Population trends of black ducks and mallards from the North American Breeding Bird Survey: Are increases in mallards associated with declines in black ducks?
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Book chapter↗
Geology topics
Sam Droege
Publications and source records attributed to Sam Droege.
A heuristic approach to validating monitoring programs based on count indices (damn the statisticians, full speed ahead)
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Book chapter↗
The Summer Atlas of North American Birds
The North American Breeding Bird Survey comprises a network of regularly censussed, road-based survey routes and constitutes the most comprehensive set of data on the relative abundance and population trends of these birds during the summer months. Its value was highlighted in 1989, when the data were used to confirm suspected population declines in a number of species of neotropical migrants breeding in the northeastern United States and Canada. In this book Jeff and Amy Price and Sam Droege have used these data to create detailed, computer-generated maps showing the relative abundance of 450 species that summer in the contiguous United States and southern Canada. Tabular information on distribution hotspots for these, and a further 50 or so species too local in occurrence to map effectively, are also presented. As a data-based survey, the focus of the maps is on places where occurrence has been systematically confirmed over a number of years. As such, the maps provide a baseline for future and more regionally based studies. Supporting chapters provide details on the survey methodology, the mapping procedures used, and some current concerns in North American bird conservation.
Book↗
Managing and monitoring birds using point counts: Standards and applications
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Book chapter↗
A proposed North American amphibian monitoring program
No abstract available.
Canadian Association of Herpetologists Bulletin↗
Within-site variability in surveys of wildlife populations
Most large-scale surveys of animal populations are based on counts of individuals observed during a sampling period, which are used as indexes to the population. The variability in these indexes not only reflects variability in population sizes among sites but also variability due to the inexactness of the counts. Repeated counts at survey sites can be used to document this additional source of variability and, in some applications, to mitigate its effects. We present models for evaluating the proportion of total variability in counts that is attributable to this within-site variability and apply them in the analysis of data from repeated counts on routes from the North American Breeding Bird Survey. We analyzed data on 98 species, obtaining estimates of these percentages, which ranged from 3.5 to 100% with a mean of 36.25%. For at least 14 of the species, more than half of the variation in counts was attributable to within-site sources. Counts for species with lower average counts had a higher percentage of within-site variability. We discuss the relative cost efficiency of replicating sites or initiating new sites for several objectives, concluding that it is frequently better to initiate new sites than to attempt to replicate existing sites.
Ecology↗
Mourning dove population trend estimates from Call-Count and North American Breeding Bird Surveys
The mourning dove ( Zenaida macrour a) Call-count Survey and the North American Breeding Bird Survey provide information on population trends of mourning doves throughout the continental United States. Because surveys are an integral part of the development of hunting regulations, a need exists to determine which survey provides precise information. We estimated population trends from 1966 to 1988 by state and dove management unit, and assessed the relative efficiency of each survey. Estimates of population trend differ ( P < 0.05) between surveys in 11 of 48 states; 9 of 11 states with divergent results occur in the Eastern Management Unit. Differences were probably a consequence of smaller sample sizes in the Callcount Survey. The Breeding Bird Survey generally provided trend estimates with smaller variances than did the Callcount Survey. Although the Callcount Survey probably provides more withinroute accuracy because of survey methods and timing, the Breeding Bird Survey has a larger sample size of survey routes and greater consistency of coverage in the Eastern Unit.
continental United States↗
Are more North American species decreasing than increasing?
Population trends for North American species are calculated for 1966-'91 and 1982-'91 using Nonh American Breeding Bird Survey data. Species are grouped into 3 systems of guild classifications representing migration status, breeding habitat and nesting substrate. Trends for these groups are summarized by time period, bioregion and physiographic region. At the continental level, declines approximately equalled increases. There are slightly more declines during the last 10 years. Prairie populations declined more than expected, while western populations increased. Scrub and grassland nesting species declined significantly in several bioregions while woodland species increased. Most guilds did not depart significantly from a ratio of 50:50 increases to decreases or have opposing trends in different bioregions. Guild group changes are usually clustered geographically. Guild and other analyses that search for patterns among population trend estimates offer an excellent means of identifying critical conservation issues.
Book chapter↗
Distribution and abundance of birds wintering in Maryland, 1988-1993
A winter bird survey was conducted throughout Maryland, primarily by volunteers, during the 6 winters of 1988 to 1993 between the dates of 10 Jan and 10 Feb. The state of Maryland is covered by 1231 blocks (9.5 sq. miles each), each comprising one-sixth of the standard U.S.G.S. 7.5 minute topographic quadrangle, and 548 of these blocks (44.5%) were surveyed for winter birds. Blocks were chosen in a systematic pattern with eventually almost every other block in the state having been surveyed as of Feb, 1993. Volunteers conducted each 4-hour survey by walking a 4-6 mile route chosen by the volunteer to sample habitats in proportion to their availability in the block. Surveys began around sunrise (~7:30 a.m.) and all birds seen or heard during the 4 hours were recorded on data sheets. The data were then used to create maps representing the distribution and relative abundance of each species of wintering bird found in at least 10 blocks in the state.
Maryland Birdlife↗
Population trends of quails in North America
We used North American Breeding Bird Survey data (1966-91) to estimate distribution, relative abundance, and populatiori trends of quails. Population trends in grassland/shrub birds sympatric with northern bobwhite (Colinus virginianus) were also examined. Northern bobwhite and scaled quail (Callipepla squamata) populations have declined since 1966. Rates of decline for these quails have increased during the past decade. California quail (C. californica), Gambel's quail (C. gambeliI), and mountain quail (Oreortyx pictus) populations have been stable over the long-term (1966-91). However, the short-term (1982-91) trend for California quail is positive, whereas Gambel's quail appear to be declining. Patterns in trends indicate similar factors may be negatively affecting breeding populations of grassland/shrub birds throughout the bobwhite's range. We discuss plausible hypotheses to explain population trends and recommend future action.
Book chapter↗
Monitoring neotropical migrants on managed land: When, where, why
Relevant wildlife monitoring on managed lands lies somewhere between monitoring everything and monitoring nothing. Knowing the population status of all birds on a managed area would be potentially useful information but would be costly to collect, but without monitoring no link between management and wildlife populations can be made. A decision making process for developing appropriate monitoring programs on managed lands is outlined.
Book chapter↗
Geographic patterns in population trends of neotropical migrants in North America
We use the route-regression method to estimate the population trends of 100 species of Neotropical migrants using data from the North American Breeding Bird Survey (BBS). We examine long-term (1966-1988) and recent (1978-1988) trends. In the long-term, more species of Neotropical migrants were increasing than were decreasing in the eastern and western parts of the continent, but recent trends indicate that more species decreased than increased in their population index in the east. Recent population declines in the eastern part of the continent were primarily associated with bird species that breed in forested habitat. No association was detected between changes in forest acreages by state and population trends of Neotropical migrants in the United States and Canada.
Book chapter↗
Breeding Bird Survey and bird banding data: Applications to raptor research and management
The Breeding Bird Survey (BBS) and Bird Banding Laboratory (BBL) are sources of information for raptor biologists. The BBS has been conducted each year since 1966 in the United States and Canada; historical bird banding records extend back to the early 20th century. BBS data can be used to document population trends and breeding distributions of many bird species. Banding data are generally collected for specific and local studies of bird populations or behavior. Past use of these data has been limited by their volume and relative inaccessibility. In this paper, we present an overview of BBS and BBL raptor data and their uses, limitations and availability.
Book chapter↗
Adaptations to tidal marshes in breeding populations of the swamp sparrow
The Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) was originally described from a small number of specimens from the tidal marshes of the Nanticoke River in southeastern Maryland. Based on our quantitative analysis of a larger series of specimens, we found that Swamp Sparrows collected during the breeding season from the Chesapeak and Delaware bays (and tributaries) and near the mouth of the Hudson River are generally less rusty, have more black in the crown and nape, and have larger bills than other Swamp Sparrows. Contrary to earlier accounts, we found M. g. nigrescens to be migratory, arriving after the spring migration and departing before the fall migration of the inland subspecies through the tidal marshes. The location of the wintering groups of M. g. nigrescens is unknown. We argue that the morphological and life history differences characterizing M. g. nigrescens reflect adaptation to tidal marshes. We base this hypothesis on the nature of the morphological differences, which are convergent with other tidal marsh breeding sparrows and other terrestrial vertebrates.
Condor↗
Wood duck population trends from the North American Breeding Bird Survey
The North American Breeding Bird Survey (BBS) has been conducted yearly since 1966, and can be used to describe relative population density and trends of birds in North America north of Mexico. Wood ducks (Air sponsa) are difficult to survey using conventional waterfowl monitoring techniques, but a large portion of their range is surveyed by the BBS. Wood ducks are detected at low densities on many BBS routes, and population trends can be estimated for most regions. Populations have been increasing throughout North America since 1966, but statistically significant increases generally occurred only in the early (1966-78) part of the period. Roadside survey methodology used in the BBS has limitations that make it inefficient as a survey technique for wood ducks, and we recommend using modified methodologies that specifically survey wood duck habitat.
Book chapter↗
Northern bobwhite, gray partridge, and ring-necked pheasant population trends (1966-1988) from the North American Breeding Bird Survey
We use North American Breeding Bird Survey data to estimate population trends for 1966-1988 for northern bobwhite (Colinus virginianus), ring-necked pheasant (Phasianus colchicus), and gray partridge (Perdix perdix). Bobwhite populations have undergone widespread declines, pheasant have undergone major declines in eastern North America with mixed trends elsewhere, gray partridge have undergone primarily population increases. We present suggestions for further uses of these data.
Book chapter↗
The North American Breeding Bird Survey
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Biological Report↗