INTRODUCTION
With the expansion of human
activities, reports of anthropogenic food consumption by wildlife are
increasing worldwide (Oro et al., 2013). Access to anthropogenic foods
by wildlife can increase human–wildlife conflict, resulting in economic
losses (e.g., predation on agricultural crops and livestock) as well as
increased risk of vehicle collisions and infectious disease transmission
among wildlife, humans, and livestock (Cote et al., 2004; Becker et al.,
2015; Honda et al., 2018; Johnson et al., 2020). Additionally,
anthropogenic food consumption can affect wildlife population dynamics
and local ecosystems via alterations in behavioral traits and
physiological conditions (Prange et al., 2004; Oro et al., 2013; Gaynor
et al., 2018; Tucker et al., 2018; Petroelje et al., 2019; Hernando et
al., 2020). To mitigate these conflicts, it is important to develop
management strategies for individuals that consume anthropogenic foods.
For managing anthropogenic food-foraging wildlife, understanding their
spatial distribution pattern is important to determine the efficient
spatial allocation of management efforts. In particular large
terrestrial mammals, even they consumed anthropogenic foods in
artificial landscapes such as agricultural crop fields, they move across
distant other habitats (Takada et al., 2002; Hata et al., 2017).
Therefore, understanding the spatial distribution patterns of
anthropogenic food-foraging individuals is necessary to prioritize areas
where limited management effort should be allocated to mitigate
conflicts. Previous studies have investigated the spatial distribution
of large terrestrial mammals by direct and indirect observations, such
as radiotelemetry and camera trap surveys (Sanderson, 1966; Rubenstein
& Hobson, 2004). However, these techniques have some limitations,
including substantial effort and costs, and inability to obtain
information about the diet and geographical location of animals
simultaneously (Rubenstein & Hobson, 2004; Hobson, 2005). Stable
isotope analysis is an alternative tool that overcomes these weaknesses
of conventional approaches (Crawford et al., 2008; Hobson et al., 2010).
The stable isotope ratios in animal tissues are related to those in the
diet (DeNiro & Epstein, 1978, 1981); when the isotope values differ
between anthropogenic and natural food resources, animal tissues reflect
the foraging history of anthropogenic foods (Mizukami et al., 2005;
Ditmer et al., 2016; Hata et al., 2017, 2021; Demeny et al., 2019).
However, only few studies have described the spatial distribution
patterns of anthropogenic food-foraging animals (Walter, 2014; Hata et
al., 2017).
Deer are typical large terrestrial mammals that move across multiple
landscapes. In middle- to high-latitude regions, deer often migrate
seasonally in accordance with snow depth and food availability (Kufeld
et al., 1989; Ball et al., 2001; Sabine et al., 2002; Igota et al.,
2004). The consumption of anthropogenic foods, including agricultural
crops, by deer has been documented and causes serious economic losses in
many countries (Fagerstone & Clay, 1997; Putman & Moore, 1998;
McCullough et al., 2009). Moreover, crop consumption has the potential
to induce deer population growth (Iijima et al., 2013; Hata et al.,
2021), which can increase agricultural crop damage and induce ecosystem
changes; the increment of browsing pressure on the forest understory,
the inhibition of woodland regeneration, and the promotion of
fluctuations in the population and community structure of various taxa,
from insects to mammals (Cote et al., 2004). To mitigate conflicts that
arise from crop consumption by deer, it is necessary to understand
spatial distribution patterns of crop-foraging deer to manage them at an
appropriate spatial scale.
In Japan, the consumption of crops, such as vegetables and pasture
grasses, by sika deer (Cervus nippon ) is well-documented and
causes serious economic losses (Ministry of Agriculture, Forestry and
Fisheries, 2018). To mitigate conflicts, damage prevention management
such as fencing and culling are conducted. Although many deer are killed
every year (e.g., about 600,000 individuals were killed in Japan in
2019, in which about 23% were by hunting and 77% by culling) (Ministry
of the Environment, 2020), agricultural damage by deer still amounts to
over 50 million dollars every year (Ministry of Agriculture, Forestry
and Fisheries, 2018). More efficient and effective management strategies
are needed to mitigate conflicts arising from crop consumption by deer.
Sika deer inhabit various landscapes from plains to high-altitude areas
(Takatsuki, 2009) and migrate seasonally, as do most ungulates at middle
and high latitudes (Igota et al., 2004; Takii et al., 2012a, b).
Therefore, agricultural crop-foraging deer may not consistently inhabit
near agricultural crop fields throughout all seasons and may move long
distances during the winter and spring, when crop production decreases.
Because the food resources for deer are limited during the winter and
spring (Yokoyama et al., 2000; Seto et al., 2015), deer culling is
suitable during these seasons when the bait-trap success improves, and
shooting also can be easy with better visibility without leaves.
Therefore, clarifying the spatial distribution pattern of crop-foraging
deer during these seasons will facilitate the efficient spatial
allocation of management efforts to mitigate conflicts.
In this study, we examined the spatial distribution pattern of
crop-foraging sika deer during the winter and spring in central Japan.
We investigated crop consumption by performing nitrogen stable isotope
analyses of bone collagen samples. The nitrogen stable isotope ratios
(δ15N) of bone collagen were expected to reflect the
foraging history and crop consumption by individual deer (Hata et al.,
2021). We examined whether deer likely to consume crops live closer to
agricultural crop fields, even during the winter and spring.