For this raptor outing we checked out an area just west of DIA (88th to 112th), and then made our way on further east to Prospect Reservoir. The weather was mild and sunny, there was no snow anywhere, and Prospect Reservoir was low and completely frozen.
One of our first stops was at a new access point to the north side of the Rocky Mountain Arsenal at Chambers and 96th Ave. The highlight here was getting to see four Northern Harriers swooping down and around a juvenile Bald Eagle, which was on the ground surrounded by prairie dogs. There are often attempts at kleptoparasitism (food stealing) among the buteos (Red-tailed, Ferruginous, and Rough-legged Hawks) and the eagles (Bald and Golden), but Northern Harriers seem to do this less often. They will sometimes engage in this behavior with Short-eared Owls, but I can’t recall seeing them swooping around an eagle like this. It didn’t seem excessively aggressive and was of short duration and apparently unsuccessful, but still an interesting behavior to observe. As seems to be the case for this winter, we saw numerous Harriers and were able to distinguish the three main plumages of females, males, and juveniles. Females – streaked brown on buff below, with a darker brown dorsal side with some paler mottling; males – smaller and almost all bright white below with black wingtips and a black trailing edge along the secondary flight feathers; and juveniles – similar to females with rich, rufous underparts and an unstreaked chest.
As usual Red-tailed Hawks were the dominant raptor of the morning. All of the birds we saw were light-morph, western Red-tails. This is the plumage that we mostly expect to see in the shortgrass prairie of eastern Colorado, however, Red-tails (as do the other buteos – broad-winged, soaring hawks) have a wide variety of looks based on age, subspecies, and color-morph. This variety of plumages can be off-putting, in distinguishing Red-tails from other buteos which is why it’s helpful to become more aware of the general shape and behavior of the different buteos. Fortunately, Red-tails have the most distinctly different silhouette with their rounded, almost truncated wing tips, and their “bulging secondaries.” These secondary flight feathers are the ones closer to the body and in Red-tails make the wing appear broader. Generally, the wings of the other buteos are proportionally more slender and pointed.
We were fortunate to get a brief look at a Merlin. The main subspecies we have in our part of North America is the pale colored Prairie Merlin. There are two other North American subspecies the Taiga (Boreal) and the Black (Pacific Northwest) which are both darker, and which are seen rarely in Colorado. There’s an interesting pattern seen in these color differences which relates to an ecological principal known as Gloger’s Rule – that is that species tend to be darker in humid regions and paler in arid regions.
Eastern Colorado has been identified as part of the core winter range for Rough-legged Hawks, but for whatever reason this has not turned out to be a great year for them and we failed to find any. For the most part they tend to arrive around mid-December, and then they are already starting to make their way northward by late February to breed in the arctic tundra.
Good birding,
Chuck
96th and 112th
Jan 27, 2024
25 species
12 participants
Cackling Goose 8
Canada Goose 4
Common Merganser 3
Rock Pigeon (Feral Pigeon) 10
Eurasian Collared-Dove 4
Mourning Dove 3
Northern Harrier 15
Red-tailed Hawk 18
Ferruginous Hawk 2
Northern Flicker 10
American Kestrel 10
Merlin (Prairie) 1
Blue Jay 1
Black-billed Magpie 14
American Crow 1
Horned Lark 300
European Starling 2000
American Robin 3
House Sparrow 40
American Goldfinch 1
White-crowned Sparrow 1
Song Sparrow 1
Western Meadowlark 70
Red-winged Blackbird 2000