Triangulating from the cairns…
An alternative burial behavior observed in Nicrophorus, namely the use of abandoned burrows (holes) for carcass interment, was studied in Colorado. In 1998 and 1999, 50 carcasses of native rodents were placed in meadow habitats known to be preferred by Nicrophorus investigator for carcass burial and rearing young. In 1998, carcasses were placed 200 cm from holes. In 1999, carcasses were placed either 100 cm from holes. In 2000, 40 pairs of beetles were provided carcasses in screened containers. Containers were assigned to one of two treatments: smoothed soil or hole. Carcasses were checked daily and carcass movement, burial, and the use of the nearby holes were noted. Broods were collected and weighed 14 days after interment. In the field, adult beetles dragged carcasses to nearby (20 cm) holes in 73% of burials, this percent decreased with increased distance to the hole. Time to interment was less for those carcasses moved to nearby holes. The proportion of successful broods (larvae present in buried carcasses) was significantly higher for those carcasses dragged to holes. For successful broods, no differences in larval size or number were found. The density of burrow openings was ?3 holes/m2. The results in dicate that burrowing rodent activity may have an indirect positive effect on Nicrophorus re productive success. The unique carcass-burial behaviors and biparental care of Nicrophorus have in terested biologists for over a century. Early descriptions of the burial process, in cluding those by Fabre (1918), Pukowski (1933), and Milne and Milne (1976), have provided the scheme that is widely understood. However, in reality there exists vari ation within the genus Nicrophorus in the degree to which burial behaviors follow this general scheme, and indeed, whether burial occurs at all (Scott, 1998). Few stud ies directly examine the effects of these variations on reproductive success. The general scheme of carcass burial is as follows (reviewed in Eggert and Muller, 1997, and Scott, 1998): adult beetles search for carcasses, locating them through chemosensory means. Both males and females defend a carcass against later-arrivals, as well as determine whether or not the carcass is of appropriate size. Adults also determine whether the substrate is suitable for burial; if not then they may make short trips to nearby terrain to locate and then move the carcass to softer substrate. Burial occurs as beetles plow through the soil beneath the carcass, allowing it to sink and be covered by soil. Burial may take anywhere from hours to days, depending on any number of factors including substrate type, temperature, and microhabitat (Scott, 1990). Depending on the species and habitat, one or both parents remain in the bur ial chamber for 8-20 days maintaining the carcass, feeding the young, and defend ing against intruders. Field studies of Nicrophorus investigator Zetterstedt carcass selection behaviors, habi tat associations, demography, and morphological variation along altitudinal gradients have been conducted since 1992 in the montane environment of southern Colorado (Smith and Heese, 1995; Smith et al., 2000; Smith and Merrick, 2001). During these projects, a variation in the burial behavior, namely the dragging of carcasses to nearby holes in the ground left by burrowing rodents, was observed to occur on numerous 1 Department of Biological Sciences, Idaho State University, Pocatello, Idaho 83209. 2 Rocky Mountain Biological Laboratory, Crested Butte, Colorado 81224. This content downloaded from 157.55.39.17 on Fri, 02 Sep 2016 05:09:45 UTC All use subject to http://about.jstor.org/terms VOLUME 73, ISSUE 3 149 occasions. The purpose of this study was to describe this specific variation in burial behavior and to measure its impact on reproductive success in Nicrophorus investi gator (Zetterstedt). Methods and Materials The experimental study was carried out at the Rocky Mountain Biological Labo ratory (RMBL) in Gothic, Colorado. The RMBL is located at 2900 m in the south ern Rocky Mountains. The vegetation is primarily of the fescue community type de scribed by Langenheim (1962). The soil is highly disturbed by burrowing rodents, primarily pocket gophers, Thomomys talpoides (Thompson et al., 1996). At this el evation, N. investigator is active aboveground from the end of June until the end of August (Smith et al., 2000). Peak reproductive activity occurs in mid-July. Although Af. defodiens is also found at this site, its reproductive activity is primarily restricted to late June (R. Smith, unpubl. data). In July 1998, an experiment was conducted to determine the maximum distance from an abandoned burrow (hole) to which TV. investigator would drag a carcass for interment. Based on previous observations of Af. investigator dragging carcasses up to 1.5 meters, distances of 20, 50, 100 and >200 cm were selected. Thirty native mouse (Peromyscus maniculatus) or vole (Microtus montanus) carcasses weighing between 18-28 grams (a size known to be preferred by N. investigator, Smith and Heese, 1995) were placed 25 meters apart in a meadow, eight each at 20 and 50 cm and seven each at 100 and 200 cm from a hole. (Existing holes were used because beetles may locate holes by chemosensory means). At each distance an area of equal diameter was carefully searched and any additional holes were filled with soil. A flag was placed at the location of the hole as well as at the initial location of the carcass. To facilitate location, a 20 cm yellow string was tied to each carcass. Carcasses were checked in the morning and late afternoon to determine whether they had been lo cated by beetles, buried in situ, dragged to a new location and buried, or dragged to the hole. The distance moved was measured. The brood was removed after 14 days of burial, and the larvae counted and weighed. At the same site, the density of nat urally occurring holes (larger than 4 cm in diameter) was measured by searching for holes at ten random points along a 60-m transect. All holes within a 1-m radius of the point were counted. In July 1999, a follow-up experiment was conducted to supplement the data com paring the relative reproductive success of in-situ burial versus use of holes. In the same meadow, 20 mouse carcasses were set out, 10 within 20 cm of a hole and 10 >1 m from a hole. As before, all other holes were filled. Each carcass was checked twice a day to determine when it was located by beetles, whether or not it was buried in-situ, dragged to a new location, or dragged to the hole. The brood was removed after 14 days of burial, and the larvae counted and weighed. In July 2000, a captive breeding experiment was conducted to more adequately control for factors related to beetle body size, number of beetles present at the car cass, soil type, carcass size, and climatic effects. Forty pairs of beetles, twenty large pairs (elytra 10.5 mm ? 0.056) and twenty small pairs (elytra 8.8 mm ? 0.050), were randomly assigned to captive breeding containers (steel cans, 15 cm diameter, 17 cm depth). Each of the containers was randomly assigned a treatment of either hole or no hole. Holes were tubes of toilet paper rolls cut in half. The tubes were dug-in level with the soil in the containers at a slight angle to allow beetles easy movement in This content downloaded from 157.55.39.17 on Fri, 02 Sep 2016 05:09:45 UTC All use subject to http://about.jstor.org/terms 150 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY
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