A new approach for analyzing bird densities from variable circular-plot counts

S.G. Fancy

Home/Archive/USGS

USGS · 70020141

A new approach for analyzing bird densities from variable circular-plot counts

S.G. Fancy

View original source ↗Export metadata ↓

Abstract

An approach for calculating bird densities from variable circular-plot counts is described. The approach differs from previous methods in that data from several surveys are pooled and detection distances are adjusted as if all distances were recorded by a single observer under a given set of field conditions. Adjustments for covariates that affect detection distances such as observer, weather, time of day, and vegetation type are made using coefficients calculated by multiple linear regression. The effective area surveyed under standard conditions is calculated from the pooled data set and then used to determine the effective area surveyed at each sampling station under the actual conditions when the station was sampled. The method was validated in two field studies where the density of birds could be determined by independent methods. Computer software for entering and analyzing data by this method is described.

Explore related subjects

Pacific Science Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

S.G. Fancy. 1997. A new approach for analyzing bird densities from variable circular-plot counts. https://pubs.usgs.gov/publication/70020141

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2025

A comparative evaluation of bait types taken by brown treesnakes or other nontarget species, including ants

Evaluating invasive species removal can help improve efficacy or application of control tools. Toxic baiting is a primary method used to suppress many invasive species, including the brown treesnake ( Boiga irregularis ) in Guam. Based on limited alternative approaches to assess tool efficacy in snake removal, bait take is often used as a proxy for snake removal, despite evidence that nontarget species remove baits in a spatially heterogeneous manner. Using photographic validation, we tested take rates of mouse, chick, and rat baits by brown treesnakes and nontargets, including invertebrates, at three sites undergoing snake removal for vertebrate conservation goals. We also identified the ant species present on baits for a subset of baits. Take rates by snakes and nontargets varied by site. We found that nontarget take (22–42%) was considerably greater than take by brown treesnakes (1–13%). In addition, baits that had ants were taken less often by snakes as compared to baits without ants (7–12% vs. 8–52%, respectively). The dominant ant species collected from ant bait stations affiliated with baits was Solenopsis spp. Ant presence appeared to have deterred brown treesnakes from consuming baits, and ant removal or prevention may improve take rates by brown treesnakes. There was not, however, a consistent correction factor that could be applied across sites to estimate brown treesnake take rates of baits without photographic validation.

Pacific Science↗

USGS2025

Ten more years of the golden pheasant (Chrysolophus pictus) on Maui, Hawaiian Islands

Since the introduction of the Golden Pheasant ( Chrysolophus pictus ) to Haleakalā volcano, Maui, three decades ago, subsequent reports have hinted at an expansion of this nascent population. We draw from a variety of data sources to learn about this pheasant's present status on Maui. First, forest bird surveys conducted every five years revealed that the frequency of Golden Pheasant detections has greatly increased, and the bird has both maintained its former distribution and expanded eastward into Haleakalā National Park (NP). Second, reports to eBird from The Nature Conservancy's Waikamoi Preserve, where Golden Pheasants first appeared on Maui, demonstrate that the frequency of observations has increased and is strongly seasonal, predominantly in the spring. Third, autonomous recording units monitoring endangered forest birds recorded pheasants too, adding new locations. Finally, trail cameras set to monitor mammals picked up pheasants as well, showing males of two color morphs: original “wild-type” and “dark-throated.” Trail cameras also documented a small juvenile at Waikamoi Preserve and both females and males in Haleakalā NP. By “connecting the dots” of mapped occurrences, we traced the pheasant's progression through a narrow band of subalpine cloud forest with open understory, extending from Waikamoi Preserve eastward to upper Kīpahulu Valley, a distance of 14 km. In summary, this body of evidence supports the claim that the Golden Pheasant has established a self-sustaining population on Maui, and we propose that the species' success there may be attributed to the minimal influence of predators and the absence of competing gallinaceous birds in its preferred habitat.

Hawaii↗

USGS2025

Pre-restoration woody species crown and vegetation community mapping using high-resolution uncrewed aerial system imagery, Palmyra Atoll

The terrestrial management plan for Palmyra Atoll includes large-scale removal of coconut ( Cocos nucifera ) as part of native forest restoration and contaminant remediation that will leave soils and vegetation communities profoundly altered. To inform those efforts and provide baseline data for restoration monitoring, woody stem crowns and vegetation communities at Palmyra Atoll were mapped using existing datasets and manual photointerpretation of high-resolution aerial imagery collected using uncrewed aerial systems. Coconut palm, grand devil's claws ( Pisonia grandis ), and numerous other species were delineated as either individual crowns, crown portions, or species patches. The extent of land area at high tide was also delineated based on vegetation patterns, topographic indicators, and deposition lines of vegetation litter and flotsam. Finally, in a novel “bottom-up” approach to vegetation community mapping, crown maps were used to delineate U.S. National Vegetation Classification System vegetation communities and other management areas. Of the more than 44,000 mapped crowns, coconut was by far the most abundant species, comprising nearly half of the mapped stems. By establishing a quantitative baseline for current habitat conditions, this project facilitates the integration of contaminant remediation recovery activities with habitat restoration planning, implementation, and monitoring at Palmyra Atoll. Results illustrate the appropriateness of the mapping approach for plant species-level censuses and cover estimation over relatively small areas to aid in inventory and monitoring and to facilitate management planning. The relatively simple mapping methods used in this study are appropriate for resource managers with limited human and computational resources to support automated mapping.

Pacific Science↗