Avian ecological functions can provide ecosystem service benefits to humans. Although the values of avian provisioning and cultural services are well understood, the values of supporting and regulating services are not. Through predation, transportation, and excretion, birds play various roles in terms of seed dispersal/pollination, controlling prey species populations, scavenging, and nutrient cycling. These behaviours provide benefits contributing to increased agricultural productivity, pest control, and habitat creation/maintenance for humans. Though attempts have been made recently to evaluate the economic significance of avian ecosystem services, such attempts remain scarce. In Japan, where people have traditionally enjoyed avian ecosystem services mainly in terms of their support of agricultural ecosystems, an understanding and evaluation of the value of avian ecosystem services is essential.
Birds provide various ecosystem services in various ecosystems around the world. In this review, I summarize our current knowledge of pollination and seed dispersal by birds. Gene flow in natural plant populations is determined by pollen and seed flow. Birds can be important pollinators and seed dispersal agents by visiting flowers or fruits. By using natural experiments, recent studies have revealed: that loss of avian pollinators leads to reduced regeneration of plants; and that birds are important seed dispersal agents facilitating the regeneration of degraded patches of forest. Studies focusing on the economic value of avian pollination or seed dispersal services are, as yet, uncommon. However, a recent study on the seed dispersal service performed by the Eurasian Jay Garrulus glandarius in the Stockholm National Urban Park, Sweden, showed that depending upon the seeding or planting technique chosen, the substitute cost per pair of jays in the park is ¥0.58 million and ¥2.52 million, respectively. Because birds also effectively disperse invasive plant species, they also provide ecosystem disservices in some instances. Further research to better understand the roles of birds in plant pollination and seed dispersal will enable better policy implementation relating to the pragmatic use of avian ecosystem services and the conservation of birds as well as biodiversity.
The sustainability of ecosystem services depends on a firm understanding of both how organisms provide these services to humans and how these organisms will be affected by environmental changes. In this study, we selected Barn Swallow Hirundo rustica, Common Cuckoo Cuculus canorus, Oriental Reed Warbler Acrocephalus orientalis, and Chestnut-cheeked Starling Agropsar philippensis, as four species for which sufficient banding data (1961–1971, 1982–2011) and sufficient observational data (Japan Meteorological Agency stations; 1953–2008) exist, making them representative of summer visitors to Japan. We analyzed: long-term changes in their periods of appearance at the national scale; the relationship between those periods and the previous winter or current spring temperature, and between those periods and the first appearance dates of plants or insects in spring. The arrival dates of adult and appearance dates of nestling Barn Swallow, Oriental Reed Warbler, and Chestnut-cheeked Starling have advanced, while the arrival date for adult Common Cuckoo has been delayed. Arrivals of Barn Swallow, Oriental Reed Warbler, and Chestnut-cheeked Starling were earlier in warmer years, but later for Common Cuckoo. The extent of long-term changes in most of our results did not deviate from those previously described from Europe and North America. The time lag between the arrival dates of these birds and the first appearance dates of spring plants and insects have not remained constant. However, the factors causing advanced or delayed arrivals and producing the phenological mismatch are not yet known. Regional differences must be considered when studying the phenological mismatch using long-term monitoring data.
SPECIAL ISSUE 2: Radioactive contamination and effects in birds after the Fukushima Nuclear Accident I
The biological proliferation of cesium-137 (137Cs) into individual birds in a forest ecosystem were examined. After the disastrous accident at Fukushima Daiichi Nuclear Power Plant in 2011, radionuclides, including 137Cs, have been deposited broadly over forested areas of northeastern Honshu, Japan. In forest, 137Cs became highly concentrated in leaf litter. The concentrations of 137Cs in the muscles and livers of five forest bird species were measured, and transfer factors from forest soil to birds were calculated. The values of transfer factors (TF) were equivalent to those reported from previous studies carried out after the Chernobyl accident. However, the TF value of Asian Stubtail Urosphena squameiceps was considerably higher than for the other bird species investigated and when compared with previously studies. Although the exact factors explaining the variation in 137Cs concentration among bird species could not be specified, the effects of foraging habitat and prey type are suggested.
We investigated the radioactive cesium concentrations in Barn Swallow Hirundo rustica nests that were collected from large areas of Japan in 2011 in order to understand the pattern of radioactive cesium contamination emitted by the Fukushima Daiichi Nuclear Power Plant accident. We collected 197 nests from 21 prefectures and measured radioactive cesium (Cs-134 and Cs-137) levels in 182 nests. Radioactive cesium contamination of nests was found in 13 prefectures. Cesium concentrations (Cs-134+Cs-137) in nests ranged from 33 to 90,000 Bq/kg in the Fukushima area, and the average concentration level in Fukushima was higher than in the other areas. There was a significantly positive relationship between radioactive cesium concentrations in nests and in the soil around the each nest site.
The population and habitat of Brent Geese Branta bernicla were investigated in the species' main wintering area in Japan (around the Tsugaru Strait) in late December 2012. A total of 1,060 individuals was found, most of which occurred in southeast Oshima Peninsula and southeast Mutsu Bay. Goose density was higher in areas with artificial revetments and rocky shore, where marine algae (the main diet of the geese) grow easily. Coastlines with offshore structures were selected as feeding habitat because eelgrass Zostera marina grows there and because wave washed seaweed can accumulate inshore of such structures, where waves are calm.