Bird Calendars

NOTES FROM NATURE

By Jerry Toll

Salt Creek Tiger Beetle

On May 27 of this year I learned of an endangered insect from an article in the Omaha World-Herald. Cincindela nevadica lincolniana, or salt creek tiger beetle, is a subspecies of tiger beetle found only in four small remaining wetlands in the Salt Creek drainage near Lincoln.

It is found nowhere else in the world. Its closest relative, C.n.knausi, is located in western Nebraska. The primary widespread population of nevadica salt-loving tiger beetles can be found from Alberta, Canada, throughout the Great Basin and south to northern Mexico.

According to Steve Spomer, an entomologist with the University of Nebraska at Lincoln, lincolniana is restricted to and reliant upon a diminished habitat. This includes the saline flats remaining by Capitol Beach in Lincoln, two separate populations near north 27th Street, including Cracker Barrel Marsh, and a fourth population SE of Ceresco.

Only about 10% of the pre-settlement salt marsh remains, which has precipitated the decline of lincolniana. This tiger beetle most likely never had a large population because its specialized habitat is small and isolated.

Restricted to a specialized saline habitat, it evolved to exploit a niche that other tiger beetles could not inhabit. The saline soil conditions found in the Salt Creek watershed have created an isolated community of plants and animals that is unique to the region.

With a life cycle of two years in the larval stage, three weeks as a pupa, and less than seven weeks in early summer as a reproducing adult that lays only 20-30 eggs, this predacious insect must rely on tenacity to overcome its slow reproductive rate. As yet researchers do not know why this survival strategy works.

Lincolniana is further restricted to the specific type of saline conditions it inhabits. It prefers exposed, moist salty pans. Other tiger beetles with which it competes prefer

more upland and/or mesic conditions. Additionally, lincolniana seems unable to emigrate between the fragmented populations, further weakening the genetic diversity and making it more vulnerable to extinction.

This summer Bill Allgeier, who works with Spomer, did a mark and recapture study on one of the populations. The preliminary result is that none of those marked adult beetles were found more than a few hundred feet away from their own population center.

Another finding this summer, according to Steve Spomer, is that the continuing drought may actually be aiding the lincolniana population. He speculates that more salt pans were exposed by drying the marshes, thus providing more habitat.

Since the study began, the population has ranged between 300 to 600 mature adults counted per year. This year the count was over 700 adults.

Not enough is known about the various stages of the life cycle to understand the effects on survivability through the various stages. This could give researchers an insight into how to increase reproductive efficiency, thus increasing the population size.

The survival of lincolniana is in jeopardy. Human development by both direct and indirect encroachment is the greatest concern. Housing and small businesses are springing up near and will soon engulf the environs if protection is not forthcoming. Fresh water runoff from parking lots can lessen the salinity of Salt Creek. These factors, combined with a low reproductive rate and a very low fragmented population, make lincolniana highly vulnerable to extinction.

Currently the salt creek tiger beetle is on the list of Nebraska endangered species, providing a measure of protection. A federal listing has been applied for. A decision was supposed to be rendered in June, but the decision is still pending in Washington.

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