Dragonfly Eyes

Dragonflies have amazing eyesight. Their compound eyes are made up up to 30,000 different facets called ommatidia. Each ommatidia is made up of lenses that are attached to sensory cells. Since the facets are pointing in multiple directions the dragonfly has almost a 360 degree field of vision. Besides an expanded field of vision the dragonflies compound eyes can see into the ultraviolet spectrum, detect the plane of polarization of light with out sunglasses, and process movement faster then we can. I guess that when you are mostly devoid of other scenes your prevailing sense, in this case sight, evolves and becomes enhanced.  

Cobra Clubtail

My favorite type of dragonfly are the members of the Gomphidae family, or clubtail dragonflies. They are named because many species have a narrow abdomen which widens at the end forming a club shape. The club is usually larger in the males then in the females and some clubtail species do not have much of a club at all. It is still easy to identify species that lack a club as members of the Gomphidae family because members of Gomphidae are the only dragonflies that have noticeably separated eyes. The cobra clubtail, pictured here, has a large club. The only species in this region with a larger club is the skillet clubtail. Like many species of clubtails the cobra is found primarily around rivers. I photographed this cobra clubtail by where the Snake River empties out into the St Croix River. 

Cobra Clubtail Dragonfly

Clubtail dragonflies are part of the family Gomphidae. They get their name from the enlarged tip at the end of the abdomen that many have. However not all clubtails have a club tail. The easiest way to tell whether a dragonfly is a member of the Gomphidae family is to see whether the eyes are separated. Gomphidae are the only dragonflies with separated eyes.

Many Gomphidae are found along rivers. The cobra clubtail pictured here is typically a river species. The nymphs prefer large rivers usually with a sandy bottom. I photographed this dragonfly at Damn Number One on the Mississippi River. The tip of the cobra clubtail is larger then most other clubtails found in this area. Only the skillet clubtail has a wider tip on their abdomen. That makes the cobra clubtail one of the easier clubtails to identify.

Clubtail dragons

Gomphidae, or clubtails, are my favorite type of dragonflies. Many have wide club type tips to their abdomen, thus their common name clubtail, however not all clubtails have a club. What distinguishes Gomphidae, clubtails and snaketails, from the other dragons is that they are the only dragonfly family who have their eyes separated. It is easy to see in the macro of a cobra clubtail face above that it is a member of the Gomphidae family.

Lock and Dam No 1 (Ford Dam)

This summer I spent quite a bit of time at the Lock and Dam No. 1 which is located between St Paul and Minneapolis. Lock and Dam No 1 is the second lock located on the Mississippi River, the only one further upstream is the Lower St Anthony Falls Lock and Dam. It crosses the Mississippi just north of where it meets the Minnesota River. It is often referred to as the Ford Dam because of the adjacent Ford Plant.

The lock and damn was built by the US Army Corps of Engineers and went into operation in 1917. It was rebuilt in 1929 and expanded from one lock to two in 1932. Although they are not as large as some of the other locks down stream the two locks at the Ford Damn are large enough, 56 feet wide by 400 feet long to handle any river traffic that needs to get by, most of which are personal watercraft.

Between 1978 and 1983 major major renovations were made to the lock and dam. Most of the manual and hydraulic components were replaced with more modern components with computer controls. An observation area was added to allow visitors to view the operations of the lock during the warmer months of the year.
The dam is a buttress style dam made out of reinforced concrete. On the St Paul Side of the river stands a hydroelectric power station. The power station and dam were once owned by Ford and they were used to power the neighboring plant. With car companies running into financial problems Ford sold the dam and power station to Brookfield Power Co in 2007.

The reason that I first visited the dam was to photograph the banding of the peregrine falcon chicks that had hatched in the nest box that was attached to the dam walls on the Minneapolis side. The banding was done by the Midwest Peregrine Foundation, who are responsible for bringing the peregrine falcon species back from extinction in the Midwestern United States and southern Canada. Because the Midwest Peregrine Foundation has ties to The Raptor Center I found out about the banding and was able to get a front row seat.

After the peregrine chicks were banded I continued to visit the dam to check in and document their progress. Feeding three growing peregrines, one male and two females, can be a tough job, fortunately there was ample prey around the dam and the adults were very adapt at their hunting techniques. Once the chicks were old enough to thermal regulate their own body temperature the female joined the male in hunting which certainly made life easier.

Eventually it came time for the young to leave the nest. There were several ledges below the nest box that ran most of the length of the lock and served as a great place for the young to learn to fly. On these ledges they were protected from people and predators, except possibly other raptors, and their long lengths made them great runways for the chicks to practice their take offs and landings. I saw two of the young take what I believe was their first real flight.

Eventually the peregrines moved on. Even though they were probably still in the area it was no longer any easy way to find them or to take pics. There were other birds that were still hanging around though. For birds like double-crested cormorants, great egret and great blue heron the area around the damn is excellent habitat with plenty of fish to eat. Occasionally an eagle or osprey would stop by to do some fishing only to get chased away by angry peregrines.

Even with hungry peregrines in the area you can still find smaller birds raising their young. Perhaps the swallows that erected their nest beneath the stairs of the observation area were just too small to be worth the chase for the peregrines. Especially when their are numerous pigeons in the area which are not quite as quick or agile as the swallows and have a lot more meat on their bones.

I also managed to find dragonflies at the dam also. Cobra clubtails are usually found around large swift rivers and streams. The overflow water that pours over the dam makes the current a little faster in this area. Plus areas that are inhabited by humans often attract bugs, like flies, mosquitoes and bees which are prey to many dragonflies.