The appealing Wood Owl is one of the species of raptors that occur in our neighbourhood. Raptors are generally beneficial to us humans because they prey on species that, if their numbers get out of hand, can become problematic to us, in both urban and rural settings.
Rats can become a health risk if they are disease carriers, and they can be a problem where food is stored. Some even gnaw on electrical house wiring. In South Africa, generally rats and mice that are problematic are introduced species. The Urban Raptor Project, based in Port Elizabeth, identifies the three species of introduced rodents as: the Norwegian/brown rat (Rattus norvegicus), the black/house/roof rat (Rattus rattus) and the house mouse (Mus musculus).
Natural predators of rats and mice include many species of raptors and small carnivores. Also several species of snake predate on rodents.
In suburban areas in South Africa, the Brown House Snake can be a beneficial presence, such as this one sunning itself in our garden on an unseasonably hot winter’s day. Brown House Snakes are constrictors and have no fangs and are not venomous
It is ironic that many of the predators that can help control populations of potentially problem animals, are themselves targeted by us humans for eradication, often deliberately. In addition, many die as “collateral damage”; that is their deaths are secondary to the target species.
In South Africa, as elsewhere, the list of routinely killed animals and birds, which if allowed to survive could assist us in controlling populations of rodents and other potentially nuisance animals, is long. It includes raptors – large and small, snakes, Wild Dogs, Caracals, species of mongoose, jackal and genet, as well as indigenous rodents that are seldom a problem, among others. And this list does not include the numerous non-target species that also die in traps and from poisons.
Although we often hear a pair Spotted Eagle Owls and a pair of Wood Owls calling in our garden at night, I have not even tried to photograph them. This photograph was taken during this Spotted Eagle Owl’s flying display at the African Bird of Prey Sanctuary in KwaZulu-Natal. Although owls are deliberately targeted for killing by some people, just as lethal for owls is secondary poisoning, commonly from rat poison that they ingest from eating poisoned rodents
Recently, someone told me that secondary poisoning by rat poison (rodenticides) is not an issue for raptors as they do not eat dead animals. As this view did not tally with what I understood to be the case, I decided to read further about the risks that rat poisons pose to raptors and other wild animals, with a view to writing this post. What I found was far more sobering than I anticipated, but we must not lose sight of the fact that reducing the use of rat poisons and helping to raise awareness of the consequences of its use is something that we all can do. I hope that this post helps us understand a little more as to why rat poisons should not be used.
Rat infestations in urban and suburban areas tend to go hand-in-hand with poor waste management as rats thrive on scavenging easy-to-find food. A major step towards controlling rat infestations would be to minimise waste, especially food and food residues, and remove or make inaccessible unavoidable waste. The same applies in our homes. Unfortunately, even these simple steps towards discouraging rats are often overlooked as using rodenticides, which seem to be regarded as a kind of panacea, is seen to be an easy option.
When the first returning migrant Yellow Billed Kites are seen in our skies in springtime, we know that winter is over. The Yellow Billed Kite’s diet includes small vertebrates and carrion. Its eating habits and the fact that it confidently hunts and scavenges in towns and villages puts it at high risk of poisoning by rodenticides. This photograph is of a rescued bird at the African Bird of Prey Sanctuary
There are several types of poisons used as rodenticides. In this post, I focus on the commonly used anti-coagulants, which thin the blood and prevent it from clotting so that poisoned animals die from internal bleeding. How long this takes, depends on the poison used, the amount consumed relative to the size of the animal, and the species-specific metabolism.
According to the United Kingdom-based Barn Owl Trust, after eating poisoned bait the time it takes for a rodent to die varies from 2 to 12 days. In some cases, an individual may not ingest enough poison to kill it (a sub-lethal dose) and continues living, carrying poison residues in the liver. Poisoned rodents that are weakened from chronic exposure or that are dying from ingesting lethal amounts are sluggish and make easy prey for raptors and other predators. In fact their easy capture can lead to poisoned animals forming an increasing proportion of the diet of predators, including owls. Raptors and carnivores eating poisoned prey suffer secondary poisoning that can cause a slow and painful death, or else the animal survives, although weakened, carrying a residue of poison in its body.
Direct deaths from rodenticides of non-target animals and birds from many different species have been recorded worldwide. The Barn Owl Trust reports that typically it takes 6 to 17 days for a Barn Owl to die after eating 3 mice containing the poison Brodifacoum, which is one of the second-generation anticoagulant rodenticides first developed in the 1970s, after rodents were showing signs of becoming resistant to first-generation anticoagulants. The Barn Owl Trust has a clear explanation of the various rodenticides here, and the Wikipedia entry on rodenticides has a useful table, see here.
According to the Environmental Protection Agency in the United States, second-generation anticoagulants are more likely to be able to kill after a single night’s feeding. Although the time taken for the rodent to die is similar to those poisoned by first-generation compounds that require several feeds, the compounds tend to remain in animal tissues longer than do first-generation ones, posing a greater risk to non-target species. Brodifacoum is one of the particularly high-risk poisons for non-target species, both raptors and mammals.
Non-target secondary poisoning commonly includes many species of raptor, including endangered species. Secondary poisoning also affects many mammals, such as those in the United States listed in this extract from a 2013 article in the Audubon Magazine (Williams, 2013).
“There’s no safe place or safe delivery system for second-generation rodenticides. After a rodent partakes, it stumbles around for three to four days, displaying itself as an especially tempting meal not just for raptors but for mammalian predators, including red foxes, gray foxes, endangered San Joaquin kit foxes, swift foxes, coyotes, wolves, raccoons, black bears, skunks, badgers, mountain lions, bobcats, fishers, dogs, and house cats—all of which suffer lethal and sublethal secondary poisoning from eating rodents. Deer, nontarget rodents, waterfowl, waterbirds, shorebirds, songbirds, and children suffer lethal and sublethal poisoning from eating bait directly.”
Small carnivores, such as mongooses, genets and Caracal, are vulnerable to secondary poisoning from rat poisons. This Slender Mongoose lives in our neighbourhood and I photographed it at the bottom of our garden
And what about the low levels of chronic exposure occurring in individuals that have not received a lethal dose? Animals and birds surviving with chronic secondary poisoning are at ongoing risk of ingesting more poisoned animals, accumulating more toxins over time. And in turn, they may be eaten by other creatures and so the poisons accumulate higher up in the food chain. This process of bioaccumulation is so extensive that numerous species, including those that do not eat rodents, have detectable amounts of rodenticides in their bodies.
Researchers are still investigating the effects of chronic low-level exposure to rodenticides on individual animals. For a detailed list of the health impacts on animals and birds weakened by chronic exposure to rat poisons, see here.
As an example of the effect of chronic exposure to anticoagulants, a study in the United States found a direct link between poison exposure and notoedric mange in bobcats. For details see this article by Laurel Serieys. The hair loss and emaciation resulting from the mange usually proves fatal, possibly related to the immune dysfunction that occurs as a result of exposure to the poisons. Such weakened animals are also vulnerable to being killed by cars. The study reports on two fetal bobcats from mothers killed by cars that were tested, and even before they were born, detectable exposure to rodenticides was found in the fetuses. In southern California, 92% of bobcats tested from samples collected between 1996 and 2012, were found to have been exposed to anticoagulants. And in New York, 49% of predatory birds tested from 1998 to 2001 were positive for anticoagulants.
Laurel Serieys, when working in South Africa for the Cape Leopard Trust as Urban Caracal Project Coordinator, tested one genet and seven caracal (all road kills) in the Western Cape, and found that all were exposed to rodenticides, with all seven caracal showing exposure to compounds from three different anticoagulant rat poisons. For details see here.
In a broader study involving analysis of the livers of 401 wild and domestic animals found dead in Spain, 40.9% were confirmed poisonings, and of these 21.1% involved anticoagulant rodenticides (AR). Grain-eating birds showed the highest prevalence of primary AR exposure (51%); that is they ate poisoned bait. Secondary exposure was high in nocturnal raptors (62%) and carnivore mammals (38%). See the 2012 abstract of the study here.
I asked a vet at a local veterinary practice, and there are many practices in this region, how many cases of pets poisoned by rodenticides are brought into his practice. He checked his records and told me that his practice has had on average 13 confirmed cases of poisoning by rodenticides per year, each year over the last 3 years. Of these, all were dogs, except one, which was a cat. This number, working out at just over one a month, is quite high given that this is just one practice out of many, and not all poisoning cases are taken to a vet. For one thing, and this is speculation, some poison victims, especially cats, just don’t make it home.
One of the raptors that is fairly common in suburban areas, including ours, is the African Goshawk. This one was photographed during its flight display at the African Bird of Prey Centre
There is an argument that first-generation anticoagulant rodenticides are better to use than second-generation ones. This is only relatively true and does not mean it is safe. It is still a poison. Recommending its use generally ignores the problem of non-lethal chronic exposure, which is not widely known about and the ongoing implications are not fully understood.
Adverse effects of first-generation anticoagulants such as coumatetralyl (the poison used in Racumin, which is actively promoted as a “safe” poison) include primary and indiscriminate poisoning of non-target species of small mammals. A 2005 study in the United Kingdom, where coumatetralyl was used, by Brakes and Smith (see here) found that the eradication of non-target small mammals, such as woodmice and voles, can lead to malnourishment and starvation among predators such as weasels, stoats and owls, and this is in addition to the adverse effects of secondary poisoning. It is noted in the same study that sub-lethal secondary poisoning does significantly weaken the mobility and fitness of affected birds and animals.
As Tammy Caine, Clinic Manager at Raptor Rescue in KwaZulu-Natal told me: “a sick raptor is often a dead raptor. The accumulation of the poison will undoubtedly make the raptor feel ill, and negatively affect its ability to hunt, leading to starvation, a compromised immune system and eventual death. No poison is safe. Period.”
After all this sobering information, it is good to know that there are methods and projects that follow non-toxic practices. Here are just three in South Africa.
One of Raptor Rescue’s projects is the Owl Box Project, a pilot project run under Predatory Bird Projects and supported by the N3 Toll Concession. The project instigates and oversees the installation of owl boxes in both urban and rural communities and encourages the protection and conservation of owls in these areas as part of environmentally friendly pest control management. In addition, the project collects comprehensive data to aid future research on urban/rural owl population dynamics. The project has supported educational outreach in rural areas, particularly targeting schools, to encourage active participation and interest in owl conservation. For more information on this project see https://www.facebook.com/owlboxproject, and for Raptor Rescue’s other projects see here.
The Urban Raptor Project in Port Elizabeth in the Eastern Cape, is involved in numerous conservation projects. It has a successful rodent control project, using carefully monitored spring traps, as well as establishing owls (they have their own owl breeding programme) and other predators in poison-free areas. They also use Rat, English Fox and Jack Russell terriers as a traditional form of rodent control. Among other places, they manage the Nelson Mandela Metro 2010 World Cup Stadium and the Port of Ngqura. They actively encourage the protection of indigenous rodents. Their website provides a wealth of information. See here.
The Township Owl Box Project run by EcoSolutions Pest Management Specialists with support from the Roots and Shoots programme under the auspices of Dr Jane Goodall, as well as the Gauteng Department of Agricultural and Rural Development, through a process of education and finding suitable school properties in townships in Gauteng, is able to introduce orphaned owls into these areas. The school children benefit from learning about and taking responsibility for the owls, the orphaned owls benefit as they are released into a managed environment, and the community benefits as the owls provide a poison-free form of rodent control. For more information see here.
A Spotted Eagle Owl, one of the commonest owls in South Africa, at the African Bird of Prey Sanctuary
Non-toxic rat traps
For serious rat infestations, lethal methods of control may be necessary. Generally, rodents gain little sympathy, but they are intelligent creatures and like any other animals, surely they should be spared the terrible suffering caused by rodenticides.
The spring trap is well known, and has a place if used correctly and monitored properly. It should never be placed outside or in an area where it can trap non-target species.
Here are three other non-toxic devices:
Electronic Rat Killers are walk-in traps that electrocute the target. These traps provide a humane and environmentally friendly way of eradicating problem rodents. One brand is known as Rat Zapper. For a description see here, and for a South African supplier see here.
Nooski Trap System shoots a latex ring around the neck or chest of a rodent entering the trap and kills the rodent within seconds – a lot quicker than the many days it takes for a rat to die from anticoagulant poisons, and with no poison used, no secondary poisoning is possible, but as with all traps it should be monitored, and dead rats disposed of safely. In the case of this trap, the killed rodents will each have a latex ring around their necks. For a description of how it works, see here. I was able to find only one South African (online) supplier here and would be interested to know if anyone has found it sold at any other outlets.
Live capture traps. Such traps need to be set preferably indoors in areas where rodents are a problem, and must be monitored regularly. Where appropriate, rodents that have not been exposed to poisons can be released in areas where raptors and other predators can hunt them, or else they can be killed using a humane and non-toxic method. See such traps at Radical Raptors here.
So what can we do?
The first step is to be aware and actively try to be informed about the hazards of rodenticides as well as related regulations and legislation. Such awareness would likely make us pledge never to use rat poisons at home or in our neighbourhood. Perhaps we can use our awareness and some of the excellent information resources available to persuade organisations that we know use rodenticides, such as our places of work or shopping centres, to find alternative methods. We can also interrogate pest control companies that claim to be environmentally friendly to find out what methods and compounds they actually do use in their rat control programmes.
Perhaps information and awareness will lead people and organisations to shift away from the use of poisons, and so in time we won’t be reading stories such as this in our local newspapers or social media.
It is not known if this Crowned Eagle died of secondary poisoning or if it was deliberately poisoned. What is known is that it died a slow and painful death from ruptured internal organs and extensive internal haemorrhaging. Surely incidents such as these motivate us not to use rat poisons?
Crowned Eagles, the second-largest eagle in southern Africa, survive in game reserves, forest patches and in plantations even on the edge of towns and suburban areas. Their main prey animals are Vervet Monkeys, dassies (Rock Hyrax) and small antelope. It is disturbing to know that they are also falling victim to rodenticides. The individual in the photographs above is at the African Bird of Prey Centre. It was found on the side of a road with a badly broken wing and toe. Although its injuries have healed, it is not strong enough to be able to hunt successfully in the wild and so cannot be released
A resident pair of Crowned Eagles as we usually see them in our neighbourhood. Flying high and free
Information sources and further reading:
African Bird of Prey Sanctuary. “Owl-Friendly” Rodent Control http://africanraptor.co.za/?page_id=4100
Brakes, C.R. & Smith, R.H. 2005. Exposure of non-target small mammals to rodenticides: Short-term effects, recovery and implications for secondary poisoning. Journal of Applied Ecology, 42(1): pp. 118-128. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2005.00997.x/full
Endangered Wildlife Trust: Birds of Prey Programme. Eagles and Farmers https://www.ewt.org.za/eBooks/booklets/Eagles%20and%20Farmers%20booklet.pdf
Raptors are the Solution http://www.raptorsarethesolution.org/
Raptors are the Solution. Rat poisons not only kill wildlife, they can also weaken and sicken them. http://www.raptorsarethesolution.org/wp-content/uploads/2016/03/RATS-fact-sheet-on-sublethal-impacts.pdf
Serieys, Laurel. 2015. Rat Poisons Kill More than Just Rats , in Game Changers by Jean Dunn. http://lifeinbalance.co.za/rat-poisons-kill-more-than-just-rats/
Serieys, Laurel. Why Do Poisons Matter? http://www.urbancarnivores.com/poisons/
Sanchez-Barbudo, P.R. Camerero & R. Mateo. 2012. Primary and secondary poisoning by anticoagulant rodenticides of non-target animals in Spain. (Abstract). Science of the Total Environment, 420: pp.280-288. http://www.sciencedirect.com/science/article/pii/S004896971200071X
Township Owl Box Project. http://ecosolutions.co.za/giving-back/township-owl-box-project
Wikipedia. 2017. Rodenticides. https://en.wikipedia.org/wiki/Rodenticide
Williams, Ted. 2013. Poisons used to kill rodents have safer alternatives: A second generation of ultra-potent rodenticides creates a first-class crisis for people, pets, and wildlife. http://www.audubon.org/magazine/january-february-2013/poisons-used-kill-rodents-have-safer
Urban Raptor Project. http://www.urbanraptorproject.co.za/index.html
Posted by Carol