Prewitt Reservoir with its extensive woodlands, marshes, ponds, prairies, and large reservoir is rightfully regarded as one of the premier places in northeast Colorado for catching fall migration.  We began this past Saturday by first checking out the inlet canal area.  This artificially created riparian zone of cottonwoods, willows, and Russian olives tends to always have a few specialties.  Usual breeders here include Yellow-billed Cuckoo, Red-headed Woodpecker, eastern Warbling Vireo (which is different in appearance and vocalizations from the western population found around Evergreen), Red-eyed Vireo, Gray Catbird, Brown Thrasher, Yellow-headed Blackbird, Orchard Oriole, Bullock’s Oriole, Baltimore Oriole, and Blue Grosbeak.  However, the only one of these species that we saw on Saturday was Gray Catbird as several of the others have already begun moving south or may have completely left.  Our other riparian highlight was getting to find four warbler species: Common Yellowthroat, Yellow, Townsend’s, and Wilson’s.

By mid-morning we were ready for the mud-trudge out to the edge of the reservoir’s receding water. Supposedly, once the corn is harvested, they will begin to refill Prewitt, but it’s very low presently, and on Saturday we had a bit of hike across the mudflats.  There were several good highlights out there.  First, there were over a thousand ducks on the distant shore that we for the most part couldn’t identify, but it was good to know they were over there.  Then, we had ten shorebird species.  American Avocets are always a crowd pleaser, and any avocet morning is a good morning.  Moving on to those species requiring a bit of work to identify, we enjoyed six Black-bellied Plovers. These are bigger than a Killdeer, being an inch longer and weighing 242% more (3.3 oz versus 8 oz).  Black-bellied distinguishing features in breeding plumage include not only a black chin, breast, and upper belly but also a bright white lower belly and undertail coverts.  They also have a large head with a pale gray cap and a large, thick, blunt, black bill.  Breeding plumage is generally gone by mid-September, so we were lucky to see these striking features.  We also saw two little Semipalmated Plovers which weigh only 1.6 oz.  Among the small plovers, the Semipalmated are distinguished by having a dark brown back, yellow-orange legs, a single black breastband, a black mask extending from in front of the eye to the nape, and a stubby orange and black bill.  They are also as cute as a bug’s ear!

Also, while we were out on the mudflats, we were treated to four swallow species.  These are mostly gone by the third week of September, so we were catching a bit of their last hurrah.  There were lots of Barn Swallows, but the real prize was getting to see several Bank Swallows.  These are our smallest North American swallow weighing 0.02 oz less than a Violet-green Swallow and having a slightly smaller wingspan.  It’s certainly another bird that falls into the “cute” category. Their distinguishing features include an all-white front contrasting sharply with a dark breastband.

Some of other birds seen out by the reservoir along with the tons of Double-crested Cormorants and American White Pelicans were three species of wading birds.  These were Great Blue Heron, Great Egret, and White-faced Ibis.  The ibis’s plumage is always a wonderful treat.  Only in breeding season do we get to see the white face, which is actually a white border surrounding a red face, along with the dark chestnut-maroon undersides and purplish flight feathers.  However, year-round we can make out the metallic green and bronze sheen of the upper wing coverts and back.  Simply an outstandingly beautiful bird!

These annual trips out to Prewitt always prove highly satisfactory.

Chuck

Prewitt Reservoir SWA
Sep 10, 2022

13 Participants
59 species (+2 other taxa)

Canada Goose  18
Blue-winged Teal  7
Northern Shoveler  2
Mallard  4
duck sp.  1000
Pied-billed Grebe  1
Rock Pigeon (Feral Pigeon)  1
Eurasian Collared-Dove  2
Mourning Dove  29
American Coot  1
American Avocet  30
Black-bellied Plover  6
Semipalmated Plover  2
Killdeer  33
Stilt Sandpiper  160
Baird’s Sandpiper  40
Least Sandpiper  8
Long-billed Dowitcher  42
Red-necked Phalarope  12
Lesser Yellowlegs  11
Franklin’s Gull  120
Ring-billed Gull  90
Herring Gull  2
Double-crested Cormorant  90
American White Pelican  170
Great Blue Heron  16
Great Egret  1
White-faced Ibis  26
Osprey  1
Northern Harrier  1
Cooper’s Hawk  1
Red-tailed Hawk  1
Belted Kingfisher  1
Downy Woodpecker  1
Northern Flicker  3
American Kestrel  1
Western Wood-Pewee  3
Blue Jay  18
Northern Rough-winged Swallow  4
Tree Swallow  1
Bank Swallow  8 
Barn Swallow  90
Cliff Swallow  13
White-breasted Nuthatch  2
Blue-gray Gnatcatcher  1
House Wren  12
Gray Catbird  11 
American Robin  3
House Sparrow  3
American Goldfinch  14
Chipping Sparrow  9
Clay-colored Sparrow  1
Spizella sp.  7
Lark Sparrow  3
Song Sparrow  4
Red-winged Blackbird  5
Common Yellowthroat  4
Yellow Warbler  1
Townsend’s Warbler  3
Wilson’s Warbler  12
Lazuli Bunting  2