Feral pigeons – the problem and its management
The feral or rock pigeon is well-established throughout New Zealand and is a common sight in cropping regions, cities and large towns. Some people enjoy seeing and feeding pigeons, particularly in urban areas, whereas others view them as vermin equivalent to rats.
But are they really a problem? As with most pest species a few have little impact but flocks of several hundred or more have the potential to cause both economic and environmental damage. Pigeons can damage buildings and decorative structures with their excrement in urban areas, and cause crop losses in rural areas. They are also known carriers of zoonotic diseases such as salmonella, but evidence of pigeon-to-human transmission is scarce.
Pigeon populations are limited in their distribution and abundance by the availability of roosting and nesting sites and by year-round availability of food. They will take advantage of seasonal foods such as sprouting cereals and legume crops, and can cause significant crop losses when in large numbers (Figure a). Farmers may need to re-sow crops if losses are high. Urban-based pigeons may congregate at grain-handling and storage facilities, and at sites where people intentionally or unintentionally feed them, such as parks and town squares.
In rural areas pigeon damage is most commonly mitigated using lethal control, either by shooting with shotguns (Figure b), or poisoning using the stupefying agent alphachloralose. Unwanted pigeons roosting and nesting in rural buildings can be eliminated at night using a torch in combination with an air rifle. Site-specific control measures in both rural and urban areas include multi-capture live traps, and exclusion from nesting and roosting sites using angled plates, plastic and metal spikes, tensioned line or wire, netting, electrified wire, barrier coil, and repellent gels. Predators can be used to manage specific pigeon populations. For example, a trained New Zealand falcon has been used to scare off pigeons at Canterbury University.
Sometimes the solution to reducing pigeon impacts is to remove food sources. In urban areas, better disposal of food refuse may be all that is required.
A fertility control agent (OvoControl® P) has been developed in the United States, and its manufacturers claim that it reduces pigeon populations by 90–95%. The agent contains nicarbazin and is fed daily to pigeons to reduce their fertility. While the product may be useful in certain urban situations in New Zealand, it is not currently registered for use here.
Pigeons are very successful opportunists, and changes in farming practices may create more opportunities for them and therefore more problems. New Zealand currently has a strong dairy-based economy, and dairy farms create reliable food sources for pigeons. Silage made from maize, triticale, oats and any other grain-based stock feed can sustain large populations of pigeons throughout the winter when cereal and legume crops are scarce. In the future, more changes to farming practices are likely as economics dictate what is profitable. Recently developed technology to produce synthetic protein may result in fewer animals farmed but greater pea production to produce the raw materials for this product – more pea paddocks also means more food for pigeons and more problems.
Urban pest managers need to determine the extent of their pigeon problem and decide whether the cost of remedial action is less than the cost of maintaining the status quo through repairing buildings and cleaning them. A control programme should not start unless its outcome is first clearly and measurably defined, there is some certainty that the planned control will achieve the desired outcome, and there is a commitment for ongoing funding until management is achieved. There will always be some people who value pigeons, and this difference of opinion will create difficulties when trying to manage their populations. Using non-lethal methods that leave some resident pigeons to satisfy the demands of individuals who value them may be the best compromise in current New Zealand society.
This work was funded by the Ministry of Business, Innovation and Employment via an Envirolink Advice Grant.