Archive for the ‘weather’ Category

Arrowhead Spiketail dragonfly (female)

May 27, 2019

An Arrowhead Spiketail dragonfly (Cordulegaster obliqua) was spotted in a sunny clearing along a small forest stream at an undisclosed location in Prince William County, Virginia USA.

21 MAY 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

This individual is a female, as indicated by her rounded hind wings, terminal appendages, and prominent ovipositor at the tip of her abdomen.

[Females in the Family Cordulegastridae (Spiketails) feature a] …pointed and spikelike (thus the group name) ovipositor, really a “pseudo-ovipositor” formed from the prolonged subgenital plate. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7005-7006). Princeton University Press. Kindle Edition.

21 MAY 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

Although the pattern of arrowhead-shaped markings visible on the dorsal side of her abdomen is unmistakeable, notice that the thorax features two stripes. The latter field mark can be used to differentiate spiketails from cruisers that have one stripe on their thorax.

21 MAY 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

Mike Powell and I have photowalked together so many times that we are comfortable working cooperatively to shoot a subject. I wanted to get a shot of the face of the Arrowhead Spiketail but was concerned it would spook the dragonfly if I were to get “up in her grill.” So I waited until Mike had taken all of the photographs he wanted before approaching the dragonlfy for her “beauty shot.” As it turns out, the model was extraordinarily tolerant and didn’t fly away until sometime after Mike and I moved on to the next site.

21 MAY 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

Notice the interrupted fern (Osmunda claytoniana) that appears in the background of every photo of the Arrowhead Spiketail.

Location, location, location.

Some species of odonates are habitat generalists, meaning they can be found almost anywhere there is water.

Habitat-specific odonates can be found only in specific habitats — for these species, finding them is all about location, location, location. Arrowhead Spiketail dragonflies are habitat-specialists.

Habitat: Small swift streams and soft-bottomed muddy seeps in forest, also streams reduced to series of small pools during drier weather. As in some other spiketails, skunk cabbage often present. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7081-7082). Princeton University Press. Kindle Edition.

Skunk cabbage (Symplocarpus foetidus) and interrupted fern (Osmunda claytoniana) were observed growing in a seep located between a dirt trail and the small stream where the Arrowhead Spiketail was spotted — the perfect place for several species of habitat-specific odonates!

The last photo shows the clearing along a small forest stream where several species of dragonflies were spotted, including the Arrowhead Spiketail featured in this blog post. The stream is no more than a few feet wide and only a few inches deep in most places.

The small stream where several species of dragonflies were spotted.

The backstory

Telephoto lenses can cause a type of distortion called “foreshortening,” as seen in the preceding photo. Mike Powell and I were standing at the edge of the stream bank trying to decide whether we wanted to go down the short, steep slope to explore the clearing when we spotted a large UFO, that is, an “Unidentified Flying Odonate.” Mike and I took “record shots” of the dragonfly; looking at the LCD of our cameras, we identified the UFO as a Gray Petaltail dragonfly (Tachopteryx thoreyi).

Mike and I had seen a Gray Petaltail at another location (near the beginning of our photowalk), but we were unable to photograph it. So down the bank we went! As it turns out, there were at least two Grays in the meadow: a female; and a male. As Mike was photographing one of the Gray Petaltails he noticed another “large dragonfly.” As we slowly moved closer to the new unknown dragonfly, I quickly realized Mike had spotted an Arrowhead Clubtail. Great catch, Mike!

Please see Female Arrowhead Spiketail dragonfly for Mike’s take on our shared experience.

Uncommon

Arrowhead Spiketail is classified as an uncommon species of odonate. The following map shows all official records for Arrowhead Clubtail (C. obliqua) in the United States of America.

DSA Distribution Viewer | Arrowhead Spiketail

Source Credit: Abbott, J.C. 2006-2019. OdonataCentral: An online resource for the distribution and identification of Odonata. Available at http://www.odonatacentral.org. (Accessed: May 27, 2019).

Key: blue dots = Dot Map Project; green dots = Accepted records; yellow dots = Pending records.

Our spotting of Arrowhead Spiketail is a new DSA record for Prince William County, Virginia.

Adult flight period

According to records for the Commonwealth of Virginia maintained by Dr. Steve Roble, Staff Zoologist at the Virginia Department of Conservation and Recreation, Division of Natural Heritage, the adult flight period for C. obliqua is 11 May to 17 July. The species is classified as uncommon. Its habitat is “small streams.”

Bear in mind, Dr. Roble’s records are for the entire state, therefore the adult flight period for C. obliqua seems to be longer than it is in reality. The adult flight period for a single site is probably shorter — more likely around one month. For example, according to records for Northern Virginia maintained by Kevin Munroe, former manager of Huntley Meadows Park, the adult flight period for Arrowhead is 28 May to 27 June (peaks in June).

Copyright © 2019 Walter Sanford. All rights reserved.

 

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Common Baskettail (teneral female)

April 29, 2018

A Common Baskettail dragonfly (Epitheca cynosura) was spotted near Painted Turtle Pond during a photowalk at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

This individual is a teneral female, as indicated by her tenuous wings and relatively short, straight terminal appendages.

Spring 2018 has been slow to spring in the mid-Atlantic USA, as evidenced by the fact that the first Common Baskettails were spotted at Painted Turtle Pond beginning in mid-April 2017.

Related Resources

Copyright © 2018 Walter Sanford. All rights reserved.

Legend of the Woolly Bear caterpillar

January 29, 2018

A “Woolly Bear caterpillar” was spotted during a photowalk at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

Wooly Bear caterpillar is the larval form of the Isabella Tiger Moth (Pyrrharctia isabella).

According to legend, …

The Woolly Bear caterpillar has 13 distinct segments of either rusty brown or black. The wider the rusty brown sections (or the more brown segments there are), the milder the coming winter will be. The more black there is, the more severe the winter. Source Credit: WOOLLY BEAR CATERPILLARS AND WEATHER PREDICTION – USING WOOLLY WORMS FOR A WINTER FORECAST, The Old Farmer’s Almanac.

Is the legend scientifically valid?

…this myth has been around since, you know, the colonial times. But in 1948, this curator of entomology from the American Museum of Natural History, Dr. Howard Curran, he did a little study. He went out to Bear Mountain, New York, and he counted the woolly bears, the bands – the brown bands of the woolly bear there. And he counted about 15 different specimens, and he made a prediction. Source Credit: The Myth of the Woolly Bear, National Public Radio.

Problem is, a sample size of 15 is insufficient for making meaningful conclusions. So looking at one caterpillar, as I did, is completely meaningless. Nonetheless, I always think of the legend whenever I see a Woolly Bear and wonder what it tells me about the upcoming winter.

Related Rescources

Copyright © 2018 Walter Sanford. All rights reserved.

Different point of view

January 15, 2018

The first photo shows “The Osprey’s at Belmont Bay,” as seen from the opposite side of Belmont Bay. “The Osprey’s” community shares a common boundary with Occoquan Bay National Wildlife Refuge, located to the left of this photo.

11 JAN 2018 | Prince William County, VA | The Osprey’s at Belmont Bay

The next photo shows the near shoreline of Belmont Bay. The bay is almost completely covered by ice after two weeks of below-freezing temperatures.

11 JAN 2018 | Fairfax County, VA | Belmont Bay

Notice the duck blind located in the water.

11 JAN 2018 | Fairfax County, VA | Belmont Bay

The following photo shows a dock and boat ramp located at the mouth of a small stream that is a tributary of Belmont Bay.

11 JAN 2018 | Fairfax County, VA | dock and boat ramp

The next photo is located upstream from the dock and boat ramp.

11 JAN 2018 | Fairfax County, VA | small tributary of Belmont Bay

The last photo shows a location far upstream from Belmont Bay. The stream is located at the bottom of a steep-sided valley.

11 JAN 2018 | Fairfax County, VA | small tributary of Belmont Bay

Tech Tip: I used my Panasonic Lumix DMC-FZ150 superzoom camera to shoot the landscape photos featured in this blog post. The camera was set for manual focus at the hyperfocal distance for an aperture of f/4, based upon the instructions provided in the excellent video tutorial by Graham Houghton, “Panasonic Lumix FZ camera easier manual focus method — super point-and-shoot tip.”

Copyright © 2018 Walter Sanford. All rights reserved.

Urban Heat Island

December 10, 2017

On 01 December 2017 I didn’t see any Autumn Meadowhawk dragonflies (Sympetrum vicinum) during a photowalk along Easy Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

In contrast, I saw several Autumn Meadowhawks perched on man-made structures such as a concrete curb in the blacktop parking lot at the refuge. All of the dragonflies were perched on vertical surfaces that received more direct insolation than horizontal surfaces. The parking area seems to be an urban heat island microclimate that exists within a larger natural area.

Male 1

The first individual is a male, as indicated by his terminal appendages. Although the male is missing one of four wings, he was able to fly well enough to move to three different perches along the curb.

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

Male 2

The next male has a full set of four wings; his wings are tattered slightly, as expected toward the end of dragonfly season.

The last photo shows the male grooming and excreting at the same time.

Related Resources

Copyright © 2017 Walter Sanford. All rights reserved.

“Winter Meadowhawk” dragonflies

December 8, 2017

The season called “winter” is defined two ways: atmospheric scientists, including meteorologists and climatologists, define winter as the three-month period from December to February; astronomers define winter as the time period that begins on the December Solstice (12/21) and ends on the March Equinox (03/21), although the actual dates for these events may vary slightly.

Several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted on the first day of climatological winter at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Therefore I think it is appropriate to call them “Winter Meadowhawks.”

The last two photos show the same male, perching on different surfaces. My guess is he was looking for a good source of thermal energy on a cool, windy day.

The Sun is always low in the sky during winter, even at its maximum altitude. Indirect incoming solar radiation (insolation) is less intense than direct insolation. The last photo shows the male dragonfly perched on a south-facing wooden board that is perpendicular to the surface of the Earth, therefore the solar energy received by the board is more intense than the energy received by the ground. This probably explains why the male moved from the ground to the board.

Enrichment

The last photo was taken on 01 December 2017 at 11:33:50 a.m. EST, as shown by the EXIF information for the image. The altitude of the Sun was 28.9° at 11:30 a.m., meaning a ray of sunlight formed an angle of 28.9° with horizontal surfaces such as the ground. At the same time, a ray of sunlight formed an angle of 61.1° with vertical surfaces such as the wooden board shown in the first and last photos. That’s the beauty of mathematics — some simple geometry shows clearly which surface received more intense insolation. Smart dragonflies!

Related Resource: Sun or Moon Altitude/Azimuth Table, U.S. Naval Observatory.

Copyright © 2017 Walter Sanford. All rights reserved.

The Road Taken

November 14, 2017

Two ruts converged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth…

With sincere apologies to Robert Frost for slight modification of the title and first stanza of his famous poem The Road Not Taken in order to convey my impressions of Fall 2017 at Occoquan Bay National Wildlife Refuge.

Tech Tip: I used my Panasonic Lumix DMC-FZ150 superzoom camera to shoot the landscape photo featured in this blog post. The camera was set for manual focus at the hyperfocal distance for an aperture of f/4, based upon the instructions provided in the excellent video tutorial by Graham Houghton, “Panasonic Lumix FZ camera easier manual focus method — super point-and-shoot tip.”

Copyright © 2017 Walter Sanford. All rights reserved.

Confused by mild fall weather

November 12, 2017

A frog-let/toad-let — my term for small frogs and toads — was spotted during a photowalk along Easy Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Turns out it’s a Spring Peeper (Pseudacris crucifer), as indicated by the dark “X” on the frog’s dorsal side.

Every spring, the sound of male Spring Peepers calling for mates is deafening. You hear them, but you see them rarely. You don’t expect to see them during the second week in November!

Some amphibians have been confused by the mild weather in Northern Virginia, thinking it’s spring. The first hard freeze this fall occurred overnight on Friday-Saturday, November 10-11, when the record-setting low temperature at Reagan National Airport (DCA) was 26°F. I hope this little one hunkered down like frogs are supposed to when it’s cold.

Related Resource: Spring Peepers, a blog post by Alonso Abugattas, Natural Resources Manager for Arlington County Parks, Virginia USA.

Copyright © 2017 Walter Sanford. All rights reserved.

New HMP Weather Station

December 10, 2016

Did you notice the new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA?

The new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA.

13 NOV 2016 | Huntley Meadows Park | new automated weather station

The old weather station, installed and maintained by Virginia Tech University, went offline after 23 September 2016.

The [old] Huntley Meadows weather station was installed to help park personnel manage water levels within the wetland. Source Credit: Huntley Meadows Wetlands Research.

The new station is up-and-running; real-time data is supposed to be available online soon.

The new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA.

13 NOV 2016 | Huntley Meadows Park | new automated weather station

Editor’s Note: The author contacted both the park manager and the natural resource manager; neither person was willing to estimate when the new weather station will go online. Look for a post update when more information is available.

Copyright © 2016 Walter Sanford. All rights reserved.

Snowy scenes along the Hike-Bike Trail

February 7, 2016

The “exposure triangle” has three corners: 1) Aperture; 2) Shutter Speed; and 3) ISO (light sensitivity). When shooting in “Program” mode and Auto ISO, all three corners of the exposure triangle are wildcards set by the camera. In “Aperture Priority” mode and Auto ISO, the user selects the aperture (lens opening) and the camera selects the shutter speed and ISO. In “Shutter Priority” mode and Auto ISO, the user selects the shutter speed and the camera selects the aperture (lens opening) and ISO. Finally, in “Manual” mode the user selects all three settings in the exposure triangle.

All of the photos in this post were shot in “Aperture Priority” mode at ISO 100. That leaves one corner of the exposure triangle for the camera to set: Shutter Speed. At an aperture of f/4 and ISO 100, the camera is set for a relatively wide lens opening and maximum light sensitivity. Ice and snow are very reflective surfaces, so it’s no surprise the camera selected fast shutter speeds to limit the amount of light received by the camera sensor. One upside of this combination of settings: Camera shake was virtually a non-factor!

The following gallery of photos shows views along the Hike-Bike Trail at Huntley Meadows Park, a little more than a week after the “Blizzard of 2016.”

The view along the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm (25mm, 35mm equivalent) | f/4 | 1/2000s | ISO 100 | -1 ev

Notice that exposure compensation (ev) was used for most of the photos. In “Aperture Priority” mode at a fixed ISO, exposure compensation affects shutter speed: negative exposure values (ev) make the shutter speed faster, further reducing the amount of light received by the camera sensor; positive exposure values make the shutter speed slower, increasing the amount of light received.

Looking downstream along a creek that crosses the Hike-Bike Trail.

Looking downstream along a creek that crosses the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1000s | ISO 100 | -1 ev

Approaching the observation platform at the terminus of the Hike-Bike Trail. Notice the chromatic aberration in the tree tops at the upper-right corner of the photo.

Looking toward the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1600s | ISO 100 | -1 ev

Looking toward the observation platform.

Approaching the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1300s | ISO 100 | 0 ev

The central wetland area, as viewed from the observation platform. Notice the observation tower is faintly visible at the far side of the wetlands.

The central wetland area, as viewed from the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/2000s | ISO 100 | -1 ev

A vernal pool located near the terminus of the Hike-Bike Trail. The pool is mostly covered by ice and snow and somewhat difficult to see in the following photo.

A vernal pool located near the terminus of the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/2000s | ISO 100 | -1 ev

A view of the “Mystery Pool.”

A view of the "Mystery Pool," Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1600s | ISO 100 | -1 ev

Heading toward the parking lot at the beginning of the Hike-Bike Trail.

The view along the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/500s | ISO 100 | 0 ev

Related Resource: The exposure triangle and exposure compensation.

Copyright © 2016 Walter Sanford. All rights reserved.


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