SHORT COMMUNICATION

Seasonal changes and altitudinal variation in deer fecalpellet decay

Shinsuke Koike & Masashi Soga & Hiroto Enari &Chinatsu Kozakai & Yui Nemoto

Received: 6 September 2012 /Revised: 1 April 2013 /Accepted: 10 April 2013 /Published online: 24 April 2013# Springer-Verlag Berlin Heidelberg 2013

Abstract Surveying dung pellet groups to estimate popula-tion size requires knowledge of the dung decay rates in dif-ferent environmental conditions. We evaluated seasonal andelevational differences in the decay rates of fresh deer pelletsin the Ashio–Nikko Mountains, Japan. At each of four sites(1,500, 1,200, 900, and 600m above sea level), we set out fourreplicates of 50 fresh deer pellets each month from September2008 to August 2009. Dung pellet groups were evaluated after24 h and again monthly. We also monitored the dung beetlefauna monthly using pitfall traps. Dung beetle activity waspositively correlated with temperature, and the rate of dungdecay was strongly correlated with dung beetle dry weight.Decay was most rapid during summer and at lower altitudes;pellets set out during winter did not decay until the following

spring. Resource managers who use dung surveys to estimatepopulation sizes in mountainous regions should consider thedecay rates at different altitudes.

Keywords Dung beetle .Cervus nippon . Fecal pelletdecay . Pellet group count . Population estimate . Sika deer

Introduction

To manage wildlife effectively, information is needed on theirabundance. Pellet group counts have been widely used as anindirect method for estimating the absolute or relative abun-dance of ungulate populations. Pellet group counts are typicallyconducted using the clearance plot or standing crop method(Staines and Ratcliffe 1987; Mayle 1996). To convert estimatesof dung density to estimates of animal density, especially by thestanding crop method, the dung decay rate must be estimated.This rate may vary among habitats and time periods, dependingupon the weather (temperature, moisture, rainfall, and evapo-ration), fiber content of the droppings, frequency of copropha-gous insects, and foraging for insects by birds (see Massei et al.1998; Mayle 1996). Some previous studies have indicated thatthe biggest influence on dung decay was the activity of dungbeetles (e.g., Hanski and Cambefort 1991).

In Japan, the distribution of sika deer (Cervus nippon)has expanded from low elevation to alpine areas [more than2,500 m above sea level (a.s.l.)] (Takatsuki 2009). Becausethe dung beetle fauna varies by elevation (Jay-Robert et al.1997; Lobo et al. 2007), the deer dung decay rate may alsodiffer dramatically with altitude, even among sites that arerelatively near to one another. To estimate the deer popula-tion of a given area, local managers must apply the appro-priate dung decay rate for each elevation level, because mostdeer habitats in Japan are in mountainous areas. However,few studies have investigated the variation in dung beetle

Communicated by C. Gortázar

S. Koike (*) :M. Soga : C. Kozakai :Y. NemotoTokyo University of Agriculture and Technology, 3-5-8 Saiwai,Fuchu 183-8509, Japane-mail: koikes@cc.tuat.ac.jp

H. EnariSatoyama Science Research Center, Faculty of Agriculture,Utsunomiya University, 350 Minemachi,Utsunomiya 321-8505, Japan

Present Address:M. SogaHokkaido University, Nishi 9, Kita 9, Kita-ku,Sapporo 080-8589, Japan

Present Address:H. EnariYamagata University, 1-23 Wakabamachi,Tsuruoka 997-8555, Japan

Present Address:C. KozakaiKanagawa Prefectural Museum of Natural History, 499 Iryuda,Odawara 250-0031, Japan

Eur J Wildl Res (2013) 59:765–768DOI 10.1007/s10344-013-0724-9

assemblages with altitude, and there are no reports of dif-ferences in dung decay rate with altitude. To avoid over- orunderestimating deer abundance, dung decay rates must beestablished for each elevation level. In this study, we esti-mated the deer dung decay rates at different altitudes.

Materials and methods

We conducted the study in the Ashio–Nikko Mountains(E36.54–36.80°, N139.22–139.49°), in part of the NikkoNational Park in Gunma and Tochigi prefectures, centralJapan. Annual mean precipitation is 2,236 mm, and annualmean temperature is 7.2 °C below 1,600m a.s.l. Four samplingsites at different altitudes were within a 30-km diameter: site A,1,500 m a.s.l.; site B, 1,200 m; site C, 900 m; and site D,600 m. We chose study sites with similar vegetation structuresto minimize the impact of vegetation on dung beetle fauna. SiteA was dominated by Quercus crispula, Fagus crenata, andAbies firma. Sites B and Cwere dominated byQ. crispula. SiteD was dominated by Quercus serrata. At all four sites, theforest floor was covered mainly with sasa grass (Sasanipponica). We placed waterproof temperature data recorders(TR-51i, T&D Corporation, Matsumoto, Japan) at each site.

Dung beetle fauna

Dung beetles were sampled using dung-baited pitfall traps inthe middle of each month from September 2008 to August2009. Plastic containers (200 mm diameter, 100 mm deep)containing 150 ml of 50 % ethylene glycol as a preservativewere buried to the rim in the ground. A plastic cup (100 mmdiameter, 50 mm deep) containing 50 g of fresh deer dung wassuspended with wire at the mouth of the container. Three trapswere buried in the soil at 20-m intervals along a transect line ateach of the four sites for 24 h. Collected beetles were identi-fied to species, dried (60 °C for 48 h), and weighed.

Pellet group decay rate

Decay rates of deer pellet groups were measured fromSeptember 2008 to August 2009. Fresh pellets were collect-ed within the study area for each investigation; pellets wereidentified as fresh if they were soft with a shiny surface andwithout any signs of decomposition or dung beetle activity.In the middle of every month, four replicates of pelletgroups (50 fresh pellets in each group, 200 pellets total)were placed on the litter at each site. The average number ofpellets per deer defecation was 50 (Horino and Nomiya2008). We monitored the number of intact pellets remainingafter 24 h and then once per month until all the pellet groupshad decayed. Individual pellets were considered to bedecayed if they were broken.

Statistical analyses

To evaluate differences in dung decay rates among seasonsand altitudes, we compared the decay rates among monthsand among the four sites using Tukey’s HSD tests.

Results

Dung beetle species composition

A total of 2,367 dung beetles (347, 707, 712, and 601,respectively, in sites A–D) belonging to two species ofGeotrupidae and 20 species of Scarabaeidae were captured.The air temperature differed among the sites in every monthof the study, with the lowest air temperatures at the highestelevation (site A) and the increasing temperature as eleva-tion decreased. There was a strong correlation between totaldry weight of dung beetles and average temperature on theday the trap was set (R2=0.53, P<0.01).

Dung decay rate

We compared dung decay rates after 24 h in each of the12 months of the study (Table 1). At all four sites, dungdecay rates were significantly higher in summer and lowerin winter. We also compared dung decay rates after 24 hamong the four sites. In December, January, and February,decay rates were zero and were not significantly differentamong the sites. In June, the decay rates were high and alsodid not differ significantly among the sites. In other months,the dung decay rates differed among the sites. There was asignificant correlation between the dung decay rates after24 h and after 1 month (R2=0.80, P<0.01). There was also asignificant correlation between the dung decay rate after24 h and the dry weight of dung beetles (R2=0.67, P<0.01).

Figure 1 shows the process of dung decay in the foursites. The dung set out between June and August quicklydecayed within 1 month at all four sites. The dung set outbetween December and February did not begin to decayuntil the next April or May. The process of decay for dungset out between September and November varied amongsites. High-altitude sites had more dung that did not decaywithin 1 month. The dung decay rates for dung set outbetween March and May also varied among the sites; thesesamples required 1–3 months to fully decay.

Discussion

Between March and November, rapid dung decay occurred;especially in summer, about 20 % of dung had decayedwithin 24 h. The dry weight of dung beetles and the 24-h

766 Eur J Wildl Res (2013) 59:765–768

dung decay rate were positively correlated, as were the 24-hand 1-month dung decay rates. These data support theargument that dung beetle activities were a major factor inthe rapid dung decay rate. Thus, if wildlife managers use theclearance plot method to assess deer populations, decayrates must be calculated, and the duration that pellet groups

remain intact must be correlated with the time betweensurveys.

Over 1 month, there were differences in dung decay rateamong altitudes; decay was faster at low altitudes. Variation inthe dung beetle fauna or abundance among the altitudes mayhave affected this result (Table 1). Other studies indicated that

Table 1 Comparisons of decay rates of known quantities of deer dungand the dry weight (in gram) of dung beetles collected monthly at fourdifferent sites. In the Ashio–Nikko Mountains, Japan, dung pellets

were set out mid-month from September 2008 to August 2009 andevaluated 24 h later

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Decay rate

Site A (1,500 m) 0(a, h) 0(a, h) 0(a, h) 1.0(a, h) 4.5(ab, h) 9.3(bc, h) 10.3(bc, i) 12.5(c, hi) 17.5(d, ij) 0(a, h) 0(a, h) 0(a, h)

Site B (1,200 m) 0(a, h) 0(a, h) 0(a, h) 3.0(a, hi) 7.5(b, hi) 13.3(c, h) 20.0(d, hi) 12.0(c, hi) 10.5(bc, i) 4.0(ab, hi) 0.8(a, h) 0(a, h)

Site C (900 m) 0(a, h) 0(a, h) 0.5(a, h) 6.8(b, i) 12.5(cd, i) 14.5(de, h) 19.5(g, hi) 17.5(ef, i) 19.3(g, j) 6.0(b, i) 2.3(a, hi) 0(a, h)

Site D (600 m) 0(a, h) 0(a, h) 4.0(a, i) 6.0(a, i) 6.8(a, h) 11.5(b, h) 13.5(bc, hi) 8.5(b, h) 8.5(c, h) 6.0(a, i) 4.5(a, i) 0(a, h)

Dry weight

Site A (1,500 m) 685 1,120 1,162 1,905 1,002 703 144

Site B (1,200 m) 143 644 2,411 3,094 3,751 2,680 2,847 1,082 160

Site C (900 m) 710 1,388 3,076 3,152 3,982 1,863 2,121 1,126 288

Site D (600 m) 1,036 2,273 2,827 3,711 3,472 1,687 2,802 1,405 341

Lowercase letters indicate significant differences in decay rate among months at each site (letters a–g) or among sites for each month (letters h–j)

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Fig. 1 Decay process of deer dung pellet groups set out in each of12 months at site A (1,500 m above sea level; open square), site B(1,200 m; closed square), site C (900 m; open circle), and site D

(600 m; closed circle) in the Ashio–Nikko Mountains, Japan, fromSeptember 2008 to August 2009. The month in the upper right of eachgraph indicates when the samples were set out

Eur J Wildl Res (2013) 59:765–768 767

air temperature had a large effect on dung decay (Wigley andJohnson 1981; Massei et al. 1998). In this study, air temper-ature correlated to the dry weight of dung beetles, so coolertemperatures may have limited dung beetle activity and thusindirectly influenced the rate of dung decay.

There were also differences in the 1-month dung decayrate among seasons. All four altitudes showed the sameseasonal decay trends: between June and August, more than90 % of dung decayed within 1 month, while no decayoccurred within 1 month between December and February.However, 1-month decay rates varied among altitudes be-tween March and May and between September andNovember. For example, in November, at site A, dung stillon the ground could have been deposited in September,October, or November, but at site D, it could only have beendeposited in November. Thus, managers who select thestanding crop method must include in their calculationshow long the dung may have been on the ground at eachaltitude to avoid overestimating the population.

Here, we showed that the dung decay process differed amongseasons and altitudes, and it may have been affected by differ-ences in dung beetle fauna with elevation. To accurately assessdeer populations, managers using the pellet group method mustfactor in the dung decay rate for each season and each altitude.

Acknowledgments We thank the field crew of the Tokyo University ofAgriculture and Technology for their assistance with conducting fieldsurveys. The Gunma District Forest Office and Nikko District ForestOffice of the Forestry Agency kindly permitted us to set traps in the

national forest. This work was funded by a Grant-in-Aid for JSPS Fellows(no. 20310142) and the Forest Agency, Japan.

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