Often in mid-winter the reservoirs of eastern Colorado can become largely or, in the case of the smaller reservoirs, completely frozen over.  At that time waterfowl tend to congregate in large numbers on the main rivers and creeks.  The South Platte just north of downtown Denver appears to be particularly attractive, perhaps due in part to the warm effluent from Denver’s wastewater treatment plant.  This past Saturday while along a stretch in this vicinity we were treated to two species of geese, fourteen duck species, a few Pied-billed Grebes, a gazillion American Coots, and, finally some Killdeer, Ring-billed Gulls, Double-crested Cormorants, Back-crowned Night-Herons, and Belted Kingfishers.  All of these species present because of the open water providing such a good place to get groceries.

By the time we get into the depth of winter all these ducks with the exception of Ruddy Duck, have already acquired their breeding plumage for the upcoming breeding season.  This is one of the reasons that winter is such a good time for beginning birders.  On the bird list below I’ve given the months in which the male ducks are in breeding plumage.  It definitely simplifies the identification process.  Nonetheless, on Saturday we still found ourselves wrestling with a few identifications.  First, let’s talk about the white-cheeked geese, i.e. Canada and Cackling Geese which until 2004 were thought to be the same species.  As might be surmised these two species look very similar, and it’s a challenge discerning which is which.  The problem is exacerbated by the fact that there are seven subspecies of Canada Geese, four of Cackling Geese, and there is considerable size variation.  Briefly, Canada Geese are larger and have a longer neck, paler breast (most), long sloping forehead, and longer bill; Cackling Geese on the other hand are smaller and have a shorter neck, darker breast, steep (verticle) forehead, and stubby bill.  Easy-peasy, right?  Yes, the extremes are pretty straight forward, but the intermediate subspecies are tricky.  Best of luck in your future goose identifications!

The other species that caused us some consternation was Greater Scaup.  Even the best of looks can cause top-notch birders to leave the ID as scaup species.  We had a female scaup on Saturday that appeared to meet just about all criteria for being a Greater, but I found it hard to be 100% certain.  For starters she was not hanging out with the abundant Lesser Scaup in the area, and she had the following characteristics (as best we were able to determine): a broader longer bill, a striking amount of white behind the bill, broad cheeks (jowls) when viewed from head-on, a rounded head sloping to the rear, a strikingly white crescent at the back of the auricular area, and the eye appearing high and forward in the head (not centered).  Part of my hesitation in being more definite is that we later saw some female Lesser Scaup that had a fair amount of white behind the bill, thus bringing into question that particular characteristic.

Among things learned on this walk was that when you hear a Killdeer perched high in a tree it’s in all likelihood actually a European Starling. Then, a final highlight of the morning was getting to see two adult Bald Eagles perched together atop a huge power pole.

Good birding, Chuck

South Platte at 78th and 64th Ave, Jan 14, 2023
Number of Taxa: 35 (ducks have the months in which males are in breeding plumage)
Number of Participants: 15

12 Cackling Goose 
84 Canada Goose 
209 Northern Shoveler – Dec-May
170 Gadwall – Sept-May
5 American Wigeon – Oct-June
53 Mallard – Oct-May 
27 Northern Pintail – Nov-June
36 Green-winged Teal – Oct-June
5 Ring-necked Duck – Oct-June
1 Greater Scaup – Oct-June
64 Lesser Scaup – Nov-June
21 Bufflehead – Oct-May
91 Common Goldeneye – Oct-June
9 Hooded Merganser – Sept-June
25 Common Merganser – Nov-July
5 Red-breasted Merganser – Nov-May
2 Ruddy Duck – Mar-Aug
3 Pied-billed Grebe
16 Rock Pigeon (Feral Pigeon) 
3 Eurasian Collared-Dove
203 American Coot
4 Killdeer 
75 Ring-billed Gull 
11 Double-crested Cormorant 
5 Black-crowned Night-Heron
1 Northern Harrier
2 Bald Eagle
4 Red-tailed Hawk
3 Belted Kingfisher
1 American Kestrel
4 Black-billed Magpie
6 American Crow
19 European Starling
2 House Finch
4 White-crowned Sparrow
3 Song Sparrow