Mark M. Peyton, Senior District Biologist, Central Nebraska Public Power and Irrigation District, P.O. Box 188, Gothenburg, Nebraska 69138, (308) 537-3582

INTRODUCTION

In 1994 the collection of 40 specimens of the American burying beetle (Nicrophorus americanus) indicated the presence of a population of this species in the dissected hills south of the Platte River located roughly between Lexington, Dawson County and North Platte, Lincoln County, Nebraska.

During 1995 and 1996, 571 trap nights of effort resulted in the collection of 442 beetles. These beetles were marked with an oil based paint and released at the site of capture.

The major focus of 1995 was to identify the range of this beetle south of the Platte River in Nebraska. In 1996 trapping was limited to two locations with major emphasis in the development of an estimate of population size and an evaluation of the marking technique.

METHODS

A modified Kozol protocol (Kozol, 1986) was used in trapping. The traps consisted of either a 20 liter bucket or 30 cm long piece of 3" PVC pipe buried in the ground so that the lip of the bucket/pipe is flush with the surface of the ground. Bait consisted of salvaged roadkill or commercially acquired euthinized white lab rats placed whole in a small container with a screen top and then put in the bottom of the trap. A lid was placed over the buckets for protection from rain and sunlight.

During 1995 a site was trapped for a minimum of five consecutive nights. If a specimen of Nicrophorus americanus was collected it was marked and released and trapping was continued at that site for the next seven nights. The maximum number of nights trapped at any location was ten.

During 1996 three sites were trapped. All three sites were areas were specimens of Nicrophorus americanus were collected during 1995. One site, located at Hiles Canyon south of Gothenburg, was trapped for 12 nights from 15 May to 22 May and again from 3 June to 9 June. The purpose of the work at this site was to identify the time in which the beetles were active. The other two sites, located in Gilman and Calla Han Canyons south west of Gothenburg, contain pastures in which red cedar (Juniperus virginia), cottonwood (Populus deltoides), and ash (Fraxinus pennsylvanica) grow in abundance.

Five traps, placed approximately 50 meters apart, were located at each site and were in operation for 22 nights at the Gilman Canyon site (3 June to 9 June, 14 June to 20 June, and 1 July to 11 July), and 13 nights (17 June to 20 June and 1 July to 11 July) at the Calla Han site.

Beetles trapped were marked with various colors of paint in specific patters in order to determine the location and time of trapping in the event of a recapture. Once the paint was dry the beetles were released at the site of capture.

Two methods for estimating the population size of Nicrophorus americanus within the identified range were attempted. The first method used the number of beetles trapped, the ratio of area trapped and an estimate of usable habitat present. This method is based, in part, upon a study of Nicrophorus americanus in Oklahoma, where Creighton (1994) determined the average total movement of an individual was 2.7 kilometers. Thus, according to Creighton's data it could be assumed each trap would attract beetles from a circle with a maximum radius of 2.7 kilometers.

We expanded that maximum radius to 5.0 kilometers to account for the observed movement of individuals in this study and that of Jon Bedick's (personal conversation). This results in each trap "covering" an area of 78.5 square kilometers. The three sites trapped within the dissected hills area south of the Platte River thus represented approximately 235.5 square kilometers, or 7.3% of the identified range. Not all of the identified range of Nicrophorus americanus in south central Nebraska is appropriate habitat for the beetle. To account for this an estimator of 50% is used to approximate the usable habitat within the range. The formula for this is as follows:

The second method, developed by Schnable (Overton, 1969) estimates total population based upon the ratio of recaptured individuals to total beetles trapped at a site. The formula for this process is:

Both techniques depend upon the ability to identify beetles previously captured. In order to evaluate the durability of the marking process twenty-three specimens of Nicrophorus orbicollis, a sympatric species, were marked with four dots of paint on the elytra and a single drop of paint on the pronotum. These were placed for seven days in a 75 liter aquarium with 4 cm of dirt in the bottom . The beetles were examined daily to determine the durability of the marks.

RESULTS

Two hundred and one specimens of Nicrophorus americanus were collected at 11 of the 25 sites investigated during 1995. These collections plus those done by personnel from the University of Nebraska State Museum (Ratcliffe, 1990, Jameson, 1991, and Bedick, in press) identified the roughly 8,355 square kilometers of dissected hills south of the Platte River in Dawson, Gosper, and Lincoln Counties as the primary range of this species in Central Nebraska

The collection of 241 beetles from three locations in 1996 results in a population size estimate of 4,275 individuals based upon extrapolation of collection data to cover the entire identified range.

The Schnabel mark-and-recapture method for estimating populations size, which is dependent upon a number of assumption not necessarily defensible in this situation, based upon the recapture of 17 beetles, an estimate of 926 individual beetles was derived for Site #2 (Gilman Canyon, Table 1a) and 653 individual beetles for Site #3 (Calla Han Canyon, Table 1b) for an average of 790 beetles per 78.5 sq. km., or 10 beetles/sq.km.. These values extrapolated over the entire range and multiplied by 0.5 as an estimate of usable habitat within this range results in an estimate of approximately 41,775 individuals.

Of the 23 Nicrophorus orbicollis marked and placed in the aquarium with 4 cm of dirt for seven days, one died, one lost all marks, and 21 retained the marks painted on the elytra. In 18 individuals, the mark painted on the pronotum was lost. On the seventh day the marks on the elytra were clear, bright, and easily seen.

DISCUSSION

The American burying beetle (Nicrophorus americanus) is the only insect in Nebraska presently on the Endangered Species list. It was once thought if this species were to be found in Nebraska it would be located in the riparian forests of the major rivers, including the Platte River. This work, however, identifies the upland grasslands and cedar tree savannas of the dissected loess hills located up to five miles south of the Platte River in Dawson, Gosper, and Lincoln Counties of Nebraska as the primary habitat for this species in this area.

Extensive tapping of riverene habitats by the University of Nebraska State Museum along the Missouri and Platte Rivers resulted in no collections of Nicrophorus americanus, while in this study five specimens were collected along the Platte River. Trapping during both 1995 and 1996 in the dissected loess hills south of the Platte resulted in the collection of 441 beetles. In addition Jon Bedick of the University of Nebraska State Museum collected over 500 specimens within the same area (personal communication). Thus, in the past three seasons approximately 1,000 specimens of the American burying beetle have been located in these upland areas.

Prior to 1994 and the work done by Central and the University State Museum only 18 specimens of Nicrophorus americanus had been collected and identified from Nebraska.

In the Recovery Plan the criteria for delisting this species in a specific region is to have three populations, identified as interbreeding members of a species isolated or separated from others, be established or discovered within the region. Each of the three populations must contain a minimum of 500 adults, and each demonstrate self-sustainability (USFWS, 1989).

Based upon the population estimates within this study it is evident this population of Nicrophorus americanus is in excess of 500 adults and thus would qualify as one of those three separate and independent populations.

Further work is necessary to determine if specimens located in the Sandhills of north- central Nebraska and those in South Dakota are distinct populations or interconnected to this population south of the Platte River in central Nebraska.

REFERENCES CITED

Creighton, Curt. 1994. "Life history, breeding ecology and movement of American burying beetles in Oklahoma and Arkansas." Presentation to the American Burying Beetle Meeting, Norman, Oklahoma.

Jameson, Mary Liz and Brett C. Ratcliffe. 1991. A survey to determine the occurrence of Nicrophorus americanus Olivier (the American Burying Beetle) on the Platte River islands near Kearney. Final report to the United States Department of the Interior, Fish and Wildlife Service, Rainwater Basin WMD. 10pp.

Kozol, Andrea J. 1990. Suggested survey protocol for Nicrophorus americanus, the American burying beetle. Report to the U.S. Fish and Wildlife Service. 6pp.

Overton, W.S. and D. E. Davis. 1969. Estimating the numbers of animals in wildlife populations. pp.403 - 495. In R. H. Giles, Jr. (ed.). Wildlife management techniques. Wildlife Society, Washington, D.C.

Ratcliffe, Brett C. 1990. A survey to determine the occurrence of Nicrophorus americanus Olivier (the American Burying Beetle) in the Gerald Gentleman Station Rail Spur Project Area. Final report to the Nebraska Public Power District.

U.S. Fish and Wildlife Service. 1991. American burying beetle (Nicrophorus americanus) recovery plan. Newton Corner, MA. 80 pp.

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Last updated by Darren A. Jack on 4/24/97