Although there is strong evidence that a few Neotropical migrant land birds have severely declini... more Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental-scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980's, but other analyses conclude that most species have had stable or increasing populations in the last 25 years. These conflicting results suggest that a new perspective is called for. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970's and stability elsewhere. As examples of the use of this first approach in single-species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue-winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit-normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.
The common practice of expressing community structure in terms of indices of diversity and evenne... more The common practice of expressing community structure in terms of indices of diversity and evenness involves a serious loss of information. Differences attributable to the accumulation of species with increasing area are ignored, differences in the density of individuals are often masked by other factors, and many combinations of species richness and relative abundance can produce the same value of the index. As an alternative we suggest (1) comparing species richness by standardizing samples either to equal numbers of individuals or to the number of individuals expected on equal-sized plots, and (2) expressing the relative abundance of species as a graph of their relative abundances arranged in a decreasing array. We present an analysis of bird census data based on the proposed methods, and we include comparisons with applications of four indices commonly used in ecology, the Shannon-Weaver index of diversity, the J' evenness index, the inverse of Simpson's measure of concentration, and Hill's evenness index. For 37 Breeding Bird Censuses taken in various terrestrial habitats across the United States and Canada, the proposed methods reveal some very general relationships about the organization of bird communities in different habitats. Equal-sized areas of mature deciduous forest and secondgrowth habitats may be equally species rich (14-24 species with •> 1 breeding territory per 6 ha); the density of individuals (territorial pairs) is generally higher in deciduous forest habitats, and the relative abundance of bird species shows more dominance (less evenness) in the deciduous forest. Mixed coniferous-deciduous forests and dense young deciduous forests have fewer species than mature eastern deciduous forests or second-growth habitats (9-16 and 7-10 species per 6 ha, respectively), although the density of individuals is approximately equal to that in second-growth habitats. Coniferous forests are species-poor (5-8 per 6 ha), and the density of territorial pairs is low (8-12 per 6 ha compared with 40-70 in deciduous forests). Although the proposed methods require assumptions that need to be evaluated carefully, we are optimistic that they will have other useful applications in the analysis of arian communities.
A modest man, he will be fondly remembered for his many achievements and his lifelong dedication ... more A modest man, he will be fondly remembered for his many achievements and his lifelong dedication to studies of birds and their habitats. Of his hundreds of publications, the best known is Birds of North America: A Guide to Field Identification, coauthored with Bertel Bruun, illustrated by Arthur Singer, and edited by Herbert Zim, published in 1966 and revised in 1983. This 'Golden Guide', with its opposing range maps, sonograms and plates comparing similar birds, set new standards for field guides. More than six million copies have been sold. Born in Belmont, Massachusetts, on 17 July 1918, Chan was birding by the age of 12. Before he had completed his undergraduate studies at
Since the colonization of North America by Europeans, a taxonomically diverse array of avian spec... more Since the colonization of North America by Europeans, a taxonomically diverse array of avian species has become extinct. The Labrador Duck (Camptorhynchus labradorium), Great Auk (Pinguinus impennis), Passenger Pigeon (Ectopistes migratorius), Carolina Parakeet (Conuropsis carolinensis), and Ivory-billed Woodpecker (Campephilus principalis) come to mind. This somber list can be expanded to include subspecies such as the Heath Hen (Tympanuchus cupido cupido) and Dusky Seaside Sparrow (Ammodramus maritimus nigrescens). Several species currently are, or are thought to be, perilously close to extinction: California Condor (Gymnogyps californianus), Whooping Crane (Grus americana), Eskimo Curlew (Numenius borealis), Bachman's Warbler (Vermivora bachmanii), and Kirtland's Warbler (Dendroica kirtlandii). Extinction, usu
Although there is strong evidence that a few Neotropical migrant land birds have severely declini... more Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental-scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980's, but other analyses conclude that most species have had stable or increasing populations in the last 25 years. These conflicting results suggest that a new perspective is called for. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970's and stability elsewhere. As examples of the use of this first approach in single-species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue-winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit-normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.
Most of the 13 papers in this monograph were delivered at the meeting of the American Ornithologi... more Most of the 13 papers in this monograph were delivered at the meeting of the American Ornithologists' Union, the Cooper Ornithological Society, and the Society of Canadian Ornithologists in Portland, Oregon, during 4-9 August 2008, in a symposium session organized and chaired by Susan M. Haig and Kevin Winker. The purpose of the symposium was to review the history of subspecies in ornithology, the relevance of subspecies to studies of biodiversity and to conservation policy under the Endangered Species Act, and examples of recent research that involves subspecies of birds. The papers added after the symposium complement the others. As organized here, the first seven papers are general in nature and the last six are examples of recently analyzed case histories. The authors present various interpretations of the concept of subspecies and of methods for assigning individuals to subspecies, but they all favor the retention of subspecies as a taxonomic category. Arguments to the contrary are presented to provide perspective. The term "subspecies" applies to either a taxonomic category in the International Code of Zoological Nomenclature (ICZN; Ride 1999) or to a particular trinomial example (e.g., Turdus migratorius migratorius, which was listed in the first AOU Checklist in 1886). In the classic summaries for North American birds (Peters et al. 1934-1987, Ridgway and Friedmann 1901-1950), subspecific designations were based on variation in measurements and plumage among specimens prepared as museum study skins. The most comprehensive recent list of birds of the world (Clements 2007) reports that ~57% of the more than 2,000 bird species from Canada to Panama have subspecies. The validity of such lists is questionable, however, because many continental subspecies
In this paper we present new statistical methods for the study of size and shape, and use these m... more In this paper we present new statistical methods for the study of size and shape, and use these methods to study the morphology of red-winged blackbirds, Agelaius phoeniceus, breeding in Florida. We use definitions of size and shape variables that permit the study of the entire statistical distribution of a given variable. We offer these methods as an alternative to classical methods based on the allometric equation in which relations are summarized in single coefficients reflecting at best the mean trend of shape with some size variables. Our alternative goal is to determine visually and geometrically meaningful size and shape variables which permit the direct study of the association of size and shape. This paper is in two parts. In the first part we discuss definitions of size and shape variables and summarize statistical results which include exact tests for sizeshape associations (Mosimann, 1970(Mosimann, , 1975a(Mosimann, , 1975b). In the second part we use these methods to study geographic variation in red-winged blackbirds in Florida. Throughout we consider the following situation: N individuals are independently sampled from some population. For each individual there are k positive measurements, all in the same units, say millimeters. For the i-th individual we then
medicine (117), agriculture (218), geology (50), the social sciences (7, 178, 193), and other dis... more medicine (117), agriculture (218), geology (50), the social sciences (7, 178, 193), and other disciplines. The opportunity for succinct summaries of large data sets, especially in the exploratory stages of an investigation, has contrib uted to an increasing interest in multivariate methods. The first applications of multivariate analysis in ecology and systematics were in plant ecology (54, 222) and numerical taxonomy (187) more than 30 years ago. In our survey of the literature, we found 20 major summaries of recent applications.
N an attempt to express habitat relationships in a new way, I have applied two methods of multiva... more N an attempt to express habitat relationships in a new way, I have applied two methods of multivariate analysis to a large set of data pertaining to the habitats of 46 species of common breeding birds. The question asked was : How do these species distribute themselves with respect to the struc- ture of the vegetation? This required (1) devising field techniques that would give quantitative measurements of the vegetation within the breeding territories of individual birds, (2) analyzing these by species in order to obtain a sample of the characteristic habitat dimensions of the species niche, (3) reconstructing the relationships among the species according to their relative habitat separation, and (4) considering the ability of the vegetational variables to describe differences among habitats mathematically. Data were gathered in the spring and summer of 1967 in Arkansas. The vegetation was sampled in O.l-acre circular plots, using singing male birds as the centers of the circles. The statistical procedures used which were principal component analysis and discriminant function analysis provided a tool for describing bird distribution objectively as ordinations of continuously-varying phenomena along gradients of vegetational structure. The relative positions of the species were located within multidimensional "habitat space." The relationship between this approach and studies involving ordinations of plant and animal communities is discussed. FIELD METHODS Estimates of the characteristics of the structure of the vegetation were obtained by means of sampling one 0.1~acre circular plot within the territory of each singing male bird. A 0.1.acre is a large enough area (radius 37 feet) that it should include an adequate sample of the vegetation. It is convenient to have a circular plot with its center at a singing perch selected by a territorial bird. This might give a biased view of habitat for species which occur in open areas and choose singing perches in places very different from their foraging areas, but this objection is minimized in the forest (including most of the species considered here). The sampling technique was a modification of the range-finder circle method recommended by Lindsey, Barton, and Miles (1958) as a very accurate and efficient procedure. The range-finder itself was found to he unnecessary. Instead, I suspended a brightly colored yardstick at or below the spot where a territorial male bird was singing. This was sighted by holding at armslength a second yardstick having a mark equal to the length of the first when viewed from the perimeter of the circle. This proved to be an accurate and efficient way of determining whether I was within the area to be sampled. A total of 4Ql 0.1.acre circles was measured in the territories of 46 species. No attempt was made to remain within a fairly uniform stand. In fact as many habitat types as
Opinions expressed by the authors of this publication are their own and do not necessarily reflec... more Opinions expressed by the authors of this publication are their own and do not necessarily reflect the opinions of the American Institute of Biological Sciences, the National Center for Ecological Analysis and Synthesis, nor the institutions with which the authors are affiliated.
There is a high degree of concordance among the patterns of geographic size variation in birds in... more There is a high degree of concordance among the patterns of geographic size variation in birds in the eastern and central United States. This is demonstrated for 12 species by assuming that wing length measurements are an indicator of body size on the intraspecific level, and by arranging the data in the form of a grid of means of wing lengths for sample areas. Maps giving isophenetic lines for wing length indicate gradually increasing size dines northward and westward from Florida in the Hairy Woodpecker (Dendrocopos villosus), Downy Woodpecker (Dendrocopos pubescens), Blue Jay (Cyanocitta cristata), Carolina Chickadee (Parus carolinensis), White-breasted Nuthatch (Sitta carolinensis), and Eastern Meadowlark (Sturnella magna). In each case there is a trend for larger (or longer-winged) birds to extend southward in the Appalachian Mountains and for smaller (or shorter-winged) birds to extend northward in the Mississippi River valley. Maps made by a computer and automatic plotter using contour intervals of 0.5 mm of mean wing length for the Downy Woodpecker, for male White-breasted Nuthatches, and for female Blue Jays show that, in addition to the pattern just mentioned, relatively longer-winged birds extend southward in the interior highlands of Arkansas, and relatively shorter-winged birds extend northward up other river valleys. These subtle relationships between intraspecific size variation and topographic features suggest that the link between the two phenomena may be precise adaptations to even minor climatic gradients. The relationship between these findings and the subspecies concept is discussed. Correlation coefficients for the pattern of variation in the Downy Woodpecker with seasonal and annual wet-bulb temperature, vapor pressure, and absolute humidity were all either equal to or higher than correlations with dry-bulb temperature. Since these variables reflect the combined effects of temperature and humidity, the obvious indication is that size variation is more closely related to this combination than to temperature alone. Additional correlations using the mean wing length data for seven other species confirmed that wet-bulb temperature patterns are more closely related to bird size than either dry-bulb temperature patterns or latitude. These relationships can be expressed numerically as regressions of mean wing length on either annual wet-bulb temperature or mean annual total heat per pound of air. Since increased evaporation at high altitudes and in arid areas accentuates the depression of a wetbulb thermometer, my hypothesis may partially account for several cases of size variation in birds cited by others as disturbing exceptions to Bergmann's ecogeographic rule. Sections of a translation of Bergmann's paper published in 1847 are given. The biological mechanisms by which these relationships are maintained are unknown, and the wide range of tolerance by birds to diurnal and seasonal temperature variations tends to mask them. If the well-established inverse relationship between weight and metabolic rate per gram of homeotherms is operative on the intraspecific level, the relationships can be discussed in terms of avenues of heat loss and of energy budget equations.
The Ornithological Monographs series, published by the American Ornithologists' Union, has been e... more The Ornithological Monographs series, published by the American Ornithologists' Union, has been established for major papers and presentations too long for inclusion in the Union's journal, The Auk.
Although there is strong evidence that a few Neotropical migrant land birds have severely declini... more Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental-scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980's, but other analyses conclude that most species have had stable or increasing populations in the last 25 years. These conflicting results suggest that a new perspective is called for. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970's and stability elsewhere. As examples of the use of this first approach in single-species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue-winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit-normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.
The common practice of expressing community structure in terms of indices of diversity and evenne... more The common practice of expressing community structure in terms of indices of diversity and evenness involves a serious loss of information. Differences attributable to the accumulation of species with increasing area are ignored, differences in the density of individuals are often masked by other factors, and many combinations of species richness and relative abundance can produce the same value of the index. As an alternative we suggest (1) comparing species richness by standardizing samples either to equal numbers of individuals or to the number of individuals expected on equal-sized plots, and (2) expressing the relative abundance of species as a graph of their relative abundances arranged in a decreasing array. We present an analysis of bird census data based on the proposed methods, and we include comparisons with applications of four indices commonly used in ecology, the Shannon-Weaver index of diversity, the J' evenness index, the inverse of Simpson's measure of concentration, and Hill's evenness index. For 37 Breeding Bird Censuses taken in various terrestrial habitats across the United States and Canada, the proposed methods reveal some very general relationships about the organization of bird communities in different habitats. Equal-sized areas of mature deciduous forest and secondgrowth habitats may be equally species rich (14-24 species with •> 1 breeding territory per 6 ha); the density of individuals (territorial pairs) is generally higher in deciduous forest habitats, and the relative abundance of bird species shows more dominance (less evenness) in the deciduous forest. Mixed coniferous-deciduous forests and dense young deciduous forests have fewer species than mature eastern deciduous forests or second-growth habitats (9-16 and 7-10 species per 6 ha, respectively), although the density of individuals is approximately equal to that in second-growth habitats. Coniferous forests are species-poor (5-8 per 6 ha), and the density of territorial pairs is low (8-12 per 6 ha compared with 40-70 in deciduous forests). Although the proposed methods require assumptions that need to be evaluated carefully, we are optimistic that they will have other useful applications in the analysis of arian communities.
A modest man, he will be fondly remembered for his many achievements and his lifelong dedication ... more A modest man, he will be fondly remembered for his many achievements and his lifelong dedication to studies of birds and their habitats. Of his hundreds of publications, the best known is Birds of North America: A Guide to Field Identification, coauthored with Bertel Bruun, illustrated by Arthur Singer, and edited by Herbert Zim, published in 1966 and revised in 1983. This 'Golden Guide', with its opposing range maps, sonograms and plates comparing similar birds, set new standards for field guides. More than six million copies have been sold. Born in Belmont, Massachusetts, on 17 July 1918, Chan was birding by the age of 12. Before he had completed his undergraduate studies at
Since the colonization of North America by Europeans, a taxonomically diverse array of avian spec... more Since the colonization of North America by Europeans, a taxonomically diverse array of avian species has become extinct. The Labrador Duck (Camptorhynchus labradorium), Great Auk (Pinguinus impennis), Passenger Pigeon (Ectopistes migratorius), Carolina Parakeet (Conuropsis carolinensis), and Ivory-billed Woodpecker (Campephilus principalis) come to mind. This somber list can be expanded to include subspecies such as the Heath Hen (Tympanuchus cupido cupido) and Dusky Seaside Sparrow (Ammodramus maritimus nigrescens). Several species currently are, or are thought to be, perilously close to extinction: California Condor (Gymnogyps californianus), Whooping Crane (Grus americana), Eskimo Curlew (Numenius borealis), Bachman's Warbler (Vermivora bachmanii), and Kirtland's Warbler (Dendroica kirtlandii). Extinction, usu
Although there is strong evidence that a few Neotropical migrant land birds have severely declini... more Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental-scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980's, but other analyses conclude that most species have had stable or increasing populations in the last 25 years. These conflicting results suggest that a new perspective is called for. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970's and stability elsewhere. As examples of the use of this first approach in single-species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue-winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit-normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.
Most of the 13 papers in this monograph were delivered at the meeting of the American Ornithologi... more Most of the 13 papers in this monograph were delivered at the meeting of the American Ornithologists' Union, the Cooper Ornithological Society, and the Society of Canadian Ornithologists in Portland, Oregon, during 4-9 August 2008, in a symposium session organized and chaired by Susan M. Haig and Kevin Winker. The purpose of the symposium was to review the history of subspecies in ornithology, the relevance of subspecies to studies of biodiversity and to conservation policy under the Endangered Species Act, and examples of recent research that involves subspecies of birds. The papers added after the symposium complement the others. As organized here, the first seven papers are general in nature and the last six are examples of recently analyzed case histories. The authors present various interpretations of the concept of subspecies and of methods for assigning individuals to subspecies, but they all favor the retention of subspecies as a taxonomic category. Arguments to the contrary are presented to provide perspective. The term "subspecies" applies to either a taxonomic category in the International Code of Zoological Nomenclature (ICZN; Ride 1999) or to a particular trinomial example (e.g., Turdus migratorius migratorius, which was listed in the first AOU Checklist in 1886). In the classic summaries for North American birds (Peters et al. 1934-1987, Ridgway and Friedmann 1901-1950), subspecific designations were based on variation in measurements and plumage among specimens prepared as museum study skins. The most comprehensive recent list of birds of the world (Clements 2007) reports that ~57% of the more than 2,000 bird species from Canada to Panama have subspecies. The validity of such lists is questionable, however, because many continental subspecies
In this paper we present new statistical methods for the study of size and shape, and use these m... more In this paper we present new statistical methods for the study of size and shape, and use these methods to study the morphology of red-winged blackbirds, Agelaius phoeniceus, breeding in Florida. We use definitions of size and shape variables that permit the study of the entire statistical distribution of a given variable. We offer these methods as an alternative to classical methods based on the allometric equation in which relations are summarized in single coefficients reflecting at best the mean trend of shape with some size variables. Our alternative goal is to determine visually and geometrically meaningful size and shape variables which permit the direct study of the association of size and shape. This paper is in two parts. In the first part we discuss definitions of size and shape variables and summarize statistical results which include exact tests for sizeshape associations (Mosimann, 1970(Mosimann, , 1975a(Mosimann, , 1975b). In the second part we use these methods to study geographic variation in red-winged blackbirds in Florida. Throughout we consider the following situation: N individuals are independently sampled from some population. For each individual there are k positive measurements, all in the same units, say millimeters. For the i-th individual we then
medicine (117), agriculture (218), geology (50), the social sciences (7, 178, 193), and other dis... more medicine (117), agriculture (218), geology (50), the social sciences (7, 178, 193), and other disciplines. The opportunity for succinct summaries of large data sets, especially in the exploratory stages of an investigation, has contrib uted to an increasing interest in multivariate methods. The first applications of multivariate analysis in ecology and systematics were in plant ecology (54, 222) and numerical taxonomy (187) more than 30 years ago. In our survey of the literature, we found 20 major summaries of recent applications.
N an attempt to express habitat relationships in a new way, I have applied two methods of multiva... more N an attempt to express habitat relationships in a new way, I have applied two methods of multivariate analysis to a large set of data pertaining to the habitats of 46 species of common breeding birds. The question asked was : How do these species distribute themselves with respect to the struc- ture of the vegetation? This required (1) devising field techniques that would give quantitative measurements of the vegetation within the breeding territories of individual birds, (2) analyzing these by species in order to obtain a sample of the characteristic habitat dimensions of the species niche, (3) reconstructing the relationships among the species according to their relative habitat separation, and (4) considering the ability of the vegetational variables to describe differences among habitats mathematically. Data were gathered in the spring and summer of 1967 in Arkansas. The vegetation was sampled in O.l-acre circular plots, using singing male birds as the centers of the circles. The statistical procedures used which were principal component analysis and discriminant function analysis provided a tool for describing bird distribution objectively as ordinations of continuously-varying phenomena along gradients of vegetational structure. The relative positions of the species were located within multidimensional "habitat space." The relationship between this approach and studies involving ordinations of plant and animal communities is discussed. FIELD METHODS Estimates of the characteristics of the structure of the vegetation were obtained by means of sampling one 0.1~acre circular plot within the territory of each singing male bird. A 0.1.acre is a large enough area (radius 37 feet) that it should include an adequate sample of the vegetation. It is convenient to have a circular plot with its center at a singing perch selected by a territorial bird. This might give a biased view of habitat for species which occur in open areas and choose singing perches in places very different from their foraging areas, but this objection is minimized in the forest (including most of the species considered here). The sampling technique was a modification of the range-finder circle method recommended by Lindsey, Barton, and Miles (1958) as a very accurate and efficient procedure. The range-finder itself was found to he unnecessary. Instead, I suspended a brightly colored yardstick at or below the spot where a territorial male bird was singing. This was sighted by holding at armslength a second yardstick having a mark equal to the length of the first when viewed from the perimeter of the circle. This proved to be an accurate and efficient way of determining whether I was within the area to be sampled. A total of 4Ql 0.1.acre circles was measured in the territories of 46 species. No attempt was made to remain within a fairly uniform stand. In fact as many habitat types as
Opinions expressed by the authors of this publication are their own and do not necessarily reflec... more Opinions expressed by the authors of this publication are their own and do not necessarily reflect the opinions of the American Institute of Biological Sciences, the National Center for Ecological Analysis and Synthesis, nor the institutions with which the authors are affiliated.
There is a high degree of concordance among the patterns of geographic size variation in birds in... more There is a high degree of concordance among the patterns of geographic size variation in birds in the eastern and central United States. This is demonstrated for 12 species by assuming that wing length measurements are an indicator of body size on the intraspecific level, and by arranging the data in the form of a grid of means of wing lengths for sample areas. Maps giving isophenetic lines for wing length indicate gradually increasing size dines northward and westward from Florida in the Hairy Woodpecker (Dendrocopos villosus), Downy Woodpecker (Dendrocopos pubescens), Blue Jay (Cyanocitta cristata), Carolina Chickadee (Parus carolinensis), White-breasted Nuthatch (Sitta carolinensis), and Eastern Meadowlark (Sturnella magna). In each case there is a trend for larger (or longer-winged) birds to extend southward in the Appalachian Mountains and for smaller (or shorter-winged) birds to extend northward in the Mississippi River valley. Maps made by a computer and automatic plotter using contour intervals of 0.5 mm of mean wing length for the Downy Woodpecker, for male White-breasted Nuthatches, and for female Blue Jays show that, in addition to the pattern just mentioned, relatively longer-winged birds extend southward in the interior highlands of Arkansas, and relatively shorter-winged birds extend northward up other river valleys. These subtle relationships between intraspecific size variation and topographic features suggest that the link between the two phenomena may be precise adaptations to even minor climatic gradients. The relationship between these findings and the subspecies concept is discussed. Correlation coefficients for the pattern of variation in the Downy Woodpecker with seasonal and annual wet-bulb temperature, vapor pressure, and absolute humidity were all either equal to or higher than correlations with dry-bulb temperature. Since these variables reflect the combined effects of temperature and humidity, the obvious indication is that size variation is more closely related to this combination than to temperature alone. Additional correlations using the mean wing length data for seven other species confirmed that wet-bulb temperature patterns are more closely related to bird size than either dry-bulb temperature patterns or latitude. These relationships can be expressed numerically as regressions of mean wing length on either annual wet-bulb temperature or mean annual total heat per pound of air. Since increased evaporation at high altitudes and in arid areas accentuates the depression of a wetbulb thermometer, my hypothesis may partially account for several cases of size variation in birds cited by others as disturbing exceptions to Bergmann's ecogeographic rule. Sections of a translation of Bergmann's paper published in 1847 are given. The biological mechanisms by which these relationships are maintained are unknown, and the wide range of tolerance by birds to diurnal and seasonal temperature variations tends to mask them. If the well-established inverse relationship between weight and metabolic rate per gram of homeotherms is operative on the intraspecific level, the relationships can be discussed in terms of avenues of heat loss and of energy budget equations.
The Ornithological Monographs series, published by the American Ornithologists' Union, has been e... more The Ornithological Monographs series, published by the American Ornithologists' Union, has been established for major papers and presentations too long for inclusion in the Union's journal, The Auk.
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Papers by Frances James