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Grassland birds have the highest rates of population declines and are among the highest priority birds for conservation in North America. Although significant effort has been conducted on the breeding ecology of many grassland birds, there have been limited investigations into wintering ecology. We used systematic mist-netting to conduct a five-year assessment of wintering return rates, patch fidelity, and response to prescribed fire for Grasshopper and Savannah Sparrows on grasslands in the Corkscrew Regional Ecosystem Watershed of southwest Florida. Mean annual apparent return rate was 23.9% for Grasshopper Sparrow and 16.1% for Savannah Sparrow, but the addition of gap-year birds (not captured in one year but captured in the following year) increased those rates to 27.7% for Grasshopper Sparrow and 17.4% for Savannah Sparrow. Patch fidelity (returning to the same net lane from the previous capture) was 73.4% between-season for Grasshopper Sparrow and 17.1% for Savannah Sparrow. Within-season patch fidelity was 69.3% for Grasshopper Sparrow and 38.7% for Savannah Sparrow. The differences between species were significant for both between-season and within-season fidelity rates. Grasshopper Sparrow capture rates were significantly higher in years one and two post- fire, but not in year three post-fire when they were similar to the pre-fire levels. The pattern of post-fire capture rates for Savannah Sparrow was similar, but the return to pre-fire levels occurred in year two post-fire. The top performing model for both Grasshopper and Savannah Sparrows was the model that included both the management unit and whether the unit was burned. The number of unique captures post-fire was significantly more for Grasshopper Sparrow (48.4%) and Savannah Sparrow (91.1%) than pre-fire. Given the continental concern for Grasshopper Sparrow and the continual loss of grassland habitat nationally and regionally, the CREW Grasslands represents important winter habitat and may be representative of the significance of south Florida to wintering grassland birds. [ABSTRACT FROM AUTHOR]

Divorce (mate switching) is widely considered an adaptive strategy that female birds use to improve their reproductive success. However, in few species are the causes and consequences of divorce well understood, and the genetic basis and inheritance of divorce have never been explored. In Savannah sparrows (Passerculus sandwichensis) breeding on Kent Island, New Brunswick, Canada, 47.0% of pairs in which both partners survived to the following breeding season ended in divorce. Secondary females, which received less parental assistance than primary females, tended to divorce when breeding success was low or when paired with small males. Unlike young females or widows, older females improved their fledging success after divorce. Young males (but not older males) suffered lower reproductive success following a divorce. However, neither the lifetime number of divorces nor whether an individual had ever divorced affected the fitness of females or males, which suggests little or no selection for the trait. We found moderate repeatability for divorce in females (although not inmales) but no additive genetic variance or evidence of maternal or paternal effects. Divorce in Savannah sparrows appears to be a nonheritable flexible behavior whose expression and consequences depend on an individual's sex, mating status, size, and age. [ABSTRACT FROM AUTHOR]

The heritability ( h2) of fitness traits is often low. Although this has been attributed to directional selection having eroded genetic variation in direct proportion to the strength of selection, heritability does not necessarily reflect a trait's additive genetic variance and evolutionary potential ('evolvability'). Recent studies suggest that the low h2 of fitness traits in wild populations is caused not by a paucity of additive genetic variance (VA) but by greater environmental or nonadditive genetic variance (VR). We examined the relationship between h2 and variance-standardized selection intensities ( i or βσ), and between evolvability (IA:VA divided by squared phenotypic trait mean) and mean-standardized selection gradients (βμ). Using 24 years of data from an island population of Savannah sparrows, we show that, across diverse traits, h2 declines with the strength of selection, whereas IA and IR (VR divided by squared trait mean) are independent of the strength of selection. Within trait types (morphological, reproductive, life-history), h2, IA, and IR are all independent of the strength of selection. This indicates that certain traits have low heritability because of increased residual variance due to the age at which they are expressed or the multiple factors influencing their expression, rather than their association with fitness. [ABSTRACT FROM AUTHOR]

The article presented a study on the prevalence of spatial scaling and population variation in three grassland sparrows. It states that Henslow's Sparrows (Ammodramus henslowii) are disseminated in central North America. Results show that in Henslow's Sparrows, prevalence was lower and variation in abundance was greater in Grasshopper Sparrows (A. savannarum) and Savannah Sparrows (Passerculus sandwichensis).

Cultural evolution can result in changes in the prevalence not only of different learned song types within bird populations but also of different segments within the song. Between 1980 and 2011, we examined changes within different segments of the single songs of male Savannah sparrows, Passerculus sandwichiensis, in an island population. Introductory notes did not change. The buzz segment showed similar stability; although a rare low-frequency variant appeared and then disappeared, the buzz segments from 1980 and 2011 were essentially identical. The middle segment, made up of discrete notes assembled into several types, was variable. However, the form of the middle segment did not affect fitness and may serve to denote individual identity. The terminal trill decreased steadily in frequency and duration over three decades. Longer trills were associated with lower reproductive success, suggesting that trill duration was under sexual selection. The notes sung between introductory notes were also associated with reproductive success. A high cluster sung in 1980–1982 disappeared altogether by 2011, and was gradually replaced by click trains, which were associated with greater reproductive success. During the final decade of the study, more clicks were added to click trains. Longer click trains, which may require vocal virtuosity and so indicate male quality, were also associated with greater reproductive success. Both trill duration and the number of clicks increased in variance during the three-decade span of the study. We suggest that such increases in variance might be a signature of directional cultural selection. Within the Savannah sparrow''s relatively short and simple learned song, cultural evolution appears to be mediated by different mechanisms for different song segments, perhaps because the segments convey different information. [Copyright &y& Elsevier]

Livestock grazing is a widespread source of habitat modification, and may affect populations of ground-nesting grassland birds by influencing rates of nest failure. Nesting attempts can fail for various reasons, and determining risk of failure from specific causes associated with livestock grazing would enhance development of range management practices in areas managed for threatened grassland bird populations. Domestic livestock may influence nest failure by affecting vegetation structure, numerical or functional responses of predators, or directly by trampling nests. We hypothesized stocking rate may influence nest fate because it affects the amount and distribution of remaining vegetation, and the number of large herbivores to which nests are exposed. In 2007 and 2008, we evaluated nest fates for savannah sparrows and horned larks under 4 stocking rates experimentally applied in 40-ha paddocks in northeastern Oregon, USA. In addition to stocking rate, we evaluated variables such as vegetation structure and predator abundance and activity to help clarify mechanisms responsible for nest failure. We used a discrete competing risks framework to estimate daily probability of nest survival and failure from specific causes. These algorithms, implemented in a stand-alone graphical user interface-driven model, allow incorporation of covariates within an information theoretic approach to model inference. Although stocking rate influenced vegetation structure, the only nest failures related to stocking rate were from trampling. Trampling events were too infrequent to test for treatment effects (only 1 nest of each species), but occurred in the moderate and high stocking treatments. Additional variables were related to variation in nest failure from predation, but we found no support for the hypothesis that these causes of failure were affected by stocking rate. For savannah sparrows, daily probability of nest success (95% CI) = 0.97 (0.96-0.98); predation = 0.018 (0.008-0.028); and trampling = 0.001 (0.000-0.004). For horned larks, daily probability of nest success = 0.96 (0.95-0.98); predation = 0.029 (0.012-0.045); and trampling = 0.003 (0.000-0.007). Our results suggest grasslands managed for livestock may generally be compatible with grassland songbird conservation, at least for the species and stocking rates examined here. The most effective conservation strategies for improving nest success will involve decreasing risk of nest predation. However, we found no evidence that management of stocking rate is an effective method for doing so. © 2012 The Wildlife Society. [ABSTRACT FROM AUTHOR]

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Although population declines of grassland songbirds in North America and Europe are well-documented, the effect of local processes on regional population persistence is unclear. To assess population viability of grassland songbirds at a regional scale (∼150,000ha), we quantified Savannah Sparrow Passerculus sandwichensis and Bobolink Dolichonyx oryzivorus annual productivity, adult apparent survival, habitat selection, and density in the four most (regionally) common grassland treatments. We applied these data to a female-based, stochastic, pre-breeding population model to examine whether current grassland management practices can sustain viable populations of breeding songbirds. Additionally, we evaluated six conservation strategies to determine which would most effectively increase population trends. Given baseline conditions, over 10years, simulations showed a slightly declining or stable Savannah Sparrow population (mean bootstrap λ =0.99; 95% CI=1.00–0.989) and severely declining Bobolink population (mean bootstrap λ =0.75; 95% CI=0.753–0.747). Savannah Sparrow populations were sensitive to increases in all demographic parameters, particularly adult survival. However for Bobolinks, increasing adult apparent survival, juvenile apparent survival, or preference by changing habitat selection cues for late-hayed fields (highest quality) only slightly decreased the rate of decline. For both species, increasing the amount of high-quality habitat (late- and middle-hayed) marginally slowed population declines; increasing the amount of low-quality habitat (early-hayed and grazed) marginally increased population declines. Both species were most sensitive to low productivity and survival on early-hayed fields, despite the fact that this habitat comprised only 18% of the landscape. Management plans for all agricultural regions should increase quality on both low- and high-quality fields by balancing habitat needs, nesting phenology, and species’ response to management. [Copyright &y& Elsevier]

Population growth and decline are particularly sensitive to changes in three key life-history parameters: annual productivity, juvenile survival, and adult survival. However, for many species these parameters remain unknown. For example, although grassland songbirds are imperiled throughout North America, for this guild, only a small number of studies have assessedthese parameters. From 2002 to 2006, in the agricultural landscape of the Champlain Valley of Vermont and New York, USA, we studied Savannah Sparrow (Passerculus sandwichensis) and Bobolink (Dolichonyx oryzivorus) demography on four grassland treatments: (I) early-hayed fields cut before 11 June and again in early- to mid-July; (2) middle-hayed fields cut once between 21 June and 10 July; (3) late-hayed fields cut after I August; and (4) rotationally grazed pastures. We assessed whether these treatments affected adult apparent survival (ϕ) and recruitment (ƒ), how sensitive these parameters were to the presence of nonbreeders and local dispersal, and the populations' ability to persist in these four habitats. On average, birds using late-hayed fields had >25% higher apparent survival than those on the more intensively managed early-hayed, middle-hayed, and grazed fields. Overall male ϕ was 35% higher than female ϕ, and Savannah Sparrow ϕ was 44% higher than Bobolink ϕ. Across all analyses and treatments, apparent survival estimates were 0.58-0.85 for male and 0.48-0.71 for female Savannah Sparrows, and 0.52-0.70 for male and 0.19-0.55 for female Bobolinks. For males of both species, potential nonbreeders decreased the precision, of and lowered appareiit survival estimates by 25%; female estimates showed little variation with the inclusion of nonbreeders. Inclusion of local dispersal observations increased apparent survival estimates and, in many cases, increased precision, though the effect was stronger for Savannah Sparrows than for Bobolinks, and also stronger for males than for females. High Savannah Sparrow apparent survival rates resulted in stable or near stable populations (λ ≈ 1), particularly in late-hayed and grazed fields, while low Bobolink apparent survival rates resulted in strongly declining populations (λ< 1) in all treatments. [ABSTRACT FROM AUTHOR]

Grassland birds are considered to be rapidly declining in North America. Management approaches for grassland birds frequently rely on prescribed burning to maintain habitat in suitable condition. We evaluated the relationships among years since burn, vegetation structure, and overwintering grassland bird abundance in Coastal prairie. Le Conte's Sparrows (Ammodramus leconteii) were most common in areas that had: (1) been burned within the previous 2 years. (2) medium density herbaceous vegetation, and (3) sparse shrub densities. Savannah Sparrows (Passerculus sandwichensis) were associated with areas: (1) burned within 1 year. (1) with sparse herbaceous vegetation, and (3) with sparse shrub densities. Sedge Wrens (Cistothorus platensis) were most common in areas that bad: ( 1) burned greater than 2 years prior and (2) dense herbaceous vegetation. Swamp Sparrows (Melospiza georgiana): (1) were most common in areas of dense shrubs. (2) not related to time since burnings, and (3) demonstrated no relationship to herbaceous vegetation densities. The relationships to fire histories for all four bird species could be explained by the associated vegetation characteristics indicating the need for a mosaic of burn rotations and modest levels of woody vegetation. [ABSTRACT FROM AUTHOR]

Subspecies, or geographic races, are diagnosable populations that, at least during the breeding season, are largely allopatric with other subspecies of the same species. In attempts to give objectivity to the subspecies concept, arbitrary rules have been applied for the recognition of subspecies (e.g., the "75% rule," whereby 75% of the individuals should be identifiable to subspecies; there are several other rules). As a case study, I examined the usefulness of the subspecies concept in describing geographic variation of a polytypic American songbird, the Savannah Sparrow (Passerculus sandwichensis). About 21 subspecies of this species have been recognized in the taxonomic literature, but much of the geographic variation is clinal. I argue that there is little value in subdividing a clinal continuum into different subspecies. Rather, the use of subspecies is best restricted to distinctive, and usually geographically isolated, populations. 1 show that this has been done for only a few of the named subspecies of Savannah Sparrows. [ABSTRACT FROM AUTHOR]

We investigated song structure and the pattern of geographic variation at the syllable and whole song levels in Savannah Sparrow, Passerculus sandwichensis (J.F. Gmelin, 1789). Songs were recorded for 179 males from eight sample populations distributed along a 230 km transect in southwestern Ontario in 2000. Subsequent analysis included measurement and comparison of structural song features and qualitative analysis of syllable and song type similarity among individuals both within and among populations, by reference to a syllable catalogue based on syllable similarity. Song type sharing within samples was not common, while song dissimilarity significantly correlated with distance among samples. Overall south–north trends appeared in two aspects of quantitative and qualitative characteristics, and the geographic differentiation of Savannah Sparrow songs was gradual, increasing with distance. At a higher level of analysis, two song groups, with qualitatively distinct structures (here termed themes), were identified. These themes showed a clinal intergrade, such that one theme was found in all individuals of the four southern samples, while in the four more northerly samples, the second theme's incidence grew progressively from 20% to 80%. However, birds singing the southern theme in populations dominated by the northern theme nevertheless produced songs that show metrical (frequency and duration) characteristics typical of the northern theme songs from their own population. Cluster analysis based on syllable and song type similarity–dissimilarity between populations linked geographically neighboring populations closely, while populations fell into two main clusters: the three most northerly and the five most southerly populations. The same cluster pattern also appeared within each theme type. [ABSTRACT FROM AUTHOR]

This article describes the different species of sparrows. Savannah sparrows show finely streaked crowns and upper parts, while, the vesper sparrows are large, long-tailed birds with prominent white outer-tail feathers. Both species, as well as the ammodramus sparrows, likely feed out in open grassy areas.

Mating with close relatives generally results in reduced reproductive success (inbreeding depression) because it increases the risk that rare deleterious recessive alleles will be expressed in offspring. None the less, incest may occur when animals have incomplete knowledge about relatedness or when the costs of avoiding inbreeding are high. Over a 17-year period, Savannah sparrows, Passerculus sandwichensis, in an island population rarely paired incestuously (9 of 1110 pairs, 15 of 1609 nesting attempts). All but one case of close inbreeding (coefficient of inbreeding, F ≥0.25) involved 1-year-old males breeding for the first time, whereas more than half of the cases involved females that were 3 years old or older. Father–daughter matings were avoided completely. Incest avoidance was apparent in the choice of genetic as well as social mates. Paternity analysis using microsatellites revealed that birds nearly always refrained from choosing close relatives as genetic mates. These results support a model of asymmetrical incest avoidance, which predicts differences in the likelihood of incestuous matings as a function of sex, age and relationship, even when coefficients of inbreeding are identical. The model and results also emphasize the importance of distinguishing types of inbreeding and considering the social and historical context of animals'' mating choices. The model may help to explain such patterns as female-biased natal dispersal in birds. [Copyright &y& Elsevier]

Current management recommendations for grassland birds in North America emphasize providing large patches of grassland habitat within landscapes that have few forest or shrubland areas. These Bird Conservation Areas are being proposed under the assumption that large patches of habitat in treeless landscapes will maintain viable populations of grassland birds. This assumption requires that patch size and landscape features affect density and nesting success of grassland birds, and that these effects are consistent among years and regions and across focal species. However, these assumptions have not yet been validated for grassland birds, and the relative importance of local vegetation structure, patch size, and landscape composition on grassland bird populations is not well known. In addition, factors influencing grassland bird nesting success have been investigated mostly in small-scale and short-duration studies. To develop management guidelines for grassland birds, we tested the spatial and temporal repeatability of the influence of patch size and landscape composition on density and nesting success of 3 grassland passerines, after controlling for local-scale vegetation structure, climate, and—when analyzing nest success—bird density. We conducted our study during 4 years (1998-2001) in 44 study plots that were set up in 3 regions of the northern tallgrass prairie in Minnesota and North Dakota, USA. In these study plots we measured density and nesting success of clay-colored sparrows (Spizella pallida), Savannah sparrows (Passerculus sandwichensis), and bobolinks (Dolichonyx oryzivorus). Statistical models indicated that density was influenced by patch size, landscape, region, and local vegetation structure more so than by local vegetation structure alone. Both magnitude and direction of the response of density to patch size varied among regions, years, and species. In contrast, the direction of landscape effects was consistent among regions, years, and between Savannah sparrows and bobolinks. In each species, this landscape effect was independent of patch size. Nesting success was not clearly influenced by patch size or landscape composition, and none of the factors that influenced avian density also influenced nesting success in any of the 3 species. General statements on ‘optimal habitat’ for grassland birds should therefore be viewed cautiously. Instead, long-term studies in different regions as well as a deeper understanding of the local system are needed to determine which factors are most important for grassland birds in a particular area. [ABSTRACT FROM AUTHOR]

The Ipswich Sparrow (Passerculus sandwichensis princeps) population on Sable Island, Nova Scotia, has been designated as "vulnerable" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Previous surveys of this population during the nesting season have varied in coverage and the rigour of statistical-survey design. In 1998 we surveyed the population using a stratified random-transect design. Estimated total numbers (±SE) were obtained along with confidence intervals calculated using bootstrap methods. The precision of our survey estimates would permit detection of population differences on the order of 20%. Higher densities of birds were observed in areas with heath, grass (fescue), and beach grass and pea vegetation types than in areas with other vegetation types. However, densities within these favoured vegetation types were constant with increasing transect length, which appears to be contrary to patterns expected from using published models of the effects of breeding habitat patch size on bird population density. Topographical constraints characteristic of Sable Island may impose limits on the birds' territorial boundaries and constrain density, independently of patch size. [ABSTRACT FROM AUTHOR]