Pacific Newt Roadkill - How to Identify Duplicate Observations

It's a difficult and very time-consuming chore to try to eliminate duplicate observations of newt roadkill, especially when there are multiple observers covering the same study area.

Since there can be hundreds and hundreds of carcasses on the road at the same time and it's hard to tell them apart when they start decomposing, one or more methods are necessary for identifying carcasses that have already been recorded in iNat. I really struggled with this issue last year.

Remove Carcasses from the Road? Or not.

In 2017, I was told by one local agency that it's illegal in CA to remove dead animals from the road. This year I was told by a rep from CA Fish & Wildlife that it's ok to remove the dead newts from the road. Because of this contradictory info, I'm confused about whether it's legal or not. See this article for more info:

Often, it's too dangerous or impractical to remove the carcasses from the road. Alma Bridge Road is a winding mountain road that is seeing more and more traffic over the years. It's dangerous enough going out on the road to take pictures of roadkill, especially when it's dark and stormy. The extra time it takes to remove a carcass just adds to the danger.

Observing How Newts Decompose to Determine Age

What I've noticed about decomposing newts:
1. The bright orange/yellow belly color seems to fade to grayish-white within 2-3 days.

2. The bright red blood is gone within 2 days.

3. If carcasses were desiccated before the rain, they absorb water and actually make the carcass look fresher.

4. When it has been raining for days and the road is wet, most of the carcasses decompose into a slimy whitish gray mass within a few days that is almost unrecognizable as a newt. This is very fast decomposition compared to what I saw when there was no rain for a week or more.

Factors that affect how fast an animal such as the newt decomposes are as follows:
* moisture: the amount of water in the environment (rain and fog condensation); organic matter decomposes faster when wet
* temperature: organic matter breaks down faster in warm weather
* integrity: how many times was the newt run over? In areas with a lot of traffic, the carcasses decompose faster.

Separating Observations of Fresh vs Decomposed Roadkill

Last year I took extreme measures to ensure that I did not double-count the corpses because I didn’t want anyone to question my numbers. When I uploaded the pictures to my computer, I sorted out the “fresh” from the “decomposed” corpses. I then compared the decomposed ones with the observations from previous weeks. If there were duplicates, I didn’t upload them to the main project, but rather added them to a project called “Decomp Study” ( so that I could understand how the newts decompose and what features to look for. This was an *extremely* time-consuming process that took hundreds of hours, and in the end, I don’t think it was worth the time and effort. Out of 2,148 decomposed newt pictures, I only found 332 duplicates (15%).

I started taking photos with the newts oriented in the same direction (head to the left, tail to the right) to facilitate comparisons.

Other Methods to Try

* At one point I tried leaving a drop of purple nail polish next to some carcasses. The nail polish dots lasted a couple of weeks. Some, however, disappeared within one week.

* You might try circling the carcasses with sidewalk chalk. This will work best during dry periods, because rain washes away the chalk marks.

* If the GPS coordinates are accurate, you might be able to export a couple weeks of project data to an Excel spreadsheet and sort on the GPS coordinates to find duplicates. I never tried this, but it might be more efficient than comparing pictures. However, when collecting data for the Decomp Study, I found that the corpses often moved from their original location (due to cars, foot traffic, rain drainage, wind?). Some corpses were even flipped over or oriented in the opposite direction over time.

Does it Matter?
There are many reasons to believe that we are undercounting the newt roadkill at Lexington. See the following post:

One could say that the duplicates offset the undercount, so it all evens out.

The best approach would be to survey the road every day and remove any corpses found. However, I don't know anyone who would be willing to do this for the 5 month migration season, especially if the powers that be are not willing or able to staunch the slaughter. Doing this kind of work takes its toll on your psyche and soul.

Posted by truthseqr truthseqr, February 24, 2020 12:01



Regardless of the agencies' conflicting opinions,I feel like if we're just flinging them off to the side, and not, say, taking them home with us, that shouldn't be an issue and I'm doing it anyway. People move dead critters like deer off the road and onto the shoulder all the time.

Seems brilliant to take the photos in a standard orientation, and I'll start doing the same. I also wonder if it would help if we all took them so that they fill a majority of the photo frame. When we're far away, and the newt is tiny in the photo, it's just that much harder to compare (and ID, for that matter.) If this kind of group data collection happens again in the future, I suggest that we start everyone off setting a standard of some sort (head to the left and whatever else) and ask everyone to take the photos in that way. It might seem slightly inconvenient at first, but now that we all see how time-consuming it can be comparing after the fact, doing them in a standard way seems worthwhile. (And dammit, this is science!)

Re: GPS coordinates, Another problem with comparing them is that they can be imprecise to begin with (not to mention those that end up in Bear Creek Redwoods!), and when there are several newts close together things could get very muddied.

Posted by newtpatrol about 1 month ago (Flag)

@newtpatrol, thanks for your helpful suggestions. That's a great idea to set standards at the beginning of the project. I participated in a study at UCSC where the chief investigator wrote a multi-page protocol that we volunteers followed. I was thinking it would be a good idea to have something like that for this project, but I never got around to writing it. And I didn't want to impose too many rules on the volunteers for fear of losing them. As it was, I received a lot of pushback when I tried to standardize tags, fields, and annotations.

Regarding removing the dead newts from the road, I support whatever you all think is best. My biggest concern is your safety. People drive crazy on that road. I don't want anyone to get hurt.

It's not too late to standardize on orientation. We could use tools like photo cropping and orientation to go back and edit previous pictures. That seems like a daunting task, though, now that there are many thousands of pictures. There were several iNatters who wanted to support the project but live too far away to participate. I wonder if some of them could help with this task?

Posted by truthseqr about 1 month ago (Flag)

Good discussion.
Removing dead newts - I started doing it today (a bit late, I know). It clears out the road, but I thought it's not very helpful: the ones I can easily remove are so dry I wouldn't think they might be fresh. The ones that are fresh aren't easily detachable, so they might still be there next week.
Decomposition - I feel like in the winter it was easier to just document everything. They decomposed so quickly that we probably underestimated the roadkills, other than overestimated them, as so many were gone by the time we came back to the same spot. But I don't think this is the case anymore. It seems that dead newts die and stay on the road for a long time. Before they dry out completely some of them get stuck to the road, and in that case they can stay there for a long time. Not sure how to solve this? It's difficult to remove them, so maybe we should mark them somehow - nail polish like Anne suggested?
Moreover, I don't know how long it takes them to decompose in current conditions - hot, dry. Would a freshly killed newt look dry and old after a couple of days? or a week? we might be missing some dead newts, thinking that they've been there forever.

Posted by merav about 1 month ago (Flag)

and I think having some guidelines is a great idea (even though might be a bit overwhelming).
and by the way - I take 2 photos of each newt, one zoomed out, one close-up, for two reasons - I can have the zoomed out photo as the first one, so it's less gross to non-roadkill users, and I avoid losing data, in case one of the photos disappears from my phone.

Posted by merav about 1 month ago (Flag)

@truthseqr I sympathize with not wanting to lose volunteers to too many rules. But I do think that if we could come up with just a few standards, and provide a simple How-To for people to do things like batch upload, adding all of the relevant tags, etc, that would make it easy, and really more streamlined than we had it this year, everyone figuring stuff out on our own. And really, we aren't just doing this for fun, we're doing it to provide useful data, so I'd hope that volunteers would appreciate the need for a little standardization. Especially if there's an explanation of how past experience led to the guidelines.

Great idea to see if the remote iNatters would be willing to work on orientation, although I wonder if it's useful at this point. It seems like we're just not recording the newts that are likely to be repeats, so there's not as much of a need. Perhaps it would be useful for just those taken during, say, end of Jan/all of Feb?

~ Stacie

Posted by newtpatrol about 1 month ago (Flag)

Hi Stacie (@newtpatrol ) I totally agree about the "how-to" protocol. That would be a very useful tool. Unfortunately, I did not have the energy to do that this year (chemo, surgery & radiation really sap your strength & energy).

I don't know what the future holds. Will there be another Lexington survey next year? Is it worth spending the time & energy developing a protocol if it won't be used? I'm not even sure I'll be alive this time next year, so it's not on the top of my priority list. In other words, I won't be writing a protocol. But feel free to write one yourself, if you want.

I've tried to document all the issues & techniques I used during the last 2 years of my data collection. All the info you'll need is fully documented in the project journals & comments, although it's scattered throughout 50 or more journal entries. At the beginning of the project, I urged all volunteers to read the journal entries for the main project and all subprojects. I even pasted the journal entries into a Word document to make it easier to read. Please see the following post:

I'm afraid people were overwhelmed with the sheer amount of info available, so I tried to provide it in smaller chunks as needed. Sometimes you have to have some experience under your belt before the info makes sense (e.g. the issues around duplicate observations, or the importance of accurate GPS coordinates).

Stacie, sorry you felt that you had to figure stuff out all alone. @merav and I have been here all along to answer questions. All volunteers had been using iNaturalist for years when they signed up for this project, so I assumed people knew how to do batch uploads and add tags, fields & annotations. Bad assumption on my part. The GPS issues seem to be camera & software specific, with lots of combinations, and that seems like an issue better addressed by iNat staff than by our team.

Something to think about: what if nothing is done to help the newts before their population is obliterated? The powers that be now have nearly 2.5 seasons' worth of data. Do they really need more?

The other newt survey team in Chileno Valley has 74 members ( I'm not sure how many are active volunteers, though). We started with 5 volunteers and are now down to 3. Interest in the project seems to be waning.

Posted by truthseqr about 1 month ago (Flag)

@merav & @newtpatrol,
You're blazing new territory in regard to what the roadkill situation looks like after an unusual number of consecutive dry days. In 2019, there were never more than 9 dry days in a row. In 2020, there have been 25 consecutive dry days in Feb/Mar plus an additional week or more with minimal rain. It will be beneficial for you to add your observations and thoughts about what you're seeing this season to this conversation. Thanks!

Posted by truthseqr 29 days ago (Flag)

wow, that's amazing! (not surprising, though). Anyways, I'm guessing most of the newts I see are old, but for sure some are still crossing. I will try and compare a few observations I made yesterday with old ones. I already found out that one of them was indeed a duplicate, so I've deleted it, and duplicated the original one, added the new photo, and then added it to the decomp project.
I find it quite puzzling.

Posted by merav 28 days ago (Flag)

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