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The Resource Pressure Lab

The Drought Map Is Not the Hog Map

Dry conditions do not produce one hog response. They change the map of usable resources.

Evidence explainer with illustrative interactive modelsResearch updated

Does drought increase feral hog activity or damage in Texas?

Drought can change where water, food, moist soil, shade, and cover remain available, but a drought category does not predict whether hogs are present or whether a specific property will be damaged. Texas observations show a modest detection pattern, not proof of movement or abundance.

The pressure can move while the most obvious evidence goes quiet.

  1. Drought classificationA weekly, expert-assessed severity map. A D2 polygon is not a map of remaining ponds.
  2. Actual resourcesWater, forage, moist soil, shade, and cover that survive locally. A pond is not proof of hog use.
  3. Possible hog responseConcentrating, shifting, travelling, or becoming less active. Hog use is not proof of imminent damage.
  4. Detectability and visible signsWhether evidence can be seen at all. A lack of fresh rooting is not proof of absence.
  5. DamageThe outcome landowners actually care about, and the layer furthest from a drought category.

No layer on that chain substitutes for the next one. Each step adds assumptions, and this page keeps them separate rather than collapsing them into a single number.

The Signs Went Quiet

Hold the county at D2 and move the remaining moisture. The classification never changes. What changes is where usable moisture sits — and, with it, where evidence can still be seen.

Illustration — not a property prediction

  • The county stayed D2. The classification did not change while you moved the slider.
  • The pasture dried and fresh rooting became harder to see. Hardened ground resists working, so the clearest sign fades first.
  • Water and green forage remained along the creek and irrigated edge. Resources moved rather than disappearing everywhere at once.
  • The map did not show where those resources remained. Drought categories do not inventory ponds, shade, or irrigation.

Less rooting can mean less rooting — not necessarily fewer hogs.

Drought Is Not One Variable

“Drought” is shorthand for several independent measurements that often disagree. Each layer answers a narrow question well and a broader question badly.

U.S. Drought Monitor category — what it can tell us

An expert-assessed, weekly, mapped classification of drought severity and how much of a county it covers. It is consistent, public, and comparable over time.

What it cannot tell us

It is a polygon, not an inventory. It does not say which ponds still hold water, which pastures still carry forage, or where moist soil remains.

These layers are kept separate on purpose. They are never combined here into a single number, index, or score.

What Texas History Showed

This is an exploratory detection-rate screen of public data by Texas Hog Dispatch. It is not peer-reviewed research, not a population estimate, and not an official product of any agency or university. It compares how often wild pigs appeared in public research-grade wildlife observations against official drought measures over a decade.

Period: 2015–2025. Research-grade public pig observations were divided by all research-grade mammal observations for the same months, as a rough control for how much reporting effort existed. That ratio, rather than raw counts, was compared against official drought measures. Controls were included to reduce the influence of platform growth over time and month-of-year seasonality.

Drought measure (one-month lag)Spearman rhoCircular-shift empirical p
D1 or worse coverage-0.2600.0001
D2 or worse coverage-0.2870.0001
D3 or worse coverage-0.2960.0077
Drought Severity and Coverage Index (DSCI)-0.2580.0001

Reading the negative direction. As drought coverage and severity increased, pigs made up a smaller share of public research-grade mammal observations. That is a statement about detection share. It does not mean there were fewer pigs. It is equally consistent with animals being harder to observe, activity shifting into cooler hours, or observers behaving differently in dry, hot months.

The effect sizes are modest. These associations describe a weak-to-moderate tendency across a decade of monthly values, not a rule that holds in any given month or place.

Why circular-shift testing was used

Drought arrives in long runs, so one month is not independent of the month before it. A standard p-value that assumes independence would overstate confidence. Circular-shift testing rebuilds the comparison many times by sliding one series in time while keeping its internal structure intact, which preserves the long runs and gives a more honest sense of how often an association this size appears by chance.

One Drought, Four Responses

The same drought category can be consistent with several different behaviors, sometimes at once. Set the conditions and see which responses published research treats as plausible.

Possibility, not prediction

These are responses that published research treats as plausible under conditions like these. No probability, risk level, timing recommendation, or predicted path is produced, and none can be.

Concentrate

When remaining water and shade are few and dependable, use can cluster around them.

Reduce activity

Under high heat, daytime activity can compress into cooler hours, so the same animals become harder to observe.

More than one response can be true at the same time. Different animals, different parts of a landscape, and different hours of the day can each behave differently under a single drought classification.

The El Paso Data Trap

Before any association can be tested, the records themselves have to survive inspection. This example shows why an unfiltered count can be badly misleading.

Unfiltered public archive result

178 records labeled El Paso County — a county on the far, dry western edge of Texas where a naive reading would suggest a substantial documented presence.

This is a data-quality audit example from the public GBIF occurrence extract used for the exploratory analysis. It is not a criticism of GBIF or iNaturalist: aggregators are supposed to preserve source records faithfully, including museum and specimen material. Filtering them appropriately is the analyst's responsibility.

Same Drought, Five Properties

Five settings can share one county classification and still differ completely in what remains available and what evidence is readable.

Resources that may remain

Little standing water, hardened soil, thinning forage, limited shade.

Signs that may still be readable

Rooting can become hard to see because dry ground resists working. Trails and tracks may persist in dust and along fence lines.

Honest interpretation

Fewer fresh signs here does not mean fewer hogs in the area. Possible pressure points are the few places moisture remains, not the open dry ground.

These are possible pressure points described in general terms. No risk score is assigned, and nothing here is guidance about where to place equipment or how to remove animals.

What the Wider Research Adds

Published work on wild pigs and wild boar in dry conditions is informative and inconsistent in equal measure, largely because different studies measure different things.

Southern United States (multi-state GPS study) · measured: Movement (GPS-tracked wild pigs)Kay et al. 2017
Citation
Kay et al. (2017). Movement Ecology.
Measured outcome
Movement (GPS-tracked wild pigs)
Finding
Movement was driven by several interacting factors and varied with the scale of the analysis, rather than following one simple environmental cue.
Do not substitute
Movement is not the same outcome as damage or detection. A multi-driver movement result cannot be read as a drought response rule.
Original source
doi.org/10.1186/s40462-017-0105-1
East and South Texas · measured: Space use across wet and dry conditionsWyckoff et al. 2012
Citation
Wyckoff et al. (2012). Wildlife Society Bulletin.
Measured outcome
Space use across wet and dry conditions
Finding
Space use differed between wetter and drier conditions, with wetter and more sheltered areas featuring in dry-period use.
Do not substitute
Space use describes where animals were, not how much damage occurred or how likely a specific property is to be affected.
Original source
doi.org/10.1002/wsb.96
Northern Australia · measured: Seasonal habitat suitability and range contraction/expansionFroese et al. 2017
Citation
Froese et al. (2017). PLOS ONE.
Measured outcome
Seasonal habitat suitability and range contraction/expansion
Finding
Suitable habitat contracted in the dry season toward moist, shaded refuge areas and expanded again in the wet season.
Do not substitute
A different continent, climate, and species context. Contraction of suitable habitat is not a Texas prediction or an abundance estimate.
Original source
doi.org/10.1371/journal.pone.0177018
Australia · measured: Use of water featuresGlanville et al. 2023
Citation
Glanville et al. (2023). Wildlife Research.
Measured outcome
Use of water features
Finding
Permanence, shade, predictability, and surrounding vegetation were associated with how water features were used, rather than the presence of water alone.
Do not substitute
Water-feature use is a habitat result, not a measure of population, and not guidance about any specific pond or tank.
Original source
doi.org/10.1071/WR22027
Europe · measured: Rooting damage in relation to prior-month rainfallCalosi et al. 2024
Citation
Calosi et al. (2024). Environmental Management.
Measured outcome
Rooting damage in relation to prior-month rainfall
Finding
Rooting damage was associated with rainfall in the preceding month, consistent with wetter soil being easier to work.
Do not substitute
This is a detectability and workability result about rooting. It should not be inverted into a claim that dry conditions mean fewer hogs.
Original source
doi.org/10.1007/s00267-024-01952-y
Europe · measured: Activity in relation to heat and rainfallGüldenpfennig et al. 2025
Citation
Güldenpfennig et al. (2025). Royal Society Open Science.
Measured outcome
Activity in relation to heat and rainfall
Finding
Heat and rainfall interacted with activity patterns, so temperature and moisture effects were not independent of one another.
Do not substitute
Activity is not damage. An activity shift can change how visible animals are without changing how many there are.
Original source
doi.org/10.1098/rsos.242208
Southern Brazil · measured: Occurrence and habitat association in a wet regionHegel et al. 2019
Citation
Hegel et al. (2019). Biota Neotropica.
Measured outcome
Occurrence and habitat association in a wet region
Finding
In this wetter landscape, local running water was a weak explanatory variable, a useful counterexample to assuming water always structures use.
Do not substitute
Wet-region results limit how far dry-region intuition can be generalized. Neither setting overrides the other.
Original source
www.scielo.br/j/bn/a/TFs448Rn3YvKktXYNSVsqQm/?lang=en

Activity, movement, space use, detection or rooting, and population are five different outcomes. A result about one of them is not evidence about another, and most disagreement between studies dissolves once the measured outcome is stated plainly.

Known, Estimated, Unknown

Known

Published values that can be looked up.

  • Official drought category, coverage, and map date for a county.
  • Counts of public historical wildlife observations.
  • Named public climate indicators such as PDSI and DSCI.

Estimated or contextual

Modeled or inferred, useful with caveats.

  • Soil-moisture values from models rather than local measurement.
  • Vegetation and forage context from satellite greenness.
  • Whether unmonitored ponds and tanks still hold water.
  • Whether a given resource is actually the limiting one.

Unknown locally

What nothing on this page can supply.

  • Whether hogs are present on a specific property.
  • How many animals, or sounder composition.
  • Exact route or time of movement.
  • Why rooting is lower in a particular place.
  • The probability of future damage.

Questions people ask

Does drought make feral hogs move farther?

Sometimes, and not always. Research describes movement as multi-driver and scale-dependent, and dry-season studies elsewhere describe contraction toward moist, shaded refuge rather than uniformly longer travel. Whether animals travel farther depends on how far apart the remaining usable resources are, which public drought data does not map.

Does less rooting mean the hogs left?

No. Hard, dry ground is harder to work, and published work associates rooting damage with recent rainfall. Less visible rooting can mean less rooting rather than fewer animals. A quiet sign is not evidence of absence.

Can a county drought category predict hog damage?

No. A drought category is a mapped severity classification, not an inventory of remaining water, forage, or moist soil, and not a statement about hog presence. Damage on a specific property cannot be predicted from a county-level category.

What did the Texas historical analysis find?

In an exploratory screen of public data from 2015 to 2025, pigs made up a modestly smaller share of research-grade mammal observations as statewide drought coverage and severity increased (one-month-lag Spearman rho between -0.258 and -0.296). At the climate-division level, wetter PDSI conditions were associated with a slightly higher observation share (rho +0.136), broadly consistent with the statewide detection direction, while direct Drought Monitor panel results were weak and not significant. These are detection-share associations, not abundance or movement measurements.

Is this a live hog activity tracker?

No. This page is an educational research explainer with illustrative interactive models. It shows no live sightings, no forecasts, no risk scores, and no property locations. The Tracker's Drought Watch card shows official U.S. Drought Monitor readings by county, and nothing more.

Methods, in plain terms

What was compared. Monthly counts of research-grade public wild pig observations in Texas were divided by monthly counts of all research-grade mammal observations in Texas, producing a detection share rather than a raw count. That share was compared against official drought measures for the same months, using a one-month lag.

Period and units. 2015–2025 statewide, and the same 2015–2025 study window across 10 Texas climate divisions for 1,320 division-months.

Controls. Adjustments were included to reduce two obvious confounders: growth in observation platform use over the decade, and month-of-year seasonality in both wildlife reporting and drought.

Statistics. Rank-based Spearman correlations, with significance assessed by circular-shift resampling so that long drought runs are not treated as independent month-to-month observations.

Record filtering. Specimen and undated archival records were excluded, as the El Paso example above illustrates.

Status. Exploratory analysis of public data by Texas Hog Dispatch, published with its limits visible. Not peer reviewed. Not a population estimate. No endorsement or partnership with Texas A&M, TPWD, NOAA, USDA, GBIF, iNaturalist, or any researcher is implied. The raw Texas A&M reporting database was not used; its public documentation is listed only as context for how reporting tools work.

Sources

Wild pig and wild boar research

Public data and agency references