Variable Circular Plot Method Research Articles

Comparing avians diversity between two university in Indonesia

IPB University and the University of Indonesia (UI) are two of the many campuses in Indonesia that take part in the UIgreenmetric ranking every year. In 2018, The two campuses were ranked in the top two of UIgreenmetric for national campuses and were committed to going to green campus. This study is important because the campus area in both universities is an area used by students as a place to study, the location of field practicums and research. Besides that, this research can be used as a reference for evaluating and improving environmental conditions at each campus. This study aims to compare the avian diversity on both campuses. Avian data was conducted at the green campus open space using the Ten Species List of MacKinnon and Variable Circular Plot Method. The observation was recorded every morning and afternoon with repetition. The comparison of bird species diversity between IPB Darmaga Campus and UI Depok Campus is included in the same classification, namely the moderate. The higher the number, the higher the species diversity classification. Still, the diversity value is higher in IPB Darmaga Campus at 2.7 compared to UI Depok Campus, which is 2.3.

Potential negative effects of construction of a high-mountain ski resort in the High Tatras, Slovakia, on breeding bird assemblages

Development of new ski resorts potentially has strong negative impacts on natural ecosystems. The objective of this paper is to analyse the potential effects of a newly proposed ski resort development plan on bird assemblages in the High Tatras Mts. of Slovakia. I tested two hypotheses that total bird abundance, species richness and diversity would decline, due (1) to the removal of tree and shrub vegetation after ski run construction and/or (2) as a result of a negative edge effect (i.e. decline along ski run edge). I censused birds in three presently occurring habitat types [successional forest (n = 26 (number of circular plots)), spruce forest (n = 22) and dwarf pine stands (n = 21) and ski runs (n = 20)] close to proposed resort site. I used a variable circular plot method on two spatial scales with radii of 25 and 50 m (three counts per plot during breeding season in 2018). Circular plot samples from ski runs were taken from the closest existing ski resort with similar environmental conditions in Tatranska Lomnica. I found that total density, species richness and diversity were negatively affected by habitat alterations near this resort, and provided evidence of negative edge effect of ski runs on bird abundance, diversity metrices and evenness. Based on these results and a literature review, I recommend that building new ski resorts not be built in strictly protected areas and that future ski resort developments be restricted to areas that have lower conservation value.

Avian population survey in the Floreana highlands: is Darwin’s Medium Tree Finch declining in remnant patches ofScalesiaforest?

SummaryIsland species typically exist in pathogen and predator sparse environments before human settlement, and are particularly vulnerable to the impacts of invasive species. In this study, we used the variable circular-plot method to estimate the density of birds in the highlands of Floreana Island, Galápagos Archipelago, where introduced parasites, predators, and habitat degradation are a known threat to endemic species. We recorded the number of birds seen and heard at 15 locations near Cerro Pajas Volcano in 2004 and 2008, an area that harbours the largest expanse of highlandScalesiaforest on Floreana Island. We estimated the change in population density for nine bird species, including five species of Darwin’s finches. We specifically address changes in population density for the locally endemic Medium Tree FinchCamarhynchus pauper, which only occurs on Floreana Island and has a small population size. Comparing 2004 and 2008, our study found lower population density in the Medium Tree Finch, but stable population density in Small Tree FinchC. parvulusand Large Tree FinchC. psittacula. Based on data from three additional highland sites surveyed in 2008, we estimate that the maximum size of the Medium Tree Finch population is 1,620 individuals. In addition to the survey data, we observed breeding males in 2006 and 2008. We found: (1) low nesting success (six out of 63 nests produced fledglings) and highPhilornis downsiparasite intensity, and (2) a biased age structure of the breeding population. No breeding males were one year old in 2006, and no males were five years old in either study year, indicating low reproductive success as well as limited lifespan. This research has contributed to the recent re-evaluation by IUCN, which has changed the Red List status of the Medium Tree Finch from ‘Vulnerable’ to ‘Critically Endangered’.

Population sizes and the conservation status of endemic and restricted-range bird species on Karakelang, Talaud Islands, Indonesia

Karakelang, largest of the Talaud Islands, Indonesia, was visited in 1999 with the aim of producing population estimates of globally threatened and Restricted-range bird species. Density estimates were calculated from primary forest and secondary habitats using the variable circular plot method. Eight of the nine restricted-range or threatened species resident on Karakelang were recorded and density estimates calculated for five of these. Two species of rail are endemic to Karakelang, Talaud Bush-hen Amaurornis magnirostris and Talaud Rail Gymnocrex talaudensis. The bush-hen was encountered in secondary habitat but occurred at higher densities in primary forest and the estimated population was 2,350–9,560 birds. The less vocal, cryptic G. talaudensis was noted just twice, in primary forest close to rivers. Both have small populations, are threatened by habitat degradation, hunting, and possibly predation by introduced rats and should be classified as threatened. Population densities of the Endangered, endemic Red-and-blue Lory Eos histrio had remained stable since the last survey in 1997. They occurred at higher densities in primary forest, but were also common in human-made habitats. The estimated population was 8,230–21,400 birds, threatened by habitat loss and trapping for the wild bird trade. Although more commonly encountered in forest, the Near Threatened Blue-naped Parrot Tanygnathus lucionensis was found at higher densities in secondary habitats, and the population was estimated at 8,130–20,700 birds. The Restricted-range Blue-tailed Imperial Pigeon D. concinna was very common on Karakelang (14,500–27,700 birds), whilst the Vulnerable Grey Imperial Pigeon D. pickeringii was recorded rarely; both species were more frequently recorded in primary forest. The endemic Talaud Kingfisher Halcyon enigma occurred at low densities (5,290–8,690 birds), in primary forest and adjacent disturbed areas. It is heavily dependent on primary forest and threatened by habitat loss, and should be classified as Vulnerable. Approximately 350 km2 of primary forest on Karakelang is protected, 250 km2 as a wildlife reserve. However, at present, management is absent and forest is threatened by agricultural encroachment, illegal logging, and fire. Given that all endemic and threatened species were encountered more frequently or occurred at higher densities in primary forests, future conservation efforts should target these protected areas. Management of reserves should involve local stakeholders from government and representatives of island communities. Wildlife trade is a major threat to Eos histrio and strict enforcement of the species' protected status should include monitoring of roost sites, patrols of harbours and markets in Talaud, Sulawesi and the Philippines, and the control of Philippine fishing boats involved in the wild bird trade. Further species-specific research and monitoring is also required.

A test of the variable circular-plot method where exact density of a bird population was known

Variable circular-plot (VCP) counts are statistically more sound than point counts because they are adjusted for the probability of detecting birds at different distances and under different conditions. However, many ornithologists use point counts rather than VCP counts because they believe that assumptions of the VCP method are almost always violated, leading to poor results, and because earlier field tests using ad hoc analysis methods gave variable and relatively poor results. We conducted the first field test of the VCP method where the exact density of a forest bird was known as part of re-establishing the 'Oma'o Myadestes obscurus in former range. All 'Oma'o in the new population were intensively monitored by radio telemetry so that the number present during four VCP censuses was known. Excluding the first census, when three of the four detections were of the same individual, differences in VCP density estimates ranged from ?34% to +24% (mean 0%) even though =18 'Oma'o were detected per survey. We review critical assumptions of the VCP method and make recommendations for data analysis based on our experience with the method on Pacific islands.

Avian Community Response to Fire and Mechanical Shrub Control in South Florida

Effects of prescribed fire and roller chopping applied in 2 seasons on woody vegetation and the associated avian community of a southwestern Florida former dry prairie were studied. There were 5 vegetation treatments with 2 replications of each; treatments were control, winter burn, winter chop, summer burn, and summer chop. Percent shrub cover was sampled with line intercept transects. Birds were censused 25 times using the variable circular plot method. Burning in either season reduced shrub cover temporarily; chopping in either season reduced shrub cover significantly and it remained reduced throughout the 15 months of this study. Bird species richness and abundance were similar in control and burn plots. Birds were not seen in summer chop plots up to 5 months posttreatment. Bird species richness and abundance remained low in both winter and summer chop plots. Bird species that were observed in chop plots were mostly open country, grassland inhabitants, indicating a trend toward prairie restoration.

The distribution, abundance and habitat preferences of the Salmon-crested Cockatoo Cacatua moluccensis on Seram, Indonesia

SummaryThe Salmon-crested Cockatoo Cacatua moluccensis is endemic to the Seram island group, Maluku Province, Indonesia. An apparently considerable population decline, attributed t o over-exploitation for the parrot trade, prompted CITES to ban all trade in the species in 1989. A short census was undertaken on Seram using the variable circular plot method. Cockatoo density estimates were highest in little-disturbed lowland forest and lowest in recently logged forest and in non-forested areas. Discriminant function analysis was used t o describe the distribution of the species. The discriminant profile suggested that cockatoos were associated with mature lowland forest closer to rather than farther away from settlements. No conclusions are possible as to the relative importance of bird capture and habitat alteration on the population of the Salmon-crested Cockatoo, but an urgent need for further standardized censuses of cockatoo populations, and for research concerning the population dynamics of this and other traded parrot species, is stressed.

On the Variable Circular Plot Method of Estimating Animal Density

The development by ornithologists of the variable circular plot method of estimating bird densities from observer-to-bird distances has led to estimation problems similar to those of line transect sampling. However, to apply line transect methods without modification requires that the distance data be transformed to areas by squaring. The implications of this transformation on the assumed shapes for the detection curve have not been investigated in the literature. This paper illustrates that application of line transect models to area data may lead to poor model performance and erroneous conclusions. Developments based on distance data are discussed briefly, and binomial models are derived for the special case in which birds are categorised simply according to whether they are within or beyond a specified distance.

A Field Test of the Variable Circular-Plot Censusing Method in a Sierran Subalpine Forest Habitat

The density and distribution of territories were determined for 21 species in a 48-ha Sierran subalpine forest study plot by an intensive program of spot-mapping and nest monitoring. About 10% of the total breeding individuals were color-banded and about 75% of the nests of all species were found. Variable circular-plot (VCP) censuses were simultaneously conducted in the same study plot. The VCP method, with minimum effort (48 stations), could describe community parameters reasonably well and could distinguish common from rare species, but could not correctly determine the relative abundances of the common species, could not correctly describe the distribution of territories within the study plot, and produced errors in density estimates for the common species that ranged from -57% to +65%. When the effort was increased threefold (144 stations), the accuracy of the method was improved so that it produced more or less acceptable relative abundances for even the common species and was marginally capable of describing the distribution of territories for 37% of the species, particularly for those species whose distributions were markedly non-uniform, but it still produced errors in density estimates for the common species that ranged from -67% to +96%. Interestingly, VCP total count often performed nearly as well as the calculated VCP density in determining relative abundances. The accuracy of the VCP method may be expected to be poor for species with low population densities, large territory sizes, high mobilities, and ventriloqual vocalizations, and for habitats that are dense and highly three-dimensional.

ESTRUCTURA Y UTILIZACION DEL FOLLAJE DE LAS COMUNIDADES DE PAJAROS EN BOSQUES TEMPLADOS DEL VALLE DE MEXICO

Températe forests are distributed over very extensivo areas in North America but in tropical Middle America are limited to montane zones, and at the present time these montane forests are threatened by man because of overpopulation. I studied the structure and use of foliage of bird communities in montane températe forests of , the Valley of México. In August and September of 1981 I censused bird communities in six températe forest study areas one each in oak woodland and pine-alder forest, and two each in pine forest and firforest using the variable circular-plot method. Overall bird densities were greater in broad-leaved forests than in coniferous forests. Species richness was similar between broad-leaved and pine forests but generally lower in fir forests. A similar trend was shown by bird species diversity (BSD). The oak woodland bird community was the most distinctive, whereas the pine-alder one was similar to the fir forests. Bird communities of the two pine forests had low similarity indices, whereas communities of fir forests had the highest índices. Qranivorous birds were very important in pine forests, whereas insectivores were the most important in broad-leaved and fir forests. Profiles of foliage stratification were used selectively by all the bird communities, and profiles of utiiization were significantly different between August and September for all the communities except that of the pine-alder forest. Among dietary categories and guilds, all but the seed-eaters used the profile of foliage stratification very selectively; this selectivity was especially marked for the salliers and the foliage gelaners. In a latitudinal gradient of températe forests over western North America and México, there were not big differences in species richness of bird communities from broad-leaved and mixed-conifer forests, but there was a decrease in the number of species from pine forests as latitude decreased. BSD decreased southwards in the broad-leaved forests and only slightly in mixed-conifer forests, whereas in pine forests BSD increased. Seed-eaters were relatively more abundant in the northem forests, whereas foliage gleaners were the most important in Southern forests, but not in the pine forests.

A Variable Circular-Plot Method for Estimating Bird Numbers

A Variable Circular-Plot Method for Estimating Bird Numbers