Denver is one of the best birding destinations in North America. Within a 40 mile span, east to west, one can explore five life zones, with elevations ranging from 5000 to 14,250 feet. Novice birders and those visiting the area want to know where to go to find a wide variety of western species. The following recommendations are based on my experience over the last thirty years; the bird lists are neither complete nor grouped by season. Regardless of where you go, birding is always most productive during the morning and late daylight hours; warm season visits to higher elevations should be planned before early afternoon, when dangerous thunderstorms often develop.
To find birds of the Colorado Piedmont, I recommend Chatfield State Park, southwest of Denver, Barr Lake State Park, northeast of Denver and Sawhill Ponds Nature Preserve, east of Boulder; these areas are excellent sites to observe American white pelicans, Swainson's hawks, cinnamon teal, western grebes and migrant waterfowl and shorebirds. To explore the Foothill Shrublands, Roxborough State Park, southwest of Denver, and Red Rocks Park, west of Denver, are suggested; golden eagles, canyon and rock wrens, scrub jays, lazuli buntings, black-headed grosbeaks, green-tailed towhees, white-throated swifts, Say's phoebes, Virginia's warblers and lesser goldfinches are found in this zone. Montane Forests are easily accessed at Mt. Falcon Park, west of Denver, and Boulder Mountain Parks, west of Boulder; there you may find mountain and western bluebirds, pygmy nuthatches, Townsend's solitaires, Steller's jays, Williamson's sapsuckers, mountain chickadees, northern pygmy owls, blue grouse, broad-tailed hummingbirds, violet-green swallows, red crossbills, western tanagers and MacGillivray's warblers.
Subalpine Forest and the Alpine Tundra zones are best explored along Colorado 103, between Evergreen Parkway and Idaho Springs (on I-70) and the Guanella Pass Road, between Georgetown (on I-70) and Grant (on US 285); the Mt. Evans toll road leads higher from Colorado 103 (at Echo Lake) and is generally open from June to September (snow conditions permitting). Subalpine birds include northern goshawks, gray jays, Clark's nutcrackers, pine grosbeaks, rosy finches, American dippers and three-toed woodpeckers. Timberline and alpine tundra species include white-tailed ptarmigan, American pipits, Wilson's warblers, white-crowned sparrows, brown-capped rosy finches, Cassin's finches and mountain bluebirds.