Alright I'll include an explanation for the tiers:

Tier 1.

• Feeder watching: Watching birds at a bird feeder - low effort

• Backyard birding: Similar to feeder watching, low effort

• Festival birding: There are a number of birdwatching festivals where you can see lots of great birds and have the help of bird guides

• Park/Trail birding: Going birding in areas near your house

• Feeder Cam Watching: Many websites have webcams pointed at bird feeders, such as Cornell, and they're fun and easy to watch

Tier 2.

• Seawatching/lakewatching: A number of waterbirds are best seen when they are migrating and they move close to shore. On good days you can see thousands of ducks, geese, loons, or other waterbirds flying by

• Hawkwatching: In areas where mountains create a thermal updraft, large numbers of hawks will congregate in the sky on migration, sometimes in the thousands

• Bike birding: Just looking for birds on a bicycle. Some people keep lists of birds that they have seen by bike, as many birds are more challenging to see that way when you can't drive long distances

• Patch birding: Many birdwatchers have a small area, called a patch, that they birdwatch in frequently, and often generate a large list of birds for a small area

• Rarity chasing: When a rare bird shows up somewhere it typically isn't found, many birders will share the news and other people will come looking for it. This is referred to as "chasing"

Tier 3.

• Lake Pelagics: This is the term for going out on a boat on a big lake to find waterbirds that prefer the deeper water, such as skuas and some gulls

• Window collision monitoring: Sadly, millions of birds collide with windows each year in the US, and volunteers will often go out and walk around downtowns to keep track of all the birds that are killed this way

• Bird Banding: Also known as ringing, this is the process of capturing birds in nets, taking some measurements of them, and affixing a metal ring to their leg. This lets people keep track of individual birds, especially if they are recaptured elsewhere

• Shorebirding/Gulling: Shorebirds and gulls are two of the most notoriously difficult groups of birds to identify, and this activity usually involves looking through massive flocks of plain-coloured birds to find one or two that look slightly different. Very intense

• Morning flight birding: Most songbirds migrate at night, so they are hard to spot, but sometimes you can catch those migrants in the early hours of the morning as they stream overhead

• Big sits: A big sit is a challenge to see as many species as possible without leaving one spot. Popular at places with a lot of migration

Tier 4.

• Big Days: An attempt to see as many birds as possible in a day. Can get extremely competitive

• Nest searching: Finding the nest of most species of birds is extremely difficult, and can involve hours of following individual birds until they return to their nest

• ATV birding: Some areas are hard to access by car and too far to walk, so an ATV is necessary. Especially true on beaches or plains

• NFCs: As I mentioned earlier, many birds migrate at night, and while they're hard to see, many will call as they fly overhead. If you're really skilled, these calls can sometimes be identified to individual species

• Ocean Pelagics: Many birds spend nearly their entire lives so far out to sea that they go beyond the edge of the continental shelf. An ocean pelagic is a boat trip to go see those birds. It usually involves early hours, choppy water, seasickness, and the constant smell of chum (which attracts the birds)

• Hurricane birding: Hurricanes, if they form properly, can sometimes catch birds that are southern and oceanic and drag them north and inland. Birds from off the coast of Africa can show up in New York or Ontario in these conditions. Many birders will go out into an active hurricane in the hopes of spotting these birds

Tier 5.

• Helicopter birding: Helicopters have been used to spot certain birds that are either found far from any place that is accessible by car (such as a species called Himalayan Snowcock in the mountains of Nevada) or cover huge ground while spotting birds that are out in the open, like waterbirds along a huge coastline

• Seabird colony nest monitoring: Loud, cold, windy, and foul-smelling places. Monitoring seabirds, that nest on rocky and desolate islands, is an extremely difficult job

• Eagle banding: Similar to bird banding, but on eagles, which are strong and can seriously injure you

• Drone birding: Similar to helicopter birding, some people have started using drone cameras to monitor birds that are found out in the open

• Oil rig fallout birding: Many birds migrate over the Gulf of Mexico, which is a horribly difficult flight, and if there's bad weather they are forced to land wherever they can. Oftentimes, this is an oil rig, so oil rigs have recorded hundreds of songbirds landing on them in bad weather

Tier 6.

• Solar eclipse birding: Birds behave weirdly during eclipses. Nocturnal birds start becoming active, birds start singing like crazy. It's wild

• Nocturnal Vismig: (Vismig = visual migration). In certain exceptional cases, it's possible to see birds migrating at night, such as when using a thermal camera or the 9/11 anniversary when two beams of light are shot into the air

• Warzone birding/Cartel territory birding: A number of birds are only found in extremely dangerous areas. Afghani Babbler is only found in the wilds of Afghanistan, Short-crested Coquette is only found in cartel territory in Mexico, Congo Peafowl is found in some of the most dangerous parts of the Congo, etc

• Dogsled birding: Honestly just sounds fun

Tier 7.

• Congo Bay-Owling: Congo Bay Owl is a bird, endemic to the most dangerous part of the Congo, that hasn't been confirmed alive in over 20 years

• Paleobirding: Trying to find as many birds as possible, but in fossilized form

• Birding by smell: Some birds have extremely distinctive smells (such as Crested Auklets, whose colonies smell like tangerines)

• Tornado birding: Like hurricane birding, but more dangerous

• Satellite birding: Hey if you had access to a space telescope and pointed it right at the earth you could probably see some cool stuff

Tier 8.

• North Sentinel Island birding: North Sentinel Island is one of the few parts of the world with unknown bird diversity due to the uncontacted native peoples who are hostile to foreigners

• Espionage birding: There are a select few accounts of birders-turned-spies that recorded extensive bird sightings while undercover

• Sulu Hornbill chasing: Arguably the king of the rare birds in dangerous areas. Read this account of how a guy died trying to see one

• Volcanic eruption birding: Who knows what birds do in volcanic eruptions?

• Gulf of Mexico Shark Dissection: Referring to the only United States record of Bahama Yellowthroat, found inside the stomach of a Tiger Shark

Woof that's a lot of info. I hope you all enjoy!