Treesearch

A modified vehicle-mounted, X-band marine radar system was used to study the movements of marbled murrelets (Brachyramphus marmoratus) at inland and coastal sites in northern California during July. The ability of the radar to discriminate murrelets from other targets, and to estimate abundance was assessed. Murrelets were detected by radar at distances up to 1.3 km. Radar recorded the distance, ground speed, flight direction, and flight behavior (such as circling). The average ground speed of murrelets was 77 km/hr (range = 56-105 km/hr). Ground-based observers recorded an average of 67%...

We have genetically mapped a gene for resistance to white pine blister rust (Cronartium ribicola Fisch.) in sugar pine (Pinus lambertiana Dougl.) by using an approach which relies on three factors: (i) the ability to assay for genetic markers in the haploid stage of the host's life cycle, using megagametophyte seed tissue; (ii) a simple and clearly defined pathosystem; and (iii) the use of random amplified polymorphic DNA (RAPD) markers that can be quickly and efficiently evaluated. Resistance to white pine blister rust in sugar pine is known to be controlled by a single dominant gene (R)....

The effectiveness of fixed-radius point counts in quantifying abundance and richness of bird species in oak-hickory, pine-hardwoods, mixed-mesophytic, beech-maple, and riparian cottonwood forests was evaluated in Arkansas, Ohio, Kentucky, and Idaho. Effects of count duration and numbers of stations and visits per stand were evaluated in May to July 1991 by conducting approximately 1000 50-m (or 40-m) fixed-radius point counts. Most (>60 percent) species and individuals were detected in the first 4 minutes of the 8-minute counts, although accumulation did not cease even after extended...

Maps generated from bird survey data are used for a variety of scientific purposes, but little is known about their bias and precision. We review methods for preparing maps from point count data and appropriate sampling methods for maps based on point counts. Maps based on point counts can be affected by bias associated with incomplete counts, primarily due to changes in proportion counted as a function of observer or habitat differences. Large-scale surveys also generally suffer from regional and temporal variation in sampling intensity. A simulated surface is used to demonstrate sampling...

As part of a comparative study of agricultural impacts on wildlife, modifications to the point count method were evaluated for surveying birds in, and adjacent to, cropland during the breeding season (May to early July) in Ontario. Location in the field, observation direction and distance, number of visits, and number of study sites per farm were examined using point counts of 5-minute duration in 1989 and 10-minute duration in 1990. Bird species number and abundance were not significantly different between point counts conducted from field-edge and field-interior (100 m or less from the...

The Nicolet National Forest Bird Survey represents one of the first systematic bird monitoring programs in a USDA National Forest. Volunteers visit approximately 500 permanently marked points biennially (250 each year) during a single weekend of mid-June. Results from the first 6 years provide a general inventory of the Forest's avifauna, documentation of geographic gradients, and evidence of significant bird-habitat relationships. The point count method has been designed to accommodate flexibility in data analysis. Birds are recorded in 0- to 3-, 3- to 5-, and 5- to 10-minute intervals to...

We conducted a series of 275 paired (on- and off-road) point counts within 4 distinct vegetation cover types in northwestern Montana. Roadside counts generated a bird list that was essentially the same as the list generated from off-road counts within the same vegetation cover type. Species that were restricted to either on- or off-road counts were rare, suggesting that restricted occurrences were a consequence of small sample sizes and not a product of habitat differences surrounding on-versus off-road points. Nevertheless, there were significant differences in the mean number of individua...

Point counts of birds are made for many reasons, including estimating local densities, determining population trends, assessing habitat preferences, and exploiting the activities of recreational birdwatchers. Problems arise unless there is a clear understanding of what point counts mean in terms of actual populations of birds. Criteria for conducting point counts depend strongly on the purposes to which they will be put. This paper provides a simple mathematical conceptualization of point counts and illustrates graphically some of the influences on them.

The dominant feature of point counts is that they do not census birds, but instead provide incomplete counts of individuals present within a survey plot. Considering a simple model for point count sampling, we demonstrate that use of these incomplete counts can bias estimators and testing procedures, leading to inappropriate conclusions. A large portion of the variability in. point counts is caused by the incomplete counting, and this within-count variation can be confounded with ecologically meaningful variation. We recommend caution in the analysis of estimates obtained from point...

The effects of point count duration and radius on detection of breeding birds were compared by recording all birds seen or heard within two consecutive 5-minute intervals and for fixed-radius (within 30 m) or unlimited radius counts. Counts were conducted on Green Ridge State Forest (GRSF) and Savage River State Forest (SRSF) in western Maryland. More than 70 percent of all detections during fixed- and unlimited-radius counts occurred within the first 5 minutes. There was little overall gain in species richness from counting an additional 5 minutes. With fixed-radius counts, eight species...