World leaders have set global and regional targets to reduce the rate of biodiversity loss by 2010, and their relative success, or failure, in meeting these aims will be measured against a set of indicators. For such indicators to be effective, they need to meet a range of practical and scientific criteria. Their development is often driven pragmatically by the information available. One such biodiversity indicator that has proven highly effective and influential in Europe is the wild bird indicator. This is based on the composite population trends of birds combined using a geometric mean and derived from national breeding bird surveys. Recent work has emphasized the importance of common species to ecosystem functioning and suggested that the depletion of their populations might significantly affect ecosystem services. National governments and the European Union are increasingly using these measures to assess sustainable development strategies, environmental and ecosystem health, as well as in the fulfillment of biodiversity targets. Equivalent indicators have been published in North America. There are a number of reasons to believe that birds might be useful indicators of biodiversity. They are sensitive to anthropogenic changes, they are well known, excellent time-series exist, and they have a resonance and connection with people and their lives. Yet, there are counter arguments and some risks in using birds in this way. Our work provides a blueprint for others to follow using similar data on birds or other taxa, and in other countries and regions. In the discussion, we review the strengths and weaknesses of using bird population trends as biodiversity indicators, and look forward to how this work might be developed. Wild bird indicators only measure a component of biodiversity change and need to be used carefully to assist policy makers and land managers in managing the natural resources and conserving nature.
We analyzed population trends of 13 waterfowl (Anseriformes) species wintering in Japan during a 14-year period (1996–2009). We used data from annual volunteer-participatory waterfowl count surveys which were conducted in Japan by the Ministry of the Environment and local prefectural governments. Population indices and long-term trends of each species were calculated using TRIM (TRends and Indices for Monitoring data). TRIM is a freeware program developed for analysis of time series count data with missing observations. During the 14 years, seven species exhibited significant long-term declines, while four species showed long-term increases. Most of the species that showed long term declines were characterized as being water-surface foraging species, species breeding in both middle and high latitude regions, or species using rice fields. Most species that showed long-term increases were characterized as diving species, species breeding at high latitude or species rarely using rice fields. We calculated composite indices for these groups. The group of water-surface foraging species showed declines in river, natural lakes and artificial lakes, except reservoirs, when each habitat was analyzed separately. In contrast, the group of diving foraging species showed an increase in estuarine habitat. We suggest that changes in: water quality, breeding habitat in the middle latitude region, and in cultivation methods in rice fields, have affected population changes of some species and groups.
We report the results of a 15-year bird census conducted on the Hokkaido University campus in Sapporo city. A standardized route census was carried out monthly by the students of the Hokkaido University Birding Club (HUBC). Bird species were classified according to their migratory status as: long-distance migrants (LDM), short-distance migrants (SDM), winter visitors (WV) and residents (R). Of a total of 88 species of birds identified, 18 were Rs, 21 LDMs, 26 SDMs and 10 WVs. The overall bird abundance for the R group was greatest, however this was strongly affected by fluctuations in the Eurasian Tree Sparrow Passer montanus population, representing more than half of the total bird abundance. This species declined sharply in 2006, and has not recovered yet. LDMs declined in both species richness and bird abundance, whereas SDMs and WVs had fluctuated annually in their abundance. Three major tendencies were detected by comparing nationwide changes of bird communities with those of the study site. 1) Overall population declines in the wintering and stopover grounds, which were aggravated by habitat degradation in the breeding grounds of the study site (White-throated Needletail Hirundapus caudacutus, Black-faced Bunting Emberiza spodocephala, Oriental Turtle Dove Streptopelia orientalis), 2) Nationwide population increase while the population declined in the study site due to intensified management of vegetation (Great Tit Parus major, Great Spotted Woodpecker Dendrocopos major), 3) Population increases in species adapted or adapting to human landscapes (Large-billed Crow Corvus macrorhynchos, Mallard Anas platyrhynchos, Slaty-backed Gull Larus schistisagus). In addition, the drastic decline of Eurasian Tree Sparrows in early 2006 was caused by a local die-off event apparently due to an infectious disease. General recognition of the academic and conservation importance of a long-term census is hoped to enhance motivation for and efforts towards a census in various areas.
Many studies have reported population declines and range contractions of bird species in agricultural landscapes around the world. However, few studies have described population trends of bird species in rice-paddy areas or identified causes of decline in these areas as opposed to other types of farmland. The Greater Painted Snipe Rostratula benghalensis is strongly dependent on rice-paddy areas for habitat. This paper uses the results of local field surveys and national survey data to document the population trends of Greater Painted Snipe in Japan. Field surveys conducted in Ibaraki Prefecture indicated a severe decline over a recent 10-year period. Data from the National Surveys on the Natural Environment also showed that the distribution of the Greater Painted Snipe has decreased nationwide from the 1970s to the 1990s. This population decline might be due to (1) the introduction of an efficient drainage system in rice fields and/or (2) a reduction in the area of flooded fallow fields with short vegetation at both breeding and wintering sites. Further work on the conservation status of this species is urgently needed.
Two 2-km line transects were deployed in Kushiro district, Hokkaido, Japan, one in woodland and one in grassland. Censuses were conducted 22 times along each route during the same breeding season. The relationship between census efforts and the number of species encountered was examined, and suitable census combinations for two-fold census and five-fold census were investigated. Furthermore, seasonal changes in individual bird numbers for major species were examined. Thirty-eight species were recorded along both routes. In woodland, 14 species considered to have established breeding territories along the route and were categorized as major species; 24 other species were categorized as minor species. Nine species were major and 29 were minor species in grassland. For both routes, occurrence rates for major species were more than 40%, while rates for most minor species were less than 20%. To analyze the relationship between census efforts and the number of species encountered, I constructed all possible combinations of census efforts by using the data compiled from 22 visits. The total number of species increased with increasing census efforts in both woodland and grassland. Approximately 90% of major bird species could be recorded in two-fold censuses and 99% in five-fold censuses. Censuses conducted twice in June or once each in May and June can provide census data for most bird species including the majority of major species along the routes, but do not allow discrimination of major and minor species. Five-fold repeat censuses allow discrimination of these two categories by using occurrence rates. Furthermore, the number of individual songbirds appeared to differ among breeding stages. To investigate these seasonal changes, the breeding season should be divided into more than five periods, and a census should be performed in each period. This protocol will also confirm the presence of 99% of major species.
Great Spotted Woodpeckers Dendrocopos major typically excavate nest holes in trees with specific physical characteristics, namely with harder outer and softer inner wood. They excavate trial holes before excavating their nest holes, occasionally expanding old trial holes into nest holes. If trees with trial holes always share the same physical characteristics with nest trees, then Great Spotted Woodpeckers should be able to detect these characteristics before excavating trial holes and nest holes. I measured wood hardness and compared it among trees with trial holes, trees with nest holes, and sound trees. The physical characteristics of sound trees, which varied little in hardness, differed markedly from those of trees with trial holes and nest holes. Many trees with trial holes showed the same pattern of wood hardness as nest trees, although one showed the reverse pattern that is with softer outer and harder inner wood. The results of this study suggest that Great Spotted Woodpeckers are able to detect trees and positions on those trees with considerable wood hardness variation, but are unable to sense whether the hardness variation is suitable for nest excavation before they excavate trial holes. Thus, Great Spotted Woodpeckers excavate trial holes and then judge whether the positions where trial holes are excavated are appropriate for nest hole excavation.
We investigated fat deposition and the timing of departure of Greater White-fronted Goose Anser albifrons at Lake Miyajimanuma, Hokkaido, which is the largest stopover site in northern Japan, focusing on the differences between seasons and between sexes. We assessed the fat mass of neck-banded geese by observing their abdominal profiles. In spring, the variation in departure dates among individuals was smaller than that in arrival dates, and there was a positive correlation between arrival dates and departure dates in the fall. The factors affecting decision-making relating to the timing of departure are assumed to be the time constraints of migration before breeding in the spring and on the duration of stay in the fall. The spring fat increase in females was larger than in the fall, and had a tendency to be larger than in males in the spring. The seasonal and sexual difference in fat mass increase seems to be explained by the requirement of fat for breeding after departing from the stopover site. This study supports the possibility that migratory birds adjust their fat mass and the timing of departure at stopover sites according to seasonal differences in events occurring after migration, such as breeding.
We investigated whether vocal communication in wild Large-billed Crows (Corvus macrorhynchos) is governed by a temporal rule as an evidence for vocal exchange. In order to examine this potential temporal rule, we analyzed the intervals between two single-note ka calls produced sequentially by two crows in gregarious situations. Two different individuals sequentially uttered ka calls at approximately 0.2–0.8-sec intervals. Such a specific time window was not observed in a simulation of ‘imaginary’ flocks, in which multiple crows independently emitted ka calls at their own pace, similar to the calls of solitary crows in the wild. These results suggest that the specific time window of inter-call intervals between different crows is not an incidental phenomenon in a crowded situation, but rather a specific event that follows a temporal rule organizing vocal communication of two crows. Our findings provide the first evidence of vocal exchange using ka calls that are organized following a precise temporal pattern in Large-billed Crows.
Since parent birds are hypothesized to adjust the level of their nest defense against predators so as to enhance the survival of their offspring, parental nest defense is expected to increase in intensity in relation to increasing clutch size. Empirical studies of bird species, in which clutch sizes have been manipulated artificially, however, have produced results contradicting such expectations, partly, it is thought, because of various errors in experimental design, such as a lack of nesting habitat control, or providing too short a time for parents to assess the value of the manipulated clutch. Hence, further evidence needed to be gathered to clarify whether the basic hypothesis is adequately supported. We manipulated the clutch size of Black-tailed Gulls Larus crassirostris and observed the responses of male parents to a crow decoy in controlled nesting habitats. The intensity of defense was not affected by the clutch size. Opportunities for future reproduction, or constant individual levels of aggressiveness of seem to best explain the observed intensity of nest defense in these long-lived Black-tailed Gulls, rather than the value of the current clutch.