John L. Confer

Prey Selection by Young Yellow Perch: The Influence of Capture Success, Visual Acuity, and Prey Choice

Abstract Field and laboratory studies of prey selection by age-0 yellow perch Perca flavescens from Oneida Lake, New York, were conducted during 1980 and 1981. In paired analyses, laboratory fish proved to be good models of those in the lake; fish in both groups ate zooplankton of the same mean sizes and shifted their preference from Diaptomus minutus to Daphnia pulex when they reached 30–35 mm total length. Increased preference for daphnids over diaptomids coincided with the ability of young yellow perch to catch the daphnids with nearly 100% success. Neither laboratory nor field fish selected the largest daphnids available, though tests showed they were physically capable of ingesting them, and experimental data on capture success, handling time, and reaction distance all suggest young yellow perch should elect the largest daphnids. We hypothesize that young yellow perch may digest large daphnids less efficiently than midsized ones. If this hypothesis is verified, optimum-foraging models should be exten...

Zooplankton Selection by Young Yellow Perch: The Influence of Light, Prey Density, and Predator Size

Abstract A study to examine the influence of light, prey density, and fish size on prey selection by age-0 yellow perch Perca flavescens was conducted at Oneida Lake, 1982–1983. Our approach was to design laboratory experiments resembling events in the lake and to compare experimental results with field observations. Both laboratory and field results demonstrated that young yellow perch ate smaller prey when light intensity increased. Under low light, young yellow perch detected and ate only the larger-bodied daphnids and fed on a broader array of prey species as light intensity increased. Above 230 1x, size selection for zooplankton was independent of prey abundance and depended mostly on fish size. A prey-selection model was developed to predict the median size of prey selected based on light intensity, fish size, percent Daphnia sp. in the environment, and prey density. At light intensities less than 230 1x, the variables of light, fish size, and percent daphnia contributed significantly (R2 = 0.34; P ...

Avian communities on utility rights-of-ways and other managed shrublands in the northeastern United States

We studied bird density and nesting success on utility rights-of-way (ROW) managed primarily by selective herbicide application in New York, Massachusetts and Maine. For comparison, we also estimated bird density in ROW managed by cutting in New Hampshire and New York and in shrublands managed by fire in the Finger Lakes National Forest (FLNF), New York. On herbicide-managed ROW, we detected a mean of 14.3 individuals and 12.2 species per point count, including many species of early-succession habitat that are declining throughout northeastern United States. Nesting success in forested landscapes of New York, Maine, and Massachusetts was 55% on the ROW, 69% in forests within 20 m of the ROW, and 63% in forests more than 20 m from the ROW. Brown-headed cowbirds (Molothrus ater) parasitized 5.3% of the nests and reduced host recruitment by even less. This suggests that ROW in forested areas support high production of shrubland birds and do not exert a measurably harmful effect on forest-nesting birds. Selective herbicide application on ROW sustained shrubland vegetation and supported high densities and high nesting success. Mechanical cutting lowered the structural diversity of vegetation the following spring and was associated with fewer individual birds and species. Cool burns in early spring produced a high structural diversity of herbs, shrubs and trees and supported a high density of birds and bird species. Long-term maintenance of shrublands by burning will require supplemental cutting to remove saplings. As reforestation continues to reduce shrubland habitat, probably below pre-colonial levels, active management for early-succession habitat will be necessary to sustain current population levels of numerous species.

STATUS AND CONSERVATION PRIORITIES OF GOLDEN-WINGED WARBLER (VERMIVORA CHRYSOPTERA) IN NORTH AMERICA

department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville, Tennessee 37996, USA; 2School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan 49931, USA; Evolutionary Biology Program, Cornell Lab of Ornithology, Ithaca, New York 14850, USA; 4 U.S. Fish and Wildlife Service, Region 3, Nongame Migratory Bird Office, Fort Snelling, Minnesota 55111, USA; ^Department of Biology, Ithaca College, Ithaca, New York 14850, USA; department of Biological Sciences, University of Cincinnati, Cincinnati, Ohio 45221, USA; and 7Conservation Science Program, Cornell Lab of Ornithology, Ithaca, New York 14850, USA

EFFECTS OF VEGETATION, INTERSPECIFIC COMPETITION, AND BROOD PARASITISM ON GOLDEN-WINGED WARBLER (VERMIVORA CHRYSOPTERA) NESTING SUCCESS

Abstract The recent decline of Golden-winged Warblers (Vermivora chrysoptera) correlates with the loss of suitable nesting habitat, range expansion by Blue-winged Warblers (V. pinus), and eastward expansion of Brown-headed Cowbirds (Molothrus ater). Multivariate statistics were used to examine effects of those factors on Golden-winged Warbler reproduction in north central New York. Herb and shrub cover were positively correlated with clutch size. Blue-winged Warbler proximity was negatively correlated with Golden-winged Warbler clutch size. Tree cover and perhaps herb cover, after adjusting for brood size, correlated with a reduced number of Golden-winged Warbler fledglings. Herbaceous cover correlated with a greater number of cowbird eggs in Golden-winged Warbler nests. Cowbird parasitism correlated with a reduction in the number of Golden-winged Warbler eggs incubated and proportion of incubated eggs that hatched. However, cowbird parasitism, after adjusting for brood size, did not significantly affect nestling success rate. Cowbirds parasitized 30% of Golden-winged Warbler nests, which reduced the number of Golden-winged Warblers fledged by ∼17%. Average herb and tree cover values were 69 and 22 in Golden-winged Warbler territories and 60 and 23 in Blue-winged Warbler territories, respectively, with herb cover significantly greater for Golden-winged Warblers. Territories in the earliest stages of succession used by Golden-winged Warblers supported larger clutches and a reduction in the strong, negative effect of Blue-winged Warbler proximity and an increase in the negative effect correlated with cowbirds, if cowbirds were locally abundant.

Computer Processing of Zooplankton—Application in Fisheries Studies

Abstract The role zooplankton play in aquatic ecosystems often depends on their abundance and their size. However, enumeration and sizing of zooplankton are tedious tasks. Here, we describe an inexpensive, semiautomated system which allows projection, counting, and sizing with a caliper, data storage and retrieval, and compilation of species-size distributions. Direct application of our computerized system for processing zooplankton to studies of fish and zooplankton is described.

Golden- and Blue-winged Warblers: Distribution, Nesting Success, and Genetic Differences in Two Habitats

Abstract We analyzed phenotypic distribution, nesting success, and genetic purity of Golden-winged Warblers (Vermivora chrysoptera) and Blue-winged Warblers (V. pinus) in two ecologically distinct nesting habitats: early-succession uplands, and swamp forests. The proportion of phenotypically pure Golden-winged Warblers in swamp forests (94%) differed significantly from uplands (53%) as did the proportion of Golden-winged Warbler pairs (93%) in swamp forests compared to uplands (48%). Only 1% of the phenotypically pure Golden-winged Warblers in swamp forests paired with either a hybrid or a Blue-winged Warbler, but 7% of the phenotypically pure Golden-winged Warblers in uplands formed a hybrid pair. The probability of nesting success for Golden-winged Warbler pairs in swamp forests (65%) was significantly higher than in uplands (37%). Mitochondrial DNA analyses indicate that all 10 phenotypically pure Golden-winged Warblers sampled from swamp forests had the ancestral Golden-winged Warbler haplotype, while 10 of 25 Golden-winged Warblers from uplands had the ancestral Blue-winged Warbler haplotype (P  =  0.033). Swamp forests may provide a source habitat for Golden-winged Warblers with a high phenotypic and genotypic purity even in sympatry with Blue-winged Warblers.

A Reassessment of the Status of Golden-winged and Blue-winged Warblers in the Hudson Highlands of Southern New York

Abstract Populations of Golden-winged Warblers (Vermivora chrysoptera) and Blue-winged Warblers (V. pinus) have coexisted in the Hudson Highlands for a century. Previous researchers in our study area suggested this unusual coexistence might be due to a low frequency of hybrids. However, during the 1998–1999 breeding season we found that 10% of the males were hybrids, a value similar to many studies elsewhere. We observed that hybrid males ceased singing and other conspicuous behaviors early in the breeding season. Pair formation and nesting by hybrids appeared to be rare, perhaps because of the reduced vigor of their displays. Most of the fieldwork by previous researchers in this area was conducted after the date when hybrids cease singing, which may account for prior reports of the absence of hybrids.

A New Estimator of, and Factors Influencing, the Sampling Variance of the Linear Index of Food Selection

Abstract Expressions were developed for a new estimator of the sampling variance of the linear index of food selection, Li. This estimator accommodates multiple samples of predators and of their environmental food supply, and can account for variability due to environmental heterogeneity and differences in feeding behavior among predators, if the number of prey counted in a sample is uncorrelated with the proportion of any prey type in that sample. Both laboratory and field studies of young yellow perch Perca flavescens feeding on zooplankton were used to identify factors influencing the estimated variance of Li. The estimated variance decreased with increasing number of fish sampled and increased with increasing observed variance among stomach contents of fish. A heterogeneity index Hri showed significant diet heterogeneity among fish in both laboratory and field experiments. Relationships between the estimated variance of Li and both the number of fish sampled and the total number of prey counted indica...

Field TesTs oF The RosenbeRg-blancheR MeThod FoR conveRTing PoinT counTs To abundance esTiMaTes

Abstract The North American Breeding Bird Survey (BBS) provides a widely used source of information on changes in bird population abundance based on data obtained for >50 years by 3-min point counts (Sauer et al. 2005). Rosenberg and Blancher (2005) provided a method that purports to convert BBS data into estimates of absolute abundance. To test this method, we compiled detection efficiencies using BBS protocol at five stations in southern New York where territories of most breeding birds were known. Following the Rosenberg-Blancher method, we assigned species to distance categories, within which it is assumed that the equivalent of 100% of a species will be detected. Field results show that individual detection efficiencies varied from 3% to 49% among 29 species. These values are similar to results from other field studies. Most males did not sing within a 3-min count during June, and the detection distances assumed by the method are much too high. We recommend that conservation priorities of the Landbird Conservation Plan by Partners in Flight should not be based on population estimates derived by such an erroneous method.