Key conclusions of the report include:

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Reactions of brown and grizzly bears to and related demographic effects of human infrastructure are complex and highly contingent. There are no invariant universally applicable standards or threshold for managing bear habitat security. Even so, the available research supports reaching generalizable conclusions that are summarized in the following bullets. Text in parentheses at the end of each point reference sections of this report that provide more details.

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• Humans have taken and invariably continue to take a consequential, if not catastrophic, toll on brown and grizzly bear populations worldwide (Sections 2 and 5).

• Humans kill bears at higher rates near human infrastructure, but with substantial variation in the magnitude of this toll (Section 4).

• Brown and grizzly bear populations fare best in the absence of all people and human infrastructure (Sections 4, 5, 6, and 7).

• As a corollary, fewer roads are better than more roads if the goal is to conserve bear populations, with no roads being best of all (Box 1; Sections 4.2, 6.1).

• Few people are better than more people, especially when in the form of little or no traffic on roads and few if any resident humans (Sections 4.2.4, 6.4.3, and 7.2).

• Bears in most populations underuse areas near human infrastructure, but with considerable variation in the extent of this underuse (Section 6).

• Bears exposed to humans and human infrastructure invariably fare better when subsidized by immigration from nearby large source areas free of human impacts (Box 2; Sections 4.2.2, 4.2.4, 4.3.5, and 7.3).

• All else equal, the extent of areas secure from human impacts needs to be greater where people are armed, intolerant, and likely to violate wildlife protection laws (Box 5; Sections 5.1.2, 5.1.3, 5.2, and 5.3).

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• Major transportation corridors often constitute fracture zones in what would otherwise be regional meta-populations, with mountainous terrain typically exacerbating this effect (Section 7.4).

• Highways are less lethal for bears when there is less traffic, lower speed limits, fewer attractants, and designs that facilitate detection of bears by drivers (Section 7.1 and 7.2).

• Human infrastructure located in naturally productive environments or associated with unsecured attractants often lures bears into fatal conflicts with people (Sections 4.3.5, 4.3.6, and 6.4.2).

• Bears are more vulnerable to disturbance and human-caused mortality in areas that lack visual and audio screening or protective rugged topography (Box 2; Sections 4.2.5 and 6.4.1).

• Most bears in most places mitigate the hazards of human infrastructure by accelerating and directing their movements to minimize the duration of their exposure (Section 6.3.2).

• When near humans, nocturnal bears experience less human-caused mortality compared to diurnal bears and are consequently more common among those bears survive interactions with people (Sections 4.3.1 and 6.3.1).

• Human-tolerant bears are better able to use human environs, but also die at higher rates compared to less tolerant bears (Sections 4.3.2 and 6.3.3).

• The disproportionate killing of human-tolerant male bears by people often leads to security-conscious adolescents and females with dependent young concentrating near human infrastructure, typically with problematic outcomes (Sections 4.3.3 and 6.3).

• Bear managers in the United States neglect impacts attributable to locating infrastructure in productive habitats without screening cover (Box 3; Sections 4.3.4).

• Most standards employed by bear managers in the United States for managing grizzly bear habitat security lack scientific justification. Some are arbitrary and capricious (Sections 4.2.2 and 4.2.3).

• A range of standards or thresholds for managing habitat security can be derived from the available research. One set of standards can be considered “conservative,” appropriate for at risk populations, and another set can be considered “middle of the road,” appropriate for larger more resilient populations.

• Conservative Standards: Road densities <0.4 km/km2 (0.6 miles/mile2) (); Buffers for defining patches of secure habitat along roads >815 m (0.5 miles) (); Buffers for defining patches of secure habitat around townsites >5,000 m (3 miles) (); Individual patches of secure habitat >870 ha (2,150 acres) in size >815 m from the nearest road and >5,000 m from the nearest townsite (); Secure habitat >75% of the regional bear distribution (); Population source areas >4,000 km2 in size (1,550 miles2) ().

• Middle of the Road Standards: Road densities <0.7 km/km2 (1.1 miles/mile2) (Sections 4.2.2 and 6.1.2); Buffers for defining patches of secure habitat along roads >400 m (0.25 miles) (Section 6.1.2); Buffers for defining patches of secure habitat around townsites >3,000 m (2 miles) (Section 6.1.2); Individual patches of secure habitat >490 ha (2,150 acres) in size >400 m from the nearest road and >3,000 m from the nearest townsite (Section 4.2.4); Secure habitat >65% of the regional bear distribution (Section 4.2.4); Population source areas >1,000 km2 in size (390 miles2) (Box 2).