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Dealing with rats

Doug Greenberg
CC BY-NC 2.0

Update as of 11:40 am on Wednesday: MK, the eagle discussed below, succumbed to her illness. According to Cape Wildlife Center, "After a valiant fight her system was simply no longer able to keep up."

A locally famous Bald Eagle from up in Arlington fell ill on Monday, and is now being treated at Cape Wildlife Center in Barnstable. The reason this eagle is sick has more to do with you and me than you might realize, and the common denominator is rats. Or rather, how we deal with rats. The eagle, like so many other hawks, eagles, owls, bobcats, and other predators that end up in wildlife clinics, is a victim of rat poison, or, to put it more clinically, anti-coagulant rodenticides.

These most common of rodent poisons are similar to commonly prescribed human blood thinners, and are available in any hardware store. Many pets and children have been sickened by them over the years, as they sell them as pellets that you could just scatter around - it’s astounding how unregulated home use of poisons is. They get into our predatory birds and mammals through what’s called secondary poisoning – the rats and mice stagger around for a while before dying, at which point the predators eat them. If they eat enough poisoned rodents, they can die. Untold numbers of hawks and owls die invisibly in the woods from these poisons, but many cases have been confirmed by wildlife clinics, including multiple Bald Eagles and way too many owls here in Massachusetts.

Maureen Murray, director of Tufts Wildlife Clinic and professor at the prestigious Cummings school of Veterinary Medicine, found that 100% of Red-tailed Hawks that died in the clinic for various reasons had detectable amounts of up to two or more of these anticoagulant rodenticides in their bodies. Dr. Murray points out that other studies have even detected these poisons in insects and songbirds, showing they permeate the food chain beyond just rodents and their predators.

So how do you deal with rats and mice? Professionals are technically required to practice what’s called Integrated Pest Management, or IPM, but it’s not clear how many actually do. IPM means dealing with the causes of the infestation first, like removing food and water sources and sealing off access. Chemical treatments should be a last resort, and limited to the lowest amount required to do the job. Anti-coagulants should never be used, but vitamin-D based poisons like D-Con could be used sparingly due to the low secondary toxicity to wildlife – just make sure pets can’t get the bait. The best backup to prevention is to use old fashioned snap traps like I do – maybe you think it’s gross, but squeamishness is not a good excuse to get lazy and poison wildlife.

What about other, wackier methods? People have tried everything from dry ice to ultrasonic repellents to smoke bombs. Lots of people claim their ultrasonic repellents work at their house, but research has been clear that they don’t. Dry ice works to smother rats in big communal burrows, but is more for the cities like New York where they need a nuclear option. So leave the dry ice for the professionals and the 80’s-style rock bands. Same with the smoke bombs – it’s unlikely you know where all the burrow exits are, and you need to block them all for these last two methods to work.

But it all starts with prevention – eliminate or block access to food and water sources. In my yard they seem able to get into my closed compost bin no matter what, so I need to switch to a more secure one. I stop feeding the birds for a while if I see any rats and use snap traps if I see them consistently, and that seems to work. I have multiple neighbors with backyard chickens, so the rats will always come back after a while. Rat populations are increasing up and down the east coast, and our increasingly mild winters here give them more chances to have litters, so there is no permanent solution. Beyond not using poison on your property, you can help the broader effort in Massachusetts by urging your legislators to support a recent bill called An Act Relative to Pesticides, which narrowly failed to pass late last year.

You can track progress of the poisoned Arlington eagle, known to the locals as MK, on the Cape Wildlife Facebook page. Ah, rats – it looks like I’m out of time. But I’ll be back next week, when I promise to get back to happier bird news.

Mark Faherty writes the Weekly Bird Report.