Fuzz: When Nature Breaks the Law

The yellow-eyed penguin of New Zealand is endangered. Part of the species’ decline is from habitat loss and getting caught in fishing nets, but a significant factor is the presence of introduced predators: stoats, rats, and feral cats (252).

In 1863, European settlers released six rabbits into New Zealand’s Otago Peninsula to remind them of their original homes. Nine years later, the land was overrun with rabbits. They starved out sheep and birds, which sent landholders into bankruptcy (254). The government passed the Rabbit Nuisance Act of 1881, allowing for not only the shooting and poisoning of rabbits but also the introduction of predatory stoats and ferrets (254). However, the stoats went after more than just the rabbits, consuming bird and turtle eggs and even adult birds and reptiles. Many of New Zealand’s native birds cannot fly, as they evolved without predators and, thus, the need to escape quickly. By 2019, more than three-quarters of New Zealand’s land vertebrates were endangered or faced extinction (254). Thus, the government started Predator Free 2050 (PF2050) to eliminate the three most problematic invasive species: stoats, brushtail possums, and rats (254). The traps set out for the stoats are meant to be humane, using a rod at the end of a piston to hit the brain, which is a fast death.

The author meets up with Bruce Warburton, who designs humane traps and animal welfare standards used to evaluate the humaneness of traps. Humane traps work quickly to bring an animal to unconsciousness or death. Traps that kill small animals quickly by breaking their necks take longer with larger animals, as the mechanism then works by strangulation and suffocation (258). A blow to the head is the swiftest, most humane way to dispatch an animal. As stoats have long, muscular necks, Warburton has modified snap traps to guide the animal’s head into just the right spot so that the bar comes down by the ears, providing instant unconsciousness (259). Standard snap traps for mice sometimes catch the animal by a limb or snout, which inflicts pain. Glue traps are not considered humane, as the animals often either die slowly of dehydration or tear through their own limbs trying to escape. Therefore, glue traps have been outlawed in New Zealand and various European countries (260-61).

Researchers have looked into replacing leg traps with traps that use carbon dioxide, considered a humane manner of death. However, at high enough levels to quickly cause unconsciousness, the gas may form an acid that causes burning and choking (262). Electronic traps have similar benefits and drawbacks. They’re fast when clean, but they can burn an animal’s legs if they’re not. New Zealand mandates that electronic traps must deliver unconsciousness in under three minutes (263).

PF2050, however, also uses poison to get rid of rats, though poison takes effect over many hours or even days. New Zealand sees this as necessary because of the rat’s high numbers, fast reproduction, and the remoteness of some of the areas where they are found. In studies, cyanide emerges as the most humane poison because it renders a victim unconscious in as little as a minute. Sometimes, the chemicals cause spasming, which appears painful, but if the animal is unconscious, it would be unaware of it (265). People seeing the spasms often do not understand that the recipient is unconscious and protest the treatment. This is why lethal injections for humans contain a paralytic, and the pesticide Avitrol, which works as a frightening device for birds though it kills a few, created a public outrage even though it was declared humane. Many pest control measures have unintended consequences, like the “Humane Coyote Getter,” a type of cyanide injector that ended up killing cows and dogs and, consequently, faces bans and lawsuits.

Anticoagulants are often used in rat poison, but death only comes after one to three days, so New Zealand doesn’t use them. Instead, PF2050 uses 1080, a weaponized form of ricin, to get rid of invasive mammals. The country’s only native mammals are bats, which have no interest in the bait, and the bait is dyed to be unattractive to birds (267). Deer that were introduced to New Zealand for hunting stock are sensitive to 1080, so the aerial drops also contain deer repellant (268). Some of New Zealand’s native birds are scavengers, so there is concern about secondary poisoning, and repellants for keas are in the works (268).

The author is impressed by how the public has embraced PF2050 and anti-invasive sentiments. One researcher speculates that it’s because the deaths occur mainly at night and in forests. Warburton, the man tasked with designing traps, decries the double standard of people raging against stoats for killing native birds when their cats and dogs also kill them. He would like housecats to be illegal (269). This raises questions for the author about where we draw the line for what to protect and what to embrace.

At the National Wildlife Research Center (NWRC) in Colorado, researchers are experimenting with gene drives on mice to find humane alternatives to poisons for pest control. The mice in the experiment are genetically modified to bear only male offspring (276). Such modifications take generations to take effect and be studied for unforeseen downstream consequences, so the enclosures at the laboratory must be secure against the gnawing mice.

Genetic modification uses CRISPR, an enzyme of bacteria, to locate, cut, and replace specific sequences of DNA. This is used to modify the mice, which will then be released on an island with a mouse problem so that the population eventually decreases. Gene drives make it so that the targeted trait is inherited by all of the offspring, not just half. However, to have an effect on the island’s population, a large number of gene-drive mice would have to be introduced, thus temporarily making the problem worse (281). There are other issues, too. The gene-drive manipulation of the embryo has to happen at exactly the right stage of embryonic development or it won’t work. Polyandry, having more than one father of a litter of offspring, occurs frequently in wild mice, so more modified males are needed. It is also unknown whether the existing population of mice will mate with the modified ones (281). Moreover, there are concerns about what might happen if a genetically modified animal escapes its controlled area and mates with other populations. However, scientists are working on a way not only to keep gene-drive animals from mating with outside populations through their own genes, but some researchers have developed a way to reverse the gene drives on fruit flies (282).

Another cutting-edge approach is to use bait laced with species-specific interfering RNA (RNAi), which could treat certain genes key for the target species’ life processes as viral RNA and destroy it (283). It is promising but still several years away from getting approval for widespread use. One issue for RNAi, as for all traps using bait, is that the animals who avoid the trap or learn to stay away from it will continue to procreate and be the harder ones to eliminate (283). California faced this issue with invasive nutria and had to radio-collar neutered nutria to locate the remaining “holdouts” (284).

What worries the author is that the list of animal pests is long, and the NWRC is part of the USDA, which protects farmers, so the decision to wipe out certain pests may be entirely financial (285). Jane Goodall spoke out against gene drives at a Genetic Biocontrol of Invasive Rodents meeting, stating that the technology is moving too fast and without guidelines and, therefore, should be stopped (285). Unforeseen developments, such as driving a species to extinction or altering an ecosystem, worry some experts.

The author visits a man named Roger, who operates a feedlot for cattle. One of the NWRC researchers gets his mice from the man’s property. Though the mice eat the feed, Roger figures it is not enough to be noticeable. His biggest concern is that they nest in machinery and chew wires, so he keeps barn cats, though the cats get hit by cars or taken by owls (287). He has foxes, so the rat population is kept in check, too. Blackbirds also come to eat the corn, but Roger doesn’t shoot them or use frightening devices because he’s seen how ineffective they are, and they don’t eat enough of the corn to be a problem. Roger gives the author hope about more people embracing coexistence with animals and using more humane methods to accomplish their goals.