Sunday, April 27, 2014

Another Day at Balcones Canyonlands NWR

Today, while Danielle attended a conference, I went back to Balcones Canyonlands NWR, where we had participated in a tour yesterday. I was looking forward to some solo birding at my own, slower pace.

Doeskin Ranch - My first stop was to return to Doeskin Ranch where we had found so many different birds near the parking lot ... OK, the guides found them and I just said "where?"  I arrived at 10:00, a bit late for birding but just in time for the sun to peep out after a morning of light drizzle. My first bird was a Bewick's Wren singing solo from the top of a short tree near the parking lot. This is probably the same one I saw yesterday.

Bewick's Wren - ISO-400, 400mm, f/16, 1/250
A number of Lark Sparrows were also singing from low bushes in small groups and a trio of Scissor-tailed Flycatchers chased each other from tree to tree.

I wandered down to the large live oak tree behind the restrooms and spent a half hour trying to get a good view of this flycatcher and determine what it was. I did not hear the call to distinguish it, so, based on the very pale coloration, low contrast tertial edges, and whitish throat, I decided it was an Ash-throated Flycatcher instead of the more colorful Great Crested Flycatcher.

Ash-throated Flycatcher - ISO-400, 400mm, f/6.3, 1/800
After I finished lurking around the parking area, I headed down the trail and ran into this Lark Sparrow foraging along the side of the path in the late morning sun. With its head extended and its feather down flat, it looked much more emaciated than the ones I saw in the bushes earlier. I let it approach me within a few feet before it figured out I was there and flew away.

Lark Sparrow - ISO-400, 400mm, f/5.6, 1/2000
Past the creek, in the middle of a grassy field, I crossed through a copse of large live oak trees with a dense undercover of shin oak. The trees were alive with the sound of songbirds, but I could not identify them nor catch a glimpse of any birds at all. This is pretty much the theme of my birding ... I need to get better at recognizing bird song.

Continuing up the trail towards the ridge, I came upon this Rufous-crowned Sparrow perched alone low to the ground. It eyed me warily and flew off as I approached further. I assume that it is molting ... or else sporting a coquettish primary feather.

Rufous-crowned Sparrow - ISO-400, 400mm, f/5.6, 1/400s (EC+0.3)
After climbing the switchbacks to the top of the ridge, I stopped at a bench and had some lunch. As I finished, I caught the notes of a Golden-cheeked Warbler. After yesterday's tour, my ears are now attuned to the buzz buzz buzz buzz laaazzzy song of that warbler. I grabbed the camera gear and went further up the trail. I could hear it in the trees below me but saw no sign of it. It stopped calling and then, a bit later, I heard it above me. I spent the next hour going up and down the trail, stopping at different spots hoping to see something, a bit like following a will-o'-the-wisp.

Up on the ridge, I saw some White-crowned Sparrows resting in the bushes and caught sight of a jay darting between the cedar trees. A Blue Jay, I believe, based on the call. The heat was too much up on the ridge, so I headed back down.

I stopped again at the copse of oak trees for a more thorough investigation of the birds therein. I saw and heard a Northern Cardinal but the other predominant song I did not recognize. There seems to be no good way to search a bird guide based on song patterns, unlike appearance. I caught a glimpse of an olive green bird and wondered if I was looking for a warbler. Later, as I was watching another Bewick's Wren, I caught a glimpse of a male Painted Bunting darting through the underbrush. I checked the song on my iBird app and found it to be the source of all of the bird songs I was hearing. Probably the olive green bird was a female Painted Bunting. Unfortunately, knowing what I was looking for did not help me see them, as they mostly darted around in the shin oak undergrowth. In all, I think I spent an hour in the copse.

Warbler Vista - At about 15:00, I gave up due to the heat. After a half-hour driving in the air-conditioned car, I felt better and decided to stop-in at the Warbler Vista area, the other main public trail system in Balcones Canyonlands NWR.

Walking down the Cactus Rocks trail, I soon started hearing more Golden-cheeked Warblers. The layout of the trail below the ridge made it much easier to spot them than it had been in at Doeskin Ranch, and I soon found one visually near trail marker 5 as it scampered about the branches foraging.

Golden-cheeked Warbler - ISO-400, 400mm, f/5.6, 1/2500s (EC+0.3)
Golden-cheeked Warbler - ISO-400, 400mm, f/5.6, 1/200s (EC+0.3)
At one point it popped back into view holding this big fat caterpillar in its beak. The guide yesterday mentioned that the new leaves on the live oak trees that come out in late April provide additional food for such insects. Seeing a bird with one put the importance of this food source into perspective.

Golden-cheeked Warbler - ISO-400, 400mm, f/5.6, 1/500s (EC+1)
As I watched, I was astounded to see the warbler flip its head repeatedly, smacking the caterpillar on the branch, just like a Kingfisher. I guess the caterpillar was too big and wriggly to go down without a beating. This shot shows the caterpillar smacking in progress.

Golden-cheeked Warbler - ISO-400, 400mm, f/5.6, 1/500s (EC+1)
I continued down the trail and heard several more warblers, catching a glimpse of a second one around trail-marker 10.  As I followed it in the binoculars, it approached a nest located about 30 feet downhill from the trail. This was a stroke of luck, as I would never have noticed the nest myself, as it was hard to see clearly from the trail - I never found a spot with a clear camera view. Naturally, I did nothing so foolish as to leave the trail and try to approach the nest!

On the tour yesterday, our guide had described how the Golden-cheeked Warbler makes its nest from strips of Ashe Juniper bark that it binds together with spiderwebs. Here before me was the finished product in the crook between high branches of a live oak tree. It looked pretty sturdy.

Well, at this point, any thought of continuing the hike was forgotten and I sat down to watch the nest. Most of the time, one bird stayed in the nest rearranging twigs. I assume this was the female as our guide indicated that the female does all of the nest building. From my angle it was hard to be sure, but I thought that at one point the nest was left empty.

The highlight of the nest watching, captured below, was seeing the male bring back a small caterpillar for its mate. Though she appears to be anticipating a bite, I did not actually see her take the caterpillar. She ducked down and the male stuck its head into the nest out of view. No indication of chicks at this point though.

Golden-cheeked Warblers on Nest- ISO-400, 400mm, f/5.6, 1/800s  (EC+0.3)
It was great to see the warblers again. I hope to finally see the Black-capped Vireo sometime this season as well.

Saturday, April 26, 2014

Balcones Songbird Festival

This morning, Danielle and I went to the Balcones Songbird Festival at the Balcones Canyonlands NWR. It was another heavily overcast morning. We visited a number of areas of the refuge; see the Balcones Canyonlands NWR Wildlife Watching and Nature Trails page for maps and information.

We went on a walking tour called "The Endangered Ones" led by Bill Reiner and John Chenoweth, with ten other guests. After meeting at the refuge headquarters, we were first taken by van to a portion of the refuge near the Bar-K airport, close to the Warbler Vista public use area. The location we visited is normally closed to visitors. It is heavy in old growth Ashe juniper, live oak, and red oak, ideal habit for the endangered Golden-cheeked Warbler. Thanks to the excellent audio identification skills of the tour leaders, we soon saw one of these birds. The male warblers stake out a territory, so there were not exactly flocks of them!

Below is the one Golden-cheeked Warbler we were able to see clearly, though we heard several others. It is perching in an Ashe juniper or "mountain cedar," upon which the species depends for nesting material. Habitat loss is the primary cause for the endangered status of these birds, as they nest only in Central Texas, where the trees were historically abundant. When we first got on site, I spotted a Black-and-white Warbler nearby, as well.

Golden-cheeked Warbler - SX-50 at full zoom, f/5, 1/60s, ISO-100

Golden-cheeked Warbler - EF 100-400mm f/4.5-4.6 at 400mm, f/5.6, 1/250s, ISO-800
Golden-cheeked Warbler - EF 100-400mm f/4.5-4.6 at 400mm, f/5.6, 1/250s, ISO-800
Golden-cheeked Warbler - EF 100-400mm f/4.5-4.6 at 400mm, f/5.6, 1/200s, ISO-800
Golden-cheeked Warbler - EF 100-400mm f/4.5-4.6 at 400mm, f/5.6, 1/250s, ISO-800
We think we saw the same male later in a more distant oak tree.

Our next stop was the Doeskin Ranch parking lot in the northern part of the refuge. This is an area normally accessible to the public during daylight hours. Officially a restroom break, this location yielded many varied birds as our guides identified and pointed out a number of species in rapid succession.

Our final stop was at the Shin Oak Observation Deck, also in the northern part of the refuge. As part of the tour, we were able to enter the refuge past the observation deck (normally not allowed) in search of the Black-capped Vireo, the second endangered species for which the refuge was established. We were able to hear several of these calling from within the low, bushy shin oak trees that dominate the open landscape in this section of the refuge and which serve as a primary habitat for these birds. However, we had no luck in seeing one visually, though we got a brief glimpse of a White-eyed Vireo.

Our guides claimed to have identified over 50 species, most by sound, over the five hours of the tour. Personally, I think I can claim the following:
  • CANW - Canyon Wren - HQ - Nesting in the HQ building!
  • BAWW - Black-and-white Warbler - Bar-K - I found this one myself, winning the prize for the first bird of the tour
  • GCWA - Golden-cheeked Warbler - Bar-K
  • MIKI - Mississippi Kite - Bar-K - a small kettle migrating above (identification by guides)
  • CCSP - Clay-colored Sparrow - Doeskin Ranch
  • LASP - Lark Sparrow - Doeskin Ranch
  • BEWR - Bewick's Wren - Doeskin Ranch
  • BLGR - Blue Grosbeak - Doeskin Ranch
  • STFL - Scissor-tailed Flycatcher - Doeskin Ranch
  • OROR - Orchard Oriole - Doeskin Ranch
  • BCTI - Black-crested Titmouse - Bar-K, Shin Oak
  • CACH - Carolina Chickadee - Shin Oak
  • SUTA - Summer Tanager - Shin Oak
  • NAWA - Nashville Warbler - Shin Oak
  • WCSP - White-crowned Sparrow - Shin Oak- a dozen of these
  • SPTO - Spotted Towhee - Shin Oak - flying between trees at a distance
  • NOHA - Northern Harrier - Shin Oak - apparently late in season for these
  • WEVI - White-eyed Vireo - Shin Oak - quick glimpse
  • BCVI - Black-capped Vireo - Shin Oak - only heard (identification by guides, confirmed by recording)
  • PABU - Painted Bunting - Bar-K, Doeskin Ranch, Shin Oak (best view)
  • TUVU - Turkey Vulture - Everywhere, as usual
Thanks to our tour leaders for a very informative morning. Not only did we see or hear a large number of birds in one session, a record for us, we also learned a lot about the refuge and its management. We learned about the capture and banding of the warblers. We learned more about the much maligned Ashe juniper and its relationship to the warblers. We also learned to identify a number of plant species. We look forward to attending next year's event!  Tomorrow, I plan to go back and revisit some of the spots at my leisure.

Bill Reiner - Tour leader

Sunday, April 20, 2014

Image Scale of 400mm Lenses with Kenko 1.4x

This post shows some tests of the "reach" of a Canon 60D using a combination of a 400mm lens and a 1.4x extender compared to that of a SX-50 HS super-zoom camera. Note that the focal lengths printed on the lenses need to be interpreted correctly and cannot simply be compared. First, the values printed on DSLR lenses are approximate;  no company is going to market a 396.45mm lens. Second, on non-DSLR lenses, the printed focal length typically refers to the size lens which, when fitted to a full framed DSLR (35mm sensor), would give the same field of view.

Since the focal length, image aspect ratio, sensor size, and number of mega-pixels all differ between the two systems, I needed a meaningful basis of comparison. Since my primary application is birding, where images are almost always cropped, the field of view is not relevant. What is important is the number of pixels "on the bird," or resolution of the image. In astrophotography, this is called the "image scale" and measures how much of the target is covered by one pixel. Thus, the question I want to answer is:
What lens would I need to use with my DSLR to give the same reach as the SX-50 HS?
To test the effective reach empirically, I mounted the cameras on a tripod and placed a target about 25 feet away. I took an image with each configuration and imported them into Photoshop as separate layers. This aligned the images based on matching pixel size. Since the SX-50 has fewer pixels on its 4000 x 3000 sensor, its image frame, shown as a green rectangle, is smaller than that of the 5184 x 3456 sensor of the Canon 60D, shown as a purple rectangle. To measure relative resolution between any two images, I used the Photoshop measuring rule tool to determine the distance in pixels between two well defined points in the target image. For a given camera, this pixel distance varies linearly with the focal length.

Here are the three test images:

Canon 60D, EF 400mm f/5.6L with Kenko 1.4x MC4 extender 
Canon 60D, EF 100-400mm f/4.5-5.6L with Kenko 1.4x MC4 extender
Canon SX-50 @ 1200mm.
The first result is that the focal length of the two DSLR lenses differ by about 5%; neither is likely exactly 400mm. However, if we assume for comparison that the EF 400mm f/5.6L prime lens is actually 400mm, then the EF 100-400mm f/4.5-5.6L zoom lens fully extended would be 380mm. With the extender attached, the prime lens would be 560mm and the zoom lens 532mm.

The second result is that the image of the SX-50 HS has about 10% less resolution (is more zoomed out) than the Canon 60D - EF 400mm f/5.6L - Kenko 1.4x combination. So again, if the prime lens is 400mm, the image produced by the SX-50 HS has a resolution equivalent to the Canon 60D with a 504mm lens attached or a 360mm lens withna 1.4x extender. Thus, using this camera, either 400mm lens with an extender gives more reach than the SX-50 HS.

Of course, results will differ for other DSLR cameras, including those with APC-C sensors having more or less than the 18 mega-pixels of the Canon 60D. For example, our Canon 450D has an APS-C sensor with 4272 x 2848 pixels. Each pixel is therefore 21% larger. Using this camera, the SX-50 HS would have a resolution equivalent to using a 612mm lens or a 437mm lens with a 1.4x extender. So, in contrast, using this camera, either 400mm lens with an extender gives less reach than the SX-50 HS.

So, in answer to my question, the reach of SX-50 HS is equivalent to either:
  • 20.2 mega-pixel APS-C with 480mm lens ( 343mm lens with 1.4x )
  • 18.0 mega-pixel APS-C with 504mm lens ( 360mm lens with 1.4x )
  • 12.0 mega-pixel APS-C with 612mm lens ( 437mm lens with 1.4x )
Note on Auto-Focus - On both the Canon 60Da and the Canon 450D, auto-focus worked reasonably quickly on either 400mm f/5.6 lens when combined with the Kenko 1.4x MC4, despite the fact that the resulting f/8 aperture is not officially supported by the phase-based auto-focus circuitry. Though it works, I found the auto-focus to be picky about the target and lighting conditions. In a poor contrast target, it would hunt and fail to lock-on focus more often than the naken lens. Contrast-based focusing, i.e. LiveView Focus, should not be affected ... but is limited to non-moving tripod targets. Would be fine on the Llano eagle nest, for example.

Saturday, April 19, 2014

Image Quality of Canon EF 100-400mm f/4.5-5.6L

This post shows a quick comparison of the image quality of our Canon EF 100-400mm f/4.5-5.6L zoom lens in comparison with our Canon EF 400mm f/5.6L prime lens which is somewhat of a gold standard for resolution and images free of chromatic aberration.

To perform the test, I mounted a scanner-bed test target on the wall and mounted the lenses on a tripod. Images were taken with a Canon 60Da using center-point AF and mirror lockup to ensure best focus. I performed a series of tests at f/5.6, f/8, and f/11.  Both lenses worked well fully open and didn't improve significantly in either resolution or CA as the lens is stopped down.

Here is a pixel-peeping comparison of the image at the center of the frames:

Canon EF 400mm f/5.6L - Center frame at 400mm, f/5.6
Canon EF 100-400mm f/4.5-5.6L - Center frame at 400mm, f/5.6
... and in the upper right corner of the frame:

Canon EF 400mm f/5.6L - Upper right corner at 400mm, f/5.6
Canon EF 100-400mm f/4.5-5.6L - Upper right corner at 400mm, f/5.6
As expected, the prime lens wins in contrast, resolution, and color-free image. However, I am pleasantly surprised by how well the zoom lens is doing. At 100mm and 200mm, the test results look better than the 70-200mm f/4L lens which I have been using for astro-photography. It looks like the 100-400mm will also be worth star testing.

Tuesday, April 15, 2014

April Lunar Eclipse From Georgetown

Last night, I stayed up for the total lunar eclipse, the first of a series of four back-to-back total eclipses visible in North America. The skies in Georgetown were clear with a bit of haze.

For this imaging sequence, I set up a Canon 60Da camera and a Canon EF 100-400mm f/4.5-5.6L lens piggybacked on my observatory telescope. I set the ISO to 100 and stopped down the lens to f/8. I captured a set of seven exposures ranging from 1/1000 to 4 seconds and repeated this pattern every ten minutes over the duration of the eclipse from 12:30 to 05:30. Multiple exposures were necessary because of the huge difference in brightness between the full and eclipsed moon, nearly 12 stops, and I had no idea ahead of time which would be best. I had wanted to automate this in my copy of Astrophotography Tool, but the current version of the software does not allow mixing of exposures less than and greater than 1 second.

The next day, I chose a representative exposure for each time interval, looking for those that gave the best detail and representation of what I was seeing at the time. I combined these in Photoshop, tweaking the exposure levels at each frame to give a smoother transition, and creating the animated GIF as show below.

Total Lunar Eclipse, April 15 2014 - Animation of frames with different exposure times
As the animation progresses, you can see the full moon obscured progressively by the Earth's shadow until there is only a think crescent left. All of these initial frames were from the 1/250 sec exposures.  At this point, the next few frames are from progressively longer exposure up to 4 sec and full eclipse. This causes the scene to brighten to simulate the eye adjusting to the dimmer view.

As the last crescent of the sun's direct illumination disappears, the colors become apparent and some stars become visible. The brightest of these is 76 Vir, not Spica which is down to the right three moon-widths and out of the field of view. The motion of these stars from frame to frame shows the rapid progression of the moon in its orbit.

During the full eclipse, the lunar disk is bathed in dim orange-red glow. This color results from sunlight in which blue light is scattered away as it travels through the Earth's lower atmosphere. It has been poetically referred to in the media as being "illuminated by all of the sunsets and sun-rises in the world." Even more interesting, just after the bright crescent of direct sunlight disappears (02:13 CDT frame) and just before it reappears (03:20 CDT frame) the edge of the moon glows blue rather than red. This is caused due to absorption of red light by ozone in the upper stratosphere. The NOAA Earth Systems Research Laboratory has a nice set of slides explaining these phenomena. The still image below shows this phenomenon.

Despite having finally found some trial software to automate the capture process so I could get some sleep, I still stayed up until 3:00 in the morning, fascinated by the view. What these images do not capture is the three-dimensional effect of the fully eclipsed moon floating in a dark sky. The full moon is normally so bright that it looks like a harsh flat disk to me. The eclipsed moon had the texture of a crescent moon but showed the full disk. To make the show even better, the planet Mars shone brightly at opposition, only a hands-width away from the moon. The bright star Spica in the constellation of Virgo was just below and to the right of the moon. At one point in the evening, I even saw a bright meteor shoot down between the the Moon and Mars ... awesome.

You can see the moon at full eclipse along with Mars and Spica in the image below. This was taken from a fixed tripod using a Canon 450D at ISO-100, f/3.5, 2 sec and a Canon EF 100mm f/2.8 USM lens. A longer exposure from a tracking mount would have given me more stars in the image. Something to try at the next eclipse.

Sunday, April 13, 2014

Attwaters Prairie Chickens at APC NWR

This weekend was the Attwater Prairie Chicken Festival at the Attwater Prairie Chicken NWR, west of Houston. This festival affords a weekend opportunity to see these highly endangered birds on their "booming grounds" or "leks". There are only about 100 left in the wild, here and at a second site near Texas City. At dawn, the male birds gather on the lek to perform courtship displays. Males who win the "dance competition" get to mate with all of the females so the stakes are high.  Did I mention this happens early in the morning...

We got up at 4:00, quite a feat for a couple of night owls, and drove down to the refuge in time for a 7:30 van tour which took us to the scene of the action. There we were allowed to set up cameras and spotting scopes behind a line about 200 ft from the lek. The weather was dark and cloudy so the 400mm f/5.6 camera lens was pretty marginal at that distance. Another birder next to us was using a massive 600mm f/4 lens and she was complaining as well.

Here is a view of the lek, a region of short grass where the males can be seen easily.

These are cropped and enlarged images of the Prairie Chickens in different poses. All of these are males. They have orange air sacs on the side of the neck that they inflate to make their "booming" noise.  The "ears" sticking up are actually long feathers that normally lie flat and cover the air sacs.

Occasionally, the males will leap into the air and flutter back down a few feet away.

As a special bonus, as we were watching the lek, a Northern Harrier began hunting in the field to our right. It did not appear interested in the Prairie Chickens. The shot shows the Harrier "hawking" over potential prey.

On an auto-tour around the park, we also saw a couple of Loggerhead Shrike posing on a barbed-wire fence ... no impaled insects, though.

We also saw some Black-Bellied Whistling Ducks, Red-Wing Blackbirds, and Turkey Vultures.

Friday, April 4, 2014

Yellow Crowned Night Herons are Back

A pair of Yellow Crowned Night Herons have shown up again this spring along the San Gabriel River near our house. We have seen two of them and are assuming they are a breeding pair.  This evening, on our walk, we were able to get photographs of both of them. They come out as the sun is fading, so hard to get a steady shot. These birds are hard to get close to. All images are taken with Canon SX-50 HS at 1200mm with heavy cropping.

Here is the first bird wading just above the weir at the crossing of the trail.  It seems to have much redder legs, coloration indicative of breeding season.

This is the second bird which we saw several hundred yards further upstream, across the river from the vulture roosting tree. Legs are less colorful than the first bird.

Update 2014-06-19 - Another one later in the season

Yellow-crowned Night Heron - Canon EF 100-400mm f/4.5-5.6L - ISO-800,  400mm, f/5.6,  1/160sec