William E. Jensen

Demographic Sensitivity of Population Change in Northern Bobwhite

Abstract The northern bobwhite (Colinus virginianus) is an economically important gamebird that is currently undergoing widespread population declines. Despite considerable research on the population ecology of bobwhites, there have been few attempts to model population dynamics of bobwhites to determine the contributions of different demographic parameters to variance of the finite rate of population change (λ). We conducted a literature review and compiled 405 estimates of 9 demographic parameters from 49 field studies of bobwhites. To identify demographic parameters that might be important for management, we used life-stage simulation analyses (LSA) to examine sensitivity of λ to simulated variation in 9 demographic parameters for female bobwhites. In a baseline LSA based on uniform distributions bounded by the range of estimates for each demographic parameter, bobwhite populations were predicted to decline (λ = 0.56) and winter survival of adults made the greatest contribution to variance of λ (r2 = 0.453), followed by summer survival of adults (r2 = 0.163), and survival of chicks (r2 = 0.120). Population change was not sensitive to total clutch laid, nest survival, egg hatchability, or 3 parameters associated with the number of nesting attempts (r2 <0.06). Our conclusions were robust to alternative simulation scenarios, and parameter rankings changed only if we adjusted the lower bounds of winter survival upwards. Bobwhite populations were not viable with survival rates reported from most field studies. Survival rates may be depressed below sustainable levels by environmental conditions or possibly by impacts of capture and telemetry methods. Overall, our simulation results indicate that management practices that improve seasonal survival rates will have the greatest potential benefit for recovery of declining populations of bobwhites.

Grassland bird responses to land management in the largest remaining tallgrass prairie.

Extensive habitat loss and changing agricultural practices have caused widespread declines in grassland birds throughout North America. The Flint Hills of Kansas and Oklahoma--the largest remaining tallgrass prairie--is important for grassland bird conservation despite supporting a major cattle industry. In 2004 and 2005, we assessed the community, population, and demographic responses of grassland birds to the predominant management practices (grazing, burning, and haying) of the region, including grasslands restored under the Conservation Reserve Program (CRP). We targeted 3 species at the core of this avian community: the Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum), and Eastern Meadowlark (Sturnella magna). Bird diversity was higher in native prairie hayfields and grazed pastures than CRP fields, which were dominated by Dickcissels. Although Dickcissel density was highest in CRP, their nest success was highest and nest parasitism by Brown-headed Cowbirds (Moluthrus ater) lowest in unburned hayfields (in 2004). Conversely, Grasshopper Sparrow density was highest in grazed pastures, but their nest success was lowest in these pastures and highest in burned hayfields, where cowbird parasitism was also lowest (in 2004). Management did not influence density and nest survival of Eastern Meadowlarks, which were uniformly low across the region. Nest success was extremely low (5-12%) for all 3 species in 2005, perhaps because of a record spring drought. Although the CRP has benefited grassland birds in agricultural landscapes, these areas may have lower habitat value in the context of native prairie. Hayfields may provide beneficial habitat for some grassland birds in the Flint Hills because they are mowed later in the breeding season than elsewhere in the Midwest. Widespread grazing and annual burning have homogenized habitat-and thus grassland-bird responses-across the Flint Hills. Diversification of management practices could increase habitat heterogeneity and enhance the conservation potential of the Flint Hills for grassland birds.

Edge Effects on Nesting Dickcissels (Spiza americana) in Relation to Edge Type of Remnant Tallgrass Prairie in Kansas

Abstract Edge effects on grassland-nesting birds should be less pronounced or absent near cropland edges of grasslands that lack wooded-edge habitat often used by nest predators and brood parasites. We compared nest predation, brood parasitism and densities of dickcissel (Spiza americana) nests in relation to distance from woodland and cropland edges of Kansas tallgrass prairie. Daily nest predation rates did not differ (P > 0.25) among distance intervals (≤50 m, 51–100 m, ≤100 m and >100 m) from either edge type or among 50-m intervals adjacent to each edge type. Brood parasitism rates by the brown-headed cowbird (Molothrus ater) were higher ≤100 m vs. >100 m from woodland edges (P = 0.04), being highest ≤50 m from woodland edges (P = 0.09). Parasitism rates were not related to distance from cropland edges, although parasitism rates ≤50 m from woodland and cropland edges were statistically similar (P = 0.16). Dickcissel nest densities were lower ≤50 m from woodland edges relative to farther distance intervals (P = 0.004), indicating dickcissel avoidance of this edge type. There was no similar pattern of nest density on cropland-edged sites, but nest densities ≤50 m from woodland and cropland edges were statistically similar (P = 0.17). Thus, some woodland edge effects on this grassland bird species were apparent but might vary geographically.

GEOGRAPHIC VARIATION IN BROWN-HEADED COWBIRD (MOLOTHRUS ATER) PARASITISM ON DICKCISSELS (SPIZA AMERICANA) IN GREAT PLAINS TALLGRASS PRAIRIE

Abstract The incidence of brood parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds“) within host species typically reflects the continental pattern in cowbird abundance across North America, where parasitism is heaviest in the Great Plains. However, we found considerable variation in cowbird parasitism on Dickcissel (Spiza americana) nests within a subregion of the Great Plains (the Flint Hills), where the highest levels of cowbird parasitism on grassland bird nests had been previously reported. Local parasitism frequencies on Dickcissel nests varied latitudinally across the Flint Hills, ranging from 0% to 92% of nests parasitized. Interestingly, we found no obvious patterns in habitat or host attributes that were associated with this steep geographic gradient in brood parasitism. Cowbird parasitism on Dickcissel nests was not correlated with the vertical density of local prairie vegetation, mean nest distance to edge, proportion of forest to grassland habitat surrounding study sites (≤5 to 10 km), geographic variation in host abundance, or Dickcissel density or nest initiation dates. Parasitism frequencies and intensities (number of cowbird eggs per parasitized nest) on Dickissel nests were only significantly related to variation in local female cowbird density. Dickcissel clutch size and apparent fledging success were negatively correlated with local cowbird parasitism levels. Geographic patterns in cowbird abundance within and among regions should be considered when establishing conservation areas for grassland birds or other cowbird hosts of concern.

Cowbird (Molothrus spp.) Ecology: A Review of Factors Influencing Distribution and Abundance of Cowbirds across Spatial Scales

Department of Biology, Villanova University, Villanova, Pennsylvania 19085, USA; Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California 93106, USA; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA; Department of Wildlife Ecology, University of Wisconsin, 1630 Linden Drive, Madison, Wisconsin 53706, USA; Division of Biology, Kansas State University, 232 Ackert Hall, Manha an, Kansas 66506, USA; School of Forest Resources, Penn State University, 2C Ferguson Building, University Park, Pennsylvania 16802, USA; and Florida Museum of Natural History, University of Florida, P.O. Box 117800, Gainesville, Florida 32611, USA

Community-Level Patterns of Host Use by the Brown-Headed Cowbird (Molothrus ater), a Generalist Brood Parasite

ABSTRACT. Quantifying community-level host use by generalist brood parasites is important because it provides a measure of the resources that parasites need for reproduction. During the 2002–2007 breeding seasons, we quantified host use by the Brown-headed Cowbird (Molothrus ater) at Konza Prairie Biological Station in northeast Kansas. Overall, 54.4% of nests (n = 2,621) of 22 passerine host species that typically accept parasitic eggs were parasitized, and parasitized nests contained an average of 1.9 ± 1.03 (SD) Brown-headed Cowbird eggs, nestlings, or both. Multiple parasitism was common on the study site in all years: 55.7% of parasitized nests (n = 1,425) received ≥2 Brown-headed Cowbird eggs. The Bells Vireo (Vireo bellii; 70.5%) and the Dickcissel (Spiza americana; 69.6%) were parasitized at a significantly greater rate than the Red-winged Blackbird (Agelaius phoeniceus, 21.9%); collectively, these three species represented 85.8% of potential host nests found in all years. The host preference of Brown-headed Cowbirds did not appear to shift among the three species and instead they exhibited a consistent preference for Dickcissel nests over the course of the breeding season and among years. Both the rate and the intensity of parasitism on Dickcissels were significantly lower during the present study than in one conducted several decades earlier at the same site. Our results indicate that cowbirds in northeast Kansas differentially parasitize hosts, that most cowbird eggs are laid in the nests of a small number of host species, and that the Dickcissel appears to be preferred over other hosts.

Topographic Patterns of Nest Placement and Habitat Quality for Grassland Birds in Tallgrass Prairie

ABSTRACT Much of the tallgrass prairie remaining in North America occurs in hilly regions, such as the Flint Hills of Kansas and Oklahoma. Despite the conservation importance of these areas for grassland birds, little is known about how topographic variation in habitat affects the nesting ecology of these species. We examined topographic patterns of nest distribution, daily nest survival and nest-site selection for three species: Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum) and Eastern Meadowlark (Sturnella magna). Dickcissels shifted from nesting more in lowlands to uplands as the season progressed. Grasshopper Sparrows and Eastern Meadowlarks generally nested in midland habitats, but seasonal differences were still evident in the relative proportions of nests found in lowlands vs. uplands. Topography did not affect nest survival of Dickcissels or Grasshopper Sparrows and had only a marginal effect on nest survival for Eastern Meadowlarks. Nest survival for Dickcissels and Grasshopper Sparrows was highly dependent on nest-site vegetation, however. Dickcissels and Eastern Meadowlarks both experienced greater daily nest survival with increasing vertical vegetation structure at nest sites, whereas daily nest survival for Grasshopper Sparrows increased with increasing cover of litter and grass. Although topography may not affect nest survival directly, it may have indirect effects mediated through nest-site vegetation because of selective nest placement. For example, Dickcissels and Eastern Meadowlarks selected sites with greater vertical vegetation structure than generally available, even in upland sites where vegetation structure was reduced. Conservation planning for grassland birds may thus need to consider how topographic variation affects habitat quality within hilly regions where much of the remaining tallgrass prairie occurs.

ORIENTATION OF GRASSHOPPER SPARROW AND EASTERN MEADOWLARK NESTS IN RELATION TO WIND DIRECTION

Abstract. Orientation of the entrances of bird nests may be especially important in grasslands, where protective cover from solar radiation and wind is minimal. We examined orientation patterns of nest-dome entrances in two grassland bird species, the Grasshopper Sparrow (Ammodramus savannarum) and the Eastern Meadowlark (Sturnella magna). We noted how these patterns changed over the nesting season and how they related to prevailing wind direction. We found that Grasshopper Sparrow (n = 333) and Eastern Meadowlark (n = 272) nests were oriented nonrandomly, toward the northeast (ā = 33.4° and 52.9°, respectively). Prevailing wind in the study region was approximately from the south (ā = 171.1°); therefore, nests of the two species were generally oriented downwind. Nest orientation of the Eastern Meadowlark shifted northward as the nesting season progressed, coinciding with a southeastward shift in prevailing wind direction. Conversely, in one year we observed a seasonal shift toward the east in nest orientation of the Grasshopper Sparrow. Nest orientation in these species may represent a trade-off between various factors, including wind and solar radiation.

Challenge of Infrared Kite Aerial Photography: A Digital Update

Kite aerial photography (KAP) is a means to acquire large-scale, highly detailed imagery for various environmental applications. Previous color-infrared KAP was developed for film-based cameras, but is now effectively obsolete. The authors have built a KAP rig and field tested a digital color-infrared camera, the Tetracam ADC, which produces results that are generally comparable with color-infrared film photography. Field testing was conducted at the Cheyenne Bottoms Preserve of The Nature Conservancy in central Kansas. The resulting images are high-contrast photographs that depict emergent vegetation in bright red-pink colors and show water bodies nearly black, as would be expected in color-infrared imagery. Color-visible digital cameras produce better apparent spatial resolution, whereas the Tetracam ADC camera provides an extended spectral range into the near-infrared. For detailed environmental field investigations involving kite aerial photography, a combination of color-visible and color-infrared cameras is recommended for improved results overall.

Geographic Patterns of Song Similarity in the Dickcissel (Spiza Americana)

Abstract Song sharing among neighboring males is a well-known, frequent outcome of song learning in oscine passerines and some other groups, but only limited investigations of the spatial scale of this phenomenon have been pursued. On the basis of recordings of 1,043 individuals, we investigated song sharing in Dickcissels (Spiza americana) at local and regional scales at sites from northern Kansas to northern Oklahoma. Classification of song elements revealed decreasing song similarity with increasing distances between individual birds at small to intermediate scales, to ~10 km. At the largest spatial scales (10–300 km between sites), there was very little similarity among sites and no obvious tendency for a decrease in similarity with increasing distances among our 30 sites. At our intensively sampled site, analyses of quantitative measurements showed that, at least for our most widely shared song element, frequency and duration were more similar in closer birds. Thus, distance between birds influences both quantitative and qualitative song similarity in Dickcissels. Variability existed among sites in the shape of the song-sharing decay curve, which indicates that other factors besides distance also govern song-sharing patterns. We found high repeatability of individual songs for both second-year (SY) and after-second-year (ASY) males throughout the season, and high conformity to the local song neighborhood in both SY and ASY males from their first recording soon after arrival in May. Returning ASY males sang the same song they had produced the previous breeding season.