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Showing papers in "The Auk in 1968"


Journal ArticleDOI
01 Jan 1968-The Auk
TL;DR: For at least 150 years anatomists (Meckel, 1816) and ornithologists (Audubon, 1831) have been interested in the olfactory sense of birds.
Abstract: FoR at least 150 years anatomists (Meckel, 1816) and ornithologists (Audubon, 1831) have been interested in the olfactory sense of birds. Only within the last decade, however, have physiological experiments defi• nitely shown that in some species of birds the chemoreceptors of the olfactory nerve respond to airborne odors (Michelsen, 1959; Tucker, 1965; Wenzel, 1965). In the intervening century or more, much rather fruitless discussion has ensued as to whether or not \"birds have a sense of smell.\

255 citations


Journal ArticleDOI
01 Jan 1968-The Auk
TL;DR: This paper analyzes in detail the phenomenon of weight recession in nestling Barn Swallows (Hirundo rustica) and presents a general survey of the literature to determine the distribution of the phenomenon among avian groups.
Abstract: IT has been noted in many species of birds that the weight of growing young increases to a peak above normal adult weight and then decreases before fledging. This phenomenon of weight recession (Edson, 1930) has been attributed to various causes (e.g., drying out of the feathers, high energy demands with rapid feather growth, starvation periods, decrease in the size of the digestive organs) but little evidence has been sought to support any of these hypotheses. This paper analyzes in detail the phenomenon of weight recession in nestling Barn Swallows (Hirundo rustica) and presents a general survey of the literature to determine the distribution of the phenomenon among avian groups.

132 citations


Journal ArticleDOI
01 Apr 1968-The Auk
TL;DR: The Red-cockaded Woodpecker (D. borealis) and the Arizona woodpecker(D. arizonae) differ greatly in the degree of sexual dimorphism of body size and bill length.
Abstract: Two recent studies on woodpeckers (Kilham, 1965; Selander, 1966) support the hypothesis of Rand (1952), which states that within a species sexual dimorphism may aid in reduction of competition for food. In an extensive discussion of intraspecific differences in foraging, Selander (1966: 143-145) diagrams the solutions open to birds faced with decreased availability of food, and Kilham (1965) discusses possible causes, other than those directly related to food supply, for the evolution of traits that reduce intersexual competition for foraging sites. Neither author discusses in detail the problem of origin of stereotyped behavioral differences between the sexes. Sexual differences in foraging behavior of two species of Dendrocopos, the Red-cockaded Woodpecker (D. borealis) and the Arizona woodpecker (D. arizonae), are described in this report, and a discussion of the possible origin of this phenomenon in woodpeckers is presented. These two species differ greatly in the degree of sexual dimorphism of body size and bill length, to which much importance has been attached (Selander and Giller, 1963; Selander, 1965, 1966). The Red-cockaded Woodpecker inhabits open pine forests of the southeastern United States. It is found only in areas where pines predominate and is probably most common on the Atlantic coastal plain. The range of this species extends northward to Virginia and Kentucky, and westward to Oklahoma and Texas (A.O.U., 1957). The range of the Arizona Woodpecker extends from extreme southern Arizona and New Mexico, where it is associated with oak woodland, south into Michoacan (Davis, 1965: 537).

113 citations



Journal ArticleDOI
01 Apr 1968-The Auk
TL;DR: This paper analyzes several bird vocalizations and interprets their patterns as the product of individual and interacting oscillators and sound modifying structures; it also suggests a model for the operation of the syrinx during sound production.
Abstract: Yet these complexities are useful not only in the study of the patterns themselves, but also for interpreting the functional anatomy of the sound producing structures, the nature of the message, and the relationships among the birds involved. This paper analyzes several bird vocalizations and interprets their patterns as the product of individual and interacting oscillators and sound modifying structures; it also suggests a model for the operation of the syrinx during sound production. To determine some of the variation and complexity in bird vocalizations I made sound spectrograms and oscillograms of song phrases sampled from the records produced by Kellogg and Allen (1959, 1962). These spectrograms indicated that the most complex fundamentals were similar to electronically produced modulations. Such modulations are easily recognized by their audible "buzzy" quality. On the spectrograms time is indicated on the horizontal axis, frequency on the vertical one. The horizontal line on some spectrograms indicates that portion of the signal shown on the corresponding oscillogram. On oscillograms time is indicated on the horizontal axis and the instantaneous relative amplitude of the sound wave on the vertical one. Some bird vocalizations are simple, in that their fundamentals are analogous to signals produced electronically by a single sine-wave oscillator. Up-slurs and down-slurs are simple changes in frequency. Other sounds are mixtures of two such independent signals. The most complex sounds discussed in this paper are amplitude-modulated (AM) and frequency-modulated (FM) signals, particular interactions between two independent oscillations and analogous to radio broadcasting waves. Explanations of the nature of such waves may be found in the Radio amateur's kandbook (Amateur Radio Relay League, 1960). In essence, AM and FM are complex waves, the shapes of which are

98 citations


Journal ArticleDOI
01 Jan 1968-The Auk

74 citations



Journal ArticleDOI
01 Jul 1968-The Auk
TL;DR: Investigations on the pigmentation and feather structure of the Gouldian Finch represents an opportunity to study carotenoid metabolism in a nondomestic species about whose genetics some information is available.
Abstract: THE GouldJan Finch, Poephila gouldiae, is among the most colorful of estrildine finches. The species is distributed through tropical northern Australia, where it inhabits grassy plains. It is nomadic over at least part of its range, is an extremely sociable species, and occurs in large flocks even during the breeding season. Because of its colorful plumage and simple diet of seeds, it enjoys considerable favor as a cage bird. One of the most interesting aspects of the plumage in this species is the occurrence in nature of a polymorphism in facial color. Three facial or head colors are known in wild birds: black, which is the most common; red, which occurs in approximately one out of four birds; and yellow or orange, which occurs in only one in every three to five thousand birds. As the color phases are known from all areas of the species' range and occur in all flocks, they are not considered separate geographic races. In addition to the three face colors, there are several mutants that involve both melanistic pigmentation (Butler, 1902) and feather structure (Immelmann, 1965, pers. comm.) but these are only poorly known. Because the Gouldian Finch is popular as a cage bird, a considerable amount of information has been obtained on the genetics of the facial colors. Southern (1946) has shown that although the black type is more common than the red, the red is dominant over black. Furthermore, the red and black alleles are sex linked. Murray (1963) showed that the gene for the rarer orange face is autosomal and recessive to both red and black. Birds that are homozygous for yellow and also for the recessive black head are black faced but have a yellow tipped beak rather than the usual red tip (Southern's \"type C\" black genotype). We undertook the investigations on the pigmentation and feather structure reported here for several reasons. The Gouldian Finch represents an opportunity to study carotenoid metabolism in a nondomestic species about whose genetics some information is available. Relatively little is known about the metabolism of these pigments in vertebrates generally and, in spite of the wide use of plumage coloration in avian systematics, practically no information is available on the pathways of carotenoid metabolism in birds. P. gouldiae is of potential general interest in an attempt to understand the control and evolution of these metabolic pathways. This finch also provides ideal material for studies on the metabolism of pigments in

70 citations


Journal ArticleDOI
01 Jul 1968-The Auk
TL;DR: This study examines the reproductive cycle of the Pintail with particular emphasis on the motivation and function of aerial activity which can be observed throughout the nesting season.
Abstract: THE social behavior of the Pintail, Anas acuta, seems to diverge most noticeably from that of other North American ducks of the genus Anas during the nesting phase of the reproductive cycle. This study examines the reproductive cycle of the Pintail with particular emphasis on the motivation and function of aerial activity which can be observed throughout the nesting season. Aerial activity during pair formation and nesting in ducks has been discussed by Hochbaum (1944), Sowls (1955), Dzubin (1955, 1957), Lebret (1961), Wiist (1960), Hori (1963), and McKinney (1965). Nonreproductive activity among young Pintails was observed to serve as a basis for comparison with reproductive behavior.

60 citations


Journal ArticleDOI
01 Jan 1968-The Auk
TL;DR: The occurrence, causation, and adaptiveness of antiphonal calling in three species of North American quail (Odontophorinae): The Bobwhite (Colinus virginianus), the California Quail (Lophortyx cali/ornicus), and the Gambel's Quails (L. gambelii).
Abstract: Tx•Is paper reports the occurrence, causation, and adaptiveness of antiph•onal calling in three species of North American quail (Odontophorinae): The Bobwhite (Colinus virginianus), the California Quail (Lophortyx cali/ornicus), and the Gambel's Quail (L. gambelii). Armstrong (1963: 180) has reviewed antiphonal singing in birds. It can be defined as the alternation of calling between members of a pair or potential mates. Timing is often so accurate that the mutual calling sounds as though it comes from one individual. Antiphonal calling is characteristic of tropical species that live in dense foliage and form an extended pair bond. It is much less common, although widespread, outside of the tropics. It presumably functions to maintain the pair bond and in some species develops through learning. Diamond and Terborgh (1968) discuss several possible functions of duetting in New Guinea birds. Precise duetting or antiphonal calling has been reported from at least two Central American species of Odontophorinae. Griscom (1932: 108), in quoting A. W. Anthony, described perfect duetting between two Dactylortyx thoracicus kept on opposite sides of a house in Quatamala. The natives stated \"th'ere would be no song if the two birds could see each other.\" Skutch (1947: 221) indicated that Odontophorus gujanensis probably duets in a manner similar to that reported by Chapman (1929: 275) for O. marmoratus. Chapman observed two birds standing one to two feet apart and singing a duet in perfect unison. The only other galliform for which antiphonal calling has been reported is Francolinus ahantensis (Holman, 1947: 630.). All these species inhabit dense vegetation that prevents visual contact at a distance.

53 citations


Journal ArticleDOI
01 Apr 1968-The Auk
TL;DR: A careful study of the functional anatomy of its syrinx in the Common Crow contradicts the view expressed by Welty (1963) that this species is not capable of vocal versatility, i.e. significant variation in pitch and variety of notes produced.
Abstract: A careful study of the functional anatomy of its syrinx in the Common Crow (Corvus brackyrkynchos) contradicts the view expressed by Welty (1963) that this species is not capable of vocal versatility, i.e. significant variation in pitch and variety of notes produced. Poor vocalizers such as most nonpasserines may have only two or three pairs of syringeal muscles, but true song birds typically have seven pairs, and as many as nine pairs have been reported in some song birds (Welty, 1963: 118-119). Owen (1866) and Ames (1965) describe the anatomy of syringeal muscles in the suborder Passeres. Shufeldt (1890) discusses the muscles of the air passages in the raven (Corvus corax sinuatus). In a preliminary study of sound production in the Common Crow, Miskimen (1951) reports seven pairs of syringeal muscles. Myers (1917) and Gross (1964) describe the functional anatomy of the chicken (Gallus domesticus) syrinx. Ruppell (1933) investigated the vocal structures of the Herring Gull (Larus argentatus). His apparatus for holding the syrinx made it possible to observe the vibration of the vocal membranes, but his review of the literature and experimental work all emphasized the importance of pressure in the interclavicular air sac during sound production. Miller (1934) was able to produce sound with the syrinx of the Great Horned Owl (Bubo virginianus) and Turkey (Meleagris gallopavo) by blowing

Journal ArticleDOI
01 Jan 1968-The Auk
TL;DR: The present paper is an analysis of all instances known to us of duetting by New Guinea birds, based largely on previously unpublished field observations, as it has been suggested that the incidence ofduetting may correlate with type of habitat, possibilities for visual contact between singers, or sexual dimorphism of plumage.
Abstract: A relatively uncommon but intriguing form of bird song, the significance of which is imperfectly understood, is synchronized duetting between a mated male and female. Most reports of birds engaging in this come from the tropics, with examples from Central America (Skutch, 1940), South America (Haverschmidt, 1947), Africa (Moreau, 1941; Thorpe, 1963; Grimes, 1966), Madagascar (van Someren, 1947), and Malaya (Young, 1942). A few examples from the temperate zone have also come to light among owls, Himalayan (Osmaston, 1941) and Australian (Robinson, 1947: 14-17) passerines, and the Canada Goose (Branta canadensis) (Collias and Jahn, 1959), Carolina Wren (Thryothorus ludovicianus), and three species of quail (Stokes and Williams, 1968) of North America. A selected list of species may be found in Van Tyne and Berger (1959: 140). The present paper is an analysis of all instances known to us of duetting by New Guinea birds, based largely on our previously unpublished field observations. As it has been suggested that the incidence of duetting may correlate with type of habitat, possibilities for visual contact between singers, or sexual dimorphism of plumage, these points are considered in each species discussed. Duets may be divided conveniently into three categories. (1) The leader (generally the male) sings one phrase, and at its conclusion the second bird (generally the female) sings another phrase. Often the follower begins so precisely upon cessation of the leader's phrase that the result may easily pass for a conventional single song, unless the observer can see the singers or is close enough to hear that different notes come from different places. For example, the Marbled Wood-Quail (Odontophorus gujanensis) calls a rapidly repeated "corcorovado," in which "corcoro" is always sung by one member of a pair and "vado" by the other (Chapman, 1929: 275; Armstrong, 1963). The term "antiphonal singing" has been used for this type of duetting, in which male and female sing alternately rather than simultaneously. In this category belong the Central American wrens described by Skutch (1940) and Amaurornis olivaceus, Pitohui kirhocephalus, and Philemon novaeguineae (see below) of New Guinea. (2) Members of a pair sing different phrases simultaneously. The synchronization between the two phrases may nevertheless be very exact; the female may begin only a fraction of a second after the male. In New Guinea the duets of Megapodius freycinet, Campochaera sloetii, and Coracina montana are of this type. (3) The male and female sing virtually identical phrases in unison. Such unison duets are practiced by Centropus toulou (Cuculidae) of Madagascar (van Someren, 1947), Aspatha gularis (Momotidae) of Central




Journal ArticleDOI
01 Jul 1968-The Auk
TL;DR: This paper explains the methods of measuring and methods of "reducing" the observations, and modifies the theory to achieve maximum practical utility, and gives reasons for believing the results valid and adequate.
Abstract: -In the Handbook of North American birds the description of egg sizes, and more particularly of egg shapes, proceeds o.n somewhat different lines from those of previous works. The present paper explains the methods of measuring and methods of "reducing" the observations. The elements actually measured are the conventional average length and breadth, plus the (unconventional) radii of the blunt and pointed ends. The standard deviations of each of these are estimated from the sample. From these measurements, all of which in effect are measurements of size, certain dimensionless quantities are derived hereinafter referred to as asymmetry, bicone, and elongation. These are specifications of shape independent of size. This paper sets forth the theory, modifies the theory to achieve maximum practical utility, and gives reasons for believing the results valid and adequate. In addition methods of sampling are discussed, and a new procedure of sampling is given for getting somewhat more representative results than heretofore. THE only figures usually given for the size of an egg are its length and its maximum diameter, hereinafter called its breadth. The older texts, such as the Catalog of eggs in the British Museum (1901) or Seebohm (1896), give the extreme values that have been encountered for these figures in some survey or other, and this specifies the "range" of lengths or breadths within which the dimensions of another egg of the same species may reasonably be expected to fall. In the Handbook of British Birds (Witherby et al., 1938), in Bent (1919), and in some other more recent texts the average value of length and breadth is given, together with the extreme values. Neither method is entirely satisfactory, for even if a hundred eggs were examined to obtain these extremes, it is obvious that if we examine another hundred, half the extremes may be exceeded. Still more recently, some authors have adopted the more useful procedure of giving the averages and the standard deviations rather than the average and the extreme values. Then, provided that the "sample" is drawn from a "normal" or "Gaussian" population of eggs-and Van Bree (1957) has shown that at least for the population he examined this assumption is sound-we can estimate the probability that an egg will depart by any given amount from the average. There is one precaution that has not normally been observed. Measurements should be strictly independent and on unbiased samples. As it has been shown (Preston and Preston, 1953) that parentage has a significant effect on egg size, a valid sample, if it is to represent a species, should have equal numbers of eggs from each parent, and indeed it would be best to have as many parents represented as possible. In the case of a human population, for example, it would not be wise, in estimating the average 454 The Auk, 85: 454-463. July, 1968 This content downloaded from 207.46.13.13 on Fri, 26 Aug 2016 06:15:40 UTC All use subject to http://about.jstor.org/terms July, 1968] Shapes of Birds' Eggs 455

Journal ArticleDOI
01 Oct 1968-The Auk
TL;DR: The purpose of the present investigation is to consider other parameters, namely food and feeding behavior, which may be very important in the relationships of Red-wings and grackles breeding on this cattail marsh.
Abstract: WIENS (1965), in a study of the behavioral interactions of Redwinged Blackbirds (Agelaius phoeniceus) and Common Grackles (Quiscalus quiscula) on a small cattail (Typha latifolia) marsh in Madison, Wisconsin, points out that the cattail habitat is "typical" for Red-wings and "unusual" for grackles, and that a potentially competitive situation exists in a marsh where the two species nest together. The emphasis of his study was on behavioral interactions and the effect of these interactions on reproduction. The purpose of the present investigation is to consider other parameters, namely food and feeding behavior, which may be very important in the relationships of Red-wings and grackles breeding on this cattail marsh. Indeed, as expressed by Orians and Collier (1963: 457), "Ecological compatibility, the prime requirement for sympatry, . . . is strongly influenced by such behavioral attributes as feeding behavior which vary remarkably in morphologically similar species." In addition, selected breeding biology data are presented from the years following Wiens' study to elucidate further the relationships of Red-wings and grackles on this marsh. For extensive discussion of the breeding biology and displays of Redwings see Beer and Tibbitts (1950) and Nero (1956). Peterson and Young (1950) and Ficken (1963) give corresponding discussions of grackles, and Wiens (1965) compares the two species.




Journal ArticleDOI
01 Jan 1968-The Auk
TL;DR: This appears to be the first unequivocal postflight sample of birds available for detailed fat studies, and comparing body weights, fat quantities, and other characteristics of the ship sample with similar data from migrating Palm Warblers collected at Florida television towers during fall migration should help to clarify certain problems relating to flight bioenergetics and fat utilization.
Abstract: ON the drizzly overcast afternoon of 24 October 1965 approximately 35 small birds landed aboard the U. S. Coast Guard Cutter "Hollyhock" between 1400 and 1800 hours. The ship's position was 76? 20' N, 210 40' W, or some 10 to 20 miles off the northeast coast of Cuba. Among the birds landing on the ship were 27 western Palm Warblers (Dendroica p. palmarum) that were captured and frozen by J. C. Dickinson, Jr. and Neil Payne of the Florida State Museum. These specimens, ultimately given to the author, provided needed data relating to bioenergetics of avian flight, fat deposits, and fat utilization. The geographic position, prevailing winds, and season indicated that the birds were on the verge of completing an extended overwater flight from the north. This appears to be the first unequivocal postflight sample of birds available for detailed fat studies, because samples heretofore reported in the literature as presumed postflight birds contained individuals that might have been aground for some time prior to collection (Odum, 1960; Odum et al., 1964; Kuroda, 1964; Johnston and McFarlane, 1966). Unfortunately, because of the geographic location of the ship sample, it is impossible to state precisely where the overwater flight originated. These birds could have come directly from southern Florida or from any points along the Atlantic seaboard, perhaps via the Bahama Islands. Nonetheless, comparing body weights, fat quantities, and other characteristics of the ship sample with similar data from migrating Palm Warblers collected at Florida television towers during fall migration should help to clarify certain problems relating to flight bioenergetics and fat utilization.






Journal ArticleDOI
01 Oct 1968-The Auk
TL;DR: Observation suggests that longspurs are daytime migrants; the authors have seen them settling to roost at dusk and frequently on the wing during the day and the proportions of sexes in the flocks along the migratory path should reveal the movement of a population adequate for nesting.
Abstract: grounds north and west of the forest. Irving postulated that longspurs nesting in the Mackenzie River Delta came from farther east in Alberta while those nesting in the Aleutians migrated along the coast or over the Gulf of Alaska, because their early arrival in the west precluded their passage through the mountains of British Columbia. It was inferred that the longspurs use both interior and coastwise routes of migration to Alaska. Reports and our observations during several migrations show that longspurs migrate in large numbers northward and westward from the prairies of Alberta through Yukon Territory but we do not know what proportions of prairie birds continue westward into western and northern Alaska or diverge northward to the Mackenzie Valley. The mountain trenches of British Columbia also appear to offer favorable northward migration routes parallel to the prairie migration to enter the stream moving westward along the headwaters of the Yukon River in Yukon Territory. Although longspurs are reported in the mountains of British Columbia (Munro and McCowan, 1947) the data are insufficient to indicate migratory programs. Observation suggests that longspurs are daytime migrants; we have seen them settling to roost at dusk and frequently on the wing during the day. The distinctive male longspur plumage permits discrimination of sex in flocks even at considerable distance. Irving noted that the majority of early migrant longspurs along the Alaska Highway and arriving on their nesting grounds at Anaktuvuk Pass were male birds, but he did not record significant numbers of females. On the nesting grounds the female birds are so secretive that their arrival and numbers are obscure. Except for the unlikely case that the females pursue a different route than the males they are to breed with, the proportions of sexes in the flocks along the migratory path should reveal the movement of a population adequate for nesting. Conversely the proportion of sexes in migrating flocks should

Journal ArticleDOI
01 Oct 1968-The Auk
TL;DR: This paper reviews the scientific and popular ornithological literature regarding the diet and feeding behavior of the Purple Martin, in order to ascertain what if any role martins play in the control of mosquito populations.
Abstract: RECENTLY articles and advertisements have appeared in newspapers and publications throughout the United States urging the public to erect bird houses in order to establish colonies of Purple Martins (Progne subis). The publicity proclaims that a martin consumes 2,000 mosquitoes per day, and either states or implies that martins provide effective biological control of mosquitoes. This is somewhat reminiscent of a controversy raised many years ago over the use of bats as mosquito control agents (see Allen, 1939; Storer, 1926). This paper reviews the scientific and popular ornithological literature regarding the diet and feeding behavior of the Purple Martin, in order to ascertain what if any role martins play in the control of mosquito populations.

Journal ArticleDOI
01 Oct 1968-The Auk
TL;DR: The evidence of molt, plumage, and voice bearing on the relationships of these species is considered, with the discovery of a hybrid between the Le Conte's and Sharp-tailed Sparrows (described below).
Abstract: THE first and second editions of the A.O.U. Check-list (1886, 1895) list the Henslow's Sparrow (now Passerherbulus henslowii) and the Le Conte's Sparrow (now Passerherbulus caudacutus) in the subgenus Coturniculus of the genus Ammodramus with the Grasshopper Sparrow (now Ammnodramus savannarum). When Ridgway (1901) raised the subgenera (Passerculus, Centronyx, Coturniculus, and Ammodramus) of Ammodramus to generic rank, he separated the Henslow's and Le Conte's Sparrows from the Grasshopper Sparrow and placed them with the former members of the subgenus Ammodramus, the Sharp-tailed Sparrow (now Ammospiza caudacuta) and the known Seaside Sparrows (now Ammospiza maritima and nigrescens), a treatment later followed by the A.O.U. (1903). The Ammodramus group remained intact, despite being renamed Ammospiza (Oberholser, 1905) and then Passerherbulus (Stone, 1907), until Oberholser (1917) split the group into four genera: Thryospiza for the Seaside Sparrows, Ammospiza for the Sharp-tailed Sparrow, Passerherbulus for the Le Conte's Sparrow, and Nemospiza for the Henslow's Sparrow. Subsequently the A.O.U. (1931) recognized the genus Ammospiza containing the Sharp-tailed and Seaside Sparrows, the genus Passerherbulus containing the Le Conte's and Henslow's Sparrows, and the genus Ammodramus, containing the Baird's (A. bairdii) and Grasshopper Sparrows. No changes have been made since, and as yet no diagnoses exist for these genera as presently constituted. More recently Tordoff and Mengel (1951) questioned the present classification when they discovered that the prealternate molt of the Le Conte's Sparrow was extensive and thus more like that of the Sharp-tailed Sparrow than that of the Henslow's Sparrow. Graber (1955) actually transferred the Le Conte's Sparrow to Ammospiza on the basis of the similarity of the juvenal plumages of the Le Conte's and Sharp-tailed Sparrows. With the discovery of a hybrid between the Le Conte's and Sharp-tailed Sparrows (described below), it seems appropriate to consider the evidence of molt, plumage, and voice bearing on the relationships of these species. Molt.-The descriptions of the molts of the species being considered are generally incomplete or erroneous. Detailed studies for most species have yet to be made. The best that can be done now is a brief comparison of what is known.

Journal ArticleDOI
01 Jul 1968-The Auk
TL;DR: It is shown that it is the younger members of the population of Goshawks (Accipiter gentilis) that invade areas south of the breeding range during autumn and winter, and there also appears to, be a differential migration of the sexes.
Abstract: In a recent paper (Mueller and Berger, 1967) we showed that it is the younger members of the population of Goshawks (Accipiter gentilis) that invade areas south of the breeding range during autumn and winter. We are now able to report that there also appears to, be a differential migration of the sexes. For some years we have been confident that an experienced worker could determine the sex of a living Goshawk simply by noting the relative size of the bird. We were reluctant to publish our findings based on sex determinations made by size alone because data from museum specimens usually indicated considerable overlap between the measurements of the sexes. Storer (1966) has recently provided an independent confirmation of the validity of our techniques of sex determination by showing that considerable sexual dimorphism exists in the size of Goshawks and that museum collectors often err in determining the sex of hawks. In the autumns of 1951 through 1964 we live-trapped, examined, and measured 105 Goshawks at the Cedar Grove Ornithological Station in southeastern Wisconsin. Wing chord was measured by placing the carpal joint of the closed wing on a metric rule placed on a table edge and pivoting the wing downward until the tip of the longest primary touched the rule. Pressing the wing flat provided a measurement of wing arc. The length of the tail was measured by inserting a thin metal rule between the central rectrices and sighting across the tips of the two longest rectrices. The birds were placed head downward in upright metal cylinders of appropriate diameter and weighed to the nearest gram on a triple-beam balance calibrated to 0.1 g. The weight of the contents of the esophagus ("crop") was estimated and subtracted from the gross weight. An examination of the plumage permitted us to place birds into three age classes: (1) Juvenals, (2) Adult I, including birds more than one but less than two years old, and (3) Adult II, including all birds more than two years old (see Storer, 1966; Mueller and Berger, 1967). We determined the sex of each bird by a series of approximations. All but seven birds were tentatively assigned to a sex class by qualitative judgment at the time of capture. The measurements of wing chord and tail length for all Goshawks handled, irrespective of age class, were graphed. For both measurements the resulting distribution resembled two normal curves. The curve with the smaller mean was composed of birds qualitatively judged to be males; the larger, females. The seven undetermined birds fell largely into the zone of overlap. These seven birds were somewhat arbitrarily assigned to one or the other of the sexes, and the