Effects of food restriction on food avoidance and risk of acute poisoning of captive feral pigeons from fonofos-treated seeds

Fonofos is a highly toxic insecticide to birds that, when used as a cereal seed treatment, has caused mortality of free-living feral pigeons (Columba livia). Pigeons kept individually under ad libitum feeding conditions in th e laboratory do not suffer lethal poisoning because they develop a strong a voidance response to fonofos-treated seed, which restricts consumption to b elow lethal levels. Two laboratory experiments were conducted to assess the role of avoidance in reducing the risk of acute poisoning of captive birds under food stress. In the first experiment, pigeons acclimatized to feed o n untreated wheat seeds for 6 h/day were presented with fonofos-treated see ds for 6 h on a testing day, following normal food surplus in one experimen tal group (eight birds) and 6 days of deprivation in another (eight birds). In the second experiment, different pigeons were acclimatized to a feeding regime of 2 h/day and treated seeds were offered without previous restrict ion (eight birds) or after 6 days of food restriction in which birds were g iven 15% of normal intake (eight birds). In the second experiment, six bird s in each experimental group were video-taped to study their feeding behavi or. Survivors at the end of the testing day were killed, and all birds were dissected and analyzed to determine carcass and pectoral muscle compositio n. Food-stressed birds lost similar to 11% of their initial body weight dur ing 6 days of total or partial food restriction, but they still had visible fat deposits and a high body fat content, indicating that they were in goo d body condition in terms of energy reserves. Consumption of treated seeds on the testing day was reduced in comparison with normal intake of untreate d seed in all birds, but there were differences between experimental groups . In ad libitum-fed birds, consumption of treated seed in each experiment a veraged 12% and 19% of normal levels, exposure to fonofos was below lethal levels, and no bird died. In food-stressed birds, consumption was higher (3 4% or 56% of normal levels for the first and second experiments, respective ly) and led to the ingestion of seed containing lethal doses of pesticide. Two birds in the first experiment and three in the second died of acute poi soning within around 2 h of initial exposure. The avoidance response develo ped quickly in both ad libitum-fed and food-stressed birds. Feeding took pl ace in most birds almost exclusively in the first 9 min of the testing day. Within this interval, birds of the two experimental groups stopped ingesti ng treated seeds around 6 min after the onset of feeding. The differences b etween experimental groups in consumption of treated seed were due to the h igher feeding rate and effective feeding time in food-stressed birds. It is concluded that although feral pigeons under severe food stress develop an early and strong conditioned food aversion to fonofos-treated seeds, avoida nce does not always prevent mortality. The need for including hunger stress as a factor in avian dietary toxicity tests to make testing conditions mor e representative of those experienced by wild birds is discussed.