Technical considerations for successful wildbird park design for Island City, Fukuoka, Japan

Prepared by SAVE International January 2014

Bird habitat has important economic value for city development and should be a central part of the wildbird park proposed for Island City. It will enhance the island’s image and meet Fukuoka City’s biodiversity goals, increase real estate values, encourage international tourism, and provide opportunities for environmental research and education. It will also allow the City to fulfill its promise to citizens to make a wildbird park for Island City that delights local people, tourists, and wild birds.

Successful design of the wildbird park requires the use of scientific information about bird needs and habitat function so that the park, even though constructed, can mimic natural processes. Below are technical considerations that must factor into wildbird park design for the Island City site.

1. Tidal opening designed to create essential habitat. The park will need one opening in the Island City dike for tidal exchange so the park water can flush. The size of tidal opening in the park has been evaluated by a U.S. team of experts and discussed with our collaborators in Fukuoka. It needs to be wide in order to create a tidal mudflat. If it is too narrow there will likely only be a deep channel incised at the opening, not the nearly flat topography of a natural mudflat (which is typically about 1000:1). In every known case the success of a tidal flat is proportional to the width of the opening. U.S. experts recommend one opening of at least 200 – 250 meters for the wildbird park. If there are compelling reasons to have multiple openings, one primary opening should still be at least 200 meters wide. This will allow the evolution of a self-sustaining mudflat that will provide clean water exchange and a tidal ecosystem that shorebirds need.

2. Overcoming the complexity of 2-meter drop with precise elevations. Design of a functioning tidal flat needs to ensure there is enough exchange of water to create a living tidal ecosystem and maintain water quality. U.S. hydrologists recommend locating the opening on the north side to get tidal water into the site at an appropriate velocity to sustain the mudflat. If water is being channeled or pumped through the park at a higher velocity than normal tidal flows it would prevent a living tidal flat from evolving. The elevation of the opening is critical because if it is too high, not enough water gets into the new mudflat at a velocity and depth for proper tidal mixing or mudflat sustenance. If it is too low, the mudflat will erode out of the wildbird park and the habitat will disappear. Experts point out that Island City is more complex than most tidal mudflat restorations because of the steep, 2-meter drop-off into Hakata Bay. They recommended that the elevation at the top of the sill where the large opening is created be at MLLW to allow for sea level rise and to reduce excavation costs. They also said to rely on the field data of local Japanese scientists regarding a final decision on the best elevation of the sea wall. To date there is only one known case where a sill-controlled tidal flat has persisted. This is a critical challenge, but if successful at Island City, it would be a significant contribution to habitat creation elsewhere and a matter of international importance in the evolving science of habitat creation.

3. Scare distance of 200 meters. The size of the wildbird park is critical if it is to provide resting and roosting habitat for the birds for which the park will be designed. Most important is to provide adequate distance for the birds to be apart from humans so they experience minimal stress. Ornithologists call this “scare distance”. In the case of the Black-faced Spoonbill they recommend a scare distance of 200 meters from every direction, including the bay side of the park, despite sightings of spoonbills in Fukuoka waterways where humans have come in much closer contact with the birds. In spite of the fact that the spoonbills frequent places during migration that have inadequate space, in every case where there is open area of 400 meters square or more, the spoonbills choose that area for roosting. The preferred site in Taiwan is 1000 meters of open water.
4. 16 hectare minimum size. A 200-meter scare distance with adequate roosting areas necessitates an area of about 16 hectares. Roosting without predator stress or human disturbance is essential for spoonbills and all other shorebirds. At the most successful ecotourism sites the scare distance is 400 meters or more. This accommodates birds and makes an enjoyable and unique educational experience for people. A good design with blinds for bird watching can be created on Island City with only a 200-meter scare distance. SAVE has simulated plans that locate a roosting area for the birds in the northeast end of the park, toward the sea wall. This allows for a higher elevation refuge, centrally located but pushed toward the sea wall for less costly construction and maintenance, and in order for some shorebirds to use the sea wall for refuge at high tide. But this will only work if there truly is no recreational boat use in that part of Hakata Bay. Then one might argue for a reduced scare distance, but ornithologists are skeptical given existing research. SAVE has tried to create a functioning wildbird park at Island City in a smaller area without success.

5. Safe roosting areas at high tide. To create an ecologically-functioning tidal flat which has no emergent vegetation except at the high elevation refuge edge requires keeping the tidal flat flat so the inundation and tidal action eliminate emergent plant growth. But to provide bird refuge at high tide requires elevations that are not regularly inundated; these areas normally vegetate and are not suitable for habitat for many shorebirds as has been the experience in the Tatara River. It may be that one refuge area has a steeper elevation change so it is high enough for everyday escape from high tide; if so this area will need to be seasonably cleared of all vegetation, reeds included. Fukuoka citizens have been involved in reed cutting in other areas of the city; there are also cases where artificial flooding or a bulldozer is seasonally used for clearing vegetation.

6. Vegetation that mimics ecosystem functions. The specific habitats for microorganisms, prey, and birds that the plan will accommodate must be thought through carefully. The main habitat consideration and value of a tidal mudflat is the absence of emergent vegetation which is typically the worst mistake designers make in restoration efforts. They put in too much vegetation, including trees, for a wildbird park to function well. The wildbird park should be designed in zones for water depths and land use including a public viewing zone with adequate scare distance that could have interpretation and ecotones along the edge to provide residents and visitors with information and experiences about wild birds and the ecosystem without entering the core of the habitat area.

7. People-friendly ecotopes. One design concept that blends human park needs with bird habitat is the creation of small ecotopes, designed as ecological gardens that would be less sensitive to disturbance and distinctively Fukuoka/Hakata Bay, around the edges of the park where environmental education might be focused. The gardens could include an experience in how it feels to be a bird looking for food or a resting spot in Fukuoka, a micro mudflat to show how it functions, small habitats for key species like worms and crabs, prey species, an exhibit of disappearing tidal flats, sea level rise, and so on. It would create not only the space needed to protect the birds but also create a wonderful link between an education center and the bird zone.

8. Cost- and maintenance-efficiency. A plan that creates jobs for retired people as part of the maintenance regime would accomplish these goals.

9. Local expertise. The above relies on precise vegetation selection, wildbird park size, opening dimensions, and topographic profiles which local experts must ultimately determine.

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