We had great weather for our Saturday visit to the oxymoronic Rocky Mountain Arsenal National Wildlife Refuge.  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.

Despite 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.  Though we did not see a lot of ducks, we did have a good variety (12 species).  The numbers for at least half these species will decline dramatically in the coming weeks as northward duck migration continues.  A definite highlight of the morning was getting to see seven species of shorebirds, including Black-necked Stilts and American Avocets.  From mid-April through mid-May is roughly the peak of shorebird migration in Colorado, and it’s fun to spend some time focusing on this group.  Only two shorebird species tend to be found in Colorado throughout the year, Killdeer and Wilson’s Snipe, and only twelve species breed here.  Beyond these there are another 25 shorebird species that have the possibility of coming through during spring and fall migration.  Some of these are dramatically obvious as to their species identification, many though can be a bit tricky.

Other highlights for the morning included Franklin’s Gull, Snowy Egret, Swainson’s Hawk, Say’s Phoebe, Rock Wren, and American Pipit.  The 13 American Pipits we saw were of interest because this is a rather uncommon species in the winter in Colorado, being largely confined to the edges of ice-free rivers and streams and sometimes around farmyards.  Then, migration kicks in and we can see them spreading into mudflats, recently plowed fields, and prairie dog colonies.  Eventually of course they end up breeding in both arctic and alpine tundra.  Our birds in the Southern Rockies represent the southern-most breeders in all of North America.

Good birding!  Chuck

Rocky Mountain Arsenal,
Apr 16, 2022
54 species

Canada Goose  30
Blue-winged Teal  1
Cinnamon Teal  1
Northern Shoveler  48
Gadwall  20
Mallard  22
Green-winged Teal  17
Canvasback  1
Redhead  3
Lesser Scaup  23
Common Goldeneye  3
Hooded Merganser  11
Ruddy Duck  1
Pied-billed Grebe  1
Rock Pigeon (Feral Pigeon)  3
Mourning Dove  22
American Coot  28
Black-necked Stilt  1
American Avocet  12
Killdeer  14
Wilson’s Snipe  2
Solitary Sandpiper  1
Greater Yellowlegs  6
Lesser Yellowlegs  11 
Franklin’s Gull  14
Ring-billed Gull  45
California Gull  1
Herring Gull  1
Double-crested Cormorant  1
Great Blue Heron  4
Snowy Egret  1
Bald Eagle  1
Swainson’s Hawk  1
Red-tailed Hawk  6
Great Horned Owl  1
Belted Kingfisher  1
Downy Woodpecker  2
Northern Flicker  1
American Kestrel  6
Say’s Phoebe  3
Black-billed Magpie  7
American Crow  3
Horned Lark  1
Tree Swallow  10
Barn Swallow  14
Rock Wren  1
European Starling  28
American Robin  18
American Pipit  13
White-crowned Sparrow  1
Song Sparrow  5
Western Meadowlark  23
Red-winged Blackbird  40
Common Grackle  7