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There are fewer owls and hawks in the Foothills each year, not from the lack of habitat or food, but from the widespread and improper use of poison bait in misguided attempts to control pack rats. The public does not realize that putting out poison bait for pack rats is not only ineffective but it also poses great risk to owls, hawks and other animals.
Pack Rats vs. Commensal Rats
Poison rat baits are developed and licensed to control "commensal" rodents. Commensal rodents - derives from the Latin cum mensa, meaning "sharing a table". Basically means they have adapted over thousands of years to living off of our garbage.
The EPA has defined the term "commensal rodents" to include only the following species: Norway rats (Rattus norvegicus), roof rats (Rattus rattus), and house mice (Mus musculus). Pack rats (Neotoma albigula) are wild animals and are not commensal rodents.
Commensal rodents typically live in urban areas with little wildlife and few natural predators.
They spend their foraging time very close to or within structures. The EPA limits poison bait use to indoors or outside, close to structures within secure bait stations in order to minimize the exposure of poison and any poisoned rodents to wildlife.
Pack rat problems occur in semi-rural areas where people have moved into the pack rat's natural habitat. The rats are opportunists and may live close to people, but still spend most of their foraging time outdoors seeking native foods. Pack rats live in areas where there are abundant wildlife and many natural predators including hawks, owls, coyotes, bobcats, ringtail cats, and snakes.
Using poison bait intended for commensal rodents on pack rats is a violation of the product label and thus, technically against the law. These poisons are highly toxic and indiscriminate. Common baits may contain only 0.005% of active ingredient, but one pellet is enough to kill a mouse; four pellets to kill a rat. Even bait placed in secure bait stations is dangerous because pack rats often remove the bait and drop it elsewhere. The removed bait may kill any animal consuming it.
Predators And Scavengers Are At Risk
Predators and scavengers are at risk directly and indirectly: directly from unsecured poisoned bait left in the open, or moved and dropped by rats. In addition, highly toxic, undigested poison can still be in the rat's stomach and therefore passed directly on to any animal that eats the rat.
Indirectly, when a pack rat consumes bait, the death process is slow—typically taking five to ten days. The rat becomes sick and slow, and is an easy target for any predator. When eaten, the active poison in the rat's blood and muscle passes up the food chain. Consuming just one sick rat is enough to kill a hawk or an owl.
All rodenticides carry a risk of secondary poisoning, but those with the active ingredient brodifacoum or difethialone pose the greatest risk to raptors. Unfortunately, these ingredients are contained in some of the most popular brands of rat bait including, but not limited to: D-Con®, D-Cease®, Enforcer ®, Final®, Generation®, Havoc® and Talon®.
Many stores and exterminators downplay or even deny the risk of secondary poisoning, but the risks are real. The EPA recently compiled an exhaustive report titled "Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative Approach". The conclusions of the report are clear: the active ingredients in the most commonly used rodenticides all can and do kill non-target animals from secondary poisoning.
Poison Makes Pack Rats Problems Worse
The irony is that poison bait does little to solve a pack rat problem and, in most cases, makes the problem worse. Poison bait by design is food to the rats. Putting out poison attracts rats, just as putting out a quail block attracts quail. Outside bait stations provide an ideal harborage for rats to hide in, safe from predators. Rats will even build nests inside of a bait station.
Putting a bait station close to a house encourages rats to spend more time in that area. Like dogs, pack rats use urine to mark objects and territory. Even if the poison kills the rats, they still have plenty of time to leave their scent before they die. The scent (just like dogs) attracts other rats from outside areas.
Most pest control companies check bait stations monthly and never clean the stations. The rats clean out the poison after a day or two and the rest of the month the station is a handy hiding place and bathroom—an ideal way to attract more rats.
Worse of all, poison bait kills the very animals that naturally control the rats. A large owl can eat 2-3 rats a night. There is no better form of rat control, but unfortunately when poison is used, the owls are the first predators to disappear.
Pack rats are wild animals most effectively dealt with by understanding their behavior and creating an environment around a home that minimizes their activity. Pack rats mature and breed quickly. In a semi-rural area, nature can produce an almost unlimited supply of rats. The key to control is limiting harborage. Each adult rat needs its own nest to survive. Limit harborage in an area and you limit the number of rats. Therefore, poison only creates empty nests to be quickly refilled by other rats.
Individual nests can be located and eliminated through trapping and complete nest removal. Some light trimming and clean-up can prevent new nests—denying pack rats the shelter they need to start a new home.
Poison bait is not intended for, nor should it be used for pack rats. There is little benefit and there are too many risks to owls, hawks and other animals to be worthwhile.