It might sound fanciful, but it works, according to an urban wildlife specialist at Cummings School of Veterinary Medicine
The usual strategy for controlling deer is hunting, but hunting is unsafe in suburbs unless it’s done with a bow and arrow, which is an inefficient way of controlling deer. Photo: Shutterstock
Populations of suburban deer have been on the rise across the U.S. for the last 50 years. Suburban landscapes are like buffet tables with their plentiful lawns, shrubs, and gardens that tempt the animals into human territory.
But in many places—like Tennessee, Ohio, Maryland, Iowa, North Carolina, and Delaware—deer have become problematic. They cause traffic accidents, disrupt yards and flora, damage crops, and contribute to the spread of Lyme disease by hosting the ticks that carry the bacteria. In Massachusetts, for example, deer-related traffic accidents have gone up by 50% over the last 10 years, prompting calls for action.
The usual strategy for controlling deer is hunting—so much so that “hunting and deer management have been synonymous for the last hundred years,” said Allen Rutberg, Ph.D., director of the M.S. in Animals in Public Policy program and the Center for Animals and Public Policy at Cummings School of Veterinary Medicine at Tufts University. But hunting is unsafe in suburbs unless it’s done with a bow and arrow, and that’s a wildly inefficient way of controlling deer.
Not many people are interested in hunting these days, anyhow. The number of hunting licenses Massachusetts sells has decreased 50% since the 1980s. On average, the national situation looks similar: the number of big game hunters decreased 20% between 2011 and 2016, and recent upticks in some states, such as Maine and Pennsylvania, have not compensated for the overall trend. Nonetheless, the Commonwealth’s efforts to address the deer issue so far center around loosening hunting restrictions.
For more than 30 years, Rutberg has been working on an alternative: Using birth control to reduce deer populations in suburbs. And in a 2024 study published in the journal Human-Wildlife Interactions, he and his colleagues suggest that this method is a feasible way of keeping suburban deer in check.
Delivered with Darts
To stop a deer from reproducing, you must first inject the deer. That’s what led Rutberg, his Ph.D. student Kali Pereira, and their team to the New York suburb Hastings-on-Hudson, 17 miles north of New York City, where they sat quietly in the early morning light, waiting for deer to appear.
The scientists carried a CO2-powered air rifle that would deliver a dart to the deer’s rump, injecting it with a vaccine called porcine zona pellucida-22, or PZP-22. Unlike human birth control, which usually manipulates hormone levels, PZP-22 makes animals produce antibodies that physically block sperm from fertilizing eggs. The vaccine has been used to prevent an overabundance of everything from wild horses to African elephants.
In Hastings-on-Hudson, some form of deer control was sorely needed. Before Rutberg and his colleagues came to town, the animals caused about 20 car accidents and a half-million dollars of damage to the local landscape every year. Those stats made the suburb a prime spot for Rutberg to test PZP-22.
In Massachusetts, for example, deer-related traffic accidents have gone up by 50% over the last 10 years, prompting calls for action. Photo: Shutterstock
Rutberg, Pereira, and their colleagues knew from previous research that another form of the vaccine, called simply PZP, could limit deer reproduction for a year, but darting deer every year is a big ask for local wildlife management. So they wanted to test PZP-22, which was designed to last longer. Rutberg and his colleagues returned to Hastings-on-Hudson year after year, from 2014 to 2021, to track the deer they’d vaccinated and look for tell-tale signs of recent pregnancies, like udders swollen with milk or fawns trailing behind them.
The results were very encouraging: An initial vaccine delivered by hand seemed to remain effective for at least two years, and 80% of deer that received a booster shot with a dart gun were still baby-free when the study ended three years later. If the vaccine is effective for around four years, wildlife managers would only need to inject each female twice to cover most of her reproductive lifespan. That’s much more feasible than darting each deer every year. And with a bit of care, the method is safe to use in residential areas.
“We can deliver the vaccine in backyards, in front yards, in parks — in all kinds of places where there are a lot of people,” Rutberg said.
Gaining Acceptance
The next question is whether it’s possible to treat enough deer to have a meaningful impact on the population size in a place like Hastings-on-Hudson. In two previous studies, researchers knocked back deer populations by about 50%, but both of those studies were done on islands where new deer can’t migrate into the area. Female deer spend their whole lives within about a square mile of where they’re born, however, so Rutberg thinks it’s unlikely that migration will dilute the effect of vaccination on the mainland. But that remains to be proven.
Otherwise, the remaining barriers to deploying PZP-22 are “as much regulatory and political as they are technical,” Rutberg said. The idea of using birth control to keep wildlife in check is still novel, and many locations have been slow to adopt the approach. The EPA also has yet to register PZP-22 as a method for managing deer, which limits state wildlife agencies to issuing permits for experimental use.
Rutberg also stresses that PZP-22 is a solution only for suburbs with dense deer populations, not for the rural areas where most hunting takes place. “We depend on having a lot of accessible deer to make this work. In Hastings, we’ll often see five deer in someone’s front yard. In rural areas, the deer are much harder to find,” he said.
How to control the deer population in rural areas is a tougher problem. In Massachusetts, lawmakers are considering changing regulations to allow hunting on Sundays and hunting with crossbows, and to reduce the distance hunters must keep between themselves and houses from 500 feet to 250 feet. “Will that make life a little bit easier for hunters? Sure,” Rutberg said. But he doesn’t think it’s enough to compensate for the steep decline in hunting that the state has experienced, so he doesn’t expect the proposed changes to make much difference in the state’s deer population.
But for certain suburbs, Rutberg thinks PZP-22 is ready to be deployed. “We’ve done enough research that we have a good tool,” he said. Now the challenge is helping communities use it.
