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Nov 20, 2002 - Benefit of migration in a female sika deer population in eastern Hokkaido, Japan. Mayumi Sakuragi,1 Hiromasa Igota,1 Hiroyuki Uno,2 Koichi ...
Blackwell Science, LtdOxford, UKEREEcological Research0912-38142003 Ecological Society of JapanJuly 2003184347354Original ArticleBenefit of migration in female sika deerM. Sakuragi et al.

Ecological Research (2003) 18, 347–354

Benefit of migration in a female sika deer population in eastern Hokkaido, Japan Mayumi Sakuragi,1 Hiromasa Igota,1 Hiroyuki Uno,2 Koichi Kaji,3* Masami Kaneko,3† Rika Akamatsu4 and Koji Maekawa1 1

Laboratory of Boreal Forest Conservation, Field Science Center for Northern Biosphere, Hokkaido University, Sapporo 060-0809, Japan, 2Eastern Hokkaido Wildlife Research Station, Hokkaido Institute of Environmental Sciences, Kushiro 085-0835, Japan, 3Hokkaido Institute of Environmental Sciences, Sapporo 060-0819, Japan and 4EnVision, Sapporo 060-0809, Japan The major factors affecting migration in large herbivores have been shown to be access to food resources and the risk of predation. Three migratory types of deer (resident, north migrant and east migrant) occur within a wintering female sika deer (Cervus nippon) population in eastern Hokkaido, Japan. We tested the hypothesis that north and east migrants feed on a higher quality diet than residents during summer, based on analyses of fecal nitrogen content. Fresh fecal pellets were collected in 18 summer ranges in the wintering area, northern area and eastern area between 1–5 August 2000. Fecal nitrogen content for all sampling sites was positively correlated with elevation, but was not correlated with distance from the wintering area. North migrants that inhabited higher (above 300 m elevation) summer ranges fed on a higher quality diet than residents. In contrast, the dietary quality of east migrants that migrated over a long distance and inhabited lower (below 300 m elevation) summer ranges was similar to that of residents. We conclude that east migrants may have gained significant benefit from the use of agricultural pastures with low population density conditions and without hunting; however, the recent population control program has reduced this benefit by avoiding the use of pasturelands. Key words: Cervus nippon; dietary quality; fecal nitrogen; seasonal migration; sika deer.

INTRODUCTION Many populations of large herbivores migrate seasonally between discrete home ranges (Fryxell & Sinclair 1988). Selection should favor those individuals that migrate, if reproductive success is enhanced by migration (Baker 1978). However, alternative strategies such as migration and nonmigration can occur within the same species or even within the same population because of environmental fluctuations and individual differences

*Author to whom correspondence should be addressed. Email: [email protected] † Present address: Department of Regional Environment Studies, Faculty of Environment Systems, Rakuno Gakuen University, Ebetsu 069-8501, Japan. Received 17 October 2002. Accepted 20 November 2002.

in the costs of migration (Fretwell 1972). Lifetime reproductive success is a function of both survivorship and birth rate (Caughley 1977), and the adaptive significance of migration can best be understood by examining the selective forces acting on these life-history parameters (Dingle 1980). The results of several studies have implicated the quality and availability of forage and the risk of predation as the ultimate factors affecting migration (Taylor & Taylor 1977; Fryxell & Sinclair 1988). Fryxell and Sinclair (1988) suggested that variation in food quality might generally be more important than absolute abundance in determining movement patterns. Clear trade-offs of migration exist for mule deer (Odocoileus hemionus) in montane areas of southern California (Nicholson et al. 1997). Migratory females use habitats that provide high quality food more often than resident females do, but deer are at an increased risk of predation during migration

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(Nicholson et al. 1997). Thus, if there is a great risk of mortality during migration, we predict that migratory deer should use habitats of higher quality than resident deer. Moreover, we also predict that distance of migration and dietary quality should be positively correlated, because risk during migration can be predicted to increase with distance of migration. Small differences in digestibility of forage or protein intake can markedly influence weight gain in ungulates (Blaxter et al. 1961; McEwan & Whitehead 1970; Verme & Ozoga 1980; White 1983; Schwartz et al. 1988), which may lead to higher fecundity (Gunn et al. 1969; Iason et al. 1986) and improved survival (Mitchell 1984). Thus, habitat quality greatly affects the life history of sika deer. Sika deer (Cervus nippon) in Hokkaido, the most northern island of Japan, declined to a threatened level a century ago (Inukai 1952), but three subpopulations (Daisetsu, Akan and Hidaka) were able to survive the crash (Nagata et al. 1998). The sika deer population in eastern Hokkaido, which originates from the Akan subpopulation (Nagata et al. 1998), has recovered and expanded its distribution during the past three decades and has occupied its potential habitats (Kaji et al. 2000). A wintering female sika deer population on the Shiranuka Hills adjoining the Akan mountains in eastern Hokkaido has a mixed pattern of migration: the population includes both migratory and resident individuals (H. Igota, unpubl. data, 2001). Migratory individuals are grouped into two types (north migrants and east migrants) based on the direction and habitats of their summer ranges (H. Igota, unpubl. data, 2001). North migrants move to high elevation (above 300 m) summer ranges in the northern mountainous area, while east migrants move to low elevation (below 300 m) summer ranges in eastern flatlands. The movement between low elevation winter ranges and high elevation summer ranges by north migrants in our study population is similar to the movements by deer in previous studies (Maruyama 1981; Schoen & Kirchhoff 1985; Garrott et al. 1987; Albon & Langvatn 1992; Takatsuki et al. 2000). Langvatn and Albon (1986) showed that in a wintering population of red deer ( C. elaphus) in Norway, migratory females that inhabited high

elevation (above 250 m) summer ranges were heavier in the autumn than resident females that inhabited low elevation (below 250 m) summer ranges, and suggested that this was because individuals moving to a high elevation had access to a higher quality diet than resident individuals. Therefore, we predicted that north migrants in our population would have a higher quality diet than residents. However, east migrants in our study moved between high elevation winter ranges and similar or low elevation summer ranges (Sakuragi et al. in press). If there is a relationship between elevation and dietary quality similar to that reported by Albon and Langvatn (1992), why do east migrants move to similar or lower elevation summer ranges than residents? The nutritional quality of natural vegetation was declining because of plant senescence (Wallmo et al. 1977); however, agricultural pastures had higher levels of crude protein than native forage and provided deer with green and succulent forage (Griffin 1991; Osborn and Jenks 1998). Agricultural pastures dominate in the eastern flatlands of Hokkaido, which east migrants inhabit during summer, unlike the other areas (Fig. 1). We predict that east migrants feed on a higher quality diet than residents, because they have access to agricultural pastures. Our objective was to examine differences in dietary quality of areas which the three migratory types of deer (resident, north migrant and east migrant) used during summer, and to test the hypotheses that both north and east migrants have a higher quality diet than residents. We also examined the relationship between elevation, distance from the Shiranuka Hills wintering area, and dietary quality.

METHODS Study area We conducted the telemetry study in eastern Hokkaido, Japan. The climate of the study area is cool and humid with an average temperature of -10.4∞C in February and 17.4∞C in August; the mean annual temperature is 3.6 ∞C. Annual precipitation is 1200 mm at Akan (Igarashi 1986).

Benefit of migration in female sika deer (a)

(b)

(c) Coniferous forests Mixed forests Deciduous forests Japanese larch forests Agricultural pastures Other

Fig. 1. Area percentage of vegetation types of the (a) wintering, (b) northern and (c) eastern areas in eastern Hokkaido, Japan.

The vegetation of the Shiranuka Hills wintering area (200–300 m), where all the radio-collared deer (Sakuragi et al. in press) were captured and residents remained throughout the year, is composed of coniferous forests, mixed forests and deciduous forests (Fig. 1a). The vegetation of the northern high elevations (northern area; above 300 m), which north migrants inhabited during summer, is primarily composed of coniferous forests and mixed forests (Fig. 1b). The vegetation of the eastern low elevations (eastern area; below 300 m), which east migrants inhabited during summer, is primarily composed of deciduous forests, plantations of Japanese larch ( Larix leptolepis) and agricultural pastures (Fig. 1c). Dominant species in coniferous forests are Yezo spruce (Picea jezoensis), Sakhalin fir (Abies sachalinensis) and Sakhalin spruce (Picea glehnii), and these are mixed with Japanese linden ( Tilia japonica) and Japanese oak (Quercus crispula) in mixed forests. Deciduous forests are composed of Japanese oak, Japanese white birch (Betula platyphylla), painted maple (Acer mono), Japanese linden, Japanese elm (Ulmus davidiana), Japanese ash (Fraxinus mandshurica), Amur cork tree (Phellodendron amurense), caster aralia (Kalopanax pictus) and willow (Salix spp.) (Igarashi 1986).

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Study analyses Most nutritional studies of ungulates have used fecal nitrogen (FN) content as an index of dietary quality because of the relationship between nitrogen and protein (Osborn & Jenks 1998). The concentration of nitrogen in feces has been correlated with dietary intake of nitrogen and has been used successfully to monitor dietary quality of blacktailed deer (O. hemionus columbianus; Leslie & Starkey 1985), white-tailed deer (O. virginianus; Howery & Pfister 1990; Jenks et al. 1996) and sika deer (Asada & Ochiai 1999). We used FN content to estimate the dietary quality in each of the summer range areas in this study. To examine the relationship between elevation, distance from the Shiranuka Hills wintering area and dietary quality, we selected 18 summer ranges of our radio-collared female sika deer with various elevations and various distances from the Shiranuka Hills wintering area in the wintering area, northern area and eastern area (Table 1). Fecal pellet groups found within the 18 summer ranges were collected between 1–5 August 2000. Sexual segregation has been reported for many ungulates (Bowyer 1986; Scarbrough & Krausman 1988; Miquelle et al. 1992; Bowyer et al. 1996) and also for sika deer (Miura 1976; Maruyama 1981); therefore, fecal pellet groups collected within the summer ranges of female sika deer were assumed to be those of females. To ensure that the concentration of FN was not degraded by exposure to environmental factors ( Jenks et al. 1990), only fresh pellet groups (within 1 or 2 days of being dropped) were collected. The sample of fecal pellets in the wintering area was only four in August 2000, so we included 10 samples collected on 11 August 1998 during our preliminary research, because no significant difference in FN was found between the samples of 1998 and 2000 (Mann–Whitney U-test; U = 10.0, Z = -1.414, P = 0.1573). All fecal samples were stored frozen until processed. Each fecal sample was dried at 70 ∞C for 48 h and then ground with a mill (Asada & Ochiai 1999). Nitrogen level in the dry matter percentage of the feces was estimated using the CHNS/O analyzer (PerkinElmer Japan, Yokohama, Kanagawa, Japan). We used a Kruskal–Wallis test and a Bonferroni correction for multiple comparisons (Rice

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Table 1 Elevation, distance from the wintering area and number of fecal pellet groups collected for the 18 sampling sites in eastern Hokkaido, Japan Site no.

Elevation (m)

Distance from the wintering area (km)

No. fecal pellet groups collected

Wintering area Northern area

3 2 30 46 9 22 57 31 23 24 18

Eastern area

36 4 6 52 12 17 33

247 370 388 404 420 426 559 575 586 629 797 515 ± 137 (SD) 277 190 188 156 99 36 17 138 ± 92 (SD)

– 7 36 10 51 34 37 17 45 17 26 28 ± 15 18 44 35 35 58 85 102 54 ± 30

14 4 4 3 7 10 2 3 1 3 5 Total = 42 2 3 4 4 8 1 5 Total = 27

Area

1989), and a Spearman’s rank correlation for assessing the relationship between elevation, distance from the wintering area and FN content.

RESULTS The mean FN content was significantly different across the three areas (Kruskal–Wallis test; P < 0.001). FN content was significantly higher in the northern area than in the wintering area (P < 0.0001) and the eastern area ( P = 0.0018). In contrast, FN content was not significantly different between the wintering area and the eastern area (P = 0.1479) (Fig. 2). The FN content for the sites within both the northern area (rs = 0.30, n = 10, P = 0.373) and the eastern area (rs = -0.18, n = 7, P = 0.662) was not significantly correlated with elevation, although FN content for all sampling sites was significantly correlated with elevation (rs = 0.59, n = 18, P = 0.015) (Fig. 3). The FN content for the sites within both the northern area (rs = 0.47, n = 10, P = 0.162) and

the eastern area (rs = 0.25, n = 7, P = 0.540) was not significantly correlated with distance from the wintering area (Fig. 4). FN content for all sampling sites was also not significantly correlated with distance from the wintering area (rs = 0.09, n = 18, P = 0.714) (Fig. 4).

DISCUSSION Our results demonstrate that migratory deer do not necessarily obtain a higher quality diet than resident deer during summer in a wintering female sika deer population. As predicted, north migrants that inhabited higher elevation summer ranges fed on a higher quality diet than the residents. The positive relationship between elevation and FN content for all sampling sites supports the conclusion that individuals moving to high elevations have access to a higher quality diet than resident individuals (Langvatn & Albon 1986; Albon & Langvatn 1992). Protein content and digestibility of vegetation are positively correlated with elevation (Van Soest 1983). Albon and Langvatn (1992) discussed the benefits of moving

Benefit of migration in female sika deer

351

3.5

** 3.0

3.0

2.5

Fecal nitrogen content (%)

Fecal nitrogen content (%)

3.5

42

2.0

27 14

1.5

2.5

2.0

1.5

* 1.0 Wintering area

Eastern area

1.0

Northern area

0

Fig. 2. Mean fecal nitrogen contents (% ± SD) in the wintering, northern and eastern areas. Values shown in the figure refer to sample size. *P < 0.01, **P < 0.0001.

20

40

60

80

100

120

Distance from the wintering area (km)

Fig. 4. Mean fecal nitrogen contents (% ± SE) at each of the 18 sites in the wintering (), northern () and eastern () areas, plotted against distance from the wintering area (km).

3.5

Fecal nitrogen content (%)

3.0

2.5

2.0

1.5

1.0 0

200

400 Elevation (m)

600

800

Fig. 3. Mean fecal nitrogen contents (% ± SE) at each of the 18 sites in the wintering (), northern () and eastern () areas, plotted against elevation.

to high elevations from the viewpoint of plant phenology. Spring migration to higher elevations where the snow melts later, temperatures are lower, and the onset of plant growth is later, allows prolonged access to a diet high in protein and low in fiber (Klein 1970; Atzler 1984) and enhanced digestibility (Bennett & Mathias 1984; Hay & Heide 1984).

In contrast, contrary to our original prediction, dietary quality of east migrants that inhabited lower elevation summer ranges was similar to that of residents. A possible reason for this is that east migrants may not use agricultural pastures as frequently as we had originally predicted. Our previous study indicated that two east migrants were located on agricultural pastures in only 6 and 17% of the locations examined every 2 h over three consecutive 24-h periods in August 2000 (Sakuragi et al. 2002), although agricultural pastures account for approximately 40% of the eastern flatlands (Fig. 1c). This is probably due to avoidance of hunting or other interactions with humans because of the aggressive culling program by the Hokkaido Government (Sakuragi et al. 2002). Indeed, damage to agricultural pastures and crops by sika deer has been decreasing since 1996 in Hokkaido (Hokkaido Government 2002). Moreover, contrary to our original prediction, dietary quality was not correlated with distance from the Shiranuka Hills wintering area in our sample. East migrants appeared to be at a greater risk than north migrants and residensts because they migrated the longest distance (Table 1) and moved through open agricultural pastures where culling by humans is intensive. Indeed, during

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previous surveys, radio-collared east migrants have died from culling by humans to protect agricultural fields (H. Igota, unpubl. data, 2001). In spite of the high risk of a long migration and the fact that east migrants do not necessarily benefit from increased access to a high quality diet by migration compared with north migrants and residents, how has the migratory strategy of east migrants evolved and why is it maintained within the population? In an assessment of habitat change over the past 30 years, Kaneko et al. (1998) found that in eastern Hokkaido, more than half of the deciduous broad-leaved forest and natural open fields had been converted to agricultural fields or plantation forests. Use of agricultural pastures and crops during summer sustained good nutritional conditions (Yokoyama et al. 1996) and a high reproductive performance (Suzuki & Ohtaishi 1993) in sika deer. Kaneko et al. (1998) and Yokoyama et al. (2000) argued that sika deer have benefited from increased forage resources after agricultural and other human developments and such landscape-level changes have increased their available food resources, leading to recent population irruptions in eastern Hokkaido (Kaji 1995). We suppose that individuals that opportunistically accessed agricultural pastures in the eastern areas by migration might have been favored in the expansion of sika deer from the Shiranuka Hills throughout eastern Hokkaido during the past 30 years under a situation of no culling pressure on female deer (i.e. only male sika deer have been hunted since 1993). However, the benefit from use of agricultural pastures may have decreased as deer density and hunting pressure increased. The migration tradition of deer is maintained through social interactions (Van Deelen et al. 1998). Offspring of east migratory females tend to be east migrants regardless of their present dietary quality because behavioral adaptations in ranging patterns to maximize the intake of digestible energy and high quality nutrients may take many generations to evolve (Clutton-Brock & Harvey 1979). Offspring learn the migration tradition from the maternal parent and individuals of the herd (Sweanor & Sandegren 1988, 1989; M. Sakuragi et al., unpubl. data, 2001) and remain faithful to those traditions throughout life (Nelson & Mech 1981, 1984; Nixon et al. 1991).

ACKNOWLEDGEMENTS We thank E. Shima, C. Iizima, M. Endo and H. Maeno for helping us with collecting fecal pellets, and T. Ito, H. Ueda, Z. Jiang and T. Yabe, M. Kayama, M. Ozawa and M. Ueno for helping us with the fecal nitrogen analyses. We are very grateful to S. Hamasaki, M. Kishimoto, Y. Kamiyama, the staff of the Wildlife Management Office, EnVision and the Hokkaido Government for capturing deer, assisting with the collection of data and supporting our work. We also thank the Akan Town Office, Shiranuka Town Office, Teshikaga Town Office, and H. Sugawara for supporting our work. We acknowledge K. Tamada, T. Saitoh and the students of the Laboratory of Boreal Forest Conservation, Hokkaido University, for stimulating discussions. This study is supported by the Hokkaido Government and by a Grant-in-Aid for Scientific Research (14000353 to MS and 14340240 to KM) from the Ministry of Education, Culture, Sports, Science and Technology and the Agency of Japan Society for the Promotion of Science.

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