Chatfield Reservoir (Jefferson/Arapahoe Counties). Kingfisher Bridge, and near the boathouse
The Lockheed Martin Discovery Pavilion Area (Jefferson County) is accessible. Just unload in the parking lot and use the crusher fines trail between the two old stone buildings. There are many species of birds in the immediate area around the buildings: House Wrens, Bullock's Oriole, Say's Phoebe, Yellow-breasted Chat, Yellow Warbler, Swallows, TVs overhead. There is a trail to the NE toward the Platte that heads out from the patio (Pavilion) and goes past the Stucco style vault toilets. The very beginning of it is accessible, with a view of some ponds to the north. The trail beyond that view is probably too much of a challenge unless you have another helper with the chair. To get to the location: C-470 to Wadsworth exit. South on Wadsworth to end. Left onto Waterton Road about 50 yards. Left at Lockheed Martin Discovery Pavilion sign. Park close to trail that heads east between two stone buildings. There is a curb cut there.
Waterton Canyon (Jefferson County) is accessible, but there is about a 1/4 mile piece of trail from the parking lots past the Kassler (Denver Water Board buildings) Center before you get to the beginning of the canyon. The surface is an old road bed with some gravel added. The parking is just beyond the Discovery Pavilion Parking. Best to go at sunrise or late in the day when it is cool and the birds are more active.
The Highline Canal and extensive sidewalk system in Cherry Creek SP (Arapahoe County) are very accessible, offering approaches to various habitats including river, grasslands, wet meadows, cattail marshes, shorelines, and lake.
Bike trails in Summit County, especially the stretch from Frisco west toward Copper Mountain, for mountain birds (hummers, white-crowned sparrows, dippers, juncos, finches, MacGillivrays, Yellow, and Wilson Warblers, etc.). However, these are extremely busy with cyclists on the weekends making birding from them a challenge under any form of travel. An early weekday morning would be far better time to visit these trails.
Wilderness on Wheels (Park County), part way up the east side of Kenosha Pass, along Hwy 285, between Bailey and Kenosha Pass. The boardwalk and trail travel along the riparian corridor of the South Fork of the Platte River. Contact Wilderness on Wheels Foundation, (303)751-3959, for more information.
Pueblo’s Nature Trail (Pueblo County), between the Nature Center and the Dam. Common birds here include: Yellow Warblers, Black-capped Chickadees, W. Wood Peewees, Bullock's Orioles, an Orchard Oriole, Indigo Buntings, Bewick's, Canyon and House Wrens, and Turkey Vultures. Yellow-billed Cuckoos, Canyon Towhees, Downy Woodpeckers, Mississippi Kites, and Red-tailed Hawks are frequently seen/heard. There is a good number of bird species along the Arkansas and the trail is easily accessible for persons in wheelchairs.
The City of Fort Collins (Larimer County) has an extensive, paved, trail system, much of which follows the Poudre River and also goes through several natural areas. This Natural Area system has not only riparian areas but also some upland grasslands. There are information kiosks at several locations, with handouts showing maps of the trail system and also of individual natural areas. If there is any specific interest you may call the Fort Collins Parks and Recreation Department, Natural Areas and Trails, at (970) 221-6360, or the Natural Resources Division at (970) 221-6600.
Wheat Ridge Greenbelt (Jefferson County). Much of it is accessible to wheelchairs and is pretty good birding. There are some places a wheelchair cannot go, but you should be able to see the common summer woodland birds.
Barr Lake (Adams County). The boardwalk near the Nature Center is accessible, and the dirt/gravel road that follows the canal would be navigable if it hasn’t rained recently.