Migratory patterns and connectivity of two North American grassland bird species

Effective management and conservation of migratory bird populations require knowledge and incorporation of their movement patterns and space use throughout the annual cycle. To investigate the little‐known migratory patterns of two grassland bird species, we deployed 180 light‐level geolocators on Grasshopper Sparrows (Ammodramus savannarum) and 29 Argos‐GPS tags on Eastern Meadowlarks (Sturnella magna) at Konza Prairie, Kansas, USA, and six US Department of Defense (DoD) installations distributed across the species' breeding ranges. We analyzed location data from 34 light‐level geolocators and five Argos‐GPS tags attached for 1 year to Grasshopper Sparrows and Eastern Meadowlarks, respectively. Grasshopper Sparrows were present on the breeding grounds from mid‐April through early October, substantially longer than previously estimated, and migrated on average ~2,500 km over ~30 days. Grasshopper Sparrows exhibited strong migratory connectivity only at a continental scale. The North American Great Lakes region likely serves as a migratory divide for Midwest and East Coast Grasshopper Sparrows; Midwest populations (Kansas, Wisconsin, and North Dakota; n = 13) largely wintered in Texas or Mexico, whereas East Coast populations (Maryland and Massachusetts, n = 20) wintered in the northern Caribbean or Florida. Our data from Eastern Meadowlarks provided evidence for a diversity of stationary and short‐ and long‐distance migration strategies. By providing the most extensive examination of the nonbreeding movement ecology for these two North American grassland bird species to date, we refine information gaps and provide key insight for their management and conservation.     

Effects of urbanization on site occupancy and density of grassland birds in tallgrass prairie fragments

Tallgrass prairies are among the most threatened ecosystems in the world. Remaining prairies tend to be small and isolated and many are associated with urban and suburban landscapes. We asked how urbanization might impact the conservation value of tallgrass prairie fragments for grassland birds by comparing the densities and the probability of occurrence of Dickcissels (Spiza americana), Grasshopper Sparrows (Ammodramus savannarum), and Eastern Meadowlarks (Sturnella magna) across 28 grasslands surrounded by low, moderate, and high levels of urbanization. We employed a hierarchical model selection approach to ask how variables that describe the vegetation structure, size and shape of grasslands, and urbanization category might explain variation in density and occurrence over two breeding seasons. Occurrence of all three species was explained by a combination of vegetation and patch characteristics, though each species was influenced by different variables and only Eastern Meadowlark occurrence was explained by urbanization. Abundance of all three species was negatively impacted by urbanization, though vegetation variables were also prevalent in the best‐supported models. We found no evidence that vegetation structure or other patch characteristics varied in a systematic way across urbanization categories. Although our results suggest that grassland bird density declines with urbanization, urban tallgrass prairies still retain conservation value for grassland birds because of the limited availability of tallgrass prairie habitat and the limited impact of urbanization on species occurrence.     

Comparison of survey methods for wintering grassland birds

ABSTRACT Although investigators have evaluated the efficacy of survey methods for assessing densities of breeding birds, few comparisons have been made of survey methods for wintering birds, especially in grasslands. In winter, social behavior and spatial distributions often differ from those in the breeding season. We evaluated the degree of correspondence between density estimates based on different survey methods. Surveys were conducted during two winters (2001–2002 and 2002–2003) on 16 grassland sites in southwestern Oklahoma. Line‐transect (using a detection function to account for birds present but not detected) and area‐search (where density was based on the total count within a given area) methods were employed. Observations on line transects were also analyzed as strip transects, where density was based on total count within a given strip width and no detection function was used. Savannah Sparrows (Passerculus sandwichensis), LeConte's Sparrows (Ammodramus leconteii), Song Sparrows (Melospiza melodia), Smith's Longspurs (Calcarius pictus), Chestnut‐collared Longspurs (C. ornatus), and Eastern Meadowlarks (Sturnella magna) were sufficiently abundant to allow comparison. Area‐search density estimates tended to be higher than line‐transect estimates for Savannah Sparrows, Song Sparrows, and Eastern Meadowlarks, suggesting that some individuals initially located close to the transect line were not detected on line transects. The area‐search and line‐transect methods gave similar density estimates for Chestnut‐collared and Smith's longspurs. Area‐search estimates of Eastern Meadowlarks were significantly higher in the second year of the study only. For this species, area‐search estimates did not differ from those of strip transects covering an equal area, so the reason for the differing meadowlark estimates is not clear. Higher density estimates using the area‐search method likely resulted from: (1) birds that might escape detection by hiding were more likely detected (flushed) during area searches because of the repeated passes through the area, and (2) birds close to the line in line transects escape detection by hiding, biasing those estimates low. We also evaluated the correspondence of density rankings for the six species as determined by the different survey methods and for the same species across survey sites. Correlations among the six species of the area‐search results with those of line transects and strip transects generally were high, increasing in 2002–2003 when densities of birds were greater. All three methods provided similar density rankings among species. Density rankings within species across sites for the four non‐longspur species generally were concordant for the three methods, suggesting that any of them will adequately reflect among‐site differences, especially when densities vary greatly across sites. Further research is needed to determine the extent to which grassland birds are missed on line transects. We suggest that workers using line transects to study these species give careful consideration and make additional efforts to satisfy the distance‐sampling assumption that all birds on or near the line are detected. If density is measured as a total count in a fixed area, we recommend that observers pass within <10 m of all points in the area.     

Winter survival of North American grassland birds is driven by weather and grassland condition in the Chihuahuan Desert

Populations of grassland birds that overwinter in the Chihuahuan Desert are declining more rapidly than other grassland birds, and survival during the non‐breeding season may have a strong influence on population trends of these species. Habitat loss and deterioration due to desertification may be contributing to these declines, and the winter ecology of grassland birds under these changing environmental conditions remains relatively unexplored. To fill this information gap, we estimated the survival of two grassland‐obligate sparrows, Baird's Sparrows (Ammodramus bairdii) and Grasshopper Sparrows (A. savannarum), on their wintering grounds in the Chihuahuan Desert, and investigated the role of habitat structure and weather on survival rates. We deployed radio‐transmitters on Baird's (N = 49) and Grasshopper (N = 126) sparrows near Janos, Chihuahua, and tracked birds from November to March during the winters of 2012–2013 and 2013–2014. Causes of mortality included avian predators, mammals, and possibly weather. We estimated an overall weekly winter survival probability of ? = 92.73% (95% CI[s] = 88.63–95.44%) for Baird's Sparrows in 2012–2013. We estimated a weekly winter survival probability of ? = 93.48% (95% CI[s] = 90.29–96.67%) and ? = 98.78% (95% CI[s] = 97.88–99.68%) for Grasshopper Sparrow in 2012–2013 and 2013–2014, respectively. Weekly winter survival was lower with colder daily minimum temperatures for both species and in areas with taller shrubs for Grasshopper Sparrows, with the shrubs potentially increasing predation risk by providing perches for Loggerhead Shrikes (Lanius ludovicianus). Our results highlight the need to maintain healthy grass structure in wintering areas to provide birds with food, protection from predators, and adequate cover from inclement weather. Our results also demonstrate that the presence of shrubs can lower winter survival, and suggest that shrub encroachment into the winter habitat of these sparrows may be an important driver of their population declines. Shrub removal could increase survival of wintering sparrows in the Chihuahuan Desert by reducing availability of perches for avian predators, thus reducing predation risk.     

Avian use of perennial biomass feedstocks as post-breeding and migratory stopover habitat

Increased production of biomass crops in North America will require new agricultural land, intensify the cultivation of land already under production and introduce new types of biomass crops. Assessing the potential biodiversity impacts of novel agricultural systems is fundamental to the maintenance of biodiversity in agricultural landscapes, yet the consequences of expanded biomass production remain unclear. We evaluate the ability of two candidate second generation biomass feedstocks (switchgrass, Panicum virgatum, and mixed-grass prairie) not currently managed as crops to act as post-breeding and fall migratory stopover habitat for birds. In total, we detected 41 bird species, including grassland specialists and species of state and national conservation concern (e.g. Henslow's Sparrow, Ammodramus henslowii). Avian species richness was generally comparable in switchgrass and prairie and increased with patch size in both patch types. Grassland specialists were less abundant and less likely to occur in patches within highly forested landscapes and were more common and likely to occur in larger patches, indicating that this group is also area-sensitive outside of the breeding season. Variation in the biomass and richness of arthropod food within patches was generally unrelated to richness and abundance metrics. Total bird abundance and that of grassland specialists was higher in patches with greater vegetation structural heterogeneity. Collectively, we find that perennial biomass feedstocks have potential to provide post-breeding and migratory stopover habitat for birds, but that the placement and management of crops will be critical factors in determining their suitability for species of conservation concern. Industrialization of cellulosic bioenergy production that results in reduced crop structural heterogeneity is likely to dramatically reduce the suitability of perennial biomass crops for birds.     

Ecological Consequences of Shifting the Timing of Burning Tallgrass Prairie

In the Kansas Flint Hills, grassland burning is conducted during a relatively narrow window because management recommendations for the past 40 years have been to burn only in late spring. Widespread prescribed burning within this restricted time frame frequently creates smoke management issues downwind. A potential remedy for the concentrated smoke production in late spring is to expand burning to times earlier in the year. Yet, previous research suggested that burning in winter or early spring reduces plant productivity and cattle weight gain while increasing the proportion of undesirable plant species. In order to better understand the ecological consequences of burning at different times of the year, plant production and species abundance were measured for 20 years on ungrazed watersheds burned annually in autumn, winter, or spring. We found that there were no significant differences in total grass production among the burns on either upland or lowland topographic positions, although spring burned watersheds had higher grass culm production and lower forb biomass than autumn and winter burned watersheds. Burning in autumn or winter broadened the window of grass productivity response to precipitation, which reduces susceptibility to mid-season drought. Burning in autumn or winter also increased the phenological range of species by promoting cool-season graminoids without a concomitant decrease in warm-season grasses, potentially widening the seasonal window of high-quality forage. Incorporating autumn and winter burns into the overall portfolio of tallgrass prairie management should increase the flexibility in managing grasslands, promote biodiversity, and minimize air quality issues caused by en masse late-spring burning with little negative consequences for cattle production.     

Habitat use and movement patterns by dependent and independent juvenile Grasshopper Sparrows during the post‐fledging period

The post‐fledging period is a critical life stage for young grassland birds. Habitat selection by recently fledged birds may differ from that of adults and may change as juveniles transition from the care and protection of parents to independence. To describe patterns of habitat selection during these important life stages, we studied habitat use by juvenile Grasshopper Sparrows (Ammodramus savannarum) in a Conservation Reserve Program grassland in Maryland. We used radio‐telemetry to track daily movement patterns of two age classes of Grasshopper Sparrows during the post‐fledging period. Sparrows were classified as either dependent (<32‐d‐old) or independent (≥32‐d‐old). We characterized the vegetation at 780 vegetation plots (390 plots where birds were located and 390 paired random plots). Microhabitats where dependent birds were found had significantly more bare ground, litter, and plant species richness than paired random plots. In addition, dependent birds were found in plots with less bare ground, more warm‐season grass cover, more total vegetation cover, and more forb cover than plots used by independent birds. Plots where independent birds were located also had significantly more bare ground than random plots. Dependent birds are less able to escape from predators because their flight feathers are not fully grown so they may benefit from remaining in areas of greater vegetation cover. However, juveniles transitioning from dependence to independence must forage on their own, possibly explaining their increased use of more open areas where foraging may be easier. To properly manage habitat for grassland birds, management strategies must consider the changing needs of birds during different stages of development. Our results highlight the importance of diverse grassland ecosystems for juvenile grassland birds during the transition to independence.     

Home range and survival characteristics of male Bachman's Sparrows in an old-growth forest managed with breeding season burns

ABSTRACT.   Prescribed burning is essential for maintaining suitable habitat for Bachman's Sparrows ( Aimophila aestivalis ), but burns conducted during the breeding season may lead to site abandonment and low survival or productivity. We monitored a color-banded population of Bachman's Sparrow in Georgia for four breeding seasons to assess home range size, site fidelity, and survival in an area managed primarily using breeding season burns. Our study area was one of the last remaining tracts of old-growth longleaf pine ( Pinus palustris ), and alternating halves of the tract were burned during the breeding season during each year of our study. Mean home range size for males ( N = 46) during the breeding season was 3.1 ha based on 95% fixed kernel analysis and 1.8 ha based on minimum convex polygons. Breeding season burning had no effect on male site fidelity and home range characteristics. The proportion of males remaining on burned areas was similar to the proportion remaining on unburned areas. Shifts in home range centroids pre- and postburn were also similar for males on unburned (median = 49.7 m) and burned (median = 65.6 m) areas. In addition, the size of home ranges that were burned ( ha) was similar to that of home ranges that were not burned ( ha). Estimated annual survival for males was 0.59. The median shift in annual home range centers calculated for 38 males observed during multiple breeding seasons was 63 m and, coupled with our survival estimates, suggest greater site fidelity than previously reported. These results suggest that breeding season burns were not as detrimental to Bachman's Sparrows as reported at other locations, and such burns may be helpful in maintaining suitable habitat.     

Diel patterns of predation and fledging at nests of four species of grassland songbirds

Although it is common for nestlings to exhibit a strong bias for fledging in the morning, the mechanisms underlying this behavior are not well understood. Avoiding predation risk has been proposed as a likely mechanism by a number of researchers. We used video surveillance records from studies of grassland birds nesting in North Dakota, Minnesota, and Wisconsin to determine the diel pattern of nest predation and fledging patterns of four ground‐nesting obligate grassland passerines (Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), Bobolink (Dolichonyx oryzivorus), and Eastern Meadowlark (Sturnella magna)). We used the nest predation pattern as a surrogate for predation activity to test whether nestlings minimized predation risk by avoiding fledging when predation activity was high and preferentially fledging when predation risk was low. Predation activity was significantly lower starting 3 hr before sunrise and ending 3 hr after sunrise, followed by a transition to a period of significantly higher activity lasting for 4 hr, before declining to an average activity level for the rest of the diel period. There was little evidence that the four grassland bird species avoided fledging during the high‐risk period and Savannah Sparrow fledged at higher rates during that period. All four species had hours during the low‐risk period where they fledged at higher rates, but only Grasshopper Sparrow fledged preferentially during that period. Bobolink and Eastern Meadowlark had multiple hours with high fledging rates throughout the daytime period, resulting in no relationship between probability of fledging and predation risk. Given the species variability in fledging pattern seen in our study, it is unlikely that there is a universal response to any driver that affects time of fledging. Further study is needed to understand the complex interplay between species ecology and drivers such as physiology, energetics, and predation in affecting grassland bird fledging behavior.     

Restoration Efforts for Plant and Bird Communities in Tallgrass Prairies Using Prescribed Burning and Mowing

Recent losses and fragmentation of tallgrass prairie habitat to agriculture and urban development have led to corresponding declines in diversity and abundance of plants and birds associated with such habitat. Mowing and burning are alternative management strategies for restoring and rejuvenating prairies in fragmented landscapes, but their specific, comparative effects are the subjects of ongoing evaluation. We compared the responses of plant and bird communities on four sets of mowed, burned, and untreated sites of small (3–10 ha), fragmented tallgrass prairies at the DeSoto National Wildlife Refuge (DNWR), Iowa, U.S.A., during May–July in 1998 and 1999. Species richness and diversity of plants, resident grassland birds, and communities of birds associated with grassland edges (edge species) were independent of treatment. Although not affecting species richness and diversity in plant communities, mowed sites ranked lower in total plant coverage and total forb coverage than burned sites or untreated sites. In contrast, untreated sites had more coverage by shrubs, suggesting that mowing and burning did retard shrub encroachment. Overall, abundance and diversity of plants and birds were generally insensitive to management strategies. Small, fragmented sites of rare habitat may not respond in the short term to management treatments and may not be capable of supporting highly diverse communities, no matter how intensively manipulated. It is more probable that diversity of native prairie communities can be enhanced and restored only through long‐term efforts, acquisition of large land units capable of supporting stable populations, and deliberate reintroduction of species of high conservation value.     

Comparison of removal‐based methods for estimating abundance of five species of prairie songbirds

Estimating species abundance is important for land managers, especially for monitoring conservation efforts. The two main survey methods for estimating avian abundance are point counts and transects. Previous comparisons of these two methods have either been limited to a single species or have not included detection probability. During the 2012 breeding season, we compared and assessed the efficiency (precision for amount of effort) of point count time of detection (PCTD) and dependent double‐observer transect (TRMO) methods based on detection probabilities and abundance estimates of five species of songbirds that use a range of habitats in a prairie system in Montana dominated by sagebrush and grassland vegetation. Our focal species included Vesper Sparrows (Pooecetes gramineus), a generalist species found in both shrub and grassland habitat, shrub‐obligate Brewer's Sparrows (Spizella breweri), and McCown's Longspurs (Rhynchophanes mccownii), Horned Larks (Eremophila alpestris), and Western Meadowlarks (Sturnella neglecta), three species of grassland obligates that prefer different grass heights. Detection probabilities were significantly higher for TRMO surveys, with less variation for all five species and differences most pronounced for Brewer's Sparrows and Horned Larks. PCTD surveys required less field effort (~8–20 fewer people minutes per plot) than TRMO surveys because the TRMO surveys required two people. However, time spent on TRMO surveys provided between 0.38 and 87 times more precision per people minute than PCTD surveys. Our results suggest that TRMO surveys provide a more efficient (measured as time spent per unit of standard error) field‐based technique in sagebrush prairie systems for the species we investigated, resulting in more precise detection and abundance estimates.     

Implications of grazing and burning of grasslands on the sustainable use of francolins (Francolinus spp.) and on overall bird conservation in the highlands of Mpumalanga province, South Africa

We investigated the densities of the Redwing Francolinus levaillantii and Greywing Francolins F. africanus and the diversity of grassland birds in general along a land-use gradient in the highlands of Mpumalanga province, South Africa. Redwing Francolins cannot tolerate intensive grazing and frequent burning and are confined largely to unburnt, ungrazed grasslands. Their density and the species richness of grassland birds in general are negatively correlated with grazing intensity. Redwing populations drop to densities that cannot be utilised by hunters on a sustainable basis in grasslands that are grazed at even moderate levels or burned annually. Nineteen bird species (including five threatened species) were confined to essentially pristine grassland and were never observed in grazed/annually burned grasslands. The Greywing Francolin is more evenly distributed (although always at sub-utilisation densities) along the grassland land-use gradient, and its density is positively correlated with grazing intensity. There are two assemblages of grassland bird species that appear to be indicative of the intensity of habitat utilisation. Populations of grassland birds in the study area are becoming increasingly dependent on isolated patches of pristine grassland and are threatened by management involving annual burning and high stocking rates on a landscape scale.     

NESTLING DIETS OF PRAIRIE PASSERINE BIRDS AT MATADOR, SASKATCHEWAN, CANADA

The nestling diets of seven species of grassland passerines were studied from gullet samples collected in 1969–1971 at Matador, Saskatchewan, Canada. Relative population densities on census plots on grazed and ungrazed prairie showed that Horned Lark Eremophila alpestris, McCown's Longspur Calcarius mccownii and Chestnut-collared Longspur C. ornatus preferred grazed areas and Sprague's Pipit Anthus spragueii, Western Meadowlark, Sturnella neglecta, Savannah Sparrow Passerculus sandwichensis and Baird's Sparrow Ammodramus bairdii preferred ungrazed prairie. Fifteen invertebrate ordinal taxa, and seeds were represented to an important extent in combined gullet contents; but two taxa, Lepidoptera (77% larvae) and grasshoppers (all Acrididae), comprised the bulk of nestling diets. Four grasshopper species contributed 70–100% of grasshoppers eaten in June-August. Overlap at the family level was also high in several other important prey. Comparison with invertebrate populations of ungrazed prairie showed that the birds ignored some abundant taxa of very small invertebrates, and apparently preferred the two least abundant groups which offered large individual prey items. Average nestling food overlap indices for the season among all species except Savannah Sparrow and Baird's Sparrow, based on taxonomic composition, was 0.85. Overlap was moderate in May and June and became very high in July and August. The number of nestlings reached a peak in June and early July when nestling food overlap was much lower than later in the season. Horned Larks avoid competition by nesting earlier than do the other species, while McCown's Longspur, which depends on grasshoppers for nestling food more than do the other species, tends to breed later in the season than the other species. Finally, data suggest that nestling food may be superabundant.     

Soil physiochemical changes following 12 years of annual burning in a humid–subtropical tallgrass prairie: a hypothesis

Burning is known to stimulate growth of grassland vegetation, promote species diversity, and inhibit natural invasion by woody plants. However, the frequency at which grasslands are burned as part of their management can affect soil nutrient content and, ultimately, productivity. The objective of this study was to characterize changes in soil physical and chemical properties in a native tallgrass prairie after 12 years of annual burning. In 1989, five soil samples from the 0 to 10 cm depth were collected along a transect through a 3 ha parcel of native tallgrass prairie in central Arkansas. Soil sampling was repeated in 2001 to assess changes over time. Results showed that soil bulk density, electrical conductivity, extractable P, Na, Fe, and Mn decreased significantly (P < 0.05), while soil organic matter, total N and C, and the C/N ratio increased significantly (P < 0.05) within the 12-year period during which annual burning was the only imposed management practice. Mean extractable K, Ca, Mg, S, and Zn levels were all lower in 2001 than in 1989, but differences were not significant, while soil pH did not change. The results of this study indicate that annual export of several essential plant nutrients during prescribed burning of relatively small, remnant prairie fragments exceeds annual imports from atmospheric deposition and/or organic matter mineralization. Annual prescribed burning may be too frequent to maintain optimal ecosystem functioning and productivity. Decreasing the frequency of prescribed burning for native grassland management may help to retain more soil nutrients to sustain a higher level of productivity.     

Fire Frequency and Mosaic Burning Effects on a Tallgrass Prairie Ground Beetle Assemblage

Fire frequency has significant effects on the biota of tallgrass prairie, including mammals, vascular plants and birds. Recent concern has been expressed that widespread annual burning, sometimes in combination with heavy livestock grazing, negatively impacts the biota of remaining prairie remnants. A common management recommendation, intended to address this problem, is to create a landscape with a mosaic of different burn regimes. Pitfall trapping was used to investigate the impacts of fire pattern on the diversity and species composition of ground beetles (Coleoptera: Carabidae) at Konza Prairie Biological Station in eastern Kansas, USA. Trapping was conducted over three seasons in landscape units burned on average every 1, 4, or 20 years, and in a fourth season across the available range of vegetative structure to assess the variability of the community within the study system. In the fifth season communities were also followed immediately after two fire events to detect within-season effects of fire and to study short-term patterns of post-disturbance community assembly. Fire frequency had comparatively minimal effects on ground beetle diversity measures, and most numerically common species were observed widely across habitat and management types. Fire frequency effects were manifested primarily in changes in abundance of common species. Colonization of burned areas apparently did not occur from juxtaposed non-burned areas, but from underground or from long distances. While these results suggest that widespread annual burning of tallgrass prairie remnants may not have dramatic effects on prairie ground beetles, we urge caution regarding the application of these results to other taxa within tallgrass prairie.     

Habitat use of urban Tree Sparrows in the process of urbanization:Beijing as a case study

The Tree Sparrow (Passer montanus) is a dom-inant species in urban bird communities.With the devel-opment of urbanization,the habitats and sources of food for Tree Sparrows are decreasing.Can the urban Tree Sparrow adapt to changes in the urban environment? To answer this question,we studied the habitat use of Tree Sparrows in eight types of urban areas in Beijing.The results show that the number of both breeding and winter-ing Tree Sparrows decreased with increasing urbanization.The habitat use of Tree Sparrows,analyzed using stepwise discriminant analysis,was positively correlated with the number of brick bungalows,coniferous and broad-leaved trees and air conditioners.It was negatively correlated with the area of high buildings and hardened roads,pedestrian and automobile flux.This indicates that the Tree Sparrow had not adapted to rapid urbanization even though it is a generally adaptable species.Urban planning should take birds such as the Tree Sparrow into consideration.     

Regional variation in abundance and response to fire by Henslow's Sparrows in Louisiana

ABSTRACT Wintering Henslow's Sparrows (Ammodramus henslowii) are generally associated with open grasslands. Results of small‐scale, regionally specific studies have not revealed larger‐scale abundance patterns, but they have shown regional differences in habitat selection. Our objective was to quantify Henslow's Sparrow abundance and vegetation associations across Louisiana, an area that includes multiple types of grassland habitats. Bird densities in longleaf pine savannas of eastern and western Louisiana were over 1.5 times higher than in northern prairies and over 13 times higher than at a site in southwestern Louisiana. The responses of Henslow's Sparrows to fire differed between eastern and western savannas, with abundance increasing three fold over the first 3 yrs after fire in the west, and decreasing three fold over that interval in the east. In both areas, habitat became unsuitable by about 5 yrs after fire, probably due to woody encroachment and loss of herbaceous plants. For sites that contained Henslow's Sparrows at least once during our study, habitat modeling revealed that neither vegetation structure nor plant species composition was important in predicting the occurrence of Henslow's Sparrows within sites or abundance among sites throughout the state, perhaps due to the variety of habitats sampled. Our results suggest that longleaf pine savannas are the most important grasslands for wintering Henslow's Sparrows in Louisiana and that overwintering habitat is probably selected based on regionally specific vegetation features. Optimal fire intervals may vary regionally, particularly between mesic flatwoods savannas and drier upland savannas, perhaps due to different rates of biomass accumulation. Management for Henslow's Sparrows should be based on region‐specific studies, recognizing that appropriate fire regimes may vary among regions.     

Tallgrass prairie pollen assemblages in mid-continental North America

The mid-continent of North America has experienced dramatic and abrupt climate change during the Holocene, but the response of grassland vegetation to past climate change has been difficult to quantify. To improve interpretation of tallgrass prairie vegetation from pollen assemblages, we acquired and analysed a surface sample set collected from 25 small ponds (less than 10 ha surface area) in the largest contiguous remnant of tallgrass prairie in the USA. We compared these tallgrass prairie assemblages to 476 modern pollen samples classified as “prairie” in the North American Surface Sample database. We then compared the surface pollen assemblages with fossil pollen assemblages from sediment cores at two sites in Kansas—Cheyenne Bottoms and Muscotah Marsh—using the modern analog technique. Pollen assemblages in the Flint Hills surface samples were very similar to each other, with an average squared chord distance of 0.19. They were different than other modern grassland pollen assemblages mainly due to higher percentages of pollen from six woody taxa: Carya, Cornus, Juniperus, Juglans, Maclura, and Platanus. Arboreal pollen percentages ranged from 17 to 62 % and did not correlate with woody cover among sites. Cheyenne Bottoms was open grassland for the past 25,000 years, but it did not have many tallgrass prairie analogs. Muscotah Marsh did not have many grassland analogs over the past 30,000 years, possibly due to its position on the prairie-forest border or its surrounding wetland vegetation.     

Effects of Patch-Burn Management on Dickcissel Nest Success in a Tallgrass Prairie

Abstract Grassland birds have declined more than any other North American habitat-associated bird community. Because most species of grassland birds evolved within heterogeneous landscapes created by the interaction of fire and grazing, traditional rangeland management that promotes homogeneity, including annual dormant-season burning combined with early-intensive grazing, might be partly responsible for these declines, especially in some regions of the Great Plains, USA. Recently, an alternative grassland management practice known as patch-burning has been promoted as a means of restoring heterogeneity to grasslands by mimicking the grazing-fire interaction that once occurred on the prairie before European settlement. From 2003 to 2004, we examined effects of patch-burning and traditional management (annual burning followed by early-intensive grazing) on the reproductive success of dickcissels (Spiza americana) in tallgrass prairie in Oklahoma. We monitored 296 dickcissel nests and found that dickcissel nesting phenology differed between traditional and patch-burned pastures. Specifically, dickcissels tended to initiate their nests later in the traditional pasture. Mean number of eggs laid and fledglings produced were similar between the treatments, but nest densities were higher in traditional pastures. Predation was the predominant cause of nest failure and was higher in traditional pastures than in patch-burned pastures. Brown-headed cowbird (Molothrus ater) parasitism was higher in traditional pastures than in patch-burned pastures. Overall, dickcissel nest success was higher in patch-burned pastures than in traditional pastures. The positive response of dickcissel nest success to patch-burn management provides further evidence that this practice can be a useful tool for grassland bird conservation. By creating a mosaic of different stature vegetation, patch-burn management enhances productivity of grassland bird species by providing a refuge area in the unburned patches that affords dickcissels and other nesting grassland birds some protection from the direct (e.g., trampling) and indirect (e.g., cowbird parasitism and predation) effects of grazing, which are not available under traditional management. Patch-burn management should be encouraged as a conservation strategy for grassland birds throughout the Great Plains.     

Habitat use of urban Tree Sparrows in the process of urbanization: Beijing as a case study

The Tree Sparrow (Passer montanus) is a dominant species in urban bird communities. With the development of urbanization, the habitats and sources of food for Tree Sparrows are decreasing. Can the urban Tree Sparrow adapt to changes in the urban environment? To answer this question, we studied the habitat use of Tree Sparrows in eight types of urban areas in Beijing. The results show that the number of both breeding and wintering Tree Sparrows decreased with increasing urbanization. The habitat use of Tree Sparrows, analyzed using stepwise discriminant analysis, was positively correlated with the number of brick bungalows, coniferous and broad-leaved trees and air conditioners. It was negatively correlated with the area of high buildings and hardened roads, pedestrian and automobile flux. This indicates that the Tree Sparrow had not adapted to rapid urbanization even though it is a generally adaptable species. Urban planning should take birds such as the Tree Sparrow into consideration. __________ Translated from Biodiversity Science, 2006, 14(5): 372–381 [译自:生物多样性]