Close encounters with a protective sow with cubs.
Surprise the bear or invade its personal space.
Get too close to a bear's food supply.
Predatory Bears (When the bear considers you as a food source).
Black bears with cubs are usually in my opinion not as dangerous as most people make them out to be as they will usually send the cubs up a tree if one is handy and stay around the tree on the ground. I have been in this situation several times and have never felt that the situation was serious, but this doesn’t mean one should take chances in any bear encounter.
Being observant and keeping alert is very important; look for signs of recent bear activity. These include droppings, tracks, evidence of digging, and claw or bite marks on trees. Avoid areas of dense bush if possible.
Noise making is usually recommended in bear country and may be a very effective way of not surprising a bear, but I personally dislike “bear bells” or making noise as it tends to spoil my wilderness experience. Some people jokingly refer to “bear bells” as “dinner bells” for the bears,
as the unusual sounds may actually trigger a curiosity response. Far more useful as a sound maker is your own voice.
Avoid crowding bears; respect their "personal space". The extent of this space will vary with each bear and each situation; it may be a few metres or a few hundred meters.
Avoid attracting bears through improper handling of food or garbage. Stay away from a bear’s fresh kill or any carrion.
Assess the situation if close contact is unavoidable. Are you dealing with a black or grizzle bear? Are there cubs involved?
Try to retreat slowly. Back up slowly and try to put more space between you and the bear. Talk calmly so that it can identify you as human, and slowly back up. Don't make direct eye contact, but keep a close look at the bear as you back away.
DO NOT RUN! This may trigger their attack response and you can't outrun a bear so don't even try. Despite rumours to the contrary, black and grizzly bears can outrun a human on any terrain, uphill or down. It’s simply a myth that bears tumble over when running downhill.
Tree climbing is usually not a good idea as you can’t climb fast enough in most cases and black bears are excellent climbers. Grizzlies are poor climbers but can reach up high and have been known to use tree branches like a ladder to get part way up trees as their claws are designed for digging, not climbing. Trees make good blockers if you plan on using bear spray.
Bears will often bluff charge before attacking. This is designed to allow enemies to back down before the bear needs to actually make contact. It evolved as a way to prevent encounters with enemies and it may provide you with an opportunity to back away.
Bear spray can be effective against some bears when used properly. If you plan to carry it, be aware that wind, spray distance (usually less than five metres, or 16 ft.), rain and product shelf life can all influence how well it works. Carefully read directions on the can prior to your trip.
Its effectiveness is not guaranteed. Just like when police use pepper spray on humans, it does not work effectively on all subjects.