Bird Population Trends Research Articles

Spatial and Temporal Variation in Bird Communities and Populations in North-Boreal Coniferous Forests: A Multiscale Approach

north-boreal coniferous forests, was studied in detail. In north-boreal coniferous forests both larger and smaller scale phenomena affect patterns observed at a particular scale, and therefore, a multiscale approach is necessary in understanding the dynamics of avian biota. The sporadic occurrence of nomadic species such as two-barred crossbills and owls reflected the importance of the large biogeographic scale: ecological events occurring in the taiga belt far away affected bird communities in northern Finland. Regional variation of bird communities in old, virgin forests was similar to the overall regional variation of avian biota, because 70-80% of bird pairs in virgin forests are habitat generalists. Regional changes in the structure of forests and the increasing harshness of the climate to the north were important for the spatial dynamics of the bird communities. The local effects of habitat alteration (forestry) on bird populations were parallel to the long-term regional population trends of birds. The patterns of between-habitat changes in bird densities caused by forest management were connected with processes at the smaller, within-habitat scale. The long-term decline of the Siberian tit owing to heavy forest management could be explained by events at a local population scale, as the offspring production of the tit was poor in heavily thinned forests. Year-to-year variation in population densities of migratory species was similar in managed and virgin forests probably due to environmental unpredictability and harshness in the north.

Population trends of forest birds in a Finnish Lapland landscape of large habitat blocks: Consequences of stochastic environmental variation or regional habitat alteration?

Birds were counted in Northern Finnish Lapland in an area situated 200 km north of the Arctic Circle in virgin forests in the 1940–1950s, and both in virgin and managed forests in 1982–1989. The area consisted of very large habitat patches: blocks of virgin and managed forests were separated and covered hundreds of square kilometers. The most abundant species fluctuated similarly both in virgin and managed forests in the 1980s. The yearly total density of tropical migrants (insectivores) was negatively correlated with the number of cold days in spring. Short-distance migrants were probably more affected by weather conditions during migration and wintering area. Species which increased and those which decreased in Northern Finland due to habitat alteration had no such trends in large virgin forests, either from the 1940–1950s to the 1980s or during the 1980s. The brambling Fringilla montifringilla was the only species having a significant within-habitat trend: it increased from 1940 to the 1950s but decreased in the 1980s. The brambling is a forest-habitat generalist, and therefore its trends are not likely to be explained by habitat alterations caused by forestry. Year-to-year variations in densities of species seem to reflect stochastic environmental changes, such as in weather conditions and seed crop. Regional population changes caused by habitat alteration are not reflected in population densities in large virgin forests. The northern taiga species preferring virgin forests ( Tetrao urogallus, Picoides tridactylus, Parus cinctus, Perisoreus infaustus and Pinicola enucleator) have drastically declined in the whole of Northern Finland due to habitat loss caused by forest management. These decreased species seem to survive in large, virgin forest, and therefore the protection of these old-aged coniferous forests is essential.

Assessing population trends of scarce birds using information in a county bird report and archive

Casual birdwatching results in the accumulation of large volumes of data in county archives, but it has received little systematic analysis. It could potentially be used to examine trends in populations of scarce birds not otherwise regularly censused. Population trends for 16 species are produced for the years 1943–1987 inclusive from data in the county bird reports and the data archive for Leicestershire, England. The species considered are buzzard, hen harrier, peregrine, hobby, quail, corncrake, barn owl, nightjar, lesser spotted woodpecker, stonechat, black redstart, nightingale, grasshopper warbler, wood warbler, hawfinch and cirl bunting. The trends are consistent with what is known elsewhere of population changes of these species. A cost-effective method of deriving a national index of population is presented for locally scarce species using records collected by birdwatchers at the county level. These indices could be invaluable in detecting trends to assist in conservation planning.

Migration Counts of Raptors at Hawk Mountain, Pennsylvania, as Indicators of Population Trends, 1934-1986

ABSTRACr.--Counts migrating hawks were initiated in 1934 at Hawk Mountain and, except for 1943-1945, have continued to the present. We analyzed the data from 1934-1986 by a standardized sample period appropriate for each species. Counts of several species known to be susceptible to detrimental effects of organochlorine pesticides crashed between 19461971. All of these populations recovered subsequently. The immature-age classes and the species with the shortest generation times recovered first after DDT use diminished in North America. These observations mostly conform to predictions made on the basis of the adverse effects of DDT and metabolites on raptors. We suggest that standardized migration counts reflect qualitative trends of most raptor populations that pass over Hawk Mountain in the autumn. Currently, populations of many species appear to be either stable or recovering from the effects of organochlorines. Possible exceptions are eastern populations of the Red-tailed Hawk (Buteo jamaicensis), American Kestrel (Falco sparverius), Broad-winged Hawk (B. platypterus), Red-shouldered Hawk (B. lineatus), and Golden Eagle (Aquila chrysaetos), which may be decreasing. Received 15 November 1988, accepted 28 July 1989. ANALYSIS of the population trends of birds has received attention recently because of observed and predicted regional or global changes in the environment and the availability of data suitable for long-term trend assessment (e.g.

Assessing Population Trends of New Hampshire Forest Birds: Local vs. Regional Patterns

Abstract We examined the changes in abundance between 1969 and 1986 of 19 forest-dwelling, mostly migratory bird species breeding in New Hampshire at 2 different scales: one local (an intensively studied 10-ha plot in unfragmented forest) and the other regional (Breeding Bird Surveys statewide). Twelve of the 19 species exhibited similar trends at both scales. Eight neither increased nor decreased, and 4 (Least Flycatcher, Winter Wren, Wood Thrush, and Swainson's Thrush) declined significantly. Others increased, decreased, or remained steady at one or the other scale. Overall, more species declined than increased both locally (8 vs. 1) and regionally (5 vs. 1). Comparisons of these patterns, combined with results of intensive studies at the local level, suggest that changes in food abundance and in vegetation structure related to forest succession on the breeding grounds, along with other processes that influence bird reproductive success and survivorship, are the most plausible explanations for most of the observed trends. Winter mortality was also identified as affecting breeding abundances, but only in short-distance migrant and permanently resident species. We have no evidence to indicate that the numbers of long-distance migrants were affected by events in their Neotropical wintering areas, although this possibility is difficult to assess from breeding-ground data. We urge caution in attributing declines of breeding forest migrant birds to tropical deforestation or similar causes until we either can eliminate alternate explanations that involve breeding-season events or have available critically needed demographic information on migrant populations in their wintering areas.

Trends in bird populations as environmental indicators

Birds can be used as a tool in environmental monitoring. This statement results from relevant research and planning work done in Finland in recent years. Monitoring is seen as continuous quantitative research using standardized methods, which will reveal changes and causes of changes in the abundance and ecology of birds. The changes caused by human activities are of most interest, but the natural dynamics also have to be studied in order to separate these two from each other. The data gathered for environmental monitoring can be used also for other purposes, e.g. for ecological research and conservation of bird populations.

Bird population trends as shown by chick ringing data

An index was derived from the annual chick ringing totals for 48 species, over the years 1950–1980 inclusive, and compared with indices calculated from the Common Bird Census and Waterways Bird Survey. Significant correlations were obtained for 18 species and it was concluded that the chick index could be used to examine population trends for these species. However, because of an absence of correlation in 30 species, it was concluded that the chick index presented here cannot generally be used as a population indicator. For the 18 species showing significant correlations, population trends over the 31 year period are described.

The influence of Dutch elm disease on bird population trends

Even bird species which do not nest or feed arboreally may be affected by elm death and felling, when understorey growth ceases to be depressed by the tree canopy. Yet assessment of the impact of Dutch elm disease is complicated by the way birds seem to prefer to remain within the area they know, even when the habitat is altered.

Effects of Changing Forest Structure on Long-Term Trends in Bird Populations in SW Finland

Effects of Changing Forest Structure on Long-Term Trends in Bird Populations in SW Finland