The dynamics of bird populations are often governed by a range of ecological processes at different spatial and temporal scales. The quantity and quality of information available from ecological surveys also depend on the scale. Thus, for a thorough understanding of the dynamics of bird populations and their effective conservation, it is necessary to establish a set of approaches suited to ecological processes at hierarchical spatial and temporal scales. This paper focuses on three ecological approaches based on behavioural ecology, landscape ecology, and macroecology, and shows how these approaches can be used effectively to understand the dynamics of bird populations in a complementary manner. Behavioural ecology is helpful in understanding processes that produce patterns in spatial and temporal population dynamics at a local scale, by revealing decision-making in individual birds. This approach also makes it possible to develop behaviour-based models to predict spatial distribution and population dynamics under novel conditions. Landscape ecology focuses on the effect of landscape structures on biodiversity dynamics at the landscape level. At a larger spatial scale (macro-scale), climate, topography, and human activities are known to influence greatly population dynamics and spatial distribution of birds, but information available at this scale is usually limited because of the difficulty in conducting intensive field surveys. Macroecological approaches thus aim to understand such relationships by first quantifying spatial and temporal dynamics of bird populations and then generalizing the revealed dynamics based on species ecological traits. This review also discusses the advantages and disadvantages of the three approaches and suggests future tasks for promoting the understanding of the dynamics of bird populations at hierarchical spatial and temporal scales.
Chronological trends in the number of birds captured (newly released) and their relationship to forest succession were studied in a coastal forest that is used by many migratory birds near the city of Niigata, Japan. Significant chronological trends in the number of individuals captured during the period 1991–2005 were seen for seven bird species in spring and six in autumn. Particularly, higher negative correlations between the number of birds captured and the dominical year were obtained for bird species showing decreasing trends. Bird species preferring sparse woodland, forest edge, or scrub, tended to decrease in spring. Herbivorous bird species, especially seed specialists, tended to decrease in autumn. These phenomena might be attributed to the dense growth of trees and shrubs and to the decline in plant species producing food for seed specialists on the forest floor caused by succession in the coastal Pinus thunbergii forest. Ground feeders tended to increase in both spring and autumn. Carnivorous bird species feeding on insects or earthworms tended to increase in autumn. This suggests that the coastal forest succession contributes to an increase in food resources for carnivorous bird species. The chronological trends in the number of birds captured might be influenced not only by forest succession in the study area, but also by the breeding results or seasonal changes in environmental selection of the bird species and nation-wide population changes. Comparisons with other research sites as well as the consideration of plant succession are important when analyzing bird-banding data as an indicator of long-term population dynamics or environmental changes.
We investigated whether there are significant differences in neck muscle mass, maximum peck force, pressure and maximum pull force between Jungle Crows Corvus macrorhynchos and Carrion Crows C. corone. The maximum peck force and pressure were measured using pressure sensitive film. The maximum pull force was measured with spring balances. For male Jungle Crows, neck muscle mass, maximum peck force, pressure and maximum pull force were 8.27 g, 26.8 N, 80.4 MPa and 9.54 N; for females they were 6.82 g, 22.3 N, 69.7 MPa and 8.25 N. Those values for male Carrion Crows were 6.69 g, 22.3 N, 59.7 MPa and 4.07 N;, whereas for females they were 4.50 g, 15.1 N, 53.2 MPa and 2.71 N. Furthermore, neck muscle mass, maximum peck force and maximum pull force were positively correlated with body mass in both species. There were no significant differences in the ratio between the cervical levator mass and the cervical depressor mass, and the maximum peck force exerted by one unit of the cervical depressor mass between Jungle and Carrion Crows. However, the maximum pull force exerted by one unit of the cervical lavator and depressor mass of Jungle Crows was significantly larger than that of Carrion Crows.
Lagopus mutus japonicus is the southernmost subspecies of Rock Ptarmigan. This susbspecies is a relic population, remaining after the most recent ice age, isolated on mountain peaks and ridges of central Honshu, Japan, where it inhabits the alpine zone. Seasonal changes in food items were investigated by observations of ptarmigan foraging behavior on Mt. Norikura. Among the total 46,523 pecks observed throughout a year, 92.9% of them were made at vegetable matter, 4.7% at animal matter and the remaining 2.4% were made at inorganic matter such as grit. Rock Ptarmigan in Japan winter in the subalpine area below 2,600 m where their main winter food consists of the buds of Betula ermanii extending above the snow. After returning to the alpine zone in April, their main diet changed for the leaves of evergreen-dwarf-shrubs including Empetrum nigrum, Vaccinium vitis-idaea, and Arcterica nana. During May and early June they were also observed feeding on small insects, Aeolian plankton, deposited on the snow surface by updrafts from the lowlands. In addition to the leaves of evergreen-dwarf-shrubs, the flowers of deciduous-dwarf-shrubs and herbaceous plants were their main foods in summer. Many kinds of fruits and seeds are eaten in autumn. It was found that the diet of ptarmigan in Honshu, changed considerably both in quantity and in quality with seasonal changes in snow conditions and plant growth. The close relationship between the seasonal diet and the life history of the ptarmigan in the alpine environment was discussed.
A survey of the at-sea distributions of 1) planktivorous Short-tailed Shearwater Puffinus tenuirostris, migrating to their northern summering area and 2) piscivorous Rhinoceros Auklet Cerorhinca monocerata, breeding in the northern Sea of Japan off Hokkaido, was carried out by ship, from 16 to 28 May 2008. Avian censuses were combined with: acoustic surveys aimed at measuring prey density, and sea surface temperature (SST) surveys. Surface Chlorophyll a distribution was obtained using satellite imagery. The density of shearwaters was correlated positively with 200 kHz SA (the index of density of zooplankton including krill) at the 10 km scale, and 200 kHz SA was correlated negatively both with SST and Chlorophyll a. However, shearwater densities were not correlated significantly with SST and Chlorophyll a. The result suggest that migrating shearwaters may be able to find patches of krill in cold water. In contrast, the density of Rhinoceros Auklets was not correlated with 38 kHz SA (the index of pelagic fish density) or 200 kHz SA at any scale.
The Japanese White-eye Zosterops japonicus is known to rob nectar from a range of introduced flowering plants. Hibiscus Hibiscus cv. flowers pierced by white-eyes for nectar robbing were surveyed on Chichi-jima, Bonin Islands, Japan, in 2009. Nectar production did not commence in hibiscus flowers until 04:00. White-eyes began robbing nectar after 06:00, and continued throughout the morning. White-eyes were only rarely observed robbing nectar during the afternoons. Nectar robbing from buds, or closed flowers, was not observed. Nectar volume and sugar concentration was correlated with flower size, respectively, and larger flowers were robbed more often than smaller ones. The Japanese White-eye seemed to choose large flowers with plentiful nectar and rob them during the optimal period when nectar secretion was at its maximum.
The Lanceolated Grasshopper Warbler Locustella lanceolata was censused along one to three 2-km transects (a total of 989) situated in 876 quadrats (4.5×5 km), in Hokkaido from late April to late July, 1976-2010. Warblers were recorded mainly in grasslands along lower and middle reaches of rivers, and those surrounding shallow lakes in Iburi, Ishikari, Tokachi, Kushiro, Nemuro, Abashiri and Soya districts. They occurred in grasslands and agricultural lands, and did not occur in woodlands and residential areas. Occurrence rates (No. of transects of occurrence/No. of transects censused) were 24.0% for grasslands and 3.4% for agricultural lands, and changed significantly in grassland during the study period.