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5 Tips for DIY Critter Detection | Part 2

In Part 1 of this article, we looked at three tips to more effectively track and gather information to help identify what sort of wildlife may have entered your home. These tips include careful recordkeeping of all wildlife indicators, distinguishing sounds, and how to seek out additional information. The final two tips relate to the thoughtful interpretation of evidence. Let’s add these two tips to our toolbag.

TIP 4 | Beware of false positives (and false negatives)

You look out your front window and the driveway is wet. You think, “It just rained.” What if, in fact, there was no rain, but the neighbor had just watered their lawn and soaked the cement?


This is an example of a false positive: a piece of evidence is interpreted to affirm a conclusion that is false.

This can certainly happen when investigating a critter issue, and I’ve been guilty of committing this blunder. For example, I once went into an attic to investigate some noises. Note: I didn’t violate Tip 3, example 3 above, as I had already confirmed no squirrels or raccoons were present. In the attic I saw bat droppings strewn across the insulation. “This is easy, “ I thought, “I’ve confirmed this house has a bat problem.” What I didn’t know at the time was that the roof has been replaced the previous year, sealing the main place where bats had previously entered. Fortunately, the inspection hadn’t stopped there. In completing the rest of the inspection I discovered the noises originated from mice. I had briefily fallen victim to a false positive.


How do you avoid a false positive? We’ll discuss that in Tip 5. But first, let’s mention a false negative. Imagine you know your Aunt Judy is supposed to call you at 3:30. Your phone rings at 3:30, but you look at the incoming phone number and it isn’t her number. You let it go to voicemail, thinking it is a telemarketer. Aunt Judy never does call, but then the next day you get an email from her asking why you didn’t answer her call at 3:30. Oops, you both discover, she switched phone carriers and now has a different number!


This is an example of a false negative: You affirm a piece of evidence as supporting a conclusion, when in fact it does not.

Again, I’ve made this blunder. I remember inspecting a chewed out hole that seemed too big to have been from a squirrel. I rationalized: Why would a squirrel make such a large hole? A hole half this size would have been adequate. This damage was from something larger, probably a raccoon. After unsuccessfully attempting to trap a raccoon, I reinspected the opening and found what I needed to change my mind: a guard hair from a squirrel. We all are prone to drawing an incorrect conclusion, and let’s look at a final tip to help avoid this.


TIP 5 | Play out the possibilities

This final tip does help address the pitfalls mentioned in Tip 4, but also simply reflects good sleuthing. To play out the possibilities is to withhold drawing a conclusion until you have considered plausible alternative explanations. To consider a conclusion as tentative helps reduce the likeliness of drawing an incorrect conclusion.


But there is a rub: Often the best person to evaluate all possibilities is the person with deep experience in that particular field. This is why the radiologists interprets the CAT scan, not you or I. However, simply recognizing the need to suspend judgment and to consider alternate explanations will help. For example:


I saw a possum traveling through my yard last night, is that what’s in my attic? Almost certainly not, as possums prefer tucking away under a deck, in a toolshed, or other locations near the ground.

I woke up to a loud thump above me. It’s gotta be a raccoon, right? Not necessarily, as sometimes an owl or large bird will land on the roof ridge, creating a deceptively loud thud.

I hear something moving around in my exterior wall every few weeks, is it mice? Pay attention to the wind forecast, it may simply be your siding shaking around.


All of these examples are one’s I’ve encountered before. In each of these cases it simply took a more thorough investigation. It took seeking out the presence or absence of evidence to settle on the best explanation.


This article is intended to help you more effectively gather and interpret critter evidence. You’ll notice we didn’t really spend time contemplating specific sounds, damage, or other evidence that we then match to particular animals. That’s for good reasons:

  1. This article would quickly shift from a blog article into a lengthy dissertation, as the number and variety of evidence to consider is so vast. The learning curve is large.

  2. My purpose here is to introduce you to effective methods in gathering and processing evidence. This will help equip you to thoughtfully handle any bit of evidence that you come across, rather than trying to match what you see or hear to some vast list, like a field guide or key. However, if you think some basic guide would be helpful, let me know and I’ll consider it as a future topic.


With that, happy sleuthing! If you have a story to share of your own critter detective work, do so in the comments below!

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