The use of seismically isolated buildings by urban wildlife in Japan

Abstract

Some wildlife species that have expanded their range into urban areas use various anthropogenic structures for breeding and resting. We investigated the use of seismically isolated buildings, with gaps between the structures and ground surface, by urban wildlife in Japan. Camera traps set in a building revealed that masked palm civets (Paguma larvata) continued to use the building for approximately 3 years. Civet feces and footprints were found in two buildings during field sign surveys. To ensure public health, civets should be prevented from invading seismically isolated buildings by covering gaps with elastic materials and avoiding placing pipes that could be used by the animals near these gaps.

As the world becomes more urbanized, concerns about biodiversity conservation and wildlife management in urban areas are rising [3, 10, 19]. Although many species have become locally extinct because of urbanization [14], several mammalian and avian species have actively colonized urban areas [1, 3, 23]. These urban wildlife species use anthropogenic food and shelter for their survival [1, 9, 15, 23]. The increased use of urban areas by urban wildlife has led to increases in the types and frequencies of human–wildlife conflicts, including economic losses and physical and psychological harms [3, 19, 23]. Thus, understanding how wildlife uses urban resources to survive is critical for the amelioration and mitigation of these conflicts.

Some urban wildlife use anthropogenic structures, such as underfloor spaces and building attics, for breeding and resting [1, 5, 23]. Frequent use of such structures by urban wildlife causes structural damage from excrement and chewing and increases the risk of disease transmission to humans and pets [1, 5, 19, 23]. To reduce the negative effects of urban wildlife, it is critical to prevent wildlife from invading anthropogenic structures such as the buildings frequently used by humans.

In recent decades, seismic isolation has been implemented in more than 15,000 structures worldwide [12]. This earthquake protection method aims to uncouple the motion of a structure from ground shaking, thereby reducing the structural forces by installing isolation devices such as laminated rubber bearings underneath the structure [11, 16]. Because of this trait, gaps exist between seismically isolated buildings and the ground surface. These gaps allow wildlife to enter seismically isolated buildings. Japan has the highest number of seismically isolated buildings worldwide [12]. Owing to the extensive distribution of these structures in densely populated areas, including urban areas, wildlife may have a variety of shelter options. Therefore, evaluating the use of seismically isolated buildings by wildlife is an essential initial step in preventing wildlife invasion of such structures.

The objective of this study was to investigate the use of isolated buildings by wildlife using camera traps and field sign surveys.

Field surveys were conducted in two buildings with seven and five stories (hereafter referred to as Buildings 1 and 2, respectively), in the eastern part of Machida, Tokyo, Japan. The subterranean spaces of Buildings 1 and 2 had floor areas of approximately 1,600 and 3,700 m², respectively. Several pipes and electrical wiring ran through the basement, some of which passed through or near the gaps between the buildings and ground. The two buildings were located approximately 500 m apart. Although the study area contained several small, fragmented forests, the surrounding area was primarily urban. The percentages of urban and forest areas within a 250-m buffer-radius around each building were approximately 55% and 35% for Building 1 and 80% and 20% for Building 2, respectively. Carnivores found in the study area included alien raccoons (Procyon lotor), masked palm civets (Paguma larvata), cats (Felis catus), native raccoon dogs (Nyctereutes procyonoides), Japanese badgers (Meles anakuma), and Japanese weasels (Mustela itatsi), although Japanese badgers are a rare species in the study area [17, 22; Seki, Y., unpublished data].

To investigate the species invading the buildings, field sign surveys were conducted throughout Buildings 1 and 2 between January and February 2019 and the species were identified according to Seki et al. [21]. Ten camera traps (Ltl-Acorn 6210, Ahuhai Ltl Acorn Electronics Co., Ltd., Guangdong, China) were installed inside Building 1 and one was placed outside between March 2019 and December 2021 to investigate how the invading mammals used the building over time (Fig. 1). The camera traps were set up on tripods 0.4–1.0 m above the ground, arranged to avoid overlapping shooting ranges, and were not baited. Three camera traps inside and one outside the building were placed facing the gaps between the building and ground, with one camera trap each inside and outside facing the same gap (hereafter referred to as Gap 1). The remaining seven camera traps were positioned to face the building floor, pipes, or wiring. These traps were programmed to record 60-sec digitized videos with no interval between triggers and normal sensitivity. However, we did not conduct camera trap surveys in Building 2.

Fig. 1.

Locations of 11 camera traps set in a seismically isolated building (Building 1). Solid and open circles represent the locations of camera traps which were placed inside Building 1 and facing the gaps between the building and ground, respectively. Arrows indicate the direction of camera traps. A, a photograph of a gap (Gap 1) taken by a camera trap set outside Building 1; B, a photograph of Gap 1 taken by a camera trap set inside Building 1.

To investigate the use of the interior of Building 1 by wildlife, we counted the number of independent images of wildlife captured using camera traps within the building. The number of independent images of wildlife that were photographed invading the building by the camera trap set outside the building were included in the count. An invasion was defined as the individuals entering the building all the way to the tip of its tail. Images were considered independent when conspecifics were captured more than 30 min apart [25]. As each camera trap was close to the other, the same species photographed more than once using the same or several camera traps within 30 min was classified as a single event. We did not compute the photographic capture rates because several camera traps did not operate properly or stopped recording during the study period because of depleted batteries. To assess the extent of mammalian invasion, the number of images showing wildlife invasion and non-invasion photographed using two camera traps placed inside and outside the building facing Gap 1 was counted. Consecutive images of conspecifics were defined as independent when they were recorded >30 min apart.

Feces and footprints of masked palm civets were found in Buildings 1 and 2 (Fig. 2). The fecal piles were generally found on electric wiring, and their footprints were found on the ground and pipes. These field signs were scattered throughout both buildings.

Fig. 2.

Images of a footprint and a fecal pile of masked palm civets found in a seismically isolated building (Building 1).

The mammals photographed inside Building 1 were masked palm civets, raccoons, and unidentified mice (Fig. 3). These three species only invaded from Gap 1 and did not invade through the other two gaps. One pipe near Gap 1 was placed horizontally, whereas a pipe near the other two gaps was placed perpendicular to the ground of the building’s subterranean space. We captured 1,107 independent images of masked palm civets, one raccoon, and 229 unidentified mice (Table 1). Masked palm civets and unidentified mice moved around using various structures, including pipes, electric wiring, ladders, and thin steel bar (12.5 mm in diameter) that supported pipes and other objects (Fig. 4). The masked palm civets scaled the thin steel bar by grasping it with all four limbs. Masked palm civets were photographed monthly for approximately 3 years (Fig. 5).

Fig. 3.

Three species that invaded a seismically isolated building (Building 1).

Table 1. Number of independent images of wildlife photographed inside a seismically isolated building (Building 1) and numbers of invading and non-invading images of wildlife photographed outside the building.

Species	Inside	Outside
		Invasion	Non-invasion
Masked palm civet	1,107	363	733
Raccoon	1	1	18
Raccoon dog	0	0	236
Weasel	0	0	1
Cat	0	0	145
Unidentified mouse	229	3	422
Bird	0	0	20

An invasion was defined as individuals entering Building 1 all the way to the tip of its tail.

Fig. 4.

Masked palm civets and unidentified mice using a pipe, electric wiring, ladder, and steel bar to navigate a seismically isolated building (Building 1).

Fig. 5.

Number of independent images of masked palm civets photographed in the interior of a seismically isolated building (Building 1). The camera trap effort may have varied each month because several traps either failed to operate correctly or ceased to function because of a potential lack of battery power during the study period.

Masked palm civets, raccoons, raccoon dogs, Japanese weasels, cats, unidentified mice, and birds were photographed near a gap outside Building 1 (Table 1). Masked palm civets frequently invaded. However, raccoon invasion was observed only once in the 19 independent images. Raccoon dogs and cats did not invade; however, they were frequently photographed outside the building.

The main finding of this study was that seismically isolated buildings, which are widespread particularly in urban areas of Japan [16, 24], provide safe havens to some urban wildlife species. This was especially the case for masked palm civets, which were observed using Building 1 regularly for extended periods. Field sign surveys provided further evidence for the observed use of Building 2 by masked palm civets. Our study of two buildings suggests the potential selection of seismically isolated buildings with large subterranean spaces as den sites for masked palm civets. Masked palm civets can easily invade seismically isolated buildings because of their excellent climbing skills. For example, civets can climb up and down square and round wooden poles with widths and diameters of 10–20 cm as well as natural trees [7, 20]. The present study also confirmed that several civet individuals climbed a steel bar with approximately 1 cm in diameter. Such climbing skills of civets would facilitate their frequent use of seismically isolated buildings. Although masked palm civets climb wooden structures such as the pillars of temples and shrines [2], they claw their way up the thicker poles [7]. Given that their claws do not catch on pipes, the slipperiness of the artificial round poles may have prevented the civets from invading the gaps with the pipe perpendicular to the ground.

Unlike masked palm civets, there were relatively few instances of raccoon invasions in seismically isolated buildings. Raccoons have a wide forearm rotation angle, which may endow them with excellent climbing skills [6]. However, the wideset hind feet of raccoons cannot effectively balance on narrow terminal tree branches [13]. This makes it more difficult for raccoons to walk on pipes. In addition, raccoon dogs and cats did not invade buildings. Saeki [18] noted that the sharp curved nails of raccoon dogs probably help them climb trees. However, the average forearm rotation angles are more than twice as low in raccoon dogs as in raccoons [6]. These results indicate that raccoon dogs can climb trees but have difficulty walking on thin tree branches and pipes. Cats generally climb trees with their claws; however, headfirst descent is difficult because their claws do not catch on the trees. In addition, pipe slipperiness prevents animal claws from catching onto pipes. Wildlife invasion of seismically isolated buildings may be influenced by several variables including wildlife morphology, pipe slipperiness, and climb direction.

Some urban wildlife populations have relatively high densities, increasing the risk of pathogen transmission through direct contact and the orofecal route [1, 4, 5, 9, 15]. The droppings of masked palm civets were found spread throughout the seismically isolated buildings. Therefore, increased feces caused by the invasion of wildlife in seismically isolated buildings may increase the risk of disease transmission to people inspecting the building condition. To reduce this risk, wildlife must be prevented from invading seismically isolated buildings. Expansion joint coverings are typically used to fill the gaps between seismically isolated buildings and the ground surface. However, gaps are occasionally not covered on either side of the coverings or in places that people do not use. Given that masked palm civets can pass through gaps as small as 8 cm² [8], even small gaps in seismically isolated buildings need to be covered with elastic materials to prevent the animals from passing through. In addition, pipes should not be placed near gaps.

In the study area, masked palm civets frequently invade seismically isolated buildings. This suggests that seismically isolated buildings, which are widespread throughout Japan, may serve as habitats for masked palm civets in urban areas. However, our study has several limitations. Our study focused on a relatively small area and examined the invasion of wildlife in only two buildings. Although we monitored their invasion for approximately 3 years, we cannot rule out the possibility that several particular individuals or particular family groups may have been repeatedly using the building. Additionally, our findings are preliminary and may not be representative of wildlife behavior in broader urban settings. Therefore, further research with broad geographical coverage is needed to more effectively understand the role of seismically isolated buildings as potential habitats for urban wildlife. Such studies would help clarify the building conditions that make them vulnerable to wildlife invasion and can contribute to strategies for mitigating potential human–wildlife conflicts in urban settings.

CONFLICTS OF INTEREST

The authors declare no competing interests.