Stephen K. Davis

NEST-SITE SELECTION PATTERNS AND THE INFLUENCE OF VEGETATION ON NEST SURVIVAL OF MIXED-GRASS PRAIRIE PASSERINES

Abstract Identification of habitat features influencing reproduction and survival are essential for the management and long-term viability of grassland bird populations. I quantified vegetation structure at nests and random sites in southern Saskatchewan, Canada, to determine which microhabitat features are important in nest-site selection by Spragues Pipit (Anthus spragueii), Savannah Sparrow (Passerculus sandwichensis), Bairds Sparrow (Ammodramus bairdii), Chestnut-collared Longspur (Calcarius ornatus), and Western Meadowlark (Sturnella neglecta). In addition, I related microhabitat features to nest survival to determine whether predation might influence their choice of nest sites. Grassland passerines exhibited nonrandom nest-placement patterns and built their nests in sites that were characterized by a greater density of dead vegetation within 30 cm of the ground, increased amounts of litter, and reduced coverage of bare ground. In addition, each species nested in taller vegetation than that found at random sites. However, nests were partitioned along a vegetation gradient ranging from relatively short and sparse (e.g., Chestnut-collared Longspur) to relatively tall and dense (e.g., Western Meadowlark). Nest survival varied with time-specific variables (nest age and date) and year, with nest-site vegetation explaining additional variation not accounted for by these effects. However, vegetation effects were highly variable compared to age effects. Diverse predator communities, spatial and temporal variation in selection pressures, and other constraints may account for inconsistent relationships between nest survival and nest-site characteristics for grassland passerines. Patrones de Selección de Sitios de Nidificación y la Influencia de la Vegetación en la Supervivencia de Nidos de Aves Paserinas de Praderas de Pastos Mixtos Resumen. La identificación de las características del ambiente que influencian la reproducción y la supervivencia son esenciales para el manejo y la viabilidad al largo plazo de las poblaciones de las aves de pastizal. Cuantifiqué la estructura de la vegetación alrededor de los nidos y en sitios aleatorios en el sur de Saskatchewan, Canadá, para determinar cuáles rasgos micro-ambientales son importantes en la selección de nidos por parte de Anthus spragueii, Passerculus sandwichensis, Ammodramus bairdii, Calcarius ornatus y Sturnella neglecta. Adicionalmente, relacioné los rasgos micro-ambientales con la supervivencia de los nidos para determinar si la depredación podría influir sobre la elección de los sitios de nidificación. Las aves paserinas de pastizal mostraron patrones no aleatorios de ubicación de los nidos y construyeron sus nidos en sitios que se caracterizaron por una densidad más alta de vegetación muerta en los primeros 30 cm desde el suelo, una mayor cantidad de hojarasca y una baja cobertura de suelo desnudo. Adicionalmente, cada especie nidificó en sitios con vegetación más alta que la de los sitios elegidos al azar. Sin embargo, los nidos se distribuyeron a lo largo de un gradiente de vegetación desde relativamente corta y esparcida (e.g., Calcarius ornatus) a relativamente alta y densa (e.g., Sturnella neglecta). La supervivencia de los nidos varió en relación con variables que dependen del tiempo (edad del nido y fecha) y del año, mientras que la vegetación de los sitios donde se ubicaron los nidos explicó una parte adicional de la variación no explicada por estos factores. Sin embargo, los efectos de la vegetación fueron muy variables comparados de modo general con los efectos de la edad. Las diferencias en las comunidades de depredadores, la variación espacial y temporal en las presiones de selección y otras limitantes podrían explicar las relaciones inconsistentes entre la supervivencia de los nidos y las características de los sitios de nidificación para las aves paserinas de pastizal.

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.

Nesting ecology of mixed-grass prairie songbirds in southern Saskatchewan

Abstract During 1996–2000, I studied the nesting ecology of Spragues Pipits (Anthus spragueii), Clay-colored Sparrows (Spizella pallida), Savannah Sparrows (Passerculus sandwichensis), Bairds Sparrows (Ammodramus bairdii), Chestnut-collared Longspurs (Calcarius ornatus), and Western Meadowlarks (Sturnella neglecta) on 47 native mixed-grass prairie pastures in southern Saskatchewan. Predation was the primary cause of nest failure and occurred at a similar frequency among the six species. Nest success and productivity varied among years and was lowest during 1997, the year of a substantial increase in meadow vole (Microtus pennsylvanicus) populations in southern Saskatchewan. Nest predation was most severe during the nestling stage with daily survival rates typically lower than those of the incubation period. Brown-headed Cowbirds (Molothrus ater) parasitized nests of all six species, with 5–29% of host nests containing cowbird eggs. Savannah Sparrows, Clay-colored Sparrows, and Western Meadowlarks incurred the highest frequency of brood parasitism. Parasitized hosts experienced lower productivity due to a combination of reductions in clutch size, hatching success, and fledging success. Overall, brood parasitism by cowbirds cost these birds between 1.3 and 2.2 young per successful nest. These results support the general contention that nest predation is the primary factor influencing grassland songbird reproductive success.

AN EVALUATION OF CANADA'S PERMANENT COVER PROGRAM: HABITAT FOR GRASSLAND BIRDS?

Abstract In the early 1990s Agriculture Canadas Permanent Cover Program (PCP) converted over 445,000 ha of cropland to perennial vegetative cover. The wildlife benefits of the PCP have not been the subject of previous research. We conducted grassland bird surveys on 629 PCP sites and 564 cropland sites across Alberta, Saskatchewan, and Manitoba between 25 May and 3 July 1998. PCP sites showed higher avian species richness than cropland, and nine of 10 commonly detected grassland bird species occurred at higher frequencies in PCP than cropland. PCP sites were characterized by taller, denser vegetation and less bare ground than cropland sites. Hayed and grazed PCP sites differed significantly in their vegetative structure and avian community composition, but did not differ in species richness or evenness. Mean bird species richness at both cropland and PCP sites was significantly lower in the aspen parkland ecoregion than in the mixed and moist-mixed grassland ecoregions. Logistic regression identified 18 geographic and vegetative variables that significantly influenced the occurrence of individual species, but models for only two species predicted both presence and absence with greater than 50% accuracy. Avian productivity on PCP lands must be determined to appraise definitively the quality of this habitat for grassland birds.

GRASSLAND SONGBIRD ABUNDANCE ALONG ROADS AND TRAILS IN SOUTHERN SASKATCHEWAN

Abstract We conducted roadside and trail-side point count surveys to determine whether grassland bird abundance differs along ditched and non-ditched sampling points in southwestern Saskatchewan. Savannah and Vesper Sparrows were more abundant along roads, while Bairds Sparrows, Chestnut-collared Longspurs, and Spragues Pipits were more abundant along trails. Clay-colored Sparrows, Horned Larks, and Western Meadowlarks were detected equally along roads and trails. The lower abundance of Spragues Pipits along roads may be attributed to the 20–30% reduction of suitable habitat associated with the road right-of-way within a point count of 100-m radius. Larger differences for Bairds Sparrows and Chestnut-collared Longspurs (42 and 56% less abundant along roads, respectively) suggest that these species tend not to establish territories adjacent to roadside ditches. Our results indicate that roadside studies designed to estimate the abundance of grassland songbirds should either include trailside counts or interpret roadside data based on the affinity of a species for roadside habitat.

GRASSLAND BIRDS NESTING IN HAYLANDS OF SOUTHERN SASKATCHEWAN: LANDSCAPE INFLUENCES AND CONSERVATION PRIORITIES

Abstract To determine the benefits to grassland birds of converting cropland to hayland in southern Saskatchewan, Canada, we quantified the relative nest abundance and success of grassland nesting birds in haylands and the influence landscape variables have on these parameters. We found nests of 26 species of grassland nesting birds, primarily waterfowl and vesper sparrow (Pooecetes gramineus). With the exception of the northern pintail (Anas acuta), few nesting attempts were recorded for species of high priority in the Prairie Pothole Bird Conservation Region. Mayfield nest success for all waterfowl (20 and 13% in 1999 and 2000, respectively) was high relative to previously reported nest success estimates in other habitat types—especially spring-seeded cropland—and was near levels thought to be required to sustain populations (15–20%). Vesper sparrow nest success (39 and 33% in 1999 and 2000, respectively) also was high relative to that reported in other studies. Haying destroyed few nests as wet weather delayed operations in 1999 and 2000. More nests may be destroyed by haying in other years as approximately 25% of nests in this study were still active on the long-term average haying date for southern Saskatchewan. Among models we developed to explain waterfowl relative nest abundance, amount of cropland in the surrounding landscape and field area were the most informative. Evidence that a specific set of landscape variables was important to models of waterfowl nest success was equivocal. Landscape variables did not explain variation in vesper sparrow relative nest abundance or nest success. Within our study area, conversion of cropland to hayland appears to provide significant benefits to a variety of grassland species, including some species of high conservation priority (e.g., northern pintail). Grassland species of conservation concern nested less frequently in hayland than in native grassland.

Post-fledging Movements of Sprague's Pipit

Abstract Spragues Pipit (Anthus spragueii) is a threatened grassland songbird that has been described as one of the least known species in North America. We attached radio transmitters to 19 Spragues Pipit nestlings in south-central Saskatchewan in 2004 and 2005 as part of a study to quantify post-fledging movements. Eleven juveniles died before leaving the nest (58%) and five survived for at least 9 days. Predation was the most common cause of mortality of young pipits both before and after fledging. Distances moved between days steadily increased but fledglings typically remained within 100 m of their nest during the first week post-fledging. Movement by fledglings after the first week were typically >100 m.

Voluntary Stewardship and the Canadian Species at Risk Act: Exploring Rancher Willingness to Support Species at Risk in the Canadian Prairies

North American temperate grasslands and the wildlife species they support are increasingly imperilled, largely due to habitat loss and degradation. Most remaining prairie is privately managed and supports livestock production. In Canada, voluntary stewardship is the preferred approach for protecting species at risk on private lands under the federal Species at Risk Act (SARA). However, attitudes of private land managers toward species at risk and their willingness to engage in stewardship are poorly understood. With data from interviews with 42 livestock producers in Saskatchewan, Canada, we describe producer characteristics, attitudes, and awareness of species at risk and evaluate how these factors influence willingness to protect species at risk. Younger producers with increased formal education, awareness, and positive attitudes were more willing to support conservation of species at risk. Voluntary stewardship under the SARA may be enhanced by rewarding producers for sound habitat management and improving trust between producers and government agencies.

Habitat use by Sprague's Pipits (Anthus spragueii) in Native Pastures and Planted, Non-Native Hay Fields

ABSTRACT. The addition of planted grasslands (i.e., fields that have been planted with exotic grass and forb species) to the North American landscape has been beneficial for the conservation of many species, but not necessarily for species that show a preference for native grasslands. Under what conditions these planted fields are attractive to native grassland specialists is unclear. Spragues Pipit (Anthus spragueii) is a native grassland specialist, but it breeds in planted grasslands in some parts of its range. We conducted a comparative study of territory and nest use by Spragues Pipits in native pastures and planted hay fields from 2006 to 2008. In planted hay fields, territories were characterized by vegetation height of 25 cm and litter depth of <1.5 cm; in native pastures, the birds used territories with 15% bare ground and <1.5 cm litter depth. Nests in both habitats were located in areas with vegetation height of 25–30 cm, whereas random areas had either taller or shorter vegetation. Territories were associated with different vegetation characteristics in both habitats. Spragues Pipits used the same nest characteristics in both habitat types, which suggests that they found areas within planted grasslands that closely resembled areas that they might use for nesting in native grasslands. Planted fields with a low amount of alfalfa and suitable vegetation height (20–30 cm) should be attractive to breeding Spragues Pipits.

Reproductive success of songbirds and waterfowl in native mixed-grass pasture and planted grasslands used for pasture and hay

ABSTRACT Conservation of grassland birds in agricultural landscapes requires an understanding of the demographic consequences of nesting in native and planted grasslands. Much of the native grassland in agricultural regions has been converted to cropland. Subsequently, seeding cropland to perennial grasslands has become a common strategy to restore habitat for grassland birds, but these grasslands also may be used as hay and pasture forage for livestock. Our objectives were to determine (1) if the abundance of grassland songbirds and the reproductive success of songbirds and waterfowl varied between native pasture and planted grassland, and (2) if the amount of grassland in the surrounding landscape influenced the abundance and reproductive success of songbirds or the nest survival of waterfowl in native and planted grasslands. Our results suggest that planted grasslands used for pasture and hay in our region are likely ecological sinks for grassland specialist songbirds. Spragues Pipit (Anthus spragueii) nested only in native pasture, and Chestnut-collared Longspur (Calcarius ornatus), Lark Bunting (Calamospiza melanocorys), and Bairds Sparrow (Ammodramus bairdii) were sometimes more abundant in planted pasture or hayfields, but fledged 1.4–4.5 times as many young per nest in native pasture. The reproductive success of waterfowl and grassland songbird generalists was similar in planted grasslands and native pasture. The abundance of all songbirds varied with the amount of grassland or cropland in the surrounding landscape, but landscape composition only weakly influenced the nest survival rates of 1 of 8 songbirds and 4 of 6 waterfowl species. Our results demonstrate that the preservation of native pasture is critical for the conservation of grassland specialists. Other grassland songbirds and waterfowl likely will benefit from the conservation of native and planted grassland and conversion of cropland to perennial grassland used for pasture and hay.