112th Ave & Barr Lake State Park, Mar 2 – with Chuck Aid

The goal for the day was winter raptors, and the area between Barr Lake and DIA is one of the best I know of that is relatively close to the Denver metro area.  So, how do we know where we might find raptors?  Well, a key place to start is by looking at where they get their groceries. Let’s look at some of our local raptors a bit more closely.

Bald Eagle (c) Bill Schmoker

Bald Eagles eat fish almost exclusively, so it makes sense that Barr Lake always has a fair number of wintering Bald Eagles. However, if a large prairie dog town is in the vicinity of their fish market, then they may bop over there to check things out – possibly, to catch an unaware “dog,” but what can be even easier is to steal one from someone else who already did all the work, what’s known as kleptoparasitism.

Golden Eagles will eat a variety of mammals, and they will cover large distances when foraging, but perhaps because they prefer their overnight canyon roosts in the foothills they tend not to be seen regularly too far out on the eastern plains.

Ferruginous Hawk (c) Bill Schmoker

Ferruginous Hawks focus primarily on ground squirrels and prairie dogs.  This is our largest Buteo (soaring hawk), weighing up to 3.5 lbs.  In contrast, a Red-tailed Hawk weighs only 2.4 lbs.  In looking closely you’ll notice the Ferruginous’ huge bill, accentuated by its long “gape” – the portion of the mouth extending back into the head, allowing for a larger mouth opening.  Also, notice its large feet compared to other Buteos.

 

 

Ferruginous Hawk (c) Bill Schmoker

Red-tails go for a bit smaller prey, primarily voles, mice, rats, and cottontails.  Prairie Falcons in the winter focus mainly on Horned Larks and Western Meadowlarks, and Northern Harriers and American Kestrels on voles.  As for Rough-legged Hawks, the third of our three Buteos being addressed here, they weigh only slightly less than Red-tails, but they have a smaller bill and smaller feet, and their primary winter prey is also voles.

So, back to our question about where to find raptors in the winter.  We need to start by determining which of the prey “grocery stores” might be the easiest for us to find, and the answer, generally, is prairie dogs.

Rough-legged Hawk (c) Rob Raker

Black-tailed Prairie Dogs have several extensive towns in the area we chose to visit on Saturday.  However, while these dogs don’t hibernate, they do tend to snuggle down in their burrows when the weather gets a bit crisp, as it was on Saturday morning as a cold-front descended on us.  As a result, we had no dogs, and therefore very few raptors.  The potential dramas that can unfold in this area along 112thAve are legendary, with numerous Ferruginous Hawks, Bald Eagles, Red-tails, an occasional Golden Eagle, and an occasional Rough-leg attempting to steal a dead prairie dog from one of the Ferruginous Hawks that has successfully made a kill.  We struck out this time, except for the numerous Bald Eagles and a solitary Great Horned Owl, we saw at Barr Lake, but we will keep this same itinerary on the books for a future outing.

White-crowned Sparrow – Gambel’s (c) Bill Schmoker

On a final note, let’s talk briefly about White-crowned Sparrows (Zonotrichia leucophrys).  We have two sub-species that predominate in Colorado.  The ones we saw on Saturday had orange bills, and white lores (the area between the eye and the bill).  These are the Z. l. gambelii subspecies.  The birds that we’ll see nesting up in the krumholtz next summer will have pinkish bills and black lores – the Z. l. oriantha subspecies.  Both can be seen during migration.  There will be a test next time I see you, so study up!

Good birding!  Chuck

112thBarr Lake SP,
24 species (+2 other taxa)
Canada Goose  120
Common Merganser  40
Rock Pigeon (Feral Pigeon)  2
Eurasian Collared-Dove  5
Ring-billed Gull  7
Bald Eagle  27
Red-tailed Hawk  5
Ferruginous Hawk  2
Great Horned Owl  1
Northern Flicker  2
American Kestrel  2
Blue Jay  3
Black-billed Magpie  9
American Crow  6
Black-capped Chickadee  8
American Robin  18
European Starling  7
House Finch  5
American Goldfinch  1
Dark-eyed Junco (Slate-colored)  3
Dark-eyed Junco (Oregon)  4
Dark-eyed Junco (Pink-sided)  2
White-crowned Sparrow (Gambel’s)  9
Western Meadowlark  2
Red-winged Blackbird  37
House Sparrow  17

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