Fritz L. Knopf

ADVANCED TECHNIQUES FOR MODELING AVIAN NEST SURVIVAL

Estimation of avian nest survival has traditionally involved simple measures of apparent nest survival or Mayfield constant-nest-survival models. However, these methods do not allow researchers to build models that rigorously assess the importance of a wide range of biological factors that affect nest survival. Models that incorporate greater detail, such as temporal variation in nest survival and covariates representative of individual nests represent a substantial improvement over traditional estimation methods. In an attempt to improve nest survival estimation procedures, we introduce the nest survival model now available in the program MARK and demonstrate its use on a nesting study of Mountain Plovers (Charadrius montanus Townsend) in Montana, USA. We modeled the daily survival of Mountain Plover nests as a function of the sex of the incubating adult, nest age, year, linear and quadratic time trends, and two weather covariates (maximum daily temperature and daily precipitation) during a six-year stud...

Great Plains Ecosystems: Past, Present, and Future

Abstract Little question exists that the main bodies of North American prairie (i.e., the tall-grass, mixed, and shortgrass) are among the most endangered resources on the continent. The purpose of this paper is to provide a past and present biological baseline by which to understand North American prairies and to provide a platform for future conservation. Events both immediate to the end of the Pleistocene and historic suggest that the present grassland conditions are different from those within which most of the grassland organisms evolved. Our analysis suggests that few grassland landscapes remain adequate in area and distribution to sustain diversity sufficient to include biota and ecological drivers native to the landscape. A robust and history-based scenario to conserve Great Plains grasslands is to 1) identify areas large enough to sustain an ecological system with all its biodiversity, 2) reverse significant losses in area of native grasslands, 3) ensure that restoration matches the grassland previously existing at that site, 4) refocus the profession of range management, and 5) establish a more meaningful agency design for grassland and natural resource management.

A test of geographic assignment using isotope tracers in feathers of known origin

We used feathers of known origin collected from across the breeding range of a migratory shorebird to test the use of isotope tracers for assigning breeding origins. We analyzed δD, δ13C, and δ15N in feathers from 75 mountain plover (Charadrius montanus) chicks sampled in 2001 and from 119 chicks sampled in 2002. We estimated parameters for continuous-response inverse regression models and for discrete-response Bayesian probability models from data for each year independently. We evaluated model predictions with both the training data and by using the alternate year as an independent test dataset. Our results provide weak support for modeling latitude and isotope values as monotonic functions of one another, especially when data are pooled over known sources of variation such as sample year or location. We were unable to make even qualitative statements, such as north versus south, about the likely origin of birds using both δD and δ13C in inverse regression models; results were no better than random assignment. Probability models provided better results and a more natural framework for the problem. Correct assignment rates were highest when considering all three isotopes in the probability framework, but the use of even a single isotope was better than random assignment. The method appears relatively robust to temporal effects and is most sensitive to the isotope discrimination gradients over which samples are taken. We offer that the problem of using isotope tracers to infer geographic origin is best framed as one of assignment, rather than prediction.

Guild structure of a riparian avifauna relative to seasonal cattle grazing

The avifauna within the willow (Salix spp.) community on the Arapaho National Wildlife Refuge (NWR) was dominated (96% of all observations each year) by 11 species of passerine birds during the summers of 1980-81. Using 28 vegetation variables measured or calculated for randomly selected points and points where birds were sighted, we assigned the species to 3 distinct response guilds relative to historical patterns of seasonal grazing. A eurytopic response guild (habitat generalists) included yellow warblers (Dendroica petechia) (YEWA), savannah sparrows (Passerculus sandwichensis) (SASP), and song sparrows (Melospiza melodia) (SOSP). A stenotopic response guild (habitat specialists) included willow flycatchers (Empidonax traillii) (WIFL). Lincolns sparrows (Melospiza lincolnii) (LISP), and white-crowned sparrows (Zonotrichia leucophrys) (WCSP). The intermediate, mesotopic response guild included American robins (Turdus migratorius) (AMRO), red-winged blackbirds (Agelaius phoeniceus) (RWBL), and brown-headed cowbirds (Molothrus ater) (BHCO). Population densities of the eurytopic response guild differed little between healthy (historically winter-grazed) and decadent (historically summer-grazed) willow communities within a year. Densities of species in the mesotopic response guild differed more dramatically, and stenotopic responseguild species were absent or accidental in decadent willows. Information on habitat use patterns of the individual species between years supported the definition of response guilds; vegetation structure was most variable in habitats of eurytopic species and least variable in habitats of stenotopic species. Comparisons between used and available vegetation features indicated that species in the stenotopic response guild used locations that differed from random on the basis of bush spacing. We hypothesize that the response-guild structure primarily reflects the impact of cattle upon the horizontal patterning of the vegetative community. J. WILDL. MANAGE. 52(2):280-290 Grazing by domestic cattle is the most common historical use of native rangelands in the western United States (Busby 1979). Ecologists have described the impacts of grazing upon breeding bird communities by comparing avian populations on adjacent sites that have been subjected to different levels of grazing (Kantrud 1981, Mosconi and Hutto 1982), on the same site before and after exclusion of grazing (Duff 1979), or both (Bock et al. 1984). Those studies generally have described patterns of species presence or abundance relative to grazing impacts upon vegetation. Birds generally respond to changes in vegetation structure as a consequence of grazing rather than to the presence of cattle per se (Bock and Webb 1984). However, avian responses to vegetative changes are neither easily defined nor consistent among sites (Wiens and Dyer 1975). Ryder (1980) reviewed studies of grazing impacts upon avian communities and categorized species as either increasers or decreasers (in abundance) with the introduction of cattle into their habitats. Studies of grazing impacts, however, generally have not elaborated on the nature of avian behavior or population responses, especially relative to all bird species within a community. Previous studies in northern Colorado have shown that seasonal grazing practices over a 75100-year period may alter the horizontal and vertical structure of a shrub-willow community as potential habitats for birds (Knopf and Cannon 1982). Our objectives were to define avian guilds within the shrub-willow community which respond similarly to structural vegetation parameters, statistically test the validity of the response-guild structure with information on species densities and habitat use, and identify vegetation parameters that cattle alter that appear important to sensitive bird species. We thank E. C. Patten for his interest and local support. Field assistance was provided by B. Bergstrom, K. Bergstrom, J. F. Ellis, E. A.

Total Body Electrical Conductivity (TOBEC) to Estimate Total Body Fat of Free-Living Birds

Traditional methods to determine total body fat are undesirable under many circumstances because they require sacrificing individual birds. Walsberg (1988) recently introduced the total body electrical conductivity (TOBEC) method for total body fat to ecological studies. In this paper we expand on Walsbergs (1988) seminal paper and show that: (1) TOBEC is accurate under a narrow array of body masses, and is therefore appropriate for intraspecific studies; (2) dead birds exhibit significantly different TOBEC than live birds; and (3) the use of metal bands does not affect TOBEC measurements. We conclude that TOBEC provides an accurate estimate of total body fat, that it is preferable to traditional methods because it does not require sacrificing the bird, measurements can be taken quickly in the field, and (most importantly to field ornithologists) body fat can now be tracked through time for individual, free-living birds.

Habitat relationships and nest site characteristics of cavity-nesting birds in cottonwood floodplains

We examined habitat relationships and nest site characteristics for 6 species of cavity-nesting birds--American kestrel (Falco sparverius), northern flicker (Colaptes auratus), red-headed woodpecker (Melanerpes erythrocephalus), black-capped chickadee (Parus atricapillus), house wren (Troglodytes aedon), and European starling (Sturnus vulgaris)--in a mature plains cottonwood (Populus sargentii) bottomland along the South Platte River in northeastern Colorado in 1985 and 1986. We examined characteristics of cavities, nest trees, and the habitat surrounding nest trees. Density of large trees (>69 cm dbh), total length of dead limbs >10 cm diameter (TDLL), and cavity density were the most important habitat variables; dead limb length (DLL), dbh, and species were the most important tree variables; and cavity height, cavity entrance diameter, and substrate condition at the cavity (live vs. dead) were the most important cavity variables in segregating cavity nesters along habitat, tree, and cavity dimensions, respectively. Random sites differed most from cavity-nesting bird sites on the basis of dbh, DLL, limb tree density (trees with >1 m dead limbs >10 cm diameter), and cavity density. Habitats of red-headed woodpeckers and American kestrels were the most unique, differing most from random sites. Based on current trends in cottonwood demography, densities of cavity-nesting birds will probably decline gradually along the South Platte River, paralleling a decline in DLL, limb tree density, snag density, and the concurrent lack of cottonwood regeneration. J. WILDL. MANAGE. 54(1):112-124 Cavity-nesting birds are a major component of many avian communities. In cottonwood bottomlands they represent 32-43% of the breeding avifauna (Sedgwick and Knopf 1986). In studies of habitat associations of cavity-nesting birds, overstory basal area, understory vegetation, tree dbh and height, and species composition all have been related to densities of cavity nesters (e.g., Anderson and Shugart 1974, McClelland et al. 1979, Raphael and White 1984). The importance of snags (dead trees) to cavity-nesting birds has been especially well documented (Haapanen 1965, Thomas et al. 1979, Scott et al. 1980, Raphael and White 1984). Both the dead and living portions of live trees provide nest substrates for cavity-nesting birds in some forest associations (Carey 1983, Sedgwick and Knopf 1986). Sedgwick and Knopf (1986) concluded that snag densities were not good predictors of breeding habitats for cavitynesting birds in cottonwood bottomlands. Alternatively, limb tree (trees with 21 m dead limbs >10 cm diameter) density and dead limb length (DLL) in live trees, both of which were correlated with cavity density, were better measures of suitable nesting habitat for cavity nest-

Residency patterns of migrating sandpipers at a midcontinental stopover

Arctic-nesting shorebirds require several refueling stops during their long migrations between breeding grounds and Central and South American wintering areas. The protection of stopover habitats for transcontinental migrants depends on whether birds fly long distances between a few select sites or fly short distances and stop at several wetlands. Although the Great Plains historically provided a vast array of wetlands for use by migrants, wetland loss and conversion have reduced the availability of stopover sites in recent decades. In this study, we examined (1) residency periods, (2) fat dynamics, and (3) migration chronology of two shorebird species, the Semipalmated Sandpiper (Calidris pusilla) and Whiterumped Sandpiper (C. fuscicollis) at Quivira National Wildlife Refuge (NWR), Kansas. Semipalmated Sandpipers had prolonged periods of species residency with overlapping arrivals and departures. Individual residency periods were highly variable and were unrelated to lipid reserves upon arrival. In contrast, White-rumped Sandpipers arrived and departed more synchronously. Birds that arrived in poor condition stayed longer than those with more body fat in 1991, but not in 1992. Wind direction did not influence patterns of departures of either species. We hypothesize that Semipalmated Sandpipers are ecologically eurytopic when migrating across the Great Plains in the spring. Highly variable patterns in arrival, residency, and lipid levels indicate that spring migration of this species is relaxed and opportunistic. White-rumped Sandpipers showed a pattern of reduced flexibility. Flight range estimates suggest that most birds require intermediate stopovers before reaching the breeding grounds. Interior wetlands appear to function as migration stopovers rather than staging areas for shorebirds.

Ecology and Conservation of Great Plains Vertebrates

Section 1. The Great Plains Landscape as Vertebrate Habitats.- 1. Landscape Gradients and Habitat Structure in Native Grasslands of the Central Great Plains.- 2. Wetlands of the Great Plains: Habitat Characteristics and Vertebrate Aggregations.- 3. Water Management and Cottonwood Forest Dynamics Along Prairie Streams.- 4. Comparative Ecology of Native and Introduced Ungulates.- Section 2. Ecology of Vertebrate Assemblages Within Grassland Landscapes.- 5. Historical Changes in the Landscape and Vertebrate Diversity of North Central Nebraska.- 6. Ecology of Fishes Indigenous to the Central and Southwestern Great Plains.- 7. Avian Community Responses to Fire, Grazing, and Drought in the Tallgrass Prairie.- 8. Effects of Fire on Bird Populations in Mixed-Grass Prairie.- 9. Ecology of Small Mammals in Prairie Landscapes.- 10. Stopover Ecology of Transitory Populations: The Case of Migrant Shorebirds.- Section 3. Conclusion.- 11. Conservation of Grassland Vertebrates.

Estimation of lipids and lean mass of migrating sandpipers

Estimation of lean mass and lipid levels in birds involves the derivation of predictive equations that relate morphological measurements and, more recently, total body electrical conductivity (TOBEC) indices to known lean and lipid masses. Using cross-validation techniques, we evaluated the ability of several published and new predictive equations to estimate lean and lipid mass of Semipalmated Sandpipers (Calidris pusilla) and White-rumped Sandpipers (C. fuscicollis). We also tested ideas of Morton et al. (1991), who stated that current statistical approaches to TOBEC methodology misrepresent precision in estimating body fat. Three published interspecific equations using TOBEC indices predicted lean and lipid masses of our sample of birds with average errors of 8-28% and 53-155%, respectively. A new two-species equation relating lean mass and TOBEC indices revealed average errors of 4.6% and 23.2% in predicting lean and lipid mass, respectively. New intraspecific equations that estimate lipid mass directly from body mass, morphological measurements, and TOBEC indices yielded about a 13% error in lipid estimates. Body mass and morphological measurements explained a substantial portion of the variance (about 90%) in fat mass of both species. Addition of TOBEC indices improved the predictive model more for the smaller than for the larger sandpiper. TOBEC indices explained an additional 7.8% and 2.6% of the variance in fat mass and reduced the minimum breadth of prediction intervals by 0.95 g (32%) and 0.39 g (13%) for Semipalmated and White-rumped Sandpipers, respectively. The breadth of prediction intervals for models used to predict fat levels of individual birds must be considered when interpreting the resultant lipid estimates.

ANNUAL SURVIVAL AND POPULATION ESTIMATES OF MOUNTAIN PLOVERS IN SOUTHERN PHILLIPS COUNTY, MONTANA

Information about the demography of declining species is especially relevant to their conservation and future recovery. Knowledge of survival rates and population size can be used to assess long-term viability and population trends, both of which are of interest to conservation biologists. We used capture–recapture techniques to study the demography of Mountain Plovers (Charadrius montanus Townsend) in southern Phillips County, Montana, USA, in 1995–2000. We used the robust design to estimate annual survival (ϕ), conditional capture (p and r) and recapture (c) probabilities, and the annual population size (N) in the presence of temporary emigration. The results support age-specific differences in annual survival that are a function of juvenile body mass and are correlated with the area occupied by prairie dogs. Body mass had a positive effect on juvenile survival; the slope coefficient for the additive effect of body mass on juvenile survival was 0.77 (95% ci = 0.25, 1.28) on a logit scale. A measure of p...