Fledgling Bachman’s Sparrows in a longleaf pine ecosystem: survival,movements, and habitat selection

Fledgling ecology remains understudied for many passerine species, yet information about the fledgling life stage is critical for understanding full-annual life cycles and population recruitment. We examined the survival, habitat selection, and movements of fledgling Bachman’s Sparrows (Peucaea aestivalis) in a longleaf pine-wiregrass (Pinus palustris-Aristida stricta) community managed with frequent prescribed fire. We captured and marked 36 fledglings on the day of fledging and used radio-telemetry to relocate them daily until independence during three breeding seasons (2014–2016). We visually confirmed the status of fledglings as live or dead during daily relocations and determined causes of mortality. We measured vegetation characteristics at fledgling locations and compared them to the characteristics of vegetation at the locations of adult males. We used a Known Fates analysis in Program MARK to estimate fledgling survival, and generalized linear mixed effect models to determine habitat selection. Estimated fledgling survival until independence was 0.31 (SE = 0.08), with most mortality during the first 4 d post-fledging. Fledglings with longer wing chords had higher rates of survival than those with shorter wing chords, possibly due to an increased ability to evade predators. Fledgling movements were restricted primarily to natal territories. Fledgling Bachman’s Sparrows were located in areas with greater woody plant, forb, and grass cover and less bare ground than available in natal territories. Similar to fledglings of other songbirds, understory woody and herbaceous plants appear to provide critical cover for fledgling Bachman’s Sparrows, and maintenance of such cover should receive consideration in management plans for longleaf pine communities.     

Behavior of adult and young grassland songbirds at fledging

The behavior of adults and young at the time of fledging is one of the least understood aspects of the breeding ecology of birds. Current hypotheses propose that fledging occurs either as a result of parent‐offspring conflict or nestling choice. We used video recordings to monitor the behavior of nestling and adult grassland songbirds at the time of fledging. We observed 525 nestlings from 166 nests of 15 bird species nesting in grasslands of Alberta, Canada, and Wisconsin, USA. Overall, 78% of nestlings used terrestrial locomotion for fledging and 22% used wing‐assisted locomotion. Species varied in propensity for using wing‐assisted locomotion when fledging, with nestling Grasshopper Sparrows (Ammodramus savannarum) and Henslow's Sparrows (Centronyx henslowii) often doing so (47% of fledgings) and nestling Song Sparrows (Melospiza melodia), Common Yellowthroats (Geothlypis trichas), and Chestnut‐collared Longspurs (Calcarius ornatus) rarely doing so (3.5% of fledgings). For 390 fledging events at 127 nests, camera placement allowed adults near nests to be observed. Of these, most young fledged (81.5%) when no adult was present at nests. Of 72 fledging events that occurred when an adult was either at or approaching a nest, 49 (68.1%) involved feeding. Of those 49 fledgings, 30 (62.1%) occurred when one or more nestlings jumped or ran from nests to be fed as an adult approached nests. The low probability of nestlings fledging while an adult was at nests, and the tendency of young to jump or run from nests when adults did approach nests with food minimize opportunities for parents to withhold food to motivate nestlings to fledge. These results suggest that the nestling choice hypothesis best explains fledging by nestlings of ground‐nesting grassland songbirds, and fledging results in families shifting from being place‐based to being mobile and spatially dispersed.     

Density and habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas

ABSTRACT Although the habitat requirements of breeding populations of Henslow's Sparrow (Ammodramus henslowii) have been examined, less is known about their habitat requirements and ecology during the nonbreeding season. We estimated population densities and quantified habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas. Densities of Henslow's Sparrows in the saline soil barrens were similar to those in the Longleaf Pine (Pinus palustris) Ecosystem of the southeastern United States, considered by many to be their primary wintering habitat. Henslow's Sparrows were closely associated with open areas with greater cover of Aristida spp. and globe beaksedge (Rhynchospora globularis), greater stem density at 11–20 cm above ground, more lichens, more herbaceous cover, more bare ground, greater occurrence of little bluestem (Schizacyrium scoparium) as the tallest vegetation, less moss, and less shrub cover than randomly selected sites. In contrast to the results of studies conducted in the Longleaf Pine Ecosystem, the presence of Henslow's Sparrows in our study was not correlated with the height of the tallest vegetation. Our results indicate that saline soil barrens of southern Arkansas support a high density of wintering Henslow's Sparrows and do so for longer postdisturbance periods than longleaf pine savanna. We also found that stem density near the ground was similar to that reported from longleaf pine savanna, but only about half that observed on their breeding grounds. Areas used by Henslow's Sparrows had more lichen and less moss cover, suggesting that those areas were drier than random sites within the barrens. Further research is needed to determine if large populations of Henslow's Sparrows winter in other saline soil barrens and if fire influences habitat associations and densities in the barrens.     

Seasonal variation in foraging conditions for Ring Ouzels Turdus torquatus in upland habitats and their effects on juvenile habitat selection

Recent studies indicate that variation in juvenile survival may be particularly important in driving avian population dynamics. The quality of habitats available to inexperienced juveniles of migrant species is critical to their survival because they must obtain enough food to build up fat reserves for migration, while avoiding predation. We radiotracked 110 juvenile Ring Ouzels Turdus torquatus, a species of high conservation concern in the UK, to quantify for the first time seasonal patterns in foraging habitat and food abundance during this potentially key life‐history period. Key attributes of foraging plots were compared with those on control plots (representing the broad habitat types selected by foraging juveniles) during 2007–08. Birds foraged on invertebrates in grass‐rich plots during June to mid‐July and then shifted to foraging mainly on moorland berries in higher‐altitude, heather‐rich plots during mid‐July to early‐September. Juveniles selected invertebrate foraging plots with low soil acidity, and increasingly selected plots with high earthworm (an important food) biomass and grass cover, but low grass and all vegetation height as the season progressed. In contrast, earthworm biomass and grass cover remained constant, and grass and all vegetation height increased, on control plots. Juveniles selected berry foraging plots with higher abundance of ripe Bilberries Vaccinium myrtillus and Crowberries Empetrum nigrum than found on control plots. Juvenile Ring Ouzels thus appear to require access to short, grass‐ and invertebrate‐rich habitat during early summer, and taller, heather‐dominated and berry‐rich areas in late summer. The use of two distinct habitat types during the pre‐migratory period illustrates the need for a detailed understanding of the requirements of juvenile birds.     

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.     

Conspecific attraction in a grassland bird, the Baird's Sparrow

ABSTRACT.   Territorial songbirds generally use song to defend territories and attract mates, but conspecific song may also serve as a cue to attract other male songbirds to a breeding site. Although known to occur in some colonial and forest-associated species, only recently have investigators examined conspecific attraction in grassland species. We used a playback experiment to examine the possible role of conspecific attraction for males searching for potentially suitable breeding habitat in a grassland specialist, the Baird's Sparrow ( Ammodramus bairdii ). Experimental playback plots and control plots with similar landscape and vegetation characteristics were established at two sites in North Dakota. Baird's Sparrows colonized three of six experimental plots and none of six control plots. Males on experimental plots established territories adjacent to the playback stations and were sometimes observed counter-singing with the playback of conspecific songs. Vegetation characteristics were similar on all study plots, and did not explain differences in bird density on our treatment plots. Although we found that playback of conspecific songs attracted male Baird's Sparrows to previously unoccupied, potentially suitable habitat, further experiments are needed to examine the importance of conspecific attraction relative to other cues that birds may use, such as vegetation features. The conservation and management implications of conspecific attraction are not completely understood, but the presence of conspecifics should be considered as a potential cue in habitat selection by all species of birds.     

Nest‐site selection and productivity of Vesper Sparrows breeding in grazed habitats

ABSTRACT Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia may have a negative impact on ground‐nesting birds, but evidence of such an impact is lacking. We examined nest‐site selection and productivity of ground‐nesting Vesper Sparrows (Pooecetes gramineus) across sites with different grazing histories. From 2006 to 2008, we monitored Vesper Sparrow nests and measured vegetation characteristics known to be affected by grazing within nest patches. We used an information‐theoretic approach to test the relative importance of grazing‐affected vegetation variables as predictors of nest‐site selection, nest survival, and nestling condition. Vesper Sparrows selected nest sites with greater cover of late‐seral grass species that decrease in occurrence in response to grazing (i.e., “decreasers”) than was available in random patches in the same territories. Daily nest survival was also lower for nests surrounded by shorter vegetation (odds ratio = 1.12). However, “decreaser” cover was not associated with either of the two indices of productivity measured (daily nest survival probability and nestling condition). In addition, vegetation height, although an important driver of success, was not linked with nest‐site selection, and no vegetation‐cover variable was positively associated with productivity, despite nest concealment being central to our predictions. This suggests that predation risk for nests in areas with shorter vegetation was being elevated through some factor unrelated to concealment. Our results show that grazing reduced both the availability of suitable habitat for and nesting success of Vesper Sparrows, indicating that grazing could pose a threat to population persistence at a broader scale and could potentially contribute to observed declines. Additional research is needed to determine if grazing guidelines in the Intermountain region of British Columbia should be amended, better enforced, or both to prevent regional declines in populations of ground‐nesting grassland birds.     

Abundance,territory sizes,and pairing success of male Henslow's Sparrows in restored warm‐ and cool‐season grasslands

Henslow's Sparrows (Ammodramus henslowii) are known to breed in restored grasslands consisting of either warm‐ or cool‐season grasses, but additional information is needed concerning their breeding biology in these two types of grasslands. We compared the abundance, territory sizes, and pairing success of male Henslow's Sparrows in grasslands in west‐central Missouri in 2010 and 2011 using a paired‐treatment design, where warm‐ and cool‐season grasslands were located in close proximity. Selection indices indicated no apparent preference by male Henslow's Sparrows for either type of grassland, and the territory sizes and pairing success of males in cool‐ and warm‐season grasslands did not differ. In addition, we found no significant differences in habitat structure between these grassland types. Thus, our results suggest that the warm‐ and cool‐season grasslands in our study provided suitable habitat for Henslow's Sparrows. Other investigators have drawn similar conclusions for Henslow's Sparrows and for grassland birds in general, with the structural characteristics and, for some species, the size of grasslands being more important for grassland birds than plant species composition.     

Habitat use by Mountain Plovers in prairie dog colonies in northeastern New Mexico

ABSTRACT Mountain Plovers (Charadrius montanus) are grassland birds that often breed in close association with colonies of black‐tailed prairie dogs (Cynomys ludovicianus). However, not all colonies provide plover nesting habitat or habitat of equal quality, and the characteristics of colonies important for plovers remain poorly understood. Over two years, I used plover distribution surveys, territory mapping, and habitat sampling to study habitat use by plovers in prairie dog colonies in shortgrass prairie in northeastern New Mexico. My objective was to document important components of plover breeding habitat in colonies by comparing characteristics of used and unused habitats at three spatial scales: colony, territory, and nest‐site. I found evidence of plover breeding in 14 of 44 colonies in 2009 and 13 of 43 colonies in 2010. Based on logistic regression, the probability of a colony being occupied by plovers was positively associated with colony size, but negatively associated with mean vegetation height. Preference for larger colonies could relate to minimum habitat requirements, or a potential tendency of this species to nest in social clusters. Shorter vegetation height was strongly correlated with greater bare ground and lower forb/subshrub cover, all characteristics that may be related to plover predator avoidance and foraging microhabitat. At both the territory and nest‐site scale, areas used by plovers had shorter vegetation, more bare ground, and less forb/subshrub cover than unused areas. Nest sites were also more sloped, perhaps to reduce risk of flooding, and located further away from the nearest prairie dog burrow, perhaps to reduce risk of disturbance. Overall, my results show that plover use of prairie dog colonies was influenced by landscape and habitat features of colonies, and suggest that large colonies are particularly valuable because they are most likely to contain adequate areas with preferred habitat characteristics.     

Responses of breeding birds in tallgrass prairie to fire and cattle grazing

ABSTRACT.   No other group of North American birds has declined as precipitously and over so large an area as has the grassland assemblage. In the Flint Hills of Kansas, the largest extant region of tallgrass prairie, annual spring burning of rangeland has largely replaced traditional regimes and natural patterns with longer intervals between burns. I examined effects of burning and low-intensity cattle grazing on abundances of seven bird species at Konza Prairie Research Natural Area in June 2002 and 2003. Every species was affected by fire, with Upland Sandpipers ( Bartramia longicauda ) more abundant, and six species—Grasshopper Sparrow ( Ammodramus savannarum ), Henslow's Sparrow ( A. henslowii ), Dickcissel ( Spiza americana ), Eastern Meadowlark ( Sturnella magna ), Brown-headed Cowbird ( Molothrus ater ), and Bell's Vireo ( Vireo bellii )—either less abundant or absent at sites in the breeding season following a fire. These results demonstrate that annual burning limits the potential of much of the Flint Hills prairie to harbor high breeding densities of many grassland birds. On the other hand, I found a trade-off between immediate and longer-term effects of burning for several grass-dependent species. Grasshopper Sparrows, Henslow's Sparrows, and Eastern Meadowlarks, although more numerous in areas that were not burned the preceding spring, were less abundant at sites burned every 4 yrs than those burned at shorter intervals. In contrast, shrub-dependent Bell's Vireos were more abundant at sites burned every 4 yrs. Upland Sandpipers, Grasshopper Sparrows, and Eastern Meadowlarks were more abundant in grazed areas. Use of alternatives to annual burning could increase habitat heterogeneity by transforming the Flint Hills into a mosaic of regularly, but asynchronously, burned pastures that would better meet the diverse habitat needs of the region's grassland birds.     

Structure and composition of grassland habitats used by wintering Smith's Longspurs: the importance of native grasses

ABSTRACT Smith's Longspurs (Calcarius pictus) are a species of concern in North America because of their limited range and apparent low population size. To better understand winter habitat needs and guide management of this species, we examined habitat associations of Smith's Longspurs in eastern Arkansas by comparing grassland patches where Smith's Longspurs flushed to randomly located patches in the same area. Smith's Longspurs were found in sparse grassland patches of relatively low height adjacent to airport runways where the native grass prairie three‐awn (Aristida oligantha) dominated ground cover and vertical structure. Smith's Longspurs were not found in vegetation plots dominated by non‐native Bermuda grass (Cynodon dactylon). Prairie three‐awn grass may provide concealment from predators and their seeds may be an important food source. Occurrence of Smith's Longspurs was also correlated with less litter, perhaps because deeper litter could make walking and searching for seeds more difficult. Availability of suitable habitat for Smith's Longspurs along airport runways may be declining due to natural succession of grassland habitat in the absence of disturbance and recent changes in management that favor Bermuda grass. Conversion and degradation of native prairie has resulted in the decline in abundance and distribution of Chestnut‐collared Longspurs (C. ornatus) and McCown's Longspurs (Rhynchophanes mccownii). Our findings suggest that conversion of native grasslands to non‐native grasslands results in loss and degradation of habitat for wintering populations of Smith's Longspurs.     

Habitat Use and Survival of Preflight Wild Turkey Broods

Abstract: Wild turkey (Meleagris gallopavo) broods spend the first several days of life on the ground until poult flight capabilities are attained. This is a critical period of wild turkey life history, with poult survival ranging from 12% to 52%. We measured vegetation in plots used by Rio Grande wild turkey (M. g. intermedia) preflight broods at 4 sites in southwest Kansas and the Texas Panhandle, USA, to determine microhabitat selection for ground roosting and to determine if microhabitat was related to poult survival. Hens selected ground-roost locations with more visual obstruction from multiple observation heights than random sites. Plots surrounding ground roosts had 1) greater visual obstruction; 2) increased tree decay; 3) higher percent grass, shrub, litter, and forb cover; and 4) lower percent bare ground cover than random sites. Grass, shrubs, and downed trees appeared to provide desired cover for ground-roosting broods. Poult survival increased with age of poult, size of brood, and density of shrubs 1–2 m tall. Plots used by broods <10 days old with above average survival contained more visual obstruction and shrubs than plots used by broods 10–16 days old with above average survival, signifying a shift in habitat use by successful broods as poults attain flight abilities. Density of shrubs 1–2 m tall in brood-use areas appears to be important for poult survival to 16 days of age on southern Great Plains rangeland habitats. Ground-level vegetative cover appears to be a significant factor in preflight poult survival. Provisions of ground-level vegetative cover should be considered during wild turkey brooding periods where increased poult survival is desired.     

From Wiens to Robel: A Review of Grassland-Bird Habitat Selection

ABSTRACT Efforts to stabilize or increase grassland bird populations require identification of suitable habitat as a first step. Although the number of studies examining grassland-bird habitat selection has increased substantially in recent years, much uncertainty exists regarding local-scale habitat variables that researchers should consider. We reviewed 57 studies and identified important vegetation features correlated with grassland bird abundance, density, occurrence, and nest and territory selection. Our objectives were to 1) guide future studies of grassland-bird habitat use by providing a reduced set of relevant vegetation characteristics, 2) challenge researchers to critically think about what variables to consider, and 3) highlight the need to include consistent definitions of terms used to describe grassland bird habitat. We identified 9 variables that were important predictors of habitat use by grassland birds: coverage of bare ground (important in 50% of the instances where it was included), grass (34% of instances), dead vegetation (33% of instances), forbs (31% of instances), and litter (29% of instances), along with an index of vegetation density (39% of instances) and volume (39% of instances), litter depth (36% of instances), and vegetation height (41% of instances). Only 25% of studies provided information on effects sizes and measures of variance. Furthermore, definitions of measured habitat variables were not consistent among studies. We provide definitions of the 9 important variables and implore authors to report effect size and measures of variance. Standardization of terms and reporting of meaningful results will facilitate replication of wildlife research and enhance our ability to recognize general patterns that emerge from observational studies of habitat use.     

Effects of Native and Non-Native Grassland Plant Communities on Breeding Passerine Birds: Implications for Restoration of Northwest Bunchgrass Prairie

One common problem encountered when restoring grasslands is the prominence of non-native plant species. It is unclear what effect non-native plants have on habitat quality of grassland passerines, which are among the most imperiled groups of birds. In 2004 and 2005, we compared patterns of avian reproduction and the mechanisms that might influence those patterns across a gradient of 13 grasslands in the Zumwalt Prairie in northeastern Oregon that vary in the degree of non-native plant cover (0.9–53.4%). We monitored the fate of 201 nests of all the breeding species in these pastures and found no association of percent non-native cover with nest densities, clutch size, productivity, nest survival, and nestling size. Regardless of the degree of non-native cover, birds primarily fed on Coleoptera, Orthoptera, and Araneae. But as percent non-native cover in the pastures increased, Orthoptera made up a greater proportion of diet and Coleoptera made up a smaller proportion. These diet switches were not the result of changes in terrestrial invertebrate abundance but may be related to decreases in percent bare ground associated with increasing cover of non-native vegetation. Measures of nest crypticity were not associated with cover of non-native vegetation, suggesting that predation risk may not increase with increased cover of non-native vegetation. Thus, the study results show that increased non-native cover is not associated with reduced food supplies or increased predation risk for nesting birds, supporting the growing body of evidence that grasslands with a mix of native and non-native vegetation can provide suitable habitat for native grassland breeding birds.     

A quantitative analysis of habitat preferences of Woodcock Scolopax rusticola in the breeding season

In Britain, prior to breeding, Woodcock Scolopax rusticola switch from feeding on pastures by night to feeding in woodland by day. Their major food is earthworms (Lumbricidae). In April and May 1985, vegetation structure and composition and soil parameters including earthworm numbers (30 habitat variables) were recorded for quadrats containing 50 feeding locations of six radio-tagged birds, seven nests and 50 random locations in Whitwell Wood, northeast Derbyshire.
Significantly different mean values between feeding and random sites were found for 11 habitat variables. Feeding sites were in younger stands, with a higher percentage ground cover of dog's mercury Mercurialisperennis and consistently high values for pH. Earthworm biomass was on average 82% greater than in random plots. Areas of beech Fagus sylvaticus were avoided. A discriminant function based on six habitat variables correctly classified 85-5% of the feeding and random sites; 70% of the feeding locations were correctly classified by a jack-knife procedure. The important factors determining where feeding occurs are probably safety from avian predators and high availability of earthworms.
Discriminant analysis of the habitats used for feeding by solitary birds, broods and for nesting produced significant functions which correctly classified 84% of sites. Nests were in areas with a high percentage cover of brambles Rubus spp. and more open ground vegetation. Broods and solitary birds used similar areas characterized by denser ground vegetation than nest sites.
The results of this study indicate that both habitat structure and food availability influence the distribution of Woodcock in the breeding season.     

No effect of habitat fragmentation on post-fledging, first-year and adult survival in the middle spotted woodpecker

Despite its relevance for the dynamics of populations, the ecological mechanisms underlying juvenile and adult survival are poorly known in most bird species. This study focuses on the effect of habitat fragmentation on early post-fledging, first-year and adult survival of the middle spotted woodpecker Dendrocopus medius by combining data of radio-tagged and ringed birds. Among juveniles, most deaths occurred during the first three weeks after fledging (survival rate: 0.359±0.077) and were mainly caused by predation. After independence, birds faced another critical period during their first autumn-winter that lowered first-year survival further (0.255±0.044), whereas adult mortality was considerably lower (annual survival rate: 0.786±0.074). We did not find any significant effect of habitat fragmentation (measured as patch size and connectivity) on juvenile or adult survival. Sex ratio at fledging did not differ significantly from parity (proportion of females: 0.513) and was not correlated to patch size. Regardless of age, survival did not differ between the sexes, suggesting that a female-biased mortality was not the mechanism behind the presence of unpaired territorial males in this population. Lighter nestlings underwent significantly higher post-fledging mortality, indicating that conditions in the nest may substantially affect survival later in life.     

How spatial heterogeneity of cover affects patterns of shrub encroachment into mesic grasslands

We used a multi-method approach to analyze the spatial patterns of shrubs and cover types (plant species, litter or bare soil) in grassland-shrubland ecotones. This approach allows us to assess how fine-scale spatial heterogeneity of cover types affects the patterns of Cytisus balansae shrub encroachment into mesic mountain grasslands (Catalan Pyrenees, Spain). Spatial patterns and the spatial associations between juvenile shrubs and different cover types were assessed in mesic grasslands dominated by species with different palatabilities (palatable grass Festuca nigrescens and unpalatable grass Festuca eskia). A new index, called RISES ("Relative Index of Shrub Encroachment Susceptibility"), was proposed to calculate the chances of shrub encroachment into a given grassland, combining the magnitude of the spatial associations and the surface area for each cover type. Overall, juveniles showed positive associations with palatable F. nigrescens and negative associations with unpalatable F. eskia, although these associations shifted with shrub development stage. In F. eskia grasslands, bare soil showed a low scale of pattern and positive associations with juveniles. Although the highest RISES values were found in F. nigrescens plots, the number of juvenile Cytisus was similar in both types of grasslands. However, F. nigrescens grasslands showed the greatest number of juveniles in early development stage (i.e. height<10 cm) whereas F. eskia grasslands showed the greatest number of juveniles in late development stages (i.e. height>30 cm). We concluded that in F. eskia grasslands, where establishment may be constrained by the dominant cover type, the low scale of pattern on bare soil may result in higher chances of shrub establishment and survival. In contrast, although grasslands dominated by the palatable F. nigrescens may be more susceptible to shrub establishment; current grazing rates may reduce juvenile survival.     

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.     

Patches of bare ground as a staple commodity for declining ground-foraging insectivorous farmland birds

Conceived to combat widescale biodiversity erosion in farmland, agri-environment schemes have largely failed to deliver their promises despite massive financial support. While several common species have shown to react positively to existing measures, rare species have continued to decline in most European countries. Of particular concern is the status of insectivorous farmland birds that forage on the ground. We modelled the foraging habitat preferences of four declining insectivorous bird species (hoopoe, wryneck, woodlark, common redstart) inhabiting fruit tree plantations, orchards and vineyards. All species preferred foraging in habitat mosaics consisting of patches of grass and bare ground, with an optimal, species-specific bare ground coverage of 30-70% at the foraging patch scale. In the study areas, birds thrived in intensively cultivated farmland where such ground vegetation mosaics existed. Not promoted by conventional agri-environment schemes until now, patches of bare ground should be implemented throughout grassland in order to prevent further decline of insectivorous farmland birds.     

Avian taxonomic and functional diversity in early stage of longleaf pine (Pinus palustris) stands restored at agricultural lands: variations in scale dependency

In agricultural landscapes, the longleaf pine initiative (LLPI) and the Bobwhite Quail Initiative (BQI) aim to restore longleaf pine forests and early successional habitats, respectively. The early stage of longleaf pine stands and grass and forb vegetation produced by a combination of both restoration programs (LLPI‐BQI) may form habitat conditions favorable to early successional bird species and other birds, increasing avian diversity. We investigated how the LLPI and BQI programs affected taxonomic and functional diversity of birds and abundance of early successional birds (grassland and scrub/shrub species), and what environmental characteristics were associated with the diversity and abundance of birds. Our study was performed at 41 fields in Georgia, United States, during 2001–2002 by considering environmental characteristics at two spatial scales: local‐scale vegetation features and restoration program type (LLPI or LLPI‐BQI) and landscape‐scale vegetation features and landscape heterogeneity. Functional evenness, species richness, and abundance of grassland and scrub/shrub species did not show a clear association with local‐ or landscape‐scale variables. Shannon‐Wiener diversity was slightly influenced by restoration program type (local‐scale variable) with higher value at LLPI‐BQI stands than at LLPI stands despite no significant differences in local vegetation features between those stands. Functional divergence was strongly positively associated with landscape‐scale variables. That is, niche differentiation increased with increasing shrub coverage within a landscape, reducing competition between abundant bird species and others. Our results suggest that although a combination of BQI and LLPI program may have a positive effect on avian taxonomic diversity, it is important to consider shrub vegetation cover within a landscape to improve functional diversity.