Grizzly Bear Attacks in the USA
Grizzly Bear Attacks in the USA Risk Calculator
Grizzly bear attacks in the USA are rare but can lead to serious injury or death, primarily in areas with grizzly populations like Alaska and national parks in the lower 48 states. This calculator estimates your chances of encountering a grizzly bear, being injured in an attack, and being killed, based on exposure, location, activity, season, and precautionary measures. The purpose is to help you understand and mitigate risks while in bear country.
Your Inputs
Select the options that best describe your situation to estimate your risk of a grizzly bear encounter, injury, or fatality.
Results
Data Sources
Exposure
| exposure_level | exposure_days | daily_encounter_rate | injury_given_encounter | fatality_given_injury |
|---|---|---|---|---|
|
1 day |
1 |
0.00000534 |
0.048 |
0.13 |
|
10 days |
10 |
0.00000534 |
0.048 |
0.13 |
|
100 days |
100 |
0.00000534 |
0.048 |
0.13 |
The number of days represents the exposure duration in grizzly bear country. The daily encounter rate (0.00000534 or 5.34e-6) is calculated as 564 close encounters divided by 105.6 million visits in Yellowstone from 1991-2022. Injury given encounter (0.048) is 27 injuries divided by 564 close encounters. Fatality given injury (0.13) is averaged from 13.1% fatality rate in North American brown bear attacks (24 fatalities / 183 attacks, 2000-2015). These values are constant across rows as they represent base rates.
- Grizzly bear and American black bear interactions with people in Yellowstone National Park
- Brown bear attacks on humans: a worldwide perspective
Location
| location | location_odds_ratio |
|---|---|
|
Alaska |
3.0 |
|
Yellowstone National Park |
0.4 |
|
Glacier National Park |
1.0 |
|
Other Lower 48 States |
0.5 |
|
Non-Grizzly Area |
0.0 |
Odds ratios are scaled relative to Glacier National Park (baseline = 1.0) based on attack frequency and estimated exposure from studies. Alaska has higher odds (3.0) due to 51 attacks (2000-2015) and high bear density. Yellowstone's lower odds (0.4) reflect adjusted rates from 29 attacks and high visitation. Other states have lower odds due to fewer grizzlies.
Activity
| activity | activity_odds_ratio |
|---|---|
|
Hiking/Camping |
1.0 |
|
Hunting |
2.0 |
|
Working Outdoors |
1.0 |
|
Other Activities |
0.5 |
Odds ratios are scaled relative to hiking/camping (baseline = 1.0). Hunting has higher odds (2.0) based on 22% of attacks occurring during hunting (2000-2015), considering stealth and attractants increase risk. Working outdoors is similar to baseline, other activities lower.
Season
| season | season_percentage_attacks | season_months |
|---|---|---|
|
Summer |
48 |
3 |
|
Other Active Months |
52 |
6 |
|
Hibernation Season |
0 |
3 |
Percentage of attacks by season is verbatim from worldwide brown bear attack data (2000-2015). Number of months is used to normalize daily risk, assuming 9 active months total.
Precautionary Measures
| precautions | encounter_risk_reduction | precautions_risk_reduction |
|---|---|---|
|
Bear Spray and Food Storage |
0.5 |
0.08 |
|
Bear Spray Only |
1.0 |
0.08 |
|
Food Storage Only |
0.5 |
1.0 |
|
No Precautions |
1.0 |
1.0 |
Risk reduction multiplier represents the remaining risk after precautions. Bear spray alone reduces injury/death risk to 0.08 (92% effectiveness). Food storage alone reduces to 0.5 based on reducing food-related attacks.
Risk Model
RiskModel: Grizzly Bear Attacks in the USA:EncounterInjuryFatality
Sorted Parameters:
encounter_risk = {daily_encounter_rate} * {exposure_days} * {location_odds_ratio} * {activity_odds_ratio} * ({season_percentage_attacks} / {season_months}) / (100 / 9) * {encounter_risk_reduction}
injury_risk = {encounter_risk}*{precautions_risk_reduction} * {injury_given_encounter}
fatality_risk = {injury_risk} * {fatality_given_injury}
Content: Your chance of having a dangerous, close encounter with a grizzly bear is {{One_In_X|{{#expr: {encounter_risk} }}|compare=RiskLadder }}.
Your chance of being injured in a grizzly bear attack is {{One_In_X|{{#expr: {injury_risk} }}|compare=RiskLadder }}.
Your chance of being killed in a grizzly bear attack is {{One_In_X|{{#expr: {fatality_risk} }}|compare=Micromorts }}.
The 100/9 factor in the encounter risk is because 100% of the attacks occur in the 9-month active season (not the 3 months the bears are hibernating).