The scavenging feeding habits of Red Kites make them susceptible to poisoning from a number of causes.
A method of attempted vermin control, which has long been illegal because of its indiscriminate nature, involves the placing of poisoned baits in the open countryside. The bait might be a dead rabbit or pheasant to which a poisonous substance has been applied. This is often a pesticide which has been developed for a specific agricultural or horticultural purpose and misusing them in this way is a serious offence. The practice of using poison baits has been illegal for over 100 years under Section 8 of the Protection of Animals Act 1911.
There is no evidence that Red Kites are being deliberately targeted, the intended victims probably being crows or foxes. However, it is inevitable that the baits will be found by scavengers such as Red Kites. Up to 2010, no fewer than 20 Yorkshire-related kite deaths from this cause had been recorded. Four deaths known to have occurred in 2010 included two three-week old chicks which were found dead in their nest, the only plausible explanation being that they were fed poisoned food found by their parents whose own fate is unknown. It is extremely difficult to establish who is responsible for causing the deaths of the kites in this way. Please see the website section 'Guidelines for dealing with casualties' for advice on how to handle a suspected poisoning case
The widespread use of rat poison poses a significant threat to Red Kites and other scavenging species. Such poisons are often referred to as being first or second generation. The first generation substances, such as warfarin and coumatetralyl, present a lesser risk to wildlife feeding on them. However, there are geographical areas in which it is officially recognised that the rat population has developed resistance to them, prompting the development of more effective, second generation, poisons.
There is a serious risk that the ease with which rat poisons can be obtained will result in them being used by inexperienced operatives. In such circumstances it is likely that more of the poison would find its way into the natural environment than would be the case if it was applied by an expert, who would effectively and economically target appropriate key areas. An essential part of a management programme is to make regular inspections to ensure that dead rats are removed and safely disposed of before they find their way into the food chain. Since 1999, eight Yorkshire Red Kites are known to have died from the effects of consuming rats which had been killed by rat poison. All kites which are submitted for poison analysis are routinely tested for rat poison. It is of particular concern that the eight Yorkshire birds which are known to have been poisoned in 2010/11 (four by illegal poison baits and four by rat poison) all tested positive for at least two different rat poisons (difenacoum and bromadiolone). Traces of a third (brodifacoum, which is strictly licensed for indoor use only), were also found in three of them. The ease with which poison substances can enter the food chain is shown in the case of the two poisoned three-week old kite chicks referred to above. Analysis showed that, during their brief lives, they had ingested the rat poisons difenacoum and bromadiolone, in addition to the carbofuran which actually killed them! Carbofuran is an insecticide, the use of which is banned in the EU.
The effects of lead-shot ingested by wildfowl, notably Mute Swans, has been widely publicised. It resulted in a total ban in England on the use of lead-shot for shooting all wildfowl species, wherever they occur.
Problems caused by lead can affect kites and other scavenging species through them feeding on prey which has been shot using lead ammunition. Reintroduced kites have undoubtedly benefited significantly from food available on shooting estates. This may be in the form of pheasants or partridges which have been shot using lead-shot, but not retrieved, or rabbits which have been rifle-shot and left out. Shooting by rifle presents less of a risk to birds scavenging on such prey, the bullet usually passing straight through the target. However, testing has revealed that this method is by no means foolproof. Minute fragments of lead break away from the bullet on impact and may be retained in the flesh around the wound.
An in-depth study into the likely effects of lead ingestion by Red Kites found that lead poisoning was likely to have been the cause of death of 9% of those birds which had been found dead for which liver samples had been analysed. The study was able to distinguish between lead used as ammunition and that derived from other sources, such as lead in petrol. It concluded that:
'The risks of Pb [lead] poisoning to this species ...... will not be eliminated until lead ammunition for hunting ...... is banned and replaced with non-toxic alternatives.'