When I initially picked mid-November as potentially a good time for catching the front end of the increased presence of winter raptors, specifically Northern Harriers, Bald Eagles, Ferruginous Hawks, Rough-legged Hawks, and Merlins, I anticipated that weather conditions might be slightly wintery. However, the weather for mid-November this year turned out to be exceedingly mild resulting in a bit less action than hoped for. And, while all these species have definitely been in Colorado for several weeks, some appear to be present in lower numbers than we might expect later in the winter. Apparently, as long as there is mild weather here and an absence of snow cover further north facilitating easier rodent predation, then there is reduced impetus for these birds to come rushing south. We did get great looks at Bald Eagles and Ferruginous Hawks, but we struck out on Rough-legged Hawks and Merlins.
Conversely, what was somewhat unexpected was the large number of Northern Harriers we encountered. These slender, long-winged, long-tailed hawks thrive in open tundra, grasslands, weedy fields, and wetlands where they capture small prey while gliding lazily and flapping gently low over the ground. As we noted on Saturday, they have an owl-like facial disc which can be lifted and lowered at will helping, as with owls, to direct the sound of scurrying prey to their ears.
While we know that female raptors are bigger than males (about twenty-five percent bigger in Red-tailed Hawks) Northern Harriers are more extreme with females weighing about thirty-three percent more than males (18 oz vs 12 oz), and the female’s wingspread is about twenty-five percent longer than the male’s. Interestingly, female Harriers, while close to the length of a Red-tail, only weigh half as much because they are such slender birds. And the males can just look downright petite compared with both the females and the Red-tails.
One other interesting aspect of the rather extreme sexual dimorphism in Harriers is the plumage difference between females and males. Females are streaked brown on buff below, with a darker brown dorsal side with some paler mottling. In contrast, males are almost all bright white below with black wingtips and a black trailing edge along the secondary flight feathers. They can have a pale gray hood, and the back and upper wings are almost all gray except for the black wing markings. Juveniles can look similar to females with rich, rufous underparts and an unstreaked chest. We saw all three plumages on Saturday.
Finally, one of the things we did not see, and which is always a nice bonus on these raptor outings, was any dark or intermediate morph buteos (Red-tails, Ferruginous, or Rough-legs). About ninety percent of our buteos (with some exceptions) are of the light morph variety, and ten percent are dark morphs – this is not a “phase,” this is the permanent plumage of these birds, and there are always a few of these around each winter, just to complicate the raptor identification process for us.
I look forward to repeating this outing in a couple of months with the hope of a bit more diversity.
Chuck
112th and the Rocky Mountain Arsenal
Nov 18, 2023
31 species (+1 other taxa)
14 participants
Snow Goose 3
Canada Goose 11
Cackling Goose 60
Cackling/Canada Goose 300
Gadwall 2
Mallard 4
Lesser Scaup 1
Bufflehead 2
Common Goldeneye 4
Rock Pigeon (Feral Pigeon) 20
Mourning Dove 11
Ring-billed Gull 20
American Coot 45
Northern Harrier 24
Bald Eagle 7
Red-tailed Hawk 13
Ferruginous Hawk 4
Hairy Woodpecker 1
Northern Flicker 3
American Kestrel 7
Say’s Phoebe 1
Black-billed Magpie 11
American Crow 25
Horned Lark 100
European Starling 130
House Sparrow 9
House Finch 7
Dark-eyed Junco 7
Dark-eyed Junco (Pink-sided) 1
Song Sparrow 2
American Goldfinch 6
White-crowned Sparrow 18
Western Meadowlark 73
Red-winged Blackbird 1020