Sonoran Desert Tortoise Population Status

 Abstract

Population trend data for species under consideration for federal protection is often limited. This study evaluated Sonoran desert tortoise (Gopherus morafkai) population trends in Arizona using iNaturalist citizen science data. We analyzed 1,402 research-grade tortoise observations and normalized them against total observations in the area to account for sampling bias. While both tortoise observations and total observations increased since the early 2010s, the ratio of tortoise to total observations declined consistently from 0.12% to 0.08% between 2017-2025. This decreasing ratio suggests either shifting observer preferences or declining tortoise encounter rates, potentially indicating population decline. These results provide concerning evidence of negative population trends for this species of conservation concern and demonstrate the utility of citizen science data for monitoring species lacking formal survey programs.

Introduction

Sonoran desert tortoise (Gopherus morafkai) live in the Sonoran desert of Arizona and northern Mexico.  A closely related species in California and Nevada, the Mojave desert tortoise (Gopherus agassizii), is Federally protected as a Threatened species under the Endangered Species Act (ESA).  The Sonoran desert tortoise is listed by AZ as a Species of Greatest Conservation Need (SGCN) and was proposed for protection under the ESA but determined "Not Warranted" in 2022.  On June 4, 2025 wildlife groups filed suit in federal court challenging that determination.  

It is difficult to find current population trend data for species that may warrant listing under the ESA, so I attempted to do so using publicly available iNaturalist data.  iNaturalist is a public repository of photographic observations of species.  

Methods

I filtered iNat for Research Grade observation of Sonoran desert tortoises in AZ and found 1,402 observations. I considered limiting the analysis to only live tortoises, but eventually decided to use all research grade observations due to the difficulty filtering. Only ~3% (44 observations) were annotated as dead , and only ~1% (12 observations) were annotated as scat.  

I created an Area of Interest (AOI) bounding box around the tortoise data to search for total RG observations.  There were a total of 1.2 million RG observations in the Sonoran desert of southern AZ.

RG tortoise observations in AZ with bounding box showing AOI.  

More tortoises are observed in places where there are more people to observe them.  Because iNat data is based on opportunitistic data collection, it is liable to biases based on where people live as well as how many people use iNat.  To attempt to correct for this, trend analyses can normalize the count of tortoise observations as a ratio of total observations in the AOI.


Data

Data table of AOI with Total RG Observations, Total Observations, RG:Total Observations Ratio, RG Tortoise Observations, and RG Tortoise: RG Total observations.

Results

Total RG observations in the AZ Sonoran desert have been increasingly consistently since the early 2010s.

Count of total RG observations in the AOI per year.

Tortoise observations have increased since 2013, with some notable dips in 2020 and 2023. It is possible that these dips are due to weather-related impacts to tortoise population, but they could also be due to differences in number of observations.  

Count of tortoise observations per year.

By comparing tortoise observations to total observations, a normalized ratio can be derived. This ratio decreases over time. There is a step change decrease in 2017, which could be a real population decrease or could be due to the huge increase in popularity of iNat in 2017.  However, even if only looking at 2017 -2025, there is still a long term decrease in the ratio of tortoise observations, from around 0.12% to 0.08% of total observations. 

Ratio of tortoise observations to RG observations. 

Discussion

The decreasing ratio of tortoise observations indicates that either people are trending to preferentially observe other species more than tortoises, or that tortoises are making up a smaller percentage of the animals people encounter.  

Despite limitations of citizen science data, these results provide concerning evidence of negative population trends for this species of conservation concern and highlight the utility of iNaturalist data for monitoring species that lack formal survey programs.

An Alzheimer's Bet Based on Biology

Alzheimer's research has been accused of being hijacked by a misleading hypothesis that only survives to enrich drug companies.  The amyloid hypothesis has been extensively critiqued, including by this essay on the blog Astral Codex Ten that looked at problems with the original paper that started (by some accounts) 30 years of misguided research.  

In response to a call for counter-arguments, David Schneider-Joseph, presented a compelling argument in favor of the amyloid hypothesis.  He even went so far as to propose a bet; that a drug targeting amyloid would achieve at least a 75% slowdown in Alzheimer's in the next 12 years.

I wouldn’t take David’s proposed bet, because I’m sure some company will find a way to gerrymander clinical endpoints to get to 75% “slowdown”.  Probably with a drug that has horrible side effects and costs north of $100,000/year.  

I would bet on the following:  the leading* therapy in 12 years will not be one whose sole intended mechanism involves amyloid production or clearance, e.g. monoclonal antibodies, small molecules, or gene editing that work directly on amyloid.  

    * “Leading” means some combination of efficacious and most widely used.

This is the important sense in which the amyloid hypothesis is wrong: it may be “correct” in some narrow biochemical sense, but it is a dead end.

In a way this is an easy bet on the status quo continuing indefinitely, because the current drugs used to treat Alzheimer's do not target amyloid.  However, I’m also bullish on emerging therapies such as creatine, lithium, calcium channels, and mitochondrial therapies including far infrared, ketones, and other ways to generally affect metabolism and autophagy/mitophagy.  Some of these might be shown to improve clearance of amyloid, but the amyloid hypothesis is not necessary or very helpful in the development of these “general" therapies.  

My prediction is based on a general model of how biology works.  Simple infectious and traumatic medical conditions seem most amenable to targeted therapies, while general conditions like mental illness, cancer, and Alzheimer’s are so complicated and depend on so many general health processes that targeted therapies tend to miss the mark.  

Ideally, we would pursue both lines of treatment, but our pharma system is biased toward patentable targeted treatments to the exclusion of all else.  The “Amyloid Mafia” is shorthand for this trend in Alzheimer’s research.  

However, even given the funding disparity between amyloid research and other treatments, non-amyloid treatments are arguably already more efficacious.  As a good Bayesian, I predict this will continue, and so this seems like a safe bet to me!