Low levels of allozyme heterozygosity in populations are often attributed to previous population ... more Low levels of allozyme heterozygosity in populations are often attributed to previous population bottlenecks; however, few experiments have examined the relationship between het- erozygosity and bottlenecks under natural conditions. The composition and number of founders of 55 experimental populations of the eastern mosquitofish (Gambusia holbrooki), maintained under simulated field conditions, were manipulated to examine the effects of bottlenecks on three components of allozyme diversity. Correlations between observed and expected values of allozyme heterozygosity, proportions of polymorphic loci, and numbers of alleles per locus were 0.423, 0.602, and 0.772, respectively. The numbers of polymorphic loci and of alleles per locus were more sensitive indicators of differences in genetic diversity between the pre-bottleneck and post- bottleneck populations than was multiple-locus heterozygosity. In many populations, single- and multiple-locus heterozygosity actually increased as a result of the founder event. The weak rela- tionship between a population's heterozygosity and the number and composition of its founders resulted from an increase in the variance of heterozygosity due to drift of allele frequencies. There was little evidence that selection influenced the loss of allozyme variation. When it is not possible to estimate heterozygosity at a large number of polymorphic loci, allozyme surveys attempting to detect founder events and other types of bottlenecks should focus on levels of locus polymorphism and allelic diversity rather than on heterozygosity.
In the Northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss ... more In the Northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss of protective barrier islands. These barrier islands provide critical habitat for wildlife, including globally significant populations of marsh and shorebirds. We investigated salt marsh restoration on two Louisiana barrier islands using presence of 8 marsh bird species as an index to evaluate restoration success. Land loss was extensive for both islands prior to restoration, with submerged marsh restored by backfilling sediment into the marsh platform. Restoration methods were similar between the two islands, although Raccoon Island was built to a higher elevation (1.1 m) than Whiskey Island (0.8m). Avian presence was estimated via passive acoustic monitoring and point counts. To evaluate restoration success, we modeled influence of habitat covariates on index species presence in restored and reference (intact) sites over three breeding seasons and modeled occupancy for 6 species. On Whiskey Island, index richness was higher in restored sites. Marsh specialists Seaside Sparrows (Ammospiza maritima) and Least Bitterns (Ixobrychus exilis) had higher occupancy in restored areas on Whiskey, while generalist species showed no response to site. These results are likely due to a strong association between habitat and vegetation type, with restored sites dominated by Spartina alterniflora and reference sites by Avicennia germinans. On Raccoon Island, species richness was low across all sites. Our results This article is protected by copyright. All rights reserved. suggest that restoration efforts were successful in creating salt marsh habitat on Whiskey but not Raccoon as of the time of our study.
During the breeding season, seabird foraging behaviors are driven by a combination of individual-... more During the breeding season, seabird foraging behaviors are driven by a combination of individual-and external-based factors. This study evaluated how two individual-based factors (body condition and sex) and two external factors (nest stage and colony size), and their interactions, were related to movement. To do so, we used movement data obtained from 22 GPS-tagequipped Brown Pelicans (Pelecanus occidentalis L., 1766) breeding in the northern Gulf of Mexico. In Brown Pelicans, the postegg-hatching phase imposes increased foraging demands on breeding adults relative to the prehatching phase. This study demonstrates that the progression of the breeding period affects the nature and intensity of the relationship between individualbased factors and movement patterns. In particular, birds in relatively lower condition traveled greater distances during foraging trips during the energetically demanding posthatching phase, but not during the incubation stage. Contrary to many seabird species studied to date, neither colony size nor sex appeared to affect Brown Pelican movement patterns. Our results suggest that nest stage is the most important factor influencing foraging movements, and that it may modulate relationships between condition and movement. More refined measures of body condition and foraging behavior will allow further insights into the movement ecology of this seabird.
... WYLIE C. BARROW, JR. ... Ether extraction is considered to be an accurate mea-sure of lipid l... more ... WYLIE C. BARROW, JR. ... Ether extraction is considered to be an accurate mea-sure of lipid levels (Blem 1990), but it is time-consuming and expensive, and it requires organ-isms to be sacrificed (Castro et al. 1990, Roby 1991). ...
Dataset includes observations of Piping Plovers made during winter shorebird surveys on Whiskey a... more Dataset includes observations of Piping Plovers made during winter shorebird surveys on Whiskey and Trinity Islands in Terrebonne Parish, Louisiana during the winter of 2013-2014. Attributes include location, behavioral, and microhabitat data as well as references to these data points in our local Access database.
Test repository for data related to nesting biology of brown pelicans in relation to barrier isla... more Test repository for data related to nesting biology of brown pelicans in relation to barrier islands in coastal Louisiana, USA.
Abstract. Unmanned aerial vehicles (UAVs) can improve detection and count accuracy of avian speci... more Abstract. Unmanned aerial vehicles (UAVs) can improve detection and count accuracy of avian species and provide an inexpensive alternative to surveying waterbirds compared to ground counts and other aerial methods. To validate this method for surveying colonial waterbirds in logistically challenging areas, we compared counts from images collected with a fixed-wing UAV to ground counts using a marked-subsample method or direct counts at three study sites: 1) in an open field using decoys that represented three colonial waterbird species; 2) constructed platforms in a swamp with colonial nesting Great Egrets (Ardea alba); and 3) an island with a large nesting colony of Brown Pelicans (Pelecanus occidentalis). Estimates or direct counts from UAV images were not significantly different from a known number of decoys or ground counts for Great Egrets but were almost twice as high compared to ground counts for juvenile Brown Pelicans. UAV flights did not cause either Great Egrets or Brown Pelicans to flush from nesting areas while ground surveys flushed the majority of adult Brown Pelicans from the survey area. UAV surveys captured images of eggs in nests that could not be observed by ground surveyors. Our results indicate that UAVs can provide a cost-effective and efficient method of surveying waterbirds with similar or improved results and little disturbance of colonies compared to ground counts.
Lipid depletion is currently believed to be the primary factor limiting flight duration of migrat... more Lipid depletion is currently believed to be the primary factor limiting flight duration of migrating birds in North America, while the influence of water loss is thought to be small. Three migrating species of passerines, wood thrush (Hylocichla mustelina), Swainson's thrush (Catharus ustulatus), and summer tanager (Piranga rubra) were captured during the 1993 spring migration just after crossing the Gulf
In the majority of birds and mammals, social monogamy is not congruent with genetic monogamy. No ... more In the majority of birds and mammals, social monogamy is not congruent with genetic monogamy. No research to date has compared social and genetic monogamy in amphibians. We analysed paternity in clutches of red-backed salamanders (Plethodon cinereus), a species in which social monogamy has been demonstrated in the laboratory, and 28% of individuals in the forest are found in male-female pairs in the noncourtship season. We collected 16 clutches of eggs of P. cinereus in the southern Appalachian Mountains of Virginia and collected tail clippings from attending mothers. We genotyped embryos and adults at five microsatellite loci in order to analyse paternity of clutches. Most clutches (84.6%) had multiple sires, with two to three sires per clutch. In this study, 25% of clutches had males in addition to females attending eggs. None of the mothers of these clutches were genetically monogamous. All attending males sired some of the offspring in the clutch that they attended (between 9% a...
Declines in populations of Painted Buntings (Passerina ciris) over the past several decades have ... more Declines in populations of Painted Buntings (Passerina ciris) over the past several decades have led to their recent classification as a species of conservation concern. To better assess their status, we investigated factors associated with productivity and abundance of a population in south-central Louisiana during 2010-2011. We monitored 41 Painted Bunting nests, 14 with video cameras, to identify predators, parasitism events, and improve nest success estimates. Vegetation measurements were also collected at nest sites and non-nest sites to quantify habitat characteristics. We used an information-theoretic approach to evaluate support for multiple models evaluating nest success. Highly supported models indicated large negative effects of Brown-headed Cowbird (Molothrus ater) parasitism, and positive effects of increased canopy cover and distance to habitat edge on daily survival rates. Our estimate of daily survival rate was 0.94 ± 0.03 and the probability of survival was 0.25 ± 0.02. Point-count data revealed that densities of Painted Buntings were greater in treeline habitats than in open scrub-shrub and mature forest edge habitats. Furthermore, treelines had higher densities of large trees (>23 cm dbh) and percent canopy cover, variables positively associated with nest success, than open scrub-shrub and forest edge habitats. In general, survival rates and causes of nest failure in southern Louisiana were similar to those determined for breeding populations of Painted Buntings at other sites. Our results suggest that treelines, despite having a high edge-to-area ratio, might be preferred nesting habitat for Painted Buntings in our study area. RESUMEN. Efecto de borde y de las características del lugar de anidamiento en eléxito reproductivo de Passerina ciris Descensos poblacionales del Gorrión Pintado (Passerina ciris), durante lasúltimas décadas, ha llevado a que la especie se considere una de preocupación. Para buscar la forma más apropiada de determinar su estatus, investigamos los factores asociados a la productividad y abundancia de una población en la parte sur-central de Luisiana, durante el 2010-2011. Monitoreamos, con cámaras de video, 41 nidos de el ave para identificar depredadores, parasitismo reproductivo y mejorar los estimados deléxito de anidamiento. Se tomaron datos sobre la vegetación en los lugares de construcción de nidos y lugares no utilizados para cuantificar las características del hábitat. Utilizamos un enfoque de información teórica para evaluar el apoyo de múltiples modelos aléxito de anidamiento. Los modelos con mayor apoyo indicaron efectos negativos del parasitismo reproductivo por parte del Tordo Pardo (Molothrus ater), y efecto positivo, en la supervivencia diaria, de un incremento en la cobertura del dosel y distancia al borde del hábitat. Nuestro estimado de sobrevivencia diaria fue de 0.94 ± 0.03 y la probabilidad de sobrevivir fue 0.25 ± 0.02. Conteos de punto revelaron que la densidad del gorrión era mayor en hábitat de líneas deárboles que en matorrales abiertos y bordes de bosques maduros. Más aun, las líneas deárboles tuvieron mayor densidad de individuos grandes (> 23 cm dbh) y porcentaje de cubierta del dosel, que lasáreas de matorrales y bordes de bosques maduros, variables positivamente asociadas con eléxito de anidamiento. En general, la tasa de sobrevivencia y causas del fracaso de nidos en la parte sur de Luisiana resultó similar a otras poblaciones estudiadas en otros lugares. Nuestros resultados sugieren que las líneas deárboles, pese a tener un relación mayor deárea-borde, pudieran ser el hábitat preferido para anidar por el Gorrión Pintado.
Gambusia af nis (Western Mosquito sh) were sampled from 18 sites representing marsh, forested wet... more Gambusia af nis (Western Mosquito sh) were sampled from 18 sites representing marsh, forested wetlands, and agricultural wetlands in south Louisiana to determine distribution and infection parameters of Eustrongylides ignotus, a potentially lethal nematode parasite of wading birds. (n = 400 per site). Overall, prevalence of infection was 0.3%, with signi cantly higher prevalence in agricultural wetlands than in marshes or swamps. Our ndings are similar to work in Florida suggesting parasite prevalence is higher in disturbed wetlands, and suggest that birds foraging in cray sh ponds and rice elds may be at increased risk of exposure.
... Many species have been documented roosting in man-made structures such as bridges (Davis and ... more ... Many species have been documented roosting in man-made structures such as bridges (Davis and Cockrum 1963, Fraze and Wilkins 1990, Lewis 1995, Riskin and Pybus 1998). Due to their permanence and accessibility relative to other roosts in southern forests (Lance et al. ...
Although differences in sampling intensity can bias comparisons of allelic richness (A) among pop... more Although differences in sampling intensity can bias comparisons of allelic richness (A) among populations, investigators often fail to correct estimates of A for differences in sample size. Methods that standardize A on the basis of the size of the smallest number of samples in a comparison are preferable to other approaches. Rarefaction and repeated random subsampling provide unbiased estimates of A with the greatest precision and thus provide greatest statistical power to detect differences in variation. Less promising approaches, in terms of bias or precision, include single random subsampling, eliminating very small samples, using sample size as a covariate or extrapolating estimates obtained from small samples to a larger number of individuals.
Understanding the interplay of dispersal and how it translates into gene flow is key to understan... more Understanding the interplay of dispersal and how it translates into gene flow is key to understanding population processes, and especially so for endangered species occupying fragmented habitats. In migratory songbirds, there is evidence that long-distance movement capabilities do not translate well into observed dispersal. Our objectives were to (i) define the fine-scale spatial genetic structure in endangered black-capped vireos to characterize dispersal patterns and (ii) to correlate dispersal dynamics to overall population genetic structure using a simulation approach. We sampled 160 individuals over 2 years to (i) describe the fine-scale genetic structuring and (ii) used this information to model scenarios to compare with actual data on change in population structuring over a 100-year interval. We found that black-capped vireos exhibit male philopatry and restricted dispersal distances, relative to females. Our simulations also support a sex-biased dispersal model. Additionally, we find that fragmentation related changes in rates of dispersal might be a likely cause for increasing levels of population structure over a 100-year period. We show that restricted sex-biased dispersal can explain population structuring in this species and that changes in dispersal rates due to fragmentation may be a continuing threat to genetic viability in this species.
Although reintroductions are an important management tool, little is known about their effects on... more Although reintroductions are an important management tool, little is known about their effects on the genetic structure of wildlife species. We studied wild turkey (Meleagris gallopavo) and white-tailed deer (Odocoileus virginianus) populations from the eastern United States to determine if the genetic similarity of populations was more affected by geographic proximity or by possible gene flow resulting from reintroduction programs. We examined allele frequencies at 5 polymorphic loci for turkeys from 22 locations and at 15 polymorphic loci for deer from 21 locations and compared genetic distances among populations for both species to geographic distances and reintroduction histories. For both species, genetic distances were smaller between pairs of populations that either had individuals transferred between them or that had both received individuals from a common source population than were distances between pairs of populations that had not been connected by reintroductions (P < 0.001). Geographic proximity of populations of both turkeys and deer was not associated with genetic similarity (P = 0.280 and 0.520, respectively). Reintroductions may have obscured genetic patterns resulting from other evolutionary processes such as gene flow through dispersal. Additionally, post-reintroduction dispersal has not erased the genetic contributions of reintroduced individuals to the populations they established. Reintroduction programs should attempt to create populations with high levels of genetic diversity and avoid unnecessary disruption of the evolutionary relationships among populations of a species. J. WILDL. MANAGE. 58(4):698-711
Low levels of allozyme heterozygosity in populations are often attributed to previous population ... more Low levels of allozyme heterozygosity in populations are often attributed to previous population bottlenecks; however, few experiments have examined the relationship between het- erozygosity and bottlenecks under natural conditions. The composition and number of founders of 55 experimental populations of the eastern mosquitofish (Gambusia holbrooki), maintained under simulated field conditions, were manipulated to examine the effects of bottlenecks on three components of allozyme diversity. Correlations between observed and expected values of allozyme heterozygosity, proportions of polymorphic loci, and numbers of alleles per locus were 0.423, 0.602, and 0.772, respectively. The numbers of polymorphic loci and of alleles per locus were more sensitive indicators of differences in genetic diversity between the pre-bottleneck and post- bottleneck populations than was multiple-locus heterozygosity. In many populations, single- and multiple-locus heterozygosity actually increased as a result of the founder event. The weak rela- tionship between a population's heterozygosity and the number and composition of its founders resulted from an increase in the variance of heterozygosity due to drift of allele frequencies. There was little evidence that selection influenced the loss of allozyme variation. When it is not possible to estimate heterozygosity at a large number of polymorphic loci, allozyme surveys attempting to detect founder events and other types of bottlenecks should focus on levels of locus polymorphism and allelic diversity rather than on heterozygosity.
In the Northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss ... more In the Northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss of protective barrier islands. These barrier islands provide critical habitat for wildlife, including globally significant populations of marsh and shorebirds. We investigated salt marsh restoration on two Louisiana barrier islands using presence of 8 marsh bird species as an index to evaluate restoration success. Land loss was extensive for both islands prior to restoration, with submerged marsh restored by backfilling sediment into the marsh platform. Restoration methods were similar between the two islands, although Raccoon Island was built to a higher elevation (1.1 m) than Whiskey Island (0.8m). Avian presence was estimated via passive acoustic monitoring and point counts. To evaluate restoration success, we modeled influence of habitat covariates on index species presence in restored and reference (intact) sites over three breeding seasons and modeled occupancy for 6 species. On Whiskey Island, index richness was higher in restored sites. Marsh specialists Seaside Sparrows (Ammospiza maritima) and Least Bitterns (Ixobrychus exilis) had higher occupancy in restored areas on Whiskey, while generalist species showed no response to site. These results are likely due to a strong association between habitat and vegetation type, with restored sites dominated by Spartina alterniflora and reference sites by Avicennia germinans. On Raccoon Island, species richness was low across all sites. Our results This article is protected by copyright. All rights reserved. suggest that restoration efforts were successful in creating salt marsh habitat on Whiskey but not Raccoon as of the time of our study.
During the breeding season, seabird foraging behaviors are driven by a combination of individual-... more During the breeding season, seabird foraging behaviors are driven by a combination of individual-and external-based factors. This study evaluated how two individual-based factors (body condition and sex) and two external factors (nest stage and colony size), and their interactions, were related to movement. To do so, we used movement data obtained from 22 GPS-tagequipped Brown Pelicans (Pelecanus occidentalis L., 1766) breeding in the northern Gulf of Mexico. In Brown Pelicans, the postegg-hatching phase imposes increased foraging demands on breeding adults relative to the prehatching phase. This study demonstrates that the progression of the breeding period affects the nature and intensity of the relationship between individualbased factors and movement patterns. In particular, birds in relatively lower condition traveled greater distances during foraging trips during the energetically demanding posthatching phase, but not during the incubation stage. Contrary to many seabird species studied to date, neither colony size nor sex appeared to affect Brown Pelican movement patterns. Our results suggest that nest stage is the most important factor influencing foraging movements, and that it may modulate relationships between condition and movement. More refined measures of body condition and foraging behavior will allow further insights into the movement ecology of this seabird.
... WYLIE C. BARROW, JR. ... Ether extraction is considered to be an accurate mea-sure of lipid l... more ... WYLIE C. BARROW, JR. ... Ether extraction is considered to be an accurate mea-sure of lipid levels (Blem 1990), but it is time-consuming and expensive, and it requires organ-isms to be sacrificed (Castro et al. 1990, Roby 1991). ...
Dataset includes observations of Piping Plovers made during winter shorebird surveys on Whiskey a... more Dataset includes observations of Piping Plovers made during winter shorebird surveys on Whiskey and Trinity Islands in Terrebonne Parish, Louisiana during the winter of 2013-2014. Attributes include location, behavioral, and microhabitat data as well as references to these data points in our local Access database.
Test repository for data related to nesting biology of brown pelicans in relation to barrier isla... more Test repository for data related to nesting biology of brown pelicans in relation to barrier islands in coastal Louisiana, USA.
Abstract. Unmanned aerial vehicles (UAVs) can improve detection and count accuracy of avian speci... more Abstract. Unmanned aerial vehicles (UAVs) can improve detection and count accuracy of avian species and provide an inexpensive alternative to surveying waterbirds compared to ground counts and other aerial methods. To validate this method for surveying colonial waterbirds in logistically challenging areas, we compared counts from images collected with a fixed-wing UAV to ground counts using a marked-subsample method or direct counts at three study sites: 1) in an open field using decoys that represented three colonial waterbird species; 2) constructed platforms in a swamp with colonial nesting Great Egrets (Ardea alba); and 3) an island with a large nesting colony of Brown Pelicans (Pelecanus occidentalis). Estimates or direct counts from UAV images were not significantly different from a known number of decoys or ground counts for Great Egrets but were almost twice as high compared to ground counts for juvenile Brown Pelicans. UAV flights did not cause either Great Egrets or Brown Pelicans to flush from nesting areas while ground surveys flushed the majority of adult Brown Pelicans from the survey area. UAV surveys captured images of eggs in nests that could not be observed by ground surveyors. Our results indicate that UAVs can provide a cost-effective and efficient method of surveying waterbirds with similar or improved results and little disturbance of colonies compared to ground counts.
Lipid depletion is currently believed to be the primary factor limiting flight duration of migrat... more Lipid depletion is currently believed to be the primary factor limiting flight duration of migrating birds in North America, while the influence of water loss is thought to be small. Three migrating species of passerines, wood thrush (Hylocichla mustelina), Swainson&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27;s thrush (Catharus ustulatus), and summer tanager (Piranga rubra) were captured during the 1993 spring migration just after crossing the Gulf
In the majority of birds and mammals, social monogamy is not congruent with genetic monogamy. No ... more In the majority of birds and mammals, social monogamy is not congruent with genetic monogamy. No research to date has compared social and genetic monogamy in amphibians. We analysed paternity in clutches of red-backed salamanders (Plethodon cinereus), a species in which social monogamy has been demonstrated in the laboratory, and 28% of individuals in the forest are found in male-female pairs in the noncourtship season. We collected 16 clutches of eggs of P. cinereus in the southern Appalachian Mountains of Virginia and collected tail clippings from attending mothers. We genotyped embryos and adults at five microsatellite loci in order to analyse paternity of clutches. Most clutches (84.6%) had multiple sires, with two to three sires per clutch. In this study, 25% of clutches had males in addition to females attending eggs. None of the mothers of these clutches were genetically monogamous. All attending males sired some of the offspring in the clutch that they attended (between 9% a...
Declines in populations of Painted Buntings (Passerina ciris) over the past several decades have ... more Declines in populations of Painted Buntings (Passerina ciris) over the past several decades have led to their recent classification as a species of conservation concern. To better assess their status, we investigated factors associated with productivity and abundance of a population in south-central Louisiana during 2010-2011. We monitored 41 Painted Bunting nests, 14 with video cameras, to identify predators, parasitism events, and improve nest success estimates. Vegetation measurements were also collected at nest sites and non-nest sites to quantify habitat characteristics. We used an information-theoretic approach to evaluate support for multiple models evaluating nest success. Highly supported models indicated large negative effects of Brown-headed Cowbird (Molothrus ater) parasitism, and positive effects of increased canopy cover and distance to habitat edge on daily survival rates. Our estimate of daily survival rate was 0.94 ± 0.03 and the probability of survival was 0.25 ± 0.02. Point-count data revealed that densities of Painted Buntings were greater in treeline habitats than in open scrub-shrub and mature forest edge habitats. Furthermore, treelines had higher densities of large trees (>23 cm dbh) and percent canopy cover, variables positively associated with nest success, than open scrub-shrub and forest edge habitats. In general, survival rates and causes of nest failure in southern Louisiana were similar to those determined for breeding populations of Painted Buntings at other sites. Our results suggest that treelines, despite having a high edge-to-area ratio, might be preferred nesting habitat for Painted Buntings in our study area. RESUMEN. Efecto de borde y de las características del lugar de anidamiento en eléxito reproductivo de Passerina ciris Descensos poblacionales del Gorrión Pintado (Passerina ciris), durante lasúltimas décadas, ha llevado a que la especie se considere una de preocupación. Para buscar la forma más apropiada de determinar su estatus, investigamos los factores asociados a la productividad y abundancia de una población en la parte sur-central de Luisiana, durante el 2010-2011. Monitoreamos, con cámaras de video, 41 nidos de el ave para identificar depredadores, parasitismo reproductivo y mejorar los estimados deléxito de anidamiento. Se tomaron datos sobre la vegetación en los lugares de construcción de nidos y lugares no utilizados para cuantificar las características del hábitat. Utilizamos un enfoque de información teórica para evaluar el apoyo de múltiples modelos aléxito de anidamiento. Los modelos con mayor apoyo indicaron efectos negativos del parasitismo reproductivo por parte del Tordo Pardo (Molothrus ater), y efecto positivo, en la supervivencia diaria, de un incremento en la cobertura del dosel y distancia al borde del hábitat. Nuestro estimado de sobrevivencia diaria fue de 0.94 ± 0.03 y la probabilidad de sobrevivir fue 0.25 ± 0.02. Conteos de punto revelaron que la densidad del gorrión era mayor en hábitat de líneas deárboles que en matorrales abiertos y bordes de bosques maduros. Más aun, las líneas deárboles tuvieron mayor densidad de individuos grandes (> 23 cm dbh) y porcentaje de cubierta del dosel, que lasáreas de matorrales y bordes de bosques maduros, variables positivamente asociadas con eléxito de anidamiento. En general, la tasa de sobrevivencia y causas del fracaso de nidos en la parte sur de Luisiana resultó similar a otras poblaciones estudiadas en otros lugares. Nuestros resultados sugieren que las líneas deárboles, pese a tener un relación mayor deárea-borde, pudieran ser el hábitat preferido para anidar por el Gorrión Pintado.
Gambusia af nis (Western Mosquito sh) were sampled from 18 sites representing marsh, forested wet... more Gambusia af nis (Western Mosquito sh) were sampled from 18 sites representing marsh, forested wetlands, and agricultural wetlands in south Louisiana to determine distribution and infection parameters of Eustrongylides ignotus, a potentially lethal nematode parasite of wading birds. (n = 400 per site). Overall, prevalence of infection was 0.3%, with signi cantly higher prevalence in agricultural wetlands than in marshes or swamps. Our ndings are similar to work in Florida suggesting parasite prevalence is higher in disturbed wetlands, and suggest that birds foraging in cray sh ponds and rice elds may be at increased risk of exposure.
... Many species have been documented roosting in man-made structures such as bridges (Davis and ... more ... Many species have been documented roosting in man-made structures such as bridges (Davis and Cockrum 1963, Fraze and Wilkins 1990, Lewis 1995, Riskin and Pybus 1998). Due to their permanence and accessibility relative to other roosts in southern forests (Lance et al. ...
Although differences in sampling intensity can bias comparisons of allelic richness (A) among pop... more Although differences in sampling intensity can bias comparisons of allelic richness (A) among populations, investigators often fail to correct estimates of A for differences in sample size. Methods that standardize A on the basis of the size of the smallest number of samples in a comparison are preferable to other approaches. Rarefaction and repeated random subsampling provide unbiased estimates of A with the greatest precision and thus provide greatest statistical power to detect differences in variation. Less promising approaches, in terms of bias or precision, include single random subsampling, eliminating very small samples, using sample size as a covariate or extrapolating estimates obtained from small samples to a larger number of individuals.
Understanding the interplay of dispersal and how it translates into gene flow is key to understan... more Understanding the interplay of dispersal and how it translates into gene flow is key to understanding population processes, and especially so for endangered species occupying fragmented habitats. In migratory songbirds, there is evidence that long-distance movement capabilities do not translate well into observed dispersal. Our objectives were to (i) define the fine-scale spatial genetic structure in endangered black-capped vireos to characterize dispersal patterns and (ii) to correlate dispersal dynamics to overall population genetic structure using a simulation approach. We sampled 160 individuals over 2 years to (i) describe the fine-scale genetic structuring and (ii) used this information to model scenarios to compare with actual data on change in population structuring over a 100-year interval. We found that black-capped vireos exhibit male philopatry and restricted dispersal distances, relative to females. Our simulations also support a sex-biased dispersal model. Additionally, we find that fragmentation related changes in rates of dispersal might be a likely cause for increasing levels of population structure over a 100-year period. We show that restricted sex-biased dispersal can explain population structuring in this species and that changes in dispersal rates due to fragmentation may be a continuing threat to genetic viability in this species.
Although reintroductions are an important management tool, little is known about their effects on... more Although reintroductions are an important management tool, little is known about their effects on the genetic structure of wildlife species. We studied wild turkey (Meleagris gallopavo) and white-tailed deer (Odocoileus virginianus) populations from the eastern United States to determine if the genetic similarity of populations was more affected by geographic proximity or by possible gene flow resulting from reintroduction programs. We examined allele frequencies at 5 polymorphic loci for turkeys from 22 locations and at 15 polymorphic loci for deer from 21 locations and compared genetic distances among populations for both species to geographic distances and reintroduction histories. For both species, genetic distances were smaller between pairs of populations that either had individuals transferred between them or that had both received individuals from a common source population than were distances between pairs of populations that had not been connected by reintroductions (P < 0.001). Geographic proximity of populations of both turkeys and deer was not associated with genetic similarity (P = 0.280 and 0.520, respectively). Reintroductions may have obscured genetic patterns resulting from other evolutionary processes such as gene flow through dispersal. Additionally, post-reintroduction dispersal has not erased the genetic contributions of reintroduced individuals to the populations they established. Reintroduction programs should attempt to create populations with high levels of genetic diversity and avoid unnecessary disruption of the evolutionary relationships among populations of a species. J. WILDL. MANAGE. 58(4):698-711
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