Listing Through Life

stercorarius (of dung, a reference to the skuas’ pursuit of other seabirds until they disgorge their food, the disgorged food once thought to be excrement) parasiticus (parasitic)

Tuesday, September 11, 2018 — 5:58 pm

Chatfield State Park, Colorado

Eighteen years ago, a Long-tailed Jaeger made an appearance in central Illinois. I drove four hours down and four hours back to see it.

Over the past few days, two of them have been seen regularly, along with a Parasitic Jaeger, at Chatfield Reservoir. As a Sabine’s Gull was also being seen there, that made two potential lifers and a second-ever sighting. I took off work an hour early and headed up.

Chatfield Reservoir is a large man-made lake created to supply Denver with water. It’s shaped like an upside-down “J” with the larger arm to the west. I had no idea where to look for the birds. I walked along the large peninsula that splits the lake, scanning constantly for large, dark gull-like birds. I found the Sabine’s Gull (previous post), but I  saw nothing that looked at all like a jaeger. I made my way back past the south boat ramp,to a narrow spit that cuts out into the lake. I still wasn’t seeing anything, and had just about determined to call it a day when another birder wandered up.

The first thing he said was that a Merlin was on the other side of a tree 25 feet away from me. I had never seen a Merlin in Colorado, or anywhere else for a long time, so this was good news. But I played it cool and casually wandered to where I could see it and get some photos.

A few minutes later, Frank (we introduced ourselves at some point) spotted the jaegers flying low over the water on the far side of the reservoir.  For the next half hour, I watched them flying back and forth across the face of the dam. They never came close to where I was standing. The birds were very close in color to the rocks on the dam wall, so they often disappeared. And then, suddenly, I’d find them again. They landed and swam from time to time, but a lot of the time they were chasing gulls, presumably to steal fish from them.

Because that’s what jaegers do. They are essentially the hawks of the sea. I saw one flying  in full-out in pursuit of a gull, and it caught the slower bird in no time flat. Sometimes, one of the smaller jaegers chased the larger one.

Which brings me to the issue of identification. This gets a little tricky. All three birds were immatures, so none of them had the distinctive tail feathers of adults. They were obviously jaegers, darker than the gulls, with flashing white patches on their primaries. Their buoyant, aggressive flight and behavior of chasing gulls is also typical of jaegers.

Two of them were smaller and slighter, with pale heads. These were the Long-tailed Jaegers. The third bird was much darker, with an almost black head and dark brown body that seemed, from a distance. to have some cinnamon tones in the good, late-afternoon light.

As I looked, Frank described the field marks of the two species. I couldn’t see much of what he was talking about, but I could see that the darker bird was just a little bit bulkier and larger than the smaller ones. The difference was apparent when they were swimming next to each other or when they were soaring and banking at the same time.

So how do I rule out Pomarine Jaeger, the third species which looks very much like the Parasitic in immature plumage? How do I justify adding Parasitic to my list when I only saw it at a great distance? Frank had been out in a boat with other birders the day before. He had close-up photos and was showing these to me on his phone as we watched. The deciding factor for me was the comparative sizes:

Long-tailed — length 15″, wingspan 38″
Parasitic — length 16.5″, wingspan 42″
Pomarine — 18.5″, wingspan 48″

The dark jaeger I saw was a little larger, but certainly not 10-inches of wingspan larger, than the smaller birds. I know that isn’t much to go on, and I hope to get back up there this weekend and get a better view. But Frank confirmed everything I was seeing.

I took a little bit of video as the Parasitic Jaeger floated on the water and then took off. It was a very long way away, so these photos from the video show nothing more than a vaguely gull-like bird with dark plumage and white patches on its primaries.

xema (a made-up word with no meaning) sabini (named for Joseph Sabine, English naturalist)

Tuesday, September 11, 2018 — 4:12 pm

Chatfield State Park, Colorado

Sabine’s Gulls breed high in the tundra along the Alaskan and Canadian coast of the Arctic Ocean. Most of them migrate along the Pacific coast, but every fall, a few show up on the larger reservoirs in central Colorado. I knew I would get one sooner or later.

One was found on Chatfield Reservoir earlier this week. I was planning on heading up this weekend, but then three jaegers — two Long-tailed and a Parasitic — were spotted at the same place, and I couldn’t let two lifers and a second-ever sighting go by.

I arrived at Chatfield State Park a little before 4:00 pm. I had no idea where any of the birds were being sighted, so I just started walking the shore, stopping frequently to scan the large lake with my binoculars and spotting scope. It wasn’t too long before I spotted a black-headed gull swimming in the center of the southwest arm of the lake.

I set up my scope and watched. Most of the time, the gull was swimming, looking back and forth alertly with its head held high. Occasionally it would flutter forward somewhere between three and 15 feet and then land again. I wasn’t close enough to see what it was chasing, if that’s what it was doing.

But I was close enough to see the diagnostic “M” wing pattern. As it’s the only gull with a black head and that pattern, I had my bird.

The photos are all stills from a video I shot by holding my phone up to my scope.

I continued down the shore and got a little closer to the bird, but it also put it in a direct line with the sun. At this point, it was swimming away from me, and I didn’t see it flutter again. When it turned its head, I was able on one or two occasions to make out the yellow tip on its black bill.

Later, on the other side of the lake, I spotted it, or another one, swimming along the face of the dam.

I chatted briefly with two other birders. I was pronouncing the name of the gull as SAY-beans. They said the first syllable with the “a” as in sad and the second syllable as bin, so SA-bins. This got me wondering, so I googled it and discovered that it’s supposed to be pronounced SA (as in sad)-beans. So we were both half right.

vireo (small green bird) cassinii (named for John Cassin, American ornithologist)

Monday, September 3, 2018 — 10:10 am

El Paso County, Colorado — Aiken Canyon Preserve

About 20 years ago, the former Solitary Vireo was split into three species. The eastern form, which I’ve seen many times, is called the Blue-headed Vireo. The southwestern form, which nests in Colorado, is now the Plumbeous Vireo. I’ve spotted several of them since we moved out here. The third form, Cassin’s Vireo, nests in the northwest and migrates through Colorado. It’s fairly rare in the spring, but much more common for a couple weeks in the fall. I’ve never seen one.

The plummage differences between the three species make things challenging. All have bold white spectacles and obvious wing bars. The Plumbeous is almost all gray, but with a touch of yellowish on the flanks in the fall. Cassin’s has more yellow on the flanks and sides and a wash of green on the back and wings.

On Sunday evening, I found a “Solitary” vireo along Monument Creek and got excited for a minute. But as I followed the bird through the scrub oak, I saw that it only had a bit of yellow on the flanks and was otherwise gray.

I went out again on Labor Day Monday morning, this time to Aiken Canyon Preserve. It was a cool, overcast morning, and I had the place to myself. I hadn’t gone far before it began raining hard. I took what shelter I could find in a clump of scrub oak, but was soon very wet. When the rain stopped 15 minutes later, I decided to continue instead of heading back to the car.

I climbed up into a rocky canyon with ponderosa pines and an understory of scrub oak and came upon a mixed flock of birds. Most of them were Pygmy Nuthatches, but I also saw Mountain Chickadees, a Wilson’s Warbler, a Yellow-rumped Warbler, three Western Wood-Pewees, and a “Solitary” vireo. This one had pale yellow all along its sides and flanks. It’s head was light gray, and its back had a greenish wash.

After getting a good look, I pulled out my camera and attempted to get a photo. It was moving fairly quickly through the lower branches of a pine. I lost sight of it, but found it again about two minutes later. Again I got good looks at the greenish back that contrasted with the gray head and the yellow sides. It flicked its wings a time or two while I was watching — I think I caught it mid-flick in a couple of the photos.

It was still a very gray day, and the bird was back-lit against the sky, so the color doesn’t really come through in the photos, although I can get a hint of the yellow sides.

It hopped from the pines into some scrub oak, and I lost it. I hung around for another 10 minutes, but didn’t spot it again. I suppose there were about four minutes from when I first saw it until it disappeared.