Tuesday, May 12, 2009

Fickle weather

I guess it goes without saying that the hawk flight predictions here are completely dependent on the accuracy of the weather forecast. Yesterday I thought today was going to be great, but instead it ended up being merely good. There was some SE wind in the morning, but by afternoon this had shifted to E and eventually even NE. Winds also were lighter than forecast, and on those light winds birds got high, for a while even so high that they were barely visible in 10X binoculars.

Tomorrow's forecast is now for less rain than initially thought, and even stronger winds than previously predicted. It'll be an interesting day, for sure. With SE winds 15-25 mph, gusting to around 40 mph (!), you have to wonder how many birds that will dump over the northeastern UP. Think of a giant vacuum cleaner sucking up birds and blowing them our way.

Today's sightings include 5 Turkey Vultures, 9 Bald Eagles, 4 Northern Harriers, 95 Sharp-shinned Hawks, 2 Cooper's Hawks, 2 Northern Goshawks, 1 Red-shouldered Hawk, 218 Broad-winged Hawks, 40 Red-tailed Hawks, 13 Rough-legged Hawks, 1 American Kestrel, 1 Merlin, and 3 Peregrine Falcons.

Let's do a bit more hawk ID workshop. Most readers probably identified the hawk at the top of this post. If you don't know what it is, no worries - I'll walk you through it.

It should be immediately obvious that this is a buteo, not a falcon, harrier, eagle or accipiter. Medium-sized bird, rounded wings, relatively short tail: buteo. We can see part of the left underwing, and on it we can see the beginning of a dark marking on the leading edge of the wing, the so-called patagial bar. Red-tailed Hawk is the only one with this field mark, and all age groups show it, so we really don't need to look for additional field marks. (Most people know about the redtail's 'belly band', but that particular field mark is invisible in this photo.)

Remember from a few days ago, that Rough-legged Hawk with the light panel in the primaries? Most young buteos show this field mark, and our bird today also shows it: observe on the (right) upperwing the contrast between the darker secondaries (i.e. flight feathers in the 'arm' of the wing) and the lighter primaries (i.e. flight feathers in the 'hand' of the wing). Observe also how on the (left) underwing, there is no terminal band on the trailing edge. Both these items - light primary panel and absence of dark trailing edge - indicate a juvenile Red-tailed Hawk. Most people know about the difference in tail color - red for adults, grayish-brown for juveniles - but that is usually not visible on a closed tail from below. But as I've demonstrated here, we don't really need it.

Here's one that's more difficult. If you know at first glance what this is, you're good. If you don't know what this is, then again let's review what is visible on this bird, and see if we can work it out. This bird is also a buteo. Now, based on what I said earlier about that patagial bar, we can rule out Red-tailed Hawk, because all redtails show that while this bird doesn't. We can also eliminate Rough-legged Hawk, for this bird has no carpal patches (i.e. big dark markings on the wrist). Virtually all roughlegs have them, although they can be less obvious on some males, where the carpal patch blends in with the rest of a heavily marked underwing. These underwings are very lightly marked, without a carpal patch, and only a very faint 'hook' on the underwing primary coverts.

It's not a Swainson's Hawk either, for that bird has darker flight feathers.

So, we're left with Broad-winged Hawk and Red-shouldered Hawk, both of which are quite distinctive in the adult plumage. Obviously - no dark trailing edge on the wing - this is a juvenile, and these two species are surprisingly similar in the juvenal plumage.

Matters are further complicated by the fact that the bird is in a glide, with half-folded wings. Both adult and juvenile Red-shouldered Hawks show light crescent-shaped panels in the 'hand' of the wing, but that feature is hard to judge on a bird with folded wings.

This is where subtle differences in shape and plumage start to become relevant. Shape: fairly long tail for a buteo (but note that juvenile buteos have longer tails and slimmer wings than adults do), and fairly slender body. These are both better for redshoulder. The dark throat and the evenly blobby markings on the body are also better for redshoulder, and this is indeed a Red-shouldered Hawk, as the following photo - with spread wings - will confirm:

Now the light crescent is visible in the hand, just where the darker 'fingers' of the hand start. Beware of buteos molting their primaries, which sometimes can create a similar impression of a crescent-shaped lighter panel. Our bird here has just started molting its flight feathers, and two feathers in each wing are missing. Red-shouldered Hawks have 10 primaries, which are usually numbered from the innermost (P1) to the outermost (P10). This bird appears to be molting P1 and P4 in each wing.

Another field mark that works well on distant birds: if you're not sure the bird is a buteo or an accipiter, it is probably a redshoulder. The basic shape is still buteo, but on the 'accipiter end of the spectrum', with a relatively long tail (for a buteo) and a slender body. Broadwing is stockier, and has pointier wings.

No comments:

Post a Comment