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Evaluation of occurrence tendency and habitat types for wading birds in Japaneserivers using datasets from the National Census on River Environments
1231,2Kota TAWA , Terutaka MORI , Yuichi KAYABA , Keigo NAKAMURA

1) River Restoration Team, Water Environment Research Group, Public Works Research Institute, Tsukuba, Japan
2) Aqua Restoration Research Center, Public Works Research Institute, Gifu, Japan
3) Water Environment Research Group, Public Works Research Institute, Tsukuba, Japan❸ Results & Discussion❶ IntroductionWader species are often among the top predators in wetland ecosystems. Many waders undertake seasonal

Wading bird species in the NCRE

Wading bird species in each Japanese region

continental-scale migration for breeding, overwintering, and resting temporarily. As such, they play importantroles as indicator species in the health of extensive wetland. The Japanese islands form part of the East Asian-Most species

inhabitant Japan
has been recorded

Australasian Flyway (EAAF), which holds the richest diversity of wading bird species among the nine flyways inin river

the world. Unfortunately, the populations of many waders have decreased drastically in the EAAF, owing to theloss of wetlands to landfills, agricultural development, and water pollutionn (Yong et al., 2018). River
environments are one of the most important habitats for these types of waders in Japan (Ezaki 1998). However,very few studies have assessed their habitat status in the river environment. Since 1990, the Ministry of Land,Infrastructure, and Transportation Government of Japan have conducted National Censuses on River
Environments (NCRE) to monitor river habitats. During these surveys, bird communities are also surveyed.

Fig. 3 Location of the NCRE target area andimportant tidal flats for wading bird habitat.
Monitoring surveys of shorebirds are conducted by
the Ministry of the Environment in these tidal flats(https://www.biodic.go.jp/moni1000/seitaikei_6.html).

Using the datasets of the NCRE, we studied the occurrence tendency and habitat types of wading birds in thelarge rivers of Japan.

Ezaki, Y. (1998). Kasen no chorui-gunshu. In: Ezaki Y, Tanaka T (eds) Mizube-kankyo no hozen. Asakura Shoten, Tokyo, pp. 142-176 (in Japanese).
Yong, D. L., Jain, A., Liu, Y., Iqbal, M., Choi, C. Y., Crockford, N. J., Millington, S., and Provencher, J. (2018). Challenges and opportunities fortransboundary conservation of migratory birds in the East Asian-Australasianflyway. Conservation Biology, 32:740-743.

❷ Method★ Target | 11 wader families (Ezaki 1998)(Ardeidae, Ciconiidae, Threskiornithidae, Gruidae, Rallidae, Rostratulidae, Scolopacidae,Charadriidae, Haematopodidae, Recurvirostridae, and Glareolidae)★ Data set | The NCRE of a periodic survey and bird community censuses(1st: 1991–1995, 2nd: 1996–2000, 3rd: 2001–2005, 4th: 2006–2015)

ETF
Fig. 1 The species numbers of wading birds that appeared in the NCRE.
Non-appearance waders are based on Takagawa (2011).

Fig. 2 The species numbers of waders in each Japaneseregion. ETF, estuary and tidal flat habitats; IF, inland
freshwater habitats like rivers, gravel-filled floodplains,lakes, marshes, and paddy fields; and IF & ETF, inland
freshwater, estuary, and tidal flat habitats.

IF & ETF⇒ Appearance in areas where have
many important tidal flats

IF⇒ No regional differencesTakagawa S, Ueta M, Amano T, Okahisa Y, Kamioki M, et al. (2011) JAVIAN Database: a species-level databaseof life history, ecology and morphology of bird species in Japan. Bird Res 7: R9–R12. (In Japanese)(excluding Hokkaido)

Wading birds with high DT ratio- 44 wader species appeared in more than 10 water systems- 11 waders (25 %) showed the highest DT ratio compared to the IT and ST ratios

Analysis of all datasets and sorting of habitat types

Table 1 The list of 11 waders that had the highest decreasing tendency (DT) ratio than the increasing tendency (IT) and stable tendency (ST) ratios.

- The occurrence data of 109
river systems from 1991 to2015.

Using inland
wetlands as

foraging &breeding sites- Classification into three types
based on their main habitats(Nakamura & Nakamura 1995)

IF

Inland freshwater habitats
Nakamura, T., & Nakamura, M. (1995). Birds’ Life in Japan with Color Pictures: birdsof marsh, shore and ocean. Hoikusha, Osaka (in Japanese).

rivers, gravel-filled floodplains, lakes,marshes, and paddy fields

ETF

Estuary and tidal flathabitats

IF & ETF

Inland freshwater, estuary,
and tidal flat habitats

Declining in theestuaries andmudflats inJapan (Amano 2006)

Evaluation of occurrence tendency＋, appearance; －, nonappearance
Appearance pattern of wader species
2nd survey

3rd survey

4th survey(1996-2000)(2001-2005)(2006-2015)++++-++++++++-- Datasets of 57 river systems that were surveyed during all four seasons- Wader species which was appeared in more than 10 river systems- Wader species were classified into three simple indexes based on theirappearance pattern- For each wader, the ratio of each index was calculated.
➡ ❶ Stable tendency; ST➡ ❷ Decreasing tendency; DT➡ ❸ Increasing tendency; IT❹ Unstable tendency- ST ratio (❶ / (❶+❷+❸+❹))- DT ratio (❷ / (❶+❷+❸+❹))- IT ratio (❸ / (❶+❷+❸+❹))❹ Conclusion

Amano, H. (2006). Status of migratory birds that use
mud flats. Chikyu Kankyo, 11:215-226 (in Japanese).

* The Common Redshank breeds only in a small area of Hokkaido.

- Importance of the river environment for wading birds in the EAAF
⇒ Species with a variety of habitat characteristics are found in rivers.
- Decline in species breeding in inland wetlands- Decline of rare species that are also inhabiting tidal flats and estuaries⇒ It may reflect that healthy wetland environments have been drastically reduced in river .
⇒ We need to restore healthy wetland environments for wading birds in rivers.

ACKNOWLEDGMENTS: We thank Yuki Yabuhara (Department of Civil and Environmental Engineering, The University of Tokushima) for very helpful comments throughout the study.