicarbazin for controlling the number of urban pigeons is marketed with maize grain and covered over with an edible silicon layer so the nicarbazin stays on the maize even when it is handled or gets wet.

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

Nicarbazin (C19H18N6O6)

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

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, hence the inability of organisms to assimilate DNC. This also happens when nicarbazin dissolves in water or goes to the surface of the ground.

Effects of nicarbazin on the reproductive functions of pigeons

Studies carried out from administering nicarbazin to urban pigeons have shown that it is not toxic to these birds.

It has also been confirmed that it has a reversible effect on the birds’ reproduction (once it stops being administered, the pigeons are able to breed again).

Nicarbazin is noted for having little toxicity on a systemic level. Even so, this compound causes a hormonal imbalance which has a very serious effect on their egg production (reduced laying) and quality: their eggs end up lighter, with thinner shells and 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.

Toxicity and side effects in other species

Nicarbazin can only have a sterilising effect if it is continually ingested and at a certain daily dose (10 grammes a day per pigeon).

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.

Birds

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

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.

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.

Birds of prey

There is no risk to birds or prey in feeding on pigeons treated with nicarbazin.

When pigeons ingest nicarbazin, they metabolise it quickly and it breaks up into two components, DCN, the active part, and HDP, which enables its absorption into bird intestines. So, when a bird of prey eats a pigeon treated with nicarbazin, it ingests the broken-up, inactive form of that product, which cannot be absorbed. Even then, the inactive nicarbazin residues that it can consume are insignificant, given the low quantity that remains in the pigeon’s tissues and organs.

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.