Rodenticides & Wildlife

The Issue

Research over many years has highlighted two main areas of concern with regard to the use of rodenticides and wildlife.

Firstly, the remains of individual birds collected are sometimes suspected to have died as a result of the irresponsible or incorrect use of plant protection products and biocides. The scope of this is monitored and reported through a variety of schemes. One of these is the Wildlife Incident Investigation Scheme (WIIS) run by the Chemicals Regulation Directorate (CRD) and Science and Advice for Scottish Agriculture (SASA) in the UK.

In Ireland, the RAPTOR Protocol involving three government agencies (the National Parks and Wildlife Service, the Regional Veterinary Laboratories of the Department of Agriculture, Food and the Marine, and the State Laboratory) has been developed to provide for the investigation of injuries and mortalities in birds of prey.

Another concern is that many species of wildlife carry low-level residues of some of the commonly-used rodenticides in their bodies. Research has shown that these residues occur in a high proportion of individuals of some wildlife species, such as barn owls, red kites, buzzards and kestrels. It is not known whether these low-level or sub-lethal residues have any adverse effects, either on the individual animals that carry them or on wildlife populations as a whole. However, those who use rodenticides should do so in ways that seek to reduce to a minimum any exposure of wildlife and other non-target animals.

Long-term monitoring data from WIIS

The Wildlife Incident Investigation Scheme (WIIS) is Europe’s most extensive post-registration surveillance scheme monitoring the effects of pesticides on wildlife.

WIIS mainly relies on reports from the public of incidents involving wildlife casualties. Further investigations normally involve post mortem analysis of carcases, chemical analysis of tissues for pesticide residues and on-site investigations to determine, if possible, the circumstances of the incident. Mortality is attributed to a pesticide if a residue is found that is above a level considered to represent lethal exposure.

WIIS incidents involving chemicals used to control vertebrate pests

The results of WIIS are published in an annual report with quarterly updates ( Since 1993, these reports have included a table giving information of individual incidents, allowing detailed analysis of WIIS incidents to be carried out (Figure 1).

The cause of each incident is attributed as abuse of a pesticide, in the form of deliberate, illegal attempts to poison animals;
misuse of a product, by careless, accidental or wilful failure to follow correct practice;
approved use of a product, according to the specified conditions of use; and
unspecified use, where the cause could not be assigned to one of the above categories.

An analysis of all 1791 WIIS incidents involving chemicals used to control vertebrate pests has been carried for the years 1993 to 2011. In terms of the numbers of active ingredients, the products involved are mainly anticoagulant rodenticides (Figure 2) but there are also non-anticoagulant rodenticides, e.g. alphachloralose and chemicals such as strychnine, which was once used for mole control but is no longer approved for use.

WIIS incidents by cause

Abuse – 576 (32.2%) were cases of ‘abuse’, where vertebrate control agents were used in deliberate attempts to harm wildlife and companion animals. This abuse often takes the form of poisoned meat baits, put out mainly for rooks, crows, magpies and foxes for the protection of game birds. These baits are indiscriminate and are also taken by other mammals, including dogs, and a wide range of birds of prey. Many of these incidents lead to criminal investigations and may result in enforcement action, including financial penalties and/or imprisonment.

The Campaign Against Illegal Poisoning is also run by the Chemicals Regulation Directorate and draws attention to this issue by publicising prosecutions ( The campaign appeared to be having some effect in the late 1990s, with incidents steadily declining. However, increases have been seen more recently (Figure 1).

The geographical distribution of these incidents shows a high degree of association with moorland used for shooting, with relatively large numbers of abuse incidents in Tayside, Co. Down, Antrim, Highland, Tyrone, North Yorkshire, Grampian, Strathclyde and Derry.

Misuse – 173 (9.7%) were incidents involving ‘misuse’ when the products were used in an inappropriate manner, either deliberate or accidental, in contravention of the approval and instructions on the label.

Approved – Only 38 (2.1%) incidents, over the period, could be attributed with certainty to the use of products in an ‘approved’ manner. This provides confidence that, when they are properly used, vertebrate control agents do not present a significant risk to wildlife and companion animals.

Unspecified – 517 (28.9%) were ‘unspecified’ incidents, where investigations did not permit a specific cause to be attributed.

Other – 487 (27.2%) were incidents in which causes other than the pesticides detected on analysis were the primary cause of death. This includes several different categories including starvation, trauma and injury. Such causes of death have only been recorded in WIIS reports since 2002 (Figure 1). These cases have increased dramatically in recent years, especially in reports from Scotland. This is because scientists running the WIIS scheme have decided to analyse for residues of rodenticides all casualties of certain species, especially birds of prey, whether pesticides were suspected as being the main cause of death or not.

RAPTOR (Recording & Addressing Persecution & other Threats to Our Raptors) Protocol in Ireland

The National Parks & Wildlife Service (NPWS) of the Irish Department of Arts, Heritage and the Gaeltacht (DAHG), publishes an annual report on bird of prey poisoning and persecution compiled on the basis of data generated through the RAPTOR protocol ( The RAPTOR protocol involving the NPWS, the Regional Veterinary Laboratories (RVLs) of the Department of Agricultrue, Food and the Marine (DAFM) and the State Laboratory) was agreed in 2011 and the first report was published in 2013. Reports generated provide information on poisoning incidents involving birds of prey as well as other direct threats including persecution

RAPTOR Protocol Incidents by Cause

Under the Irish RAPTOR protocol, non-habitat related threats to birds of prey, including poisoning, persecution and collisions are investigated. Specimens for testing are collected by NPWS rangers and following X-Ray examination by a designated veterinarian, are submitted to a Regional Veterinary Laboratory for post mortem examination. Samples taken are submitted to the State Laboratory for chemical analysis. Data generated, which includes information on poisons detected as well as the location and frequency of incidents, are essential for the investigation and assessment of incidents involving birds of prey. The intelligence gathered is used in planning enforcement, education and awareness activities as well as in policy formation.

Between 2011 and 2013, second generation anticoagulant rodenticides were detected in 22 raptor incidents and other poisons were reported in 34 incidents. The total number of poisoning or persecution incidents in those years was 75 – all carcases were analysed for traces of rodenticides. Some incidents involved multiple injuries and deaths. The number of wildlife individuals known to have been poisoned between 2011 and 2013 was just under 200. Poisoning accounts for more recorded persecution deaths of birds of prey in Ireland than shooting or trapping, in terms of what is discoverable – the full extent of poisoning or persecution is likely to be far greater than reported, since many incidents remain undiscovered, unreported or carcases are scavenged. While alphachloralose or illegal poisons such as carbofuran and paraquat have been used in cases where birds of prey have been deliberately targeted, the prevalence of traces of rodenticides in otherwise healthy individuals is also a cause of concern.

Data generated through the RAPTOR protocol are used to inform policy makers, manufacturers and users on the impact of rodenticides on protected wildlife. CRRU Ireland supports the development of quantitative techniques for the analysis of rodenticide in wildlife.

Low-level rodenticide residues in UK and Irish Wildlife

For many years scientists at what is now the Centre for Ecology and Hydrology have monitored residues of certain environmental pollutants in birds. This is called the Predatory Bird Monitoring Scheme ( The scheme is funded by several agencies, one of which is CRRU.

During the 1980s barn owls in the UK were found to carrying residues of some of the most commonly-used anticoagulant rodenticides. Most of the birds were apparently otherwise healthy and there was no evidence that the residual traces present, were having any adverse effects on the birds that carried them. 
Nevertheless, as methods of analysis grew more sophisticated and the frequency of carcase collection was increased, it was found during the 1990s that up to 40% of barn owls carried traces of rodenticides. This indicated that at some time during their lives the birds had taken one or more rodents that had been treated with rodenticides.

More recently even more sophisticated and sensitive methods of chemical analysis have been used which can detect extremely low level residues. The new data available from the PBMS, supplemented by data on buzzards from SASA, show that at some time in their lives a high proportion of many important species of birds of prey have been exposed to rodenticides (Table 2).

Although owls and kestrels may occasionally take rats and house mice for food, analysis of their food preferences shows that in the UK they feed mainly on non-target small mammals, such as field mice and voles. It is difficult to explain the extent of exposure of owls and kestrels to rodenticides by their consumption of contaminated target rodents. It is likely that they are indirectly exposed when non-target rodents take rodenticide baits during application of rodenticides.
This information on rodenticide residues in owls must be seen in the context of the fact that the most common documented cause of death in barn owls is collision with road traffic.

Recognition of the level of exposure of barn owls to anticoagulants resulted in the search for residues in other wildlife species. It has been shown that populations of several other species also contain residues of anticoagulants, including red kites, kestrels, buzzards, polecats, stoats and weasels (Figure 3).

 It has yet to be established the effect on population dynamics, if any, exposure to non-lethal residual traces of rodenticides may have in these species.

In Ireland, research carried out by BirdWatch Ireland, in collaboration with the Centre for Ecology and Hydrology, UK, and University College Cork has shown that barn owls are extensively contaminated with anticoagulants like their UK counterparts. Several small mammal species, such as the field vole and bank vole, which are important prey of barn owls in the UK, are either absent from Ireland or have limited distribution. As a consequence, Irish barn owls are more likely to feed on house mice and Norway rats that are the target of control programmes based on anticoagulants. Although a similar proportion of barn owls in Ireland were found to carry detectable residual traces of second generation anticoagulant rodenticides (88%) as in the UK, available evidence suggests that the levels present were considerably higher in Irish barn owls.

Recent research published by SASA has brought to light another area of concern. For the first time extensive studies have been conducted on sparrowhawks and peregrine falcons. In spite of these species feeding mainly on small birds taken on the wing, 46% of sparrowhawks and 35% of peregrines contained residues of rodenticides. This demonstrates that the birds that are their prey are being accidentally exposed to these chemicals.

Data generated in accordance with the Irish RAPTOR protocol confirmed the presence of traces of rodenticides in peregrine falcons. Although non-raptor species are generally not tested under the protocol, traces of rodenticides were also been found in otters.

Once again, there is no evidence that populations of these species are in any immediate danger as a result of such non-lethal exposure. Some other species such as stoats and weasels are actively controlled by gamekeepers to protect game birds. A UK survey has shown that polecat numbers have increased dramatically during recent years and this species is now present in parts of the UK where it has not been seen for more than a century.

Surveys conducted by the British Trust for Ornithology have similarly shown that over the last 10-15 years populations of some of the species most exposed to rodenticides, including barn owls, red kites and common buzzards, have actually increased significantly. These increases are as a result of the release of captive-bred birds and other important conservation efforts such as the provision of nest boxes and a concerted effort to prevent persecution by illegal shooting and poisoning.
In Ireland the buzzard has made a great recovery and is now breeding in almost every county, while the re-introduced red kite population is also doing well, but the barn owl has suffered significant decline in recent years.

However, the widespread distribution of these low-level residues of anticoagulants in wildlife is of concern and we must do all we can to prevent it.

Information about wildlife exposure from other Countries

The UK and Ireland are not the only European countries from which there is documented evidence of the exposure of non-target animals to rodenticides.

A similar picture is emerging from Denmark. Recent research from there has shown that residues of anticoagulants are found in more than 90% of individuals in a range of species including stoat, weasel, barn owl, red kite, common buzzard, kestrel and tawny owl. It is interesting to note that for many years all rat control in Denmark has been conducted only by professional pest controllers. Therefore, it seems that a restriction of use of anticoagulants to use only by trained professionals is unlikely to reduce exposure of non-target animals unless additional mitigation measures are also applied.