Field identification of the White-footed Mouse (Peromyscus leucopus noveboracensis) and Long-tail... more Field identification of the White-footed Mouse (Peromyscus leucopus noveboracensis) and Long-tailed Deer Mouse (Peromyscus maniculatus gracilis) is difficult because of their similar external morphology. Peromyscus were sampled by live-trapping during a five-year period (1992-1996) at the Arnot Teaching and Research Forest, Van Etten, New York and identified to species by electrophoresis of their salivary amylase. No electromorphs were shared between P. leucopus and P. maniculatus, thus permitting unambiguous species identification of individuals. Means and ranges of four external measurements (ear, head-body, hind-foot, and tail) and tail to head-body ratio were determined for amylase-genotyped live mice. Although some body measurements did differ on average between the two species (ear, head-body, and tail for adults; hind-foot and tail for juveniles), the ranges of these overlap considerably. When the four external measurements (excluding the tail to head-body ratio) were used to...
Early increased sophistication of human tools is thought to be underpinned by adaptive morphology... more Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow's bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii)...
Avian Ecology and Conservation in an Urbanizing World, 2001
American Crows (Corvus brachyrhynchos) have become common suburban and urban birds in the last 50... more American Crows (Corvus brachyrhynchos) have become common suburban and urban birds in the last 50 years, using these environments for roosting and breeding. I studied crows in upstate New York from 1989 to 1999, and compared reproductive success, survival, and social behavior of crows in suburban and rural areas. Although both suburban and rural crows maintained permanent territories, suburban American Crows had smaller territories and nested at higher densities. Both suburban and rural crows periodically left their territories in fall and winter to join foraging aggregations and to roost at night. The proportion of nests attended by auxiliaries did not differ, but suburban nests were attended by larger families. Overall nest success was higher in suburban areas. Success rates during the egg stage of the nest cycle did not differ between habitat, but suburban nests had higher success during the nestling stage of the nest cycle. Survival of crows post fledging was better in suburban areas, but after one year annual survival rates did not differ between the habitats. Birds raised in one habitat tended to breed in the same habitat. Although clutch sizes and egg hatchability did not differ between the habitats, rural nests produced nearly one more young per successful nest and significantly larger young than suburban crows, suggesting that food resources were better in rural areas. Data from a drought year, a time of apparent food shortage, suggested that suburban food resources also were less dependable than those in rural areas. The increase in American Crows over the last 25 years in eastern North America may be due in part to the successful exploitation of suburban nesting habitats.
Avian Ecology and Conservation in an Urbanizing World, 2001
Corvid populations are increasing worldwide in response to urbanization. We investigated the resp... more Corvid populations are increasing worldwide in response to urbanization. We investigated the response of American Crows (Corvus brachyrhynchos) to urbanization by (1) comparing rates of winter population change between urban and nonurban locations (using standard Christmas Bird Counts); (2) quantifying population size along a gradient of urbanization in western Washington; and (3) pooling studies from eastern (New York), midwestern (Wisconsin), and western North America (Washington and California) relating survivorship, reproduction, and space use to urbanization. American Crow populations tend to be densest and increasing most rapidly in urban areas of North America. This appears to be facilitated by small space needs of crows in urban relative to suburban, rural, and exurban areas. Crow survivorship is high across the urban gradient, but reproduction and hence population growth, peaks in suburban and rural settings. Local demographic considerations appear unable to account for changing winter crow populations. Rather, we hypothesize that urban crow populations may be increasing primarily as 332 Chapter 16 surplus crows from suburban and rural areas disperse into the city where anthropogenic food sources are easily located, rich, and concentrated. This hypothesis likely is affected by local crow sociality. In the western United States, where pre-breeders often form flocks able to exploit urban riches, our dispersal hypothesis may be accurate. But, in midwestern and eastern areas, where crows migrate south for winter or remain on territories to help rather than float as pre-breeders, dispersal may not be adequate to fuel urban population growth. Refuse, invertebrates, and small vertebrates appeared to be more common food items than the nest contents of other birds. This, and the typically diverse suite of nest predators in any area, may explain why the rate of predation on artificial nests we placed throughout the urban gradient was not highly correlated with the abundance of crows. We encourage researchers to study how urbanization affects important mechanisms (like nest predators and predation) so environmental policy will benefit from a detailed, scientific understanding of how avian communities are structured.
The Fish Crow is known by its nasal, falsetto call, different from the harsh cawing of the Americ... more The Fish Crow is known by its nasal, falsetto call, different from the harsh cawing of the American Crow. It is slightly smaller than the American Crow, with a smaller bill and more slender, pointed wings. Its plumage is glossier with more iridescence on the upper parts. Its flight is like the American Crow but quicker, and it sails more.
Previous research on inter-individual variation in the calls of corvids has largely been restrict... more Previous research on inter-individual variation in the calls of corvids has largely been restricted to single call types, such as alarm or contact calls, and has rarely considered the effects of age on call structure. This study explores structural variation in a contextually diverse set of "caw" calls of the American crow (Corvus brachyrhynchos), including alarm, foraging recruitment and territorial calls, and searches for structural features that may be associated with behavioural context and caller sex, age, and identity. Automated pitch detection algorithms are used to generate 23 pitch-related and spectral parameters for a collection of caws from 18 wild, marked crows. Using principal component analysis and mixed models, we identify independent axes of acoustic variation associated with behavioural context and with caller sex, respectively. We also have moderate success predicting caller sex and identity from call structure. However, we do not find significant acousti...
In this article, the authors reveal the symbolic role of cranes at Neolithic Çatalhöyük, Turkey. ... more In this article, the authors reveal the symbolic role of cranes at Neolithic Çatalhöyük, Turkey. Worked bones of the Common Crane (Grus grus) are interpreted as coming from a spread wing used in dances, a ritual practice perhaps connected with the celebration of marriage.
West Nile virus (WNV) is transmitted between avian hosts in enzootic cycles by a mosquito vector.... more West Nile virus (WNV) is transmitted between avian hosts in enzootic cycles by a mosquito vector. The virus has significant disease effects on humans and equines when it bridges into an epizootic cycle. Since the initial epidemic of WNV in 1999, perennial outbreaks in New York State suggest the local establishment of natural foci with perpetuation of the virus among susceptible hosts rather than reintroduction of the virus. The factors that play a role in the perpetuation of the virus are not fully understood. American crows (Corvus brachyrhynchos) are known to be highly susceptible to infection with the virus. We investigate the factors that put crows at risk of infection in Tompkins County, New York during the period of 2000 through 2008 in a case-control study. Cases were crow carcasses that were found dead and tested positive for WNV using real time reverse transcription (RT-PCR) or VecTest R. Data on putative risk factors were collected and assessed for significance of association with the presence of WNV using logistic regression analysis to evaluate the significance of each factor while simultaneously controlling for the effect of others. The risk of a crow carcass testing WNV positive varied with age, season of the year, and ecological area where the carcass was found. Crows that were more than one year old were 4 times more likely to be WNV positive in comparison to birds that were less than one year of age. It was three times more likely to find WNV positive carcasses in residential areas in comparison to rural areas. The risk of testing WNV positive did not vary by sex of the crow carcasses.
Proceedings of the Royal Society B: Biological Sciences, 2009
Disease-mediated inbreeding depression is a potential cost of living in groups with kin, but its ... more Disease-mediated inbreeding depression is a potential cost of living in groups with kin, but its general magnitude in wild populations is unclear. We examined the relationships between inbreeding, survival and disease for 312 offspring, produced by 35 parental pairs, in a large, open population of cooperatively breeding American crows ( Corvus brachyrhynchos ). Genetic analyses of parentage, parental relatedness coefficients and pedigree information suggested that 23 per cent of parental dyads were first- or second-order kin. Heterozygosity–heterozygosity correlations suggested that a microsatellite-based index of individual heterozygosity predicted individual genome-wide heterozygosity in this population. After excluding birds that died traumatically, survival probability was lower for relatively inbred birds during the 2–50 months after banding: the hazard rate for the most inbred birds was 170 per cent higher than that for the least inbred birds across the range of inbreeding ind...
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
We assessed the changes in abundance of American crows in the northeastern U.S. following the arr... more We assessed the changes in abundance of American crows in the northeastern U.S. following the arrival of West Nile virus (WNV), with two aims. First, we determined the impact and spatial extent of the initial epizootic that began in New York City. Second, we examined whether two existing surveillance programs monitoring for WNV (data from 2000 New York State dead bird testing, and 2000 mosquito testing) accurately predicted the observed impact of the disease on crow populations as measured using data from the North American Christmas Bird Count. The rationale for this second aim was that the two WNV surveys were new and with unknown biases and sensitivity, while the Christmas Bird Count has existed for decades, providing monitoring before the arrival of WNV in North America and a long time series of data useful in gauging sensitivity. As a result, the Christmas Bird Count represents a good benchmark against which to compare the two new surveillance programs. Consistency among these three sources of information was low, suggesting that while dead bird and mosquito surveys can currently indicate the later stages of severe outbreaks, the ability to consistently detect early stages of outbreaks is questionable.
Parent birds of many species eat the fecal sacs produced by their nestlings. Two hypotheses have ... more Parent birds of many species eat the fecal sacs produced by their nestlings. Two hypotheses have been proposed to explain why the parents ingest, rather than simply remove the sacs. (1) The parental nutrition hypothesis proposes that the parent benefits energetically or nutritionally from ingesting the sacs (Morton 1979, Gliick 1988); and (2) the economic disposal hypothesis postulates that parents incur some costs from eating waste products, but the cost of eating them is less than the benefits gained from being allowed to remain at the nest (Hurd et al. 199 1). Behavioral data on nesting Florida Scrub Jays (Aphelocoma c. coerulescens) and American Crows (Corvus brachyrhynchos) support the parental nutrition, and not the economic disposal hypothesis. In both species, when two parents were present at the production of fecal sacs, the most nutritionally stressed parent, the female, ate significantly more sacs than her mate. On occasions where one adult left the nest immediately after fecal sac production and one remained, the departing adult was not more likely to dispose of the sac in either species. In neither species was a departing adult more likely to carry off a fecal sac than eat it.
Previous research on individual differences in the acoustic structure of vocalizations and vocal ... more Previous research on individual differences in the acoustic structure of vocalizations and vocal recognition has largely focused on the contexts of parent-offspring interactions, territory defense, sexual interactions, and group cohesion. In contrast, few studies have examined individual differences in the acoustic structure of mobbing and alarm calls. The purpose of this study was to explore individual differences in the acoustic structure of the inflected alarm caw of the American Crow (Corvus brachyrhynchos). The alarm caws of 15 wild, marked individuals were recorded and 25 acoustic measurements were made automatically using customized software. A stepwise discriminant function analysis showed that 20 of the 25 variables were important in discriminating among individuals, with 65% classification success. We used factor analysis to reduce the large number of variables to a set of seven meaningful call features. All of these features differed among individuals, suggesting that American Crows have the potential to discriminate among individual birds on the basis of call structure alone. Five of the features differed between the sexes, with call frequency being the most significant. One clearly subordinate male clustered with the females, raising the possibility that social status partially determines the sex-based differences. Encoding of individual identity in alarm contexts may be adaptive if receiver vigilance and approach urgency depend on the status, reliability, or family membership of the alarm signaler.
Understanding the benefits of cooperative breeding for group members of different social and demo... more Understanding the benefits of cooperative breeding for group members of different social and demographic classes requires knowledge of their reproductive partitioning and genetic relatedness. From 2004-2007, we examined parentage as a function of relatedness and social interactions among members of 21 American crow (Corvus brachyrhynchos) family groups. Paired female breeders monopolized maternity of all offspring in their broods, whereas paired male breeders sired 82.7% of offspring, within-group auxiliary males sired 6.9% of offspring, and extragroup males sired 10.4% of offspring. Although adult females had fewer opportunities for direct reproduction as auxiliaries than males, they appeared to have earlier opportunities for independent breeding. These different opportunities for direct reproduction probably contributed to the male biased adult auxiliary sex ratio. Patterns of reproductive partitioning and conflict among males were most consistent with a synthetic reproductive skew model, in which auxiliaries struggled with breeders for a limited reproductive share, beyond which breeders could evict them. Counter to a frequent assumption of reproductive skew models, female breeders appeared to influence paternity, although their interests might have agreed with the interests of their paired males. Unusual among cooperative breeders, close inbreeding and incest occurred in this population. Incest avoidance between potential breeders did not significantly affect reproductive skew.
Journal of Veterinary Diagnostic Investigation, 2010
The American crow (Corvus brachyrhynchos) is a common urban and rural inhabitant of the Northeast... more The American crow (Corvus brachyrhynchos) is a common urban and rural inhabitant of the Northeast and Midwest United States that is commonly infected with West Nile virus (WNV). The current study was initiated to determine non-WNV-associated causes of mortality in the American crow. All animals (40/40) tested negative for WNV infection via polymerase chain reaction and had no evidence of infection based on immunohistochemistry. Common gross necropsy findings included external trauma (6/40), hepatosplenomegaly (6/40), poxviral dermatitis (5/40), and pneumonia (3/40). Common histologic findings included endoparasitism (32/40), multifocal hepatic and splenic necrosis (7/40), pigment accumulation in the spleen (5/40), and disseminated bacterial infection (3/40). The most significant and debilitating diseases included fungal pneumonia and poxvirus-associated lesions. The present report increases the knowledge of diseases present in the American crow population.
The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven ... more The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven primarily by females is controversial. In cooperatively breeding American crows, we compared predictions of four female benefits hypotheses-the genetic diversity, good genes, genetic compatibility, and direct benefits hypotheses-to our predictions if EPP was primarily male driven. We found that genetically diverse broods were not more successful, extrapair young were not in better condition and did not have a higher survival probability, and, contrary to prediction, offspring sired by within-group extrapair males were more inbred than within-pair offspring. There was evidence of direct benefits, however: provisioning rate and number of surviving offspring were higher in groups containing within-group extrapair sires. Females therefore derived no apparent benefits from extragroup extrapair males but both direct benefits and genetic costs from within-group extrapair males. We suggest that males and females both influence the distribution of EPP in this system.
Proceedings of the Royal Society B: Biological Sciences, 2010
Cooperatively breeding American crows (Corvus brachyrhynchos) suffer a severe disease-mediated su... more Cooperatively breeding American crows (Corvus brachyrhynchos) suffer a severe disease-mediated survival cost from inbreeding, but the proximate mechanisms linking inbreeding to disease are unknown. Here, we examine indices of nestling body condition and innate immunocompetence in relationship to inbreeding and disease mortality. Using an estimate of microsatellite heterozygosity that predicts inbreeding in this population, we show that inbred crows were in relatively poor condition as nestlings, and that body condition index measured in the first 2-33 days after hatching, in addition to inbreeding index, predicted disease probability in the first 34 months of life. Inbred nestlings also mounted a weaker response along one axis of innate immunity: the proportion of bacteria killed in a microbiocidal assay increased as heterozygosity index increased. Relatively poor body condition and low innate immunocompetence are two mechanisms that might predispose inbred crows to ultimate disease mortality. A better understanding of condition-mediated inbreeding depression can guide efforts to minimize disease costs of inbreeding in small populations.
We assessed the changes in abundance of American crows in the northeastern U.S. following the arr... more We assessed the changes in abundance of American crows in the northeastern U.S. following the arrival of West Nile virus (WNV), with two aims. First, we determined the impact and spatial extent of the initial epizootic that began in New York City. Second, we examined whether two existing surveillance programs monitoring for WNV (data from 2000 New York State dead bird testing, and 2000 mosquito testing) accurately predicted the observed impact of the disease on crow populations as measured using data from the North American Christmas Bird Count. The rationale for this second aim was that the two WNV surveys were new and with unknown biases and sensitivity, while the Christmas Bird Count has existed for decades, providing monitoring before the arrival of WNV in North America and a long time series of data useful in gauging sensitivity. As a result, the Christmas Bird Count represents a good benchmark against which to compare the two new surveillance programs. Consistency among these three sources of information was low, suggesting that while dead bird and mosquito surveys can currently indicate the later stages of severe outbreaks, the ability to consistently detect early stages of outbreaks is questionable.
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
Field identification of the White-footed Mouse (Peromyscus leucopus noveboracensis) and Long-tail... more Field identification of the White-footed Mouse (Peromyscus leucopus noveboracensis) and Long-tailed Deer Mouse (Peromyscus maniculatus gracilis) is difficult because of their similar external morphology. Peromyscus were sampled by live-trapping during a five-year period (1992-1996) at the Arnot Teaching and Research Forest, Van Etten, New York and identified to species by electrophoresis of their salivary amylase. No electromorphs were shared between P. leucopus and P. maniculatus, thus permitting unambiguous species identification of individuals. Means and ranges of four external measurements (ear, head-body, hind-foot, and tail) and tail to head-body ratio were determined for amylase-genotyped live mice. Although some body measurements did differ on average between the two species (ear, head-body, and tail for adults; hind-foot and tail for juveniles), the ranges of these overlap considerably. When the four external measurements (excluding the tail to head-body ratio) were used to...
Early increased sophistication of human tools is thought to be underpinned by adaptive morphology... more Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow's bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii)...
Avian Ecology and Conservation in an Urbanizing World, 2001
American Crows (Corvus brachyrhynchos) have become common suburban and urban birds in the last 50... more American Crows (Corvus brachyrhynchos) have become common suburban and urban birds in the last 50 years, using these environments for roosting and breeding. I studied crows in upstate New York from 1989 to 1999, and compared reproductive success, survival, and social behavior of crows in suburban and rural areas. Although both suburban and rural crows maintained permanent territories, suburban American Crows had smaller territories and nested at higher densities. Both suburban and rural crows periodically left their territories in fall and winter to join foraging aggregations and to roost at night. The proportion of nests attended by auxiliaries did not differ, but suburban nests were attended by larger families. Overall nest success was higher in suburban areas. Success rates during the egg stage of the nest cycle did not differ between habitat, but suburban nests had higher success during the nestling stage of the nest cycle. Survival of crows post fledging was better in suburban areas, but after one year annual survival rates did not differ between the habitats. Birds raised in one habitat tended to breed in the same habitat. Although clutch sizes and egg hatchability did not differ between the habitats, rural nests produced nearly one more young per successful nest and significantly larger young than suburban crows, suggesting that food resources were better in rural areas. Data from a drought year, a time of apparent food shortage, suggested that suburban food resources also were less dependable than those in rural areas. The increase in American Crows over the last 25 years in eastern North America may be due in part to the successful exploitation of suburban nesting habitats.
Avian Ecology and Conservation in an Urbanizing World, 2001
Corvid populations are increasing worldwide in response to urbanization. We investigated the resp... more Corvid populations are increasing worldwide in response to urbanization. We investigated the response of American Crows (Corvus brachyrhynchos) to urbanization by (1) comparing rates of winter population change between urban and nonurban locations (using standard Christmas Bird Counts); (2) quantifying population size along a gradient of urbanization in western Washington; and (3) pooling studies from eastern (New York), midwestern (Wisconsin), and western North America (Washington and California) relating survivorship, reproduction, and space use to urbanization. American Crow populations tend to be densest and increasing most rapidly in urban areas of North America. This appears to be facilitated by small space needs of crows in urban relative to suburban, rural, and exurban areas. Crow survivorship is high across the urban gradient, but reproduction and hence population growth, peaks in suburban and rural settings. Local demographic considerations appear unable to account for changing winter crow populations. Rather, we hypothesize that urban crow populations may be increasing primarily as 332 Chapter 16 surplus crows from suburban and rural areas disperse into the city where anthropogenic food sources are easily located, rich, and concentrated. This hypothesis likely is affected by local crow sociality. In the western United States, where pre-breeders often form flocks able to exploit urban riches, our dispersal hypothesis may be accurate. But, in midwestern and eastern areas, where crows migrate south for winter or remain on territories to help rather than float as pre-breeders, dispersal may not be adequate to fuel urban population growth. Refuse, invertebrates, and small vertebrates appeared to be more common food items than the nest contents of other birds. This, and the typically diverse suite of nest predators in any area, may explain why the rate of predation on artificial nests we placed throughout the urban gradient was not highly correlated with the abundance of crows. We encourage researchers to study how urbanization affects important mechanisms (like nest predators and predation) so environmental policy will benefit from a detailed, scientific understanding of how avian communities are structured.
The Fish Crow is known by its nasal, falsetto call, different from the harsh cawing of the Americ... more The Fish Crow is known by its nasal, falsetto call, different from the harsh cawing of the American Crow. It is slightly smaller than the American Crow, with a smaller bill and more slender, pointed wings. Its plumage is glossier with more iridescence on the upper parts. Its flight is like the American Crow but quicker, and it sails more.
Previous research on inter-individual variation in the calls of corvids has largely been restrict... more Previous research on inter-individual variation in the calls of corvids has largely been restricted to single call types, such as alarm or contact calls, and has rarely considered the effects of age on call structure. This study explores structural variation in a contextually diverse set of "caw" calls of the American crow (Corvus brachyrhynchos), including alarm, foraging recruitment and territorial calls, and searches for structural features that may be associated with behavioural context and caller sex, age, and identity. Automated pitch detection algorithms are used to generate 23 pitch-related and spectral parameters for a collection of caws from 18 wild, marked crows. Using principal component analysis and mixed models, we identify independent axes of acoustic variation associated with behavioural context and with caller sex, respectively. We also have moderate success predicting caller sex and identity from call structure. However, we do not find significant acousti...
In this article, the authors reveal the symbolic role of cranes at Neolithic Çatalhöyük, Turkey. ... more In this article, the authors reveal the symbolic role of cranes at Neolithic Çatalhöyük, Turkey. Worked bones of the Common Crane (Grus grus) are interpreted as coming from a spread wing used in dances, a ritual practice perhaps connected with the celebration of marriage.
West Nile virus (WNV) is transmitted between avian hosts in enzootic cycles by a mosquito vector.... more West Nile virus (WNV) is transmitted between avian hosts in enzootic cycles by a mosquito vector. The virus has significant disease effects on humans and equines when it bridges into an epizootic cycle. Since the initial epidemic of WNV in 1999, perennial outbreaks in New York State suggest the local establishment of natural foci with perpetuation of the virus among susceptible hosts rather than reintroduction of the virus. The factors that play a role in the perpetuation of the virus are not fully understood. American crows (Corvus brachyrhynchos) are known to be highly susceptible to infection with the virus. We investigate the factors that put crows at risk of infection in Tompkins County, New York during the period of 2000 through 2008 in a case-control study. Cases were crow carcasses that were found dead and tested positive for WNV using real time reverse transcription (RT-PCR) or VecTest R. Data on putative risk factors were collected and assessed for significance of association with the presence of WNV using logistic regression analysis to evaluate the significance of each factor while simultaneously controlling for the effect of others. The risk of a crow carcass testing WNV positive varied with age, season of the year, and ecological area where the carcass was found. Crows that were more than one year old were 4 times more likely to be WNV positive in comparison to birds that were less than one year of age. It was three times more likely to find WNV positive carcasses in residential areas in comparison to rural areas. The risk of testing WNV positive did not vary by sex of the crow carcasses.
Proceedings of the Royal Society B: Biological Sciences, 2009
Disease-mediated inbreeding depression is a potential cost of living in groups with kin, but its ... more Disease-mediated inbreeding depression is a potential cost of living in groups with kin, but its general magnitude in wild populations is unclear. We examined the relationships between inbreeding, survival and disease for 312 offspring, produced by 35 parental pairs, in a large, open population of cooperatively breeding American crows ( Corvus brachyrhynchos ). Genetic analyses of parentage, parental relatedness coefficients and pedigree information suggested that 23 per cent of parental dyads were first- or second-order kin. Heterozygosity–heterozygosity correlations suggested that a microsatellite-based index of individual heterozygosity predicted individual genome-wide heterozygosity in this population. After excluding birds that died traumatically, survival probability was lower for relatively inbred birds during the 2–50 months after banding: the hazard rate for the most inbred birds was 170 per cent higher than that for the least inbred birds across the range of inbreeding ind...
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
We assessed the changes in abundance of American crows in the northeastern U.S. following the arr... more We assessed the changes in abundance of American crows in the northeastern U.S. following the arrival of West Nile virus (WNV), with two aims. First, we determined the impact and spatial extent of the initial epizootic that began in New York City. Second, we examined whether two existing surveillance programs monitoring for WNV (data from 2000 New York State dead bird testing, and 2000 mosquito testing) accurately predicted the observed impact of the disease on crow populations as measured using data from the North American Christmas Bird Count. The rationale for this second aim was that the two WNV surveys were new and with unknown biases and sensitivity, while the Christmas Bird Count has existed for decades, providing monitoring before the arrival of WNV in North America and a long time series of data useful in gauging sensitivity. As a result, the Christmas Bird Count represents a good benchmark against which to compare the two new surveillance programs. Consistency among these three sources of information was low, suggesting that while dead bird and mosquito surveys can currently indicate the later stages of severe outbreaks, the ability to consistently detect early stages of outbreaks is questionable.
Parent birds of many species eat the fecal sacs produced by their nestlings. Two hypotheses have ... more Parent birds of many species eat the fecal sacs produced by their nestlings. Two hypotheses have been proposed to explain why the parents ingest, rather than simply remove the sacs. (1) The parental nutrition hypothesis proposes that the parent benefits energetically or nutritionally from ingesting the sacs (Morton 1979, Gliick 1988); and (2) the economic disposal hypothesis postulates that parents incur some costs from eating waste products, but the cost of eating them is less than the benefits gained from being allowed to remain at the nest (Hurd et al. 199 1). Behavioral data on nesting Florida Scrub Jays (Aphelocoma c. coerulescens) and American Crows (Corvus brachyrhynchos) support the parental nutrition, and not the economic disposal hypothesis. In both species, when two parents were present at the production of fecal sacs, the most nutritionally stressed parent, the female, ate significantly more sacs than her mate. On occasions where one adult left the nest immediately after fecal sac production and one remained, the departing adult was not more likely to dispose of the sac in either species. In neither species was a departing adult more likely to carry off a fecal sac than eat it.
Previous research on individual differences in the acoustic structure of vocalizations and vocal ... more Previous research on individual differences in the acoustic structure of vocalizations and vocal recognition has largely focused on the contexts of parent-offspring interactions, territory defense, sexual interactions, and group cohesion. In contrast, few studies have examined individual differences in the acoustic structure of mobbing and alarm calls. The purpose of this study was to explore individual differences in the acoustic structure of the inflected alarm caw of the American Crow (Corvus brachyrhynchos). The alarm caws of 15 wild, marked individuals were recorded and 25 acoustic measurements were made automatically using customized software. A stepwise discriminant function analysis showed that 20 of the 25 variables were important in discriminating among individuals, with 65% classification success. We used factor analysis to reduce the large number of variables to a set of seven meaningful call features. All of these features differed among individuals, suggesting that American Crows have the potential to discriminate among individual birds on the basis of call structure alone. Five of the features differed between the sexes, with call frequency being the most significant. One clearly subordinate male clustered with the females, raising the possibility that social status partially determines the sex-based differences. Encoding of individual identity in alarm contexts may be adaptive if receiver vigilance and approach urgency depend on the status, reliability, or family membership of the alarm signaler.
Understanding the benefits of cooperative breeding for group members of different social and demo... more Understanding the benefits of cooperative breeding for group members of different social and demographic classes requires knowledge of their reproductive partitioning and genetic relatedness. From 2004-2007, we examined parentage as a function of relatedness and social interactions among members of 21 American crow (Corvus brachyrhynchos) family groups. Paired female breeders monopolized maternity of all offspring in their broods, whereas paired male breeders sired 82.7% of offspring, within-group auxiliary males sired 6.9% of offspring, and extragroup males sired 10.4% of offspring. Although adult females had fewer opportunities for direct reproduction as auxiliaries than males, they appeared to have earlier opportunities for independent breeding. These different opportunities for direct reproduction probably contributed to the male biased adult auxiliary sex ratio. Patterns of reproductive partitioning and conflict among males were most consistent with a synthetic reproductive skew model, in which auxiliaries struggled with breeders for a limited reproductive share, beyond which breeders could evict them. Counter to a frequent assumption of reproductive skew models, female breeders appeared to influence paternity, although their interests might have agreed with the interests of their paired males. Unusual among cooperative breeders, close inbreeding and incest occurred in this population. Incest avoidance between potential breeders did not significantly affect reproductive skew.
Journal of Veterinary Diagnostic Investigation, 2010
The American crow (Corvus brachyrhynchos) is a common urban and rural inhabitant of the Northeast... more The American crow (Corvus brachyrhynchos) is a common urban and rural inhabitant of the Northeast and Midwest United States that is commonly infected with West Nile virus (WNV). The current study was initiated to determine non-WNV-associated causes of mortality in the American crow. All animals (40/40) tested negative for WNV infection via polymerase chain reaction and had no evidence of infection based on immunohistochemistry. Common gross necropsy findings included external trauma (6/40), hepatosplenomegaly (6/40), poxviral dermatitis (5/40), and pneumonia (3/40). Common histologic findings included endoparasitism (32/40), multifocal hepatic and splenic necrosis (7/40), pigment accumulation in the spleen (5/40), and disseminated bacterial infection (3/40). The most significant and debilitating diseases included fungal pneumonia and poxvirus-associated lesions. The present report increases the knowledge of diseases present in the American crow population.
The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven ... more The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven primarily by females is controversial. In cooperatively breeding American crows, we compared predictions of four female benefits hypotheses-the genetic diversity, good genes, genetic compatibility, and direct benefits hypotheses-to our predictions if EPP was primarily male driven. We found that genetically diverse broods were not more successful, extrapair young were not in better condition and did not have a higher survival probability, and, contrary to prediction, offspring sired by within-group extrapair males were more inbred than within-pair offspring. There was evidence of direct benefits, however: provisioning rate and number of surviving offspring were higher in groups containing within-group extrapair sires. Females therefore derived no apparent benefits from extragroup extrapair males but both direct benefits and genetic costs from within-group extrapair males. We suggest that males and females both influence the distribution of EPP in this system.
Proceedings of the Royal Society B: Biological Sciences, 2010
Cooperatively breeding American crows (Corvus brachyrhynchos) suffer a severe disease-mediated su... more Cooperatively breeding American crows (Corvus brachyrhynchos) suffer a severe disease-mediated survival cost from inbreeding, but the proximate mechanisms linking inbreeding to disease are unknown. Here, we examine indices of nestling body condition and innate immunocompetence in relationship to inbreeding and disease mortality. Using an estimate of microsatellite heterozygosity that predicts inbreeding in this population, we show that inbred crows were in relatively poor condition as nestlings, and that body condition index measured in the first 2-33 days after hatching, in addition to inbreeding index, predicted disease probability in the first 34 months of life. Inbred nestlings also mounted a weaker response along one axis of innate immunity: the proportion of bacteria killed in a microbiocidal assay increased as heterozygosity index increased. Relatively poor body condition and low innate immunocompetence are two mechanisms that might predispose inbred crows to ultimate disease mortality. A better understanding of condition-mediated inbreeding depression can guide efforts to minimize disease costs of inbreeding in small populations.
We assessed the changes in abundance of American crows in the northeastern U.S. following the arr... more We assessed the changes in abundance of American crows in the northeastern U.S. following the arrival of West Nile virus (WNV), with two aims. First, we determined the impact and spatial extent of the initial epizootic that began in New York City. Second, we examined whether two existing surveillance programs monitoring for WNV (data from 2000 New York State dead bird testing, and 2000 mosquito testing) accurately predicted the observed impact of the disease on crow populations as measured using data from the North American Christmas Bird Count. The rationale for this second aim was that the two WNV surveys were new and with unknown biases and sensitivity, while the Christmas Bird Count has existed for decades, providing monitoring before the arrival of WNV in North America and a long time series of data useful in gauging sensitivity. As a result, the Christmas Bird Count represents a good benchmark against which to compare the two new surveillance programs. Consistency among these three sources of information was low, suggesting that while dead bird and mosquito surveys can currently indicate the later stages of severe outbreaks, the ability to consistently detect early stages of outbreaks is questionable.
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
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