^Maiken Winter - Academia.edu (original) (raw)

Papers by ^Maiken Winter

The productivity of birds is one of the most critical components of their natural history affecte... more The productivity of birds is one of the most critical components of their natural history affected by habitat quality. Birds might occur at high densities in a given habitat patch but have low nesting success. Such "population sinks" would not be detected if observers relied solely on estimates of bird density. Therefore, it is essential to monitor nests and determine their outcomes. Although interest in grassland-nesting passerines has increased greatly during the last decade, we still know little about factors affecting their nesting success. To stimulate more research in this area, we summarize several methods for nest­ searching and provide suggestions for optimizing its success in tall grass prairie. As a case study, we provide some data from a study on grassland-nesting birds in the northern tallgrass prairie.

According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza a... more According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza americana) and Henslow' s Sparrow (Ammodrumus henslowii) have declined severely during the last 30 years. The reasons for their population declines seem to differ; habitat fragmentation on the breeding grounds has been suggested to have little negative impact on Dickcissels, but appears to be a major reason for Henslow' s Sparrow declines. Previous reports on the status of Dickcissels and Henslow' s Sparrows largely were based on density estimates without considering the nesting biology of the two species. My comparison of the nesting biology of Dickcissel and Henslow' s Sparrow provides some insight into potential factors that might contribute to their population declines. During 1995-1997, I studied the nesting biology of Dickcissels and Henslow' s Sparrows in fragments of native tallgrass prairie in southwestern Missouri. Both species had similar clutch sizes, rates of hatching success, and numbers of young fledged per successful nest. Dickcissels tended to have lower rates of nesting success and higher rates of brood parasitism by Brown-headed Cowbirds (Molothrus a&r) than Henslow' s Sparrows. Although several vegetation characteristics at the nest differed between successful and depredated nests in Dickcissels, no differences were found between successful and depredated Henslow' s Sparrow nests or between parasitized and unparasitized Dickcissel nests. My results indicate that Dickcissels might reproduce less successfully than Henslow' s Sparrows in southwestern Missouri, and might therefore be of higher conservation concern on the breeding ground than previously thought.

Royal Society open science, 2016

Climate change probably has severe impacts on animal populations, but demonstrating a causal link... more Climate change probably has severe impacts on animal populations, but demonstrating a causal link can be difficult because of potential influences by additional factors. Assessing global impacts of climate change effects may also be hampered by narrow taxonomic and geographical research foci. We review studies on the effects of climate change on populations of amphibians and reptiles to assess climate change effects and potential biases associated with the body of work that has been conducted within the last decade. We use data from 104 studies regarding the effect of climate on 313 species, from 464 species-study combinations. Climate change effects were reported in 65% of studies. Climate change was identified as causing population declines or range restrictions in half of the cases. The probability of identifying an effect of climate change varied among regions, taxa and research methods. Climatic effects were equally prevalent in studies exclusively investigating climate factors...

According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza a... more According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza americana) and Henslow' s Sparrow (Ammodrumus henslowii) have declined severely during the last 30 years. The reasons for their population declines seem to differ; habitat fragmentation on the breeding grounds has been suggested to have little negative impact on Dickcissels, but appears to be a major reason for Henslow' s Sparrow declines. Previous reports on the status of Dickcissels and Henslow' s Sparrows largely were based on density estimates without considering the nesting biology of the two species. My comparison of the nesting biology of Dickcissel and Henslow' s Sparrow provides some insight into potential factors that might contribute to their population declines. During 1995-1997, I studied the nesting biology of Dickcissels and Henslow' s Sparrows in fragments of native tallgrass prairie in southwestern Missouri. Both species had similar clutch sizes, rates of hatching success, and numbers of young fledged per successful nest. Dickcissels tended to have lower rates of nesting success and higher rates of brood parasitism by Brown-headed Cowbirds (Molothrus a&r) than Henslow' s Sparrows. Although several vegetation characteristics at the nest differed between successful and depredated nests in Dickcissels, no differences were found between successful and depredated Henslow' s Sparrow nests or between parasitized and unparasitized Dickcissel nests. My results indicate that Dickcissels might reproduce less successfully than Henslow' s Sparrows in southwestern Missouri, and might therefore be of higher conservation concern on the breeding ground than previously thought.

Planning for bird conservation has become increasingly reliant on remote sensing, geographical in... more Planning for bird conservation has become increasingly reliant on remote sensing, geographical information systems, and, especially, models used to predict the occurrence of bird species as well as their density and demographics. We address the role of such tools by contrasting two models used in bird conservation. One, the Mallard (Anas platyrhynchos) productivity model, is very detailed, mechanistic, and based on an enormous body of research. The Mallard model has been extensively used with success to guide management efforts for Mallards and certain other species of ducks. The other model, the concept of Bird Conservation Areas, is simpler, less mechanistic, and less wellgrounded in research. This concept proposes that large patches of suitable habitat in a proper landscape will be adequate to maintain populations of birds. The Bird Conservation Area concept recently has been evaluated in the northern tallgrass prairie, where its fundamental assumptions have been found not to hold consistently. We argue that a more comprehensive understanding of the biology of individual species, and how they respond to habitat features, will be essential before we can use remotely sensed information and geographic information system products with confidence.

Conservation Biology, 1999

Between 1995 and 1997, we studied breeding birds in fragments of native tallgrass prairie in sout... more Between 1995 and 1997, we studied breeding birds in fragments of native tallgrass prairie in southwestern Missouri to determine the effect of habitat fragmentation on grassland bird populations. Data on density and nesting success collected in 13 prairie fragments of various sizes revealed three levels of area sensitivity. The most area-sensitive species, Greater Prairie-Chicken (Tympanuchus cupido), was absent from small prairie fragments. An intermediate form of area sensitivity was apparent in only one species, Henslow's Sparrow (Ammodramus henslowii), which occurred in lower densities in small than in large prairie fragments. Based on census (i.e., distributional) data, only those two species were area-sensitive (i.e., negatively affected by habitat fragmentation) in southwestern Missouri. A species can be sensitive not only on a distributional level, however, but also by having lower nesting success in small than in large prairie fragments. The Dickcissel (Spiza americana) was the only species that was area-sensitive on such a demographic level. These data indicate that we cannot rely solely on census data to describe the sensitivity of grasslandnesting species to habitat fragmentation, but that we also need to investigate demographic data (e.g., nesting success). Whereas it has previously been shown that density measures of forest-nesting birds do not reliably reflect nesting success in habitat fragments of various sizes, ours is the first study that describes this pattern for grassland-nesting species. Patrones de Sensitividad de Area en Aves que Nidan en Pastizales

The Condor, 2006

Larger birds are generally more strongly affected by habitat loss and fragmentation than are smal... more Larger birds are generally more strongly affected by habitat loss and fragmentation than are smaller ones because they require more resources and thus larger habitat patches. Consequently, conservation actions often favor the creation or protection of larger over smaller patches. However, in grassland systems the boundaries between a patch and the surrounding landscape, and thus the perceived size of a patch, can be indistinct. We investigated whether eight grassland bird species with different body sizes perceived variation in patch size and landscape structure in a consistent manner. Data were collected from surveys conducted in 44 patches of northern tallgrass prairie during 1998-2001. The response to patch size was very similar among species regardless of body size (density was little affected by patch size), except in the Greater Prairie-Chicken (Tympanuchus cupido), which showed a threshold effect and was not found in patches smaller than 140 ha. In landscapes containing 0%-30% woody vegetation, smaller species responded more negatively to increases in the percentage of woody vegetation than larger species, but above an apparent threshold of 30%, larger species were not detected. Further analyses revealed that the observed variation in responses to patch size and landscape structure among species was not solely due to body size per se, but to other differences among species. These results indicate that a stringent application of concepts requiring larger habitat patches for larger species appears to limit the number of grassland habitats that can be protected and may not always be the most effective conservation strategy.

The Condor, 2009

... data) found that Savannah Sparrows were parasitized most heavily (resulting in lowest nest su... more ... data) found that Savannah Sparrows were parasitized most heavily (resulting in lowest nest survival) on sites with the lowest overall nest densities ... can vary among habitats, across spatial and temporal scales, and among and within species (Hahn and Hatfield 1995, Shaffer et al ...

The Condor, 2009

... under the assumption that birds' singing activity is tied to the time of inc... more ... under the assumption that birds' singing activity is tied to the time of increasing light at dawn. ... randomized within the data set (Table 1). The degree of smoothness of each effect in the ... Thisnoise is particularly prominent at peak singing times for birds not singing in the previous 5 ...

The Wilson Bulletin, 2004

Basic nesting information on grassland passerines is needed for improving grassland bird manageme... more Basic nesting information on grassland passerines is needed for improving grassland bird management. Among the information needs are (1) the suitability of nesting habitat, (2) periods during the breeding season in which birds are most vulnerable to disturbances, and (3) ...

USGS Northern …, 2003

∗State University of New York †University of Minnesota - Crookston ‡Northern Prairie Wildlife Res... more ∗State University of New York †University of Minnesota - Crookston ‡Northern Prairie Wildlife Research Center ∗∗Northern Prairie Wildlife Research Center This paper is posted at DigitalCommons@University of Nebraska - Lincoln. http://digitalcommons.unl.edu/ ...

Journal of Wildlife Management, 2005

The structure of vegetation in grassland systems, unlike that in forest systems, varies dramatica... more The structure of vegetation in grassland systems, unlike that in forest systems, varies dramatically among years on the same sites, and among regions with similar vegetation. The role of this variation in vegetation structure on bird density and nesting success of grassland birds is poorly understood, primarily because few studies have included sufficiently large temporal and spatial scales to capture the variation in vegetation structure, bird density, or nesting success. To date, no large-scale study on grassland birds has been conducted to investigate whether grassland bird density and nesting success respond similarly to changes in vegetation structure. However, reliable management recommendations require investigations into the distribution and nesting success of grassland birds over larger temporal and spatial scales. In addition, studies need to examine whether bird density and nesting success respond similarly to changing environmental conditions. We investigated the effect of vegetation structure on the density and nesting success of 3 grassland-nesting birds: clay-colored sparrow (Spizella pallida), Savannah sparrow (Passerculus sandwichensis), and bobolink (Dolichonyx oryzivorus) in 3 regions of the northern tallgrass prairie in 1998-2001. Few vegetation features influenced the densities of our study species, and each species responded differently to those vegetation variables. We could identify only 1 variable that clearly influenced nesting success of 1 species: clay-colored sparrow nesting success increased with increasing percentage of nest cover from the surrounding vegetation. Because responses of avian density and nesting success to vegetation measures varied among regions, years, and species, land managers at all times need to provide grasslands with different types of vegetation structure. Management guidelines developed from small-scale, short-term studies may lead to misrepresentations of the needs of grassland-nesting birds.

The Condor, 2000

We tested how edges affect nest survival and predator distribution in a native tallgrass prairie ... more We tested how edges affect nest survival and predator distribution in a native tallgrass prairie system in southwestern Missouri using artificial nests, natural nests of Dickcissels (Spiza americana) and Henslow's Sparrows (Ammodramus henslowii), and mammal track stations. Survival of artificial nests was lower within 30 m of forest edge. Nesting success of Dickcissels and Henslow's Sparrows was lower within 50 m to a shrubby edge than at greater distances, whereas fates of nests were not related to distances to roads, agricultural fields, or forests. Evidence from clay eggs placed in artificial nests indicated that mid-sized carnivores were the major predators within 30 m of forest edges. Furthermore, mid-sized carnivores visited track stations most frequently within 50 m of forest edges. Because proximity of woody habitat explained more variation in nest survival and mammal activity than did fragment size, it appears that edge effects were more pronounced than area effects. Edge effects appeared to be caused mainly by greater exposure of nests to midsized carnivores. We argue that, based on edge avoidance behavior, ''grassland-interior'' species such as the Henslow's Sparrow respond to edge effects mainly by a decrease in density, whereas habitat generalists such as the Dickcissel are affected mainly by a decrease in nesting success.

Conservation …, 2003

Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassl... more Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassland bird declines in North America due to the adverse effects of fragmentation on breeding bird abundance and reproductive success. To assess the effects of fragmentation on the reproductive success of grassland birds, we measured rates of nest predation and brood parasitism for four species of birds (Grasshopper Sparrow [ Ammodramus savannaru ], Henslow's Sparrow[ Ammodramus henslowii ], Eastern Meadowlark [ Sturnella magna ], and Dickcissel [ Spiza Americana ]) in 39 prairie fragments ranging from 24 to Ͼ 40,000 ha in size in five states in the mid-continental United States. Throughout the region, nest-predation rates were significantly influenced by habitat fragmentation. Nest predation was highest in small (Ͻ 100 ha) and lowest in large (Ͼ 1000 ha) prairie fragments. Rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater), however, were not consistently related to fragment size and instead were more strongly related to regional cowbird abundance, being significantly higher in regions with high cowbird abundance. Differences in nest-predation rates between large fragments (54-68% of all nests lost to predators) and small fragments (78-84% lost to predators) suggest that fragmentation of prairie habitats may be contributing to regional declines of grassland birds. Maintaining grassland bird populations, therefore, may require protection and restoration of large prairie areas.

Little is known about the breeding biology of the Le Conte's Sparrow (Ammodramus leconteil), prob... more Little is known about the breeding biology of the Le Conte's Sparrow (Ammodramus leconteil), probably because of its secretive nature. We provide new information on several aspects of Le Conte's Sparrow breeding biology, including rates of nest parasitism by Brown-headed Cowbirds (Molothrus ater) and potential factors affecting breeding densities and nesting success of the species. Our study was conducted in the tallgrass prairie of northwestern Minnesota and southeastern North Dakota during 1998-2002. Breeding densities varied among years, but this variation was not clearly linked to climatic patterns. Vegetation had some influence on densities of Le Conte's Sparrows; densities were highest in grasslands with moderate amounts of bare ground. Prairie patch size and the percentage of shrubs and trees in the landscape had no recognizable influence on density. Nesting success was highly variable among sites and years and increased slightly with distance from trees. Rates of nest parasitism were low (1 of 50 nests parasitized), and clutch sizes were similar to those of other studies of Le Conte's Sparrows. SINOPSIS. Habitat y anidamiento deAmmodramus leconteii en las praderas de yerbas altas del norte Se concoce poco sobre el anidamiento del pinzon Ammodramus leconteii, probablemente por su naturaleza secretiva. Proveemos informacion de varios aspectos de la biologia reproductiva, incluyendo la tasa de parasitismo de parte de Molothrus ater, y los factores potenciales que afectan la densidad reproductiva y el exito de anidamiento de la especie. El estudio se llevo a cabo de 1998-2002, en las praderas de yerbas altas del noroeste de Minesota y el sureste de Dakota del Norte. La densidad reproductiva vario entre los diferentes ahos de estudio, aunque la variacion no estuvo vinculada a patrones climaticos. La vegetacion influyo en la densidad del ave: se encontraron las mayores densidades en yerbasales con areas moderadas de suelo desnudo. El tamaho del parcho y el porcentaje de arbustos y arboles en el paisaje, no influyo en la densidad. El exito de anidamiento resulto variable entre localidades y ahos, y aumento en algo con la distancia a los arboles. La tasa de parasitismo fue baja (1 de 50 nidos) y el tamaho de la camada fue similar al de otros estudios del ave.

The productivity of birds is one of the most critical components of their natural history affecte... more The productivity of birds is one of the most critical components of their natural history affected by habitat quality. Birds might occur at high densities in a given habitat patch but have low nesting success. Such "population sinks" would not be detected if observers relied solely on estimates of bird density. Therefore, it is essential to monitor nests and determine their outcomes. Although interest in grassland-nesting passerines has increased greatly during the last decade, we still know little about factors affecting their nesting success. To stimulate more research in this area, we summarize several methods for nest­ searching and provide suggestions for optimizing its success in tall grass prairie. As a case study, we provide some data from a study on grassland-nesting birds in the northern tallgrass prairie.

According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza a... more According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza americana) and Henslow' s Sparrow (Ammodrumus henslowii) have declined severely during the last 30 years. The reasons for their population declines seem to differ; habitat fragmentation on the breeding grounds has been suggested to have little negative impact on Dickcissels, but appears to be a major reason for Henslow' s Sparrow declines. Previous reports on the status of Dickcissels and Henslow' s Sparrows largely were based on density estimates without considering the nesting biology of the two species. My comparison of the nesting biology of Dickcissel and Henslow' s Sparrow provides some insight into potential factors that might contribute to their population declines. During 1995-1997, I studied the nesting biology of Dickcissels and Henslow' s Sparrows in fragments of native tallgrass prairie in southwestern Missouri. Both species had similar clutch sizes, rates of hatching success, and numbers of young fledged per successful nest. Dickcissels tended to have lower rates of nesting success and higher rates of brood parasitism by Brown-headed Cowbirds (Molothrus a&r) than Henslow' s Sparrows. Although several vegetation characteristics at the nest differed between successful and depredated nests in Dickcissels, no differences were found between successful and depredated Henslow' s Sparrow nests or between parasitized and unparasitized Dickcissel nests. My results indicate that Dickcissels might reproduce less successfully than Henslow' s Sparrows in southwestern Missouri, and might therefore be of higher conservation concern on the breeding ground than previously thought.

Royal Society open science, 2016

Climate change probably has severe impacts on animal populations, but demonstrating a causal link... more Climate change probably has severe impacts on animal populations, but demonstrating a causal link can be difficult because of potential influences by additional factors. Assessing global impacts of climate change effects may also be hampered by narrow taxonomic and geographical research foci. We review studies on the effects of climate change on populations of amphibians and reptiles to assess climate change effects and potential biases associated with the body of work that has been conducted within the last decade. We use data from 104 studies regarding the effect of climate on 313 species, from 464 species-study combinations. Climate change effects were reported in 65% of studies. Climate change was identified as causing population declines or range restrictions in half of the cases. The probability of identifying an effect of climate change varied among regions, taxa and research methods. Climatic effects were equally prevalent in studies exclusively investigating climate factors...

According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza a... more According to data from the North American Breeding Bird Survey, populations of Dickcissel (Qiza americana) and Henslow' s Sparrow (Ammodrumus henslowii) have declined severely during the last 30 years. The reasons for their population declines seem to differ; habitat fragmentation on the breeding grounds has been suggested to have little negative impact on Dickcissels, but appears to be a major reason for Henslow' s Sparrow declines. Previous reports on the status of Dickcissels and Henslow' s Sparrows largely were based on density estimates without considering the nesting biology of the two species. My comparison of the nesting biology of Dickcissel and Henslow' s Sparrow provides some insight into potential factors that might contribute to their population declines. During 1995-1997, I studied the nesting biology of Dickcissels and Henslow' s Sparrows in fragments of native tallgrass prairie in southwestern Missouri. Both species had similar clutch sizes, rates of hatching success, and numbers of young fledged per successful nest. Dickcissels tended to have lower rates of nesting success and higher rates of brood parasitism by Brown-headed Cowbirds (Molothrus a&r) than Henslow' s Sparrows. Although several vegetation characteristics at the nest differed between successful and depredated nests in Dickcissels, no differences were found between successful and depredated Henslow' s Sparrow nests or between parasitized and unparasitized Dickcissel nests. My results indicate that Dickcissels might reproduce less successfully than Henslow' s Sparrows in southwestern Missouri, and might therefore be of higher conservation concern on the breeding ground than previously thought.

Planning for bird conservation has become increasingly reliant on remote sensing, geographical in... more Planning for bird conservation has become increasingly reliant on remote sensing, geographical information systems, and, especially, models used to predict the occurrence of bird species as well as their density and demographics. We address the role of such tools by contrasting two models used in bird conservation. One, the Mallard (Anas platyrhynchos) productivity model, is very detailed, mechanistic, and based on an enormous body of research. The Mallard model has been extensively used with success to guide management efforts for Mallards and certain other species of ducks. The other model, the concept of Bird Conservation Areas, is simpler, less mechanistic, and less wellgrounded in research. This concept proposes that large patches of suitable habitat in a proper landscape will be adequate to maintain populations of birds. The Bird Conservation Area concept recently has been evaluated in the northern tallgrass prairie, where its fundamental assumptions have been found not to hold consistently. We argue that a more comprehensive understanding of the biology of individual species, and how they respond to habitat features, will be essential before we can use remotely sensed information and geographic information system products with confidence.

Conservation Biology, 1999

Between 1995 and 1997, we studied breeding birds in fragments of native tallgrass prairie in sout... more Between 1995 and 1997, we studied breeding birds in fragments of native tallgrass prairie in southwestern Missouri to determine the effect of habitat fragmentation on grassland bird populations. Data on density and nesting success collected in 13 prairie fragments of various sizes revealed three levels of area sensitivity. The most area-sensitive species, Greater Prairie-Chicken (Tympanuchus cupido), was absent from small prairie fragments. An intermediate form of area sensitivity was apparent in only one species, Henslow's Sparrow (Ammodramus henslowii), which occurred in lower densities in small than in large prairie fragments. Based on census (i.e., distributional) data, only those two species were area-sensitive (i.e., negatively affected by habitat fragmentation) in southwestern Missouri. A species can be sensitive not only on a distributional level, however, but also by having lower nesting success in small than in large prairie fragments. The Dickcissel (Spiza americana) was the only species that was area-sensitive on such a demographic level. These data indicate that we cannot rely solely on census data to describe the sensitivity of grasslandnesting species to habitat fragmentation, but that we also need to investigate demographic data (e.g., nesting success). Whereas it has previously been shown that density measures of forest-nesting birds do not reliably reflect nesting success in habitat fragments of various sizes, ours is the first study that describes this pattern for grassland-nesting species. Patrones de Sensitividad de Area en Aves que Nidan en Pastizales

The Condor, 2006

Larger birds are generally more strongly affected by habitat loss and fragmentation than are smal... more Larger birds are generally more strongly affected by habitat loss and fragmentation than are smaller ones because they require more resources and thus larger habitat patches. Consequently, conservation actions often favor the creation or protection of larger over smaller patches. However, in grassland systems the boundaries between a patch and the surrounding landscape, and thus the perceived size of a patch, can be indistinct. We investigated whether eight grassland bird species with different body sizes perceived variation in patch size and landscape structure in a consistent manner. Data were collected from surveys conducted in 44 patches of northern tallgrass prairie during 1998-2001. The response to patch size was very similar among species regardless of body size (density was little affected by patch size), except in the Greater Prairie-Chicken (Tympanuchus cupido), which showed a threshold effect and was not found in patches smaller than 140 ha. In landscapes containing 0%-30% woody vegetation, smaller species responded more negatively to increases in the percentage of woody vegetation than larger species, but above an apparent threshold of 30%, larger species were not detected. Further analyses revealed that the observed variation in responses to patch size and landscape structure among species was not solely due to body size per se, but to other differences among species. These results indicate that a stringent application of concepts requiring larger habitat patches for larger species appears to limit the number of grassland habitats that can be protected and may not always be the most effective conservation strategy.

The Condor, 2009

... data) found that Savannah Sparrows were parasitized most heavily (resulting in lowest nest su... more ... data) found that Savannah Sparrows were parasitized most heavily (resulting in lowest nest survival) on sites with the lowest overall nest densities ... can vary among habitats, across spatial and temporal scales, and among and within species (Hahn and Hatfield 1995, Shaffer et al ...

The Condor, 2009

... under the assumption that birds' singing activity is tied to the time of inc... more ... under the assumption that birds' singing activity is tied to the time of increasing light at dawn. ... randomized within the data set (Table 1). The degree of smoothness of each effect in the ... Thisnoise is particularly prominent at peak singing times for birds not singing in the previous 5 ...

The Wilson Bulletin, 2004

Basic nesting information on grassland passerines is needed for improving grassland bird manageme... more Basic nesting information on grassland passerines is needed for improving grassland bird management. Among the information needs are (1) the suitability of nesting habitat, (2) periods during the breeding season in which birds are most vulnerable to disturbances, and (3) ...

USGS Northern …, 2003

∗State University of New York †University of Minnesota - Crookston ‡Northern Prairie Wildlife Res... more ∗State University of New York †University of Minnesota - Crookston ‡Northern Prairie Wildlife Research Center ∗∗Northern Prairie Wildlife Research Center This paper is posted at DigitalCommons@University of Nebraska - Lincoln. http://digitalcommons.unl.edu/ ...

Journal of Wildlife Management, 2005

The structure of vegetation in grassland systems, unlike that in forest systems, varies dramatica... more The structure of vegetation in grassland systems, unlike that in forest systems, varies dramatically among years on the same sites, and among regions with similar vegetation. The role of this variation in vegetation structure on bird density and nesting success of grassland birds is poorly understood, primarily because few studies have included sufficiently large temporal and spatial scales to capture the variation in vegetation structure, bird density, or nesting success. To date, no large-scale study on grassland birds has been conducted to investigate whether grassland bird density and nesting success respond similarly to changes in vegetation structure. However, reliable management recommendations require investigations into the distribution and nesting success of grassland birds over larger temporal and spatial scales. In addition, studies need to examine whether bird density and nesting success respond similarly to changing environmental conditions. We investigated the effect of vegetation structure on the density and nesting success of 3 grassland-nesting birds: clay-colored sparrow (Spizella pallida), Savannah sparrow (Passerculus sandwichensis), and bobolink (Dolichonyx oryzivorus) in 3 regions of the northern tallgrass prairie in 1998-2001. Few vegetation features influenced the densities of our study species, and each species responded differently to those vegetation variables. We could identify only 1 variable that clearly influenced nesting success of 1 species: clay-colored sparrow nesting success increased with increasing percentage of nest cover from the surrounding vegetation. Because responses of avian density and nesting success to vegetation measures varied among regions, years, and species, land managers at all times need to provide grasslands with different types of vegetation structure. Management guidelines developed from small-scale, short-term studies may lead to misrepresentations of the needs of grassland-nesting birds.

The Condor, 2000

We tested how edges affect nest survival and predator distribution in a native tallgrass prairie ... more We tested how edges affect nest survival and predator distribution in a native tallgrass prairie system in southwestern Missouri using artificial nests, natural nests of Dickcissels (Spiza americana) and Henslow's Sparrows (Ammodramus henslowii), and mammal track stations. Survival of artificial nests was lower within 30 m of forest edge. Nesting success of Dickcissels and Henslow's Sparrows was lower within 50 m to a shrubby edge than at greater distances, whereas fates of nests were not related to distances to roads, agricultural fields, or forests. Evidence from clay eggs placed in artificial nests indicated that mid-sized carnivores were the major predators within 30 m of forest edges. Furthermore, mid-sized carnivores visited track stations most frequently within 50 m of forest edges. Because proximity of woody habitat explained more variation in nest survival and mammal activity than did fragment size, it appears that edge effects were more pronounced than area effects. Edge effects appeared to be caused mainly by greater exposure of nests to midsized carnivores. We argue that, based on edge avoidance behavior, ''grassland-interior'' species such as the Henslow's Sparrow respond to edge effects mainly by a decrease in density, whereas habitat generalists such as the Dickcissel are affected mainly by a decrease in nesting success.

Conservation …, 2003

Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassl... more Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassland bird declines in North America due to the adverse effects of fragmentation on breeding bird abundance and reproductive success. To assess the effects of fragmentation on the reproductive success of grassland birds, we measured rates of nest predation and brood parasitism for four species of birds (Grasshopper Sparrow [ Ammodramus savannaru ], Henslow's Sparrow[ Ammodramus henslowii ], Eastern Meadowlark [ Sturnella magna ], and Dickcissel [ Spiza Americana ]) in 39 prairie fragments ranging from 24 to Ͼ 40,000 ha in size in five states in the mid-continental United States. Throughout the region, nest-predation rates were significantly influenced by habitat fragmentation. Nest predation was highest in small (Ͻ 100 ha) and lowest in large (Ͼ 1000 ha) prairie fragments. Rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater), however, were not consistently related to fragment size and instead were more strongly related to regional cowbird abundance, being significantly higher in regions with high cowbird abundance. Differences in nest-predation rates between large fragments (54-68% of all nests lost to predators) and small fragments (78-84% lost to predators) suggest that fragmentation of prairie habitats may be contributing to regional declines of grassland birds. Maintaining grassland bird populations, therefore, may require protection and restoration of large prairie areas.

Little is known about the breeding biology of the Le Conte's Sparrow (Ammodramus leconteil), prob... more Little is known about the breeding biology of the Le Conte's Sparrow (Ammodramus leconteil), probably because of its secretive nature. We provide new information on several aspects of Le Conte's Sparrow breeding biology, including rates of nest parasitism by Brown-headed Cowbirds (Molothrus ater) and potential factors affecting breeding densities and nesting success of the species. Our study was conducted in the tallgrass prairie of northwestern Minnesota and southeastern North Dakota during 1998-2002. Breeding densities varied among years, but this variation was not clearly linked to climatic patterns. Vegetation had some influence on densities of Le Conte's Sparrows; densities were highest in grasslands with moderate amounts of bare ground. Prairie patch size and the percentage of shrubs and trees in the landscape had no recognizable influence on density. Nesting success was highly variable among sites and years and increased slightly with distance from trees. Rates of nest parasitism were low (1 of 50 nests parasitized), and clutch sizes were similar to those of other studies of Le Conte's Sparrows. SINOPSIS. Habitat y anidamiento deAmmodramus leconteii en las praderas de yerbas altas del norte Se concoce poco sobre el anidamiento del pinzon Ammodramus leconteii, probablemente por su naturaleza secretiva. Proveemos informacion de varios aspectos de la biologia reproductiva, incluyendo la tasa de parasitismo de parte de Molothrus ater, y los factores potenciales que afectan la densidad reproductiva y el exito de anidamiento de la especie. El estudio se llevo a cabo de 1998-2002, en las praderas de yerbas altas del noroeste de Minesota y el sureste de Dakota del Norte. La densidad reproductiva vario entre los diferentes ahos de estudio, aunque la variacion no estuvo vinculada a patrones climaticos. La vegetacion influyo en la densidad del ave: se encontraron las mayores densidades en yerbasales con areas moderadas de suelo desnudo. El tamaho del parcho y el porcentaje de arbustos y arboles en el paisaje, no influyo en la densidad. El exito de anidamiento resulto variable entre localidades y ahos, y aumento en algo con la distancia a los arboles. La tasa de parasitismo fue baja (1 de 50 nidos) y el tamaho de la camada fue similar al de otros estudios del ave.