Boston stops using rodenticides that can also kill raptors and pets, looks at expanding rat birth-control pilot

City rat fighters have largely stopped using anti-coagulants that kill not only rats, but any wild predators and pets that might eat them and is instead now relying on relying on pumping carbon monoxide and carbon dioxide into burrows to asphyxiate them, according to John Ulrich, who oversees ISD's rat control efforts.

The one exception: BWSC sewers, where nobody has yet to come up with an alternative for rat killing, Ulrich said. Also, the ban does not apply to private property owners, who are still putting out enough of the now ubiquitous black bait stations that one Allston group sponsored an art competition to decorate empty stations.

Ulrich testified this morning at a City Council hearing on the possibility of adding birth control to the city's armament against the bewhiskered vermin, based on a year-long pilot on Cranston Street in Jamaica Plain, in which residents put out containers of rodent birth control disguised as a delicious, high-protein pellets made with, among other ingredients, peanut butter. The goal was not to kill rats immediately, but to ultimately reduce their numbers as adults stopped having babies.

The pellets, made by a non-profit called Wisdom Good Works cause no ill effects to rats - except to inhibit their fertility - or to any animals that might eat them or the pellets. Alaina Gonzalez-White, Wisdom Good Works' director of operations, said the pellets were actually specifically designed to taste good, at least to rats, to encourage them to eat them - and by putting them into small open containers, to return to them rather than going to all the bother or scampering into a dumpster or gnawing through a plastic trash bin.

In turn, rodent birth control, if adopted citywide, would actually further enhance natural rat control because fewer predators would die from eating the rodenticides, which make both rats and animals that eat them die through internal bleeding, she said.

ISD Commissioner Tania Del Rio said the pilot seemed to result in mixed results, that the number of 311 complaints about rats from the Cranston Street area actually doubled over the course of the pilot, from 83 complaints to 154. But she acknowledged 311 complaints are a very imperfect proxy for actual results, that people might have learned about the study and been extra encouraged to make rat reports. Gonzalez-White said her team had cameras focused on some of the 31 pellet stations on Cranston Street and that while rat numbers did increase at first - as news spread among the rat grapevine about the new food - eventually, the numbers decreased dramatically because the female rats were no longer giving birth.

One Cranston Street resident who testified said she actually saw a dramatic reduction in her yard's rat population after a year of refilling a container with roughly 20 ounces of the stuff once a week.

She said that about seven years ago, she started noticing a dramatic increase in the number of rats in the neighborhood and her yard, to the point where she couldn't sit on her patio at night without hearing the constant scampering and scurrying of rats.

She decided not to use one of the black bait stations because she didn't want to risk poisoning any cats who might eat the rats or squirrels who might eat the bait. Snap traps worked, to the point where she killed at least 30 rats, but then she read up on how fast rats reproduce and realized that was just a drop in the bucket. She and her neighbors tried a liquid rat fertility depressor, but it did nothing except get really disgusting when it got either too hot or too cold. In contrast, the pellets, after awhile, just worked, she said.

"After six months, we no longer saw or heard rats in our backyard," she said.

At the hearing, officials and councilors concluded that should rat birth control prove effective over a larger area than one street, it would likely be just one tool among many to bring rats under control in Boston, that just as important, if not more so, would be changing people's behavior, even through such simple things as making sure dumpsters are closed - and getting people to stop feeding their pets outdoors.

Officials said that for a second pilot, if one is done, they would try a larger area in a part of the city that seems to be particularly overrun by rats, such as the North End, Back Bay, the Common, Allston/Brighton and parts of Dorchester.

Regardless of the steps the city takes, however, officials from several animal concerns, including the MSPCA, the city's own animal shelter, the Animal Rescue League and the New England Wildlife Center, which runs a wildlife hospital in Weymouth, urged the city to work towards a ban on "second-generation anti-coagulants," by private users as well, because they are so deadly to other animals. They said the chemicals are in roughly 96% of the bait now used in Boston.

Zak Mertz, New England Wildlife Center CEO, told counselors his staff probably sees 50 to 100 animals a year suffering from rodenticide poisoning, which included a great horned owl from the Arnold Arboretum that took 90 days to restore to health. He cited another case involving two great horned owl adults and their two hatchlings, three of which died from feeding on a single contaminated rat.

The surviving hatchling took a year of recovery before it could be released to the wild, he said.

He added that in that year, the hatchling ate a total of roughly 2,000 uncontaminated rats, which he said shows just how effective nature can be at controlling rats, if it's allowed to. Also, he said, it's not just an issue for apex predators, such as raptors, coyotes and foxes, but for scavengers as well, such as crows and turkey vultures. He added that just last week, his center saw three chipmunks suffering from rodenticide poisoning.

Martha Smith Blackmore, who provides veterinary services to animals at the city animal shelter in Roslindale, said that since 2019, 199 hawks, falcons and owls have been brought into the shelter. And while some were injured flying into buildings or electric lines, most were poisoned. And only 20% were stable enough to be transferred to the Weymouth animal hospital, she said.

She added that besides killing predators outright, the current generation of rodenticides causes another problem: They don't immediately kill the rats, but they do weaken their immune systems, making them more likely to become carriers of infectious diseases, in particular, leptospirosis, which can cause liver and kidney failure in dogs - and spread to people.