We caught a small taste of winter for the start to our Saturday visit to the oxymoronic Rocky Mountain Arsenal National Wildlife Refuge, but then the day warmed up nicely.  This extensive 16,000-acre refuge immediately north of Denver has quite a history progressing from native shortgrass prairie to farmland to twenty years of chemical weapons manufacturing (mustard gas, napalm, white phosphorous, lewisite, chlorine gas, and sarin), to twenty years of pesticide manufacturing, to the present wildlife sanctuary.  Briefly, the army purchased the land in 1942; in the early 1960’s chemical weapons manufacturing was halted and pesticide manufacturing commenced; in the 1970’s a National Resource Damage Assessment conducted by the US Fish and Wildlife Service estimated that at least 20,000 ducks had died during a ten-year period and that dead mammals and birds were a regular occurrence; in 1984 it was selected as a Superfund site for cleanup; in 1992 it became a National Wildlife Refuge and cleanup activities were increased; in 2007 bison were introduced; in 2010 the cleanup was considered complete, though soil and water monitoring continues and there are restrictions on well water use, residential development, consumption of fish and game from the arsenal and agricultural use; and in 2015 black-footed ferrets (America’s most endangered mammal) were reintroduced.  A portion of the refuge (1,084 acres) is still managed by the U.S. Army as it still may contain chemical weapons devices and cannot be safely integrated into the wildlife refuge.

Notwithstanding this dire history, and ongoing lawsuits related to groundwater contamination, the Arsenal is a wonderful place to visit with its extensive cottonwood groves, multiple ponds, and wonderfully intact patches of shortgrass prairie.  However, even with all this good habitat, we missed out on several of our common landbirds – no Downy Woodpecker, Black-capped Chickadee, White-breasted Nuthatch, or American Goldfinch.  We even struck out on Bald Eagle.  Otherwise, what we did see were birds that can be expected at this time of year, and in particular we got to sort through a nice variety of ducks all in their breeding plumage.  These will largely be heading north in the next month.  Conversely, we’re at that time of year when shorebirds are starting to show up on their way north, but we only had a few Killdeer.  

Our real highlight of the morning was a single Horned Grebe. These guys occur uncommonly in Colorado during the winter, but as they migrate north March through April, we can see a few more regularly.  It’s a good show because early on they are in their winter plumage – all white and black, but by the time they clear out, a couple of months from now, they will have acquired their striking breeding plumage – a largely rufous body and neck with a black head having a large, bright yellow patch – the horn – swooping back behind the eye.

Rocky Mountain Arsenal NWR
Mar 7, 2026
31 species
12 participants

Canada Goose  32
Northern Shoveler  3
Gadwall  160
American Wigeon  2
Mallard  36
Green-winged Teal  12
Redhead  8
Ring-necked Duck  6
Lesser Scaup  10
Bufflehead  32
Common Goldeneye  18
Hooded Merganser  28
Common Merganser  20
Rock Pigeon (Feral Pigeon)  134
Mourning Dove  3
American Coot  12
Killdeer  13
Ring-billed Gull  60
Horned Grebe  1
Great Blue Heron  1
Red-tailed Hawk  6
Northern Flicker  7
American Kestrel  1
Black-billed Magpie  3
Horned Lark  20
European Starling  15
American Robin  1
House Finch  8
White-crowned Sparrow  3
Western Meadowlark  16
Red-winged Blackbird  34