Learning from Nature

Posted on November 17, 2011 by SBrown

Each summer when I see Turkey vultures ride into the sky on thermal updrafts and soar overhead it takes me back to my childhood and learning from nature with my father, aircraft designer Alexander M. Lippisch. Best known for the ME163 rocket fighter, Lippisch was inspired by nature for most of his unconventional aircraft designs. The swept wing tailless ME163 rocket fighter, for example, was based on the delta shaped seed pod of the Javan cucumber, Zanonia macrocarpa, that an uncle had given him.

While Lippisch was working for the Office of Naval Research (leave it to the government to assign an expert in supersonic flight to design boat hulls) he met aerophysicist Dr. August Raspet. A highly skilled sailplane pilot, Raspet spent many hours in gliders. But no matter how skillfully he was able to glide his way among the air currents it was never as well as the ever present turkey vultures. Their ability to soar and maneuver through the air far surpassed his sailplane’s performance. Lippisch had also observed these birds and was fascinated by how they used air currents, floating lazily, banking and turning at will with never a wing flap. Both men were interested in studying bird flight to determine if application of its principles could be applied to the design of conventional aircraft.

“Your observation on the Turkey Buzzard (vulture) is very interesting. Had I completed the performance measurements of the Buzzard which I tried several years ago we could have analyzed the data to determine the effective aspect ratio.” (Raspet to Lippisch letter, 10 March, 1948.)

This shared interest resulted in a productive collaboration.

Turkey vulture in flight

Raspet began his measurements of Turkey vulture flight performance in 1949, after being appointed director of the Department of Aerospace engineering at Mississippi State University . He followed the birds in his sailplane comparing their performance in spirals, relative climb rates, as well as cross-country straight flights. In order to make actual measurements of the difference in performance between the sailplane and bird, a camera in the nose of his sailplane filmed bird flight and a ground observer filmed the sailplane. The soaring speeds of the birds during spiraling flight could be measured against that of the glider by evaluating the films.

“On my Kite [Kirby-Kite sailplane] I get the real soaring effect by flying right at stall and letting the ship wallow in and out of lifting zones. Recently I followed a buzzard at 800′ all over the area in this manner.”(Raspet letter to Lippisch, 2 April, 1949.)

After analyzing measurements of the wild bird’s flying skills Raspet wondered whether ”feathers are necessary on a sailplane.”

Correspondence between Raspet and Lippisch discussed how the analysis of Turkey vulture flight could be applied to tackle two of the major problems of conventional aircraft design: how to maintain a smooth (laminar) airflow over the wing surface and how to reduce the major drag induced by the whirling mass of air flow (vortices) over the wing tips. From Raspet’s measurements and observations they learned that vultures change the shape of their wings to maintain a smooth (laminar) flow of air over the wing surface. This increases lift and reduces drag. Regarding the wing tip vortices Raspet wrote,

“In fact, it can happen that the tip feathers actually reduce the tip losses to a point where the complete planform of the wing is aerodynamically active.” (Sailplane Project of Mississippi State College”, p. 3)

Turkey vulture using slotted wing tips increase lift and reduce drag

Based on these observations Lippisch proposed use of small wings or wing slots to recover the energy lost at the wing tips of conventional aircraft. He received a patent for this design in 1956.

(From Henry V. Borst, The Aerodynamics of the Unconventional Air Vehicles of A. Lippisch. 1980 )

Raspet ‘s research resulted in his receiving a long term federally-funded program to study how laminar flow could be achieved in low-speed aircraft and the application of composite materials in aircraft design. Tragically, he died in the crash of a Piper Cub demonstrating boundary layer modifications on April 27th, 1960.

Buckeye Butterflies Breeding at Timberhill

Posted on November 6, 2011 by SBrown

Common Buckeye

One of the most common butterflies at Timberhill is the Buckeye (Junonia coenia), a medium sized brown peacock butterfly. Distinguished by the bold pattern of eyespots, white bars and orange cell bars on its wings this species is found throughout the United States (except the northwest) but is most common in the southern states. Buckeyes do not overwinter in Iowa and specimens seen here are ones that have migrated north from the south in late spring. It is presumed that they migrate south in the fall. The description in Butterflies of Iowa poses the question do they breed in Iowa? They do at Timberhill.

In order for butterflies to breed a site must have the plants the larvae feed on. Of those preferred by Buckeyes Bastard toadflax, wild petunia, and slender false foxglove are all abundant at Timberhill. In late August and September the longitudinally striped caterpillars with their pattern of branching spines were easy to spot feeding on slender false foxgloves, Agalinis tenuifolia. These annuals are stimulated by fire and are particularly abundant in the old corn field in our West Creek unit. Large clumps bloom throughout the field in late summer.

Buckeye larva on slender false foxglove

Below is a photo of the hard outer shell of a Buckeye chrysalid from which an imago, the perfectly formed butterfly, emerged in September, 2011. Buckeyes have 2-3 broods between May and October. The chrysalid stage lasts only two weeks in the fall. Presumably that gives the adult stage plenty of time to head south. However, we were still seeing occasional adult specimens as late as November 4. Shouldn’t they have headed south by then?

Buckeye chrysalis

Late Summer Camouflage: Goldenrod Crab Spider & Goldenrod Stowaway

Posted on October 17, 2011 by SBrown

You have to look closely to spot either of these two species, the Goldenrod crab spider and the Goldenrod stowaway moth. Both fend off predators by camouflaging themselves in the inflorescences of yellow flowering plants such as goldenrod.

On a sunny afternoon last month I was in the Hidden Prairie looking for native pollinators on goldenrod when I saw a honeybee hanging at an odd angle from a goldenrod inflorescence. It wasn’t until I looked closely that I could see that the bee had been caught in a Goldenrod crab spider’s fangs. This spider does not spin a web. It sits in wait on goldenrod and ambushes its prey. The spider’s venomous bite paralyzes the prey, then it liquefies the body contents and sucks it dry.

Goldenrod crab spider and honeybee prey

Camouflage is the Goldenrod crab spider’s, Misumina vatia, primary defense. In this photo you can see how well this Misumina blended into the goldenrod blossom before it ambushed the honeybee. Misumina prefers to hunt from goldenrod since this species attracts so many pollinators. However, it can change color (yellow or white) over a period of several days to blend into other flowers.

Goldenrod stowaway moth

Later that day we saw this goldenrod stowaway moth, Cirrophanus triangulifer, spending the day in a Bur marigold, Bidens polylepis, along the driveway. Bright golden yellow with deeper gold-ochraceous markings it blends in perfectly with yellow inflorescences. On wing in August and September its larvae feed on Bidens species.

Bur Marigold, Bidens polylepis

LASIOGLOSSUM VERSATUM: DIVORCE BEE STYLE

Posted on October 2, 2011 by SBrown

On a recent sunny day Bill and I had the unexpected pleasure of following naturalist Laura Rericha on walk through our restoration. Laura and Dr. Gerould Wilhelm were co-authors of the 2007 Timberhill Savanna: Assessment of Landscape Management. It was by watching and listening to them in the field that I gained a true understanding of savanna restoration.

Laura and Jerry’s first visit to Timberhill was in 2003, ten years after Bill and I had begun restoring Timberhill. Although we were having excellent results from our management, others were highly critical of our methods. We were told that we should be planting savanna indicator species, and that we were burning too frequently at the wrong time of year. In any case it didn’t matter since everyone knew there were no oak savanna remnants worth saving in Decatur County, Iowa.

Thanks to Jerry and Laura that has all changed. On his first visit in June, 2003, Jerry noted 206 native vascular plants. (Finding 180 species in a single survey usually indicates a high quality remnant.) When Laura surveyed the ants for the Timberhill study she identified fifty two species, two of which were new to the Iowa list. (The Iowa lists contains 100 species.) Laura and Jerry’s work gave Timberhill legitimacy.

On her own initiative Laura has mastered ornithology, botany, and myrmecology. Her current research is surveying the native bees of the Midwest. Wild native bees such bumblebees and sweat bees evolved with the plants they pollinate. They are seriously threatened by loss of natural habitat. Currently four dozen native wild bees are listed on the Xerces Society’s red list.

L. versatum worker bee looking for a home

Thanks to Laura, Bill and I were able to observe the behavior of Lasioglossum versatum a greenish black sweat bee that nests in the soil. She pointed out swarms of Lasioglossum versatum workers circling over and around small holes in the soil. The holes were entrances to an aggregation of L. versatum nests that spread over the trail and into the adjacent woodland.

From a small entrance (3-5 mm.) in the soil the nests extend underground through tunnels with branch burrows and individual cells for eggs and larvae. Several fertilized queens hibernate in each nest during the winter and will produce the next generation the following spring. (They do not tunnel new nests each year.) As winter approaches the queens must prepare for propagation of their species.

When they sense cold weather approaching the queens drive the worker bees out of the nests. After hard frost there will be no more flowering plants to supply the bees’ pollen. To survive diapause with enough food for the larvae the queens must drive the workers out of the nests. Fascinated we watched the worker bees frustration as they swarmed over and around the nest aggregation. Whenever a worker came close to nest entrance a queen’s head moved into the opening, blocking the hole. The queens will continue to guard the nests until there is no longer any threat of the workers returning.

L. versaturm queen blocking nest entrance

Were we to follow the protocol of burning every three years we would probably not have been able to observe this drama. The ground would have been covered with leaf duff, obscuring the nest entrances. Would Lasioglossum versatum even be nesting here if the ground was covered with dead leaves?

Reference: Charles D. Michener. “The Bionomics of a Primitively Social Bee, Lasioglossum versatum (Hymenoptera: Halictidae). Journal of the Kansas Entomological Society. Vol. 39, No. 2 (Apr., 1966), pp, 193-217.

Timberhill Map: Finding the Boundaries

Posted on September 19, 2011 by SBrown

Timberhill Map

When our lawyer did a title search prior to closing on our first purchase of Decatur County land he warned,

“Be careful they don’t slip an extra forty acres in on you.”

Our lawyer believed that land was only worth buying if it could produce an income. The overstocked woodlands we had purchased had no value except for hunting and harvesting firewood. But to Bill and me the land was beautiful. I’ll never forget walking the East Savanna trail the day after we closed. Falling leaves brushed my shoulder as I walked up hill under a canopy of oak trees. I couldn’t believe this mosaic of woodlands and prairie openings was really ours.

In 2001 when we were negotiating to purchase the West 40 we sought advice from an appraiser regarding price. Looking across the fence at the W40 hickory woodland overgrown with eastern red cedar and honey locust he shook his head in disgust. Why would we even consider buying such worthless land? But the West 40 not only had wildflowers such as purple prairie clover and bottle gentian not found on our east property but there was a remnant white oak and bur oak savanna. We also knew that the West 40 had never been plowed.

Since our land was considered so worthless no one had ever located the exact boundaries. The only permanent survey markers mounted on steel posts designated an abandoned right of way that used to run through the middle of the east savanna. Whatever the original Government Land Office surveyor had available when he surveyed the property in 1847 marked the rest of the survey points. For example, a harrow bar marked the southwest corner between the West 40 and West Creek. The northwest corner was marked by a buggy axle buried in the creek, the southeast corner a buggy pole brace. A wringer spindle (iron spindle of a wringer washer), chips of crockery or a peg fashioned from the wood of a nearby tree and placed under a large stone marked other survey points. To quote the survey map, “a stone “under E & W fence about 2 feet west of fence line south”, and “stone & jig under gray boulder”.

Permanent survey marker on steel post between fencelines

There were fence lines but they were confusing. At the corner between the east property and the West 40 the east fence line ended forty feet south of it’s continuation to the west. A road that used to run along this line had been abandoned in 1938 and the property divided between the landowners. But the owners kept the fence lines where they were, one that ran on the south side of the road and another on the north. When we purchased the West 40 we asked the county surveyor to mark the corners with permanent survey markers. Standing near where he thought the buggy pole brace might be he swung the metal detector back and forth until it indicated buried metal. With a shovel he found the buggy pole brace and set a permanent survey marker 1 foot south to the south. The exact location of the survey point was noted on the permanent survey record. To find the northwest corner he had to wade into the creek. This time he set the permanent survey marker south of the actual survey point and drove nails into a nearby post and box elder from which another surveyor could shoot the actual survey point.

Since then Decatur County land such as ours has increased in value. However, the increased value is not in its beauty or restoration potential but its ability to produce deer. We are now surrounded by hunters who have paid up to $3000 per acre for private hunting grounds. They know exactly where the boundaries are and monitor them constantly with trail cameras to deter poachers.