Mallard swimming, Glasgow, Scotland

Mallard duck population

Feeding ducks is popular but can cause problems, particularly on enclosed waters that aren't flushed by rivers or regular flooding.

Overpopulation problems

The population of birds on a pond and the food supply are very closely linked. More food means more mallards.

A regular supply of extra food can lead to artificially large numbers of ducks nesting in the area and also encourage large numbers of unattached birds (particularly males) to stay. Forcible mating of unattached females by groups of males can become regular and can make feeding breaks dangerous for the already exhausted incubating females. 

Young females, breeding for the first time, may die, unaware of the danger and already weak from egg production. Many females are forced to nest away from the pond, increasing the danger to newly-hatched ducklings.

If the food supply remains reliable and adequate for all the ducks over a long period of time, the population can increase from year to year and the birds will become increasingly sedentary. Increasing build up of droppings in the pond favours the growth of algae, which smothers aquatic plants and can deprive the water of oxygen. 

Algal growth is unsightly and smelly, and in hot weather can be a source of botulism. Botulism is a fatal form of food poisoning in animals and man, and millions of waterfowl throughout the world die from it each year. The toxin affects the nervous system and birds die from respiratory failure or drowning.

 Mallard swimming with people in background, Glasgow