The Harmful Effects of Rodenticides

Posted by:

Over the past week our team has noticed a slight influx of migratory raptor species at our Wild Bird Sanctuary and throughout the Upper Keys. This signals to us that migration season is right around the corner; a time when our hospital staff will be treating injured Cooper’s Hawks, Board-winged Hawks, and many other species of aerial predators. Many of the raptors that fly through the Florida Keys during their southward migration hunt for small mammals including rats and mice. So many hawks and falcons will be visiting the Keys over the next few months, and it’s paramount that we ensure they have plenty of healthy food, free of toxins and poison, for them to hunt. For this reason, we strongly discourage the use of rodenticides (rat poison).

The Harm
Part of the reason that we felt compelled to focus on rodenticides for this week’s blog entry comes from the fact that our hospital team is currently working to rehabilitate a Barn Owl (Tyto alba) that most likely ingested a rat or another small animal that had rodenticides in its system. Upon its intake, the owl exhibited decreasing alertness, anemia, and it had several hematomas; tell-tale signs of secondary poisoning. Once rodenticides have been ingested, these chemicals are very difficult (sometimes impossible) to break down via regular metabolic activity. This causes the toxic chemicals used in rodenticides to build up and accumulate in the animal that ingested it. This concept is known as bioaccumulation. If this process continues long enough and raptors continue to eat these poisoned rodents, then a lethal dose of rodenticides can accumulate in an owl’s system as well, leading to its death (i). Once the mouse/rat is killed, everything that was in its system remains, including poisonous chemicals. This creates a huge problem for raptors such as hawks and owl that have no way of discerning between poisoned and healthy prey (iii).

There are different types of rodenticides, and the most dangerous type are second-generation anticoagulant rodenticides (ii). These chemicals are considered to be super toxic, and they work by inhibiting an animal’s ability to produce vitamin K. This disables the animal’s blood clotting ability, causing the animal to bleed uncontrollably, leading to a slow, painful death. Frequently rodents can ingest these types of slow-acting poisons multiple times before dying. This can create scenarios in which the animals are hindered greatly, making them easy targets to unaware predators. A study conducted in 2011 by Maureen Murray of the Tufts Cummings School of Veterinary Medicine found that 86% of raptor livers that were examined contained rodenticides (iii).

These dangers aren’t just limited to wildlife. During a survey conducted by the Environmental Protection Agency that took place between 1999 and 2003, it was found that, “at least 25,549 children under age six ingested enough rodenticide to suffer poisoning symptoms.” It’s also estimated that the Center for Disease Control fields over 15,000 calls per year from parents concerning children ingesting rodenticides (iii). Rodents are known to redistribute food items to different locations away from the original source. This can lead to rodents moving rodenticides to areas of a home or public place that’s easily accessible for children or wildlife.

Preventative Measures
So if you can’t use rodenticides to take care of pests in your home, then what are some better ways to keep your home rodent free? We’d like to offer you a few options to prevent rodents from invading your home and other spaces (ii).

1. Refrain from leaving pet food and water outdoors, especially overnight. Make sure that pet food and supplies are stored indoors in sealed containers.
2. Seal all gaps around building attics and any other openings that penetrate the building’s exterior. Rodents can squeeze through a hole the size of quarter, so use sweep seals under doors.
3. Ivy plants provide shelter and food for rodents. When it grows near walls, ivy can also give rodents a convenient way to climb, forming a ladder to get to windows, attics, and other interior spaces.
4. Keep compost piles, cut grass, and tree trimmings far away from structures.
5. Use a squirrel guard to protect bird feeders from rodents, and keep the ground area clean of birdseed.
6. Keep outdoor cooking areas and grills clean.
7. Keep firewood and other materials that could be used by rodents to create nests off the ground.
8. Use plastic trash and recycling bins with lids.
9. Clean up trash in garden areas regularly.


The Optimal Solution
Taking everything into consideration, the best way to regulate rodents and other pests is to allow ecosystems to take care of themselves. By allowing raptors to hunt for rats and mice as they naturally would, in habitats that are healthy and free of toxic chemicals, then ecosystems can maintain a necessary balance.

Ian Martin, Education Coordinator, 2016

(i) US Evirnmental Protection Agency: Rodent Control Pesticide Safety Review

(ii) Center for Biological Diversity: Rodenticides

(iii) Audubon: Poisons Used to Kill Rodents Have Safer Alternatives

  Related Posts

Add a Comment