2 does standing in field

If you read this blog, you are probably a deer fan. Deer are known as the ghost of the forest. But they aren’t too keen on labels. I can’t blame them. It limits potential. 

Deer are the most widely distributed game species in North America. Since they get along well with people, you can find deer just about anywhere including agricultural areas. You’re thinking of course deer live in farm country. It’s an endless buffet. But North America and, likewise, deer distribution are very different today compared to pre-colonial times. Human-altered landscapes allowed deer to break free from the forest and see the world!

We’ve been growing crops for centuries now. And deer are well versed in the delicacies of corn, soybeans, alfalfa, and more. But seeds aren’t the only thing we’ve been spreading. Modern agricultural practices are chemical intensive. Pesticides are applied to seeds and sprayed on growing crops. And deer are really bad at reading the Safety Data Sheet (SDS) and even worse at following re-entry intervals

What does that mean for deer and the people who eat them?

Neonicotinoid pesticides are the most widely used class of insecticides in the world. The first commercial neonic was patented in 1985. Their use became popular in the late 1990s. Of the 133 million acres of corn, soybean, wheat, cotton, and sorghum in North America, over 98% are treated with a neonic

Neonics are popular because of their high specificity to insects and low toxicity to birds and mammals. But we should all know by now that if you pull one string in an ecosystem, it unravels much more than intended. Neonics have been implicated in the downfall of pollinators which caused the European Commission to ban the outdoor use of 3 neonics in 2018. The EPA released an interim decision for 5 neonics in January 2020 proposing additional personal protective equipment and restrictions on when they can be applied to blooming crops. Indirectly, neonics affect the food supply of insect-eating birds reducing bird biodiversity and act as an appetite suppressant to migrating birds delaying migration and reducing survival. 

None of that is good news but what about deer? Neonics are absorbed by plants, highly water soluble, and persist in soils. Food, water, and dirt – all things consumed by deer. 

Given the relatively recent arrival of neonics on the ag scene, there isn’t much research out there but there is some. The first paper to suggest that neonics might be affecting deer was published in 2011 when a rash of ruminants with brachygnathia superior were documented in Montana. This corresponded with other vertebrate species exhibiting developmental malformations strongly suggesting endocrine disruption by an environmental cause. It also corresponded with widespread use of neonics perhaps interacting with other pesticides. While there are data to support the disruptive effects of these interactions, the research only showed correlation, not causation.

In 2018, a review of the literature was published on the direct and indirect effects of neonics on vertebrates. While the toxicity (the amount needed to cause death in a controlled lab setting) varied from non-toxic to moderately toxic, the indirect effects were more concerning by manifesting as reproductive problems, such as reduced sperm production, adverse effects on the fertilization process, reduced rates of pregnancy, higher rates of embryo death, stillbirth and premature birth, and reduced weights of offspring. Other sublethal effects noted: genotoxic and cytotoxic effects, neuro-behavioural disorders of offspring (including those dosed in utero), lesions of the thyroid, retinal atrophy, reduced movement, and increased measures of anxiety and fear.

None of that sounds good but these are results seen in lab rats. And the lab does not always translate to the real world and rats aren’t deer (no matter what some people may say).

Those deformed deer from Montana prompted a more structured experiment to see if neonics were at play. Captive does and fawns were administered various field-relevant does of a neonic in North Dakota (2019) – levels that would be found in drinking water on the landscape. Here’s what they found:

1) control deer consumed more water than treatment groups [deer in treatment groups tried to avoid contaminated water]

2) imidacloprid [the specific neonic tested] was present in the organs of our control group, indicating environmental contamination

3) as imidacloprid increased in the spleen [which plays a key role in immune system function], fawn survival, thyroxine levels, jawbone lengths, body weight, and organ weights decreased

4) adult female imidacloprid levels in the genitals were negatively correlated with genital organ weight and,

5) behavioral observations indicated that imidacloprid levels in spleens were negatively correlated with activity levels in adult females and fawns

Ok – there is no getting around this one. Neonics definitely had an effect on our favorite vertebrate. I would be remiss if I didn’t point out this was a small sample (20 adult does and their corresponding fawns over a 2 year period) but this kind of intensive monitoring is difficult and expensive. However, 367 samples of free-ranging deer in North Dakota were tested from 2009 to 2017 using the same methodology and found neonic concentrations 2.8 times higher in the liver and 3.5 times higher in the spleen than in the captive deer used in this experiment. 

So there is definitely evidence that neonics affect behavior (reduced activity) and suppress immune function (impair spleen function). Both of which play a role in individual survival. But will that affect deer populations?

One thing we do know at the Deer Forest Study is that as long as female survival is high deer populations are robust. But we also know that systems under stress (be they forest or species) are more vulnerable and less resilient in the face of threats (both known and unknown). Exposure to neonics and other chemicals cause a crack in the system. Is that one crack enough to crumble the foundation? Probably not but get enough cracks and you’re left with a tragic Surfside Condo collapse

And I won’t even speculate on what this means for people who consume venison. Realistically, we probably have more avenues of exposure in our everyday lives that consuming deer containing neonics is pretty far down the list of concerns. 

All of the deer in my freezer are harvested from an agricultural area using the standard 21st century pesticides. They are free ranging but probably far from organic. 

-Jeannine Fleegle
Wildlife Biologist
PGC Deer and Elk Section

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