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A Western Nature Ramble on Antelope Island, Utah

Although we often become very attached to the habitats and creatures found in our local area, it can be very beneficial to take a trip to a place that is in stark contrast to our usual surroundings. This reminds us of the incredible variety in nature and stimulates our thinking about the origin and purpose of biodiversity under very different climatic and geographic conditions. Once a year we visit two of our kids that live in the Salt Lake City area and experience the natural wonders of the valleys and mountains of Utah.

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One of my favorite places in early fall is Antelope Island that lies in the Great Salt Lake; it is very little developed and represents a more primitive time before humans dominated the landscape. In addition to resident species there are large numbers of migrant birds not often seen so easily. Yet the very high salinity (about five times sea water) restricts aquatic animal life to two major species, brine shrimp and brine flies. Yet these small invertebrates occur in massive numbers and form the basis of the food chain for birds of many species. This illustrates an ecological principle that extreme environments usually have low species diversity, but very high productivity of these tolerant species. Access to the island is via a causeway that provides a great view of the water birds. Every year is different but the current droughts have reduced the lake level (normally at about 4200 feet elevation). As recently as 16,000 years ago the lake level was about 1000 feet higher and a horizontal scar or terrace along the adjacent mountains clearly shows the level of Lake Bonneville at that time. This provides a highly visual example of the large natural changes that occur during normal fluctuations in climate.

It seems impossible that large birds could feed on tiny flies and brine shrimp but they do so. The common Franklin's gull is a summer breeder which I observed snatching tiny flies with its bill with a strange movement of the head. They migrate to the western coast of South America during the winter. This is one of several black-headed gulls in their breeding plumage which are so similar that they can be difficult to identify. The bird shown is a non-breeding adult and the black hood is partially lost. Why do these related gulls all have black hoods during breeding season and why do they look so similar? It is interesting that the eye is emphasized in Franklin's gull whereas in the magpie the eye is completely obscured by the black head and neck.

Another water bird that can be present in huge numbers is the eared grebe. It has an interesting life history that involves breeding in western inland fresh water lakes, migration and stopovers in huge numbers at a few saline lakes, and wintering along the Pacific and Gulf coasts. It probably feeds mainly on brine shrimp. It has a bright red eye that is presumably important in courtship.

Several members of the corvid family (crows, jays & magpies) were present and I was impressed at the differences in color between the two largest examples- the raven and the black billed magpie. The raven is completely black as are the crows. Yet the related magpie has a startling black and white pattern. Both of these birds are intelligent, persistent and successful omnivores. Why are they so different in color? Is the pattern of the magpie an advertisement or camouflage in certain situations? Some of the most flashy animal patterns can be disruptive and a means of concealment under the right conditions- just consider the zebra. The raven and magpie are both permanent residents and interesting birds to watch.

I had a brief opportunity to look at the most impressive avian predator in the area, the golden eagle. A two to three year old eagle soared overhead and I was able to get a quick photograph that documented its presence. The golden is more of a predator and less of a scavenger than the bald eagle and it certainly must find a great deal of potential mammalian prey on this island.

I encountered a harem of prong-horned antelopes under the very watchful eye of a male. Look at the photo of the male and consider the interesting coloration of this very swift runner. The two tone color of the body (darker on back and lighter on the belly) is broken by a large white rump. The rump color reminds me of the white tailed deer and how this is displayed when it runs away in alarm. Is this designed to confuse a predator and/or lead the members of the herd in one direction? In Pennsylvania the white tail/rump were simulated in displays along roadways in an effort to dissuade deer from crossing highways where they were being struck by cars. This made the assumption (not yet clearly proven) that the white rump is a sign of fright that is recognized by deer and possibly antelopes.

The most impressive large mammal was the bison or buffalo which is present on Antelope Island in huge numbers. I came across a herd of hundreds that were crossing from one side of the island to the other, thundering down the hills, across the road and onto the grasslands next to the lake. Given the near extinction of buffalo, it is reassuring to see them in such numbers that recreate in a small sense the massive herds that once occurred. The influence of these grazers on grasslands is important to recreation of the prairies that once covered vast stretches of the western US.

So when you get a chance to travel, I encourage you to go on a nature ramble and compare what you find with your home territory. But watch out- you may find it a lot more interesting than the city sights.

Bill Dunson

Galax, VA & Englewood, FL

wdunson@comcast.net

http://www.galaxgazette.com/blogs

http://lemonbayconservancy.org/dunson_archives.htm

http://lemonbayconservancy.org/wildflower.htm