Influence Of Habitat Variables Research Articles

Breeding site records of three sympatric vultures in a mountainous cliff in Kahara-Thathri, Jammu & Kashmir, India

The current communication deals with the breeding records of three sympatric vultures, viz., Himalayan Vulture Gyps himalayensis, Egyptian Vulture Neophron percnopterus, and Bearded vulture Gypaetus barbatus from a mountain cliff in Kahara, Thathri, a part of upper Chenab catchment in the union territory of Jammu and Kashmir. Made of twigs and lined by dry grass, the nests mostly east-facing, were built on the ledges or in cavities and small caves on cliffs well protected from predators. The inaccessibility, rugged topography (for nesting) and the abundant food base (gorals, monkeys, langurs, pikas, and rodents) make it an ideal nesting location for the vultures. Authors suggested that intensive studies are required to be taken up on the resource apportionment and influence of habitat variables (climate, terrain, disturbance) on the nest site characteristics in such rugged landscapes.

Nest Height and Vertical Vegetation Associated with Black-capped Vireo Breeding Success in Southwest Texas

Vireo atricapilla (Black-capped Vireo) is an endangered songbird whose habitat use has been well studied in central portions of its breeding range, which is characterized by successional vegetation communities. To expand our understanding of habitat use as it relates to reproductive success, we studied Black-capped Vireo habitat use at the territory and nest-site scales in southwest Texas in 2009 and 2010, an area characterized by xeric and stable vegetation communities. We measured vegetation in territories and at nests to evaluate the influence of habitat variables on nest parasitism and nest survival. Our results showed that Black-capped Vireo nest-site use in southwest Texas differed from that in breeding areas of central Texas and Oklahoma. Black-capped Vireos in southwest Texas used nest sites with a wide range of woody cover (70 ± 13%) and used Juniperus spp. (junipers) as a nest substrate proportionately more than its availability in territories, which is contradictory to previously published literature. Nest parasitism increased significantly with greater nest height, likely due to increased visibility to Molothrus ater (Brown-headed Cowbird). Increasing height of vertical cover above the nest was associated with decreased overall nest survival, likely because nests placed in habitat with taller vegetation are more susceptible to avian predators and Brown-headed Cowbird parasitism. Unlike the findings of studies conducted in the northern part of the species' breeding range, we found that parasitism did not increase the likelihood of depredation or abandonment. Our results indicate that Black-capped Vireo habitat structure and composition, as well as factors influencing nest success in Southwest Texas, differ from their breeding habitat in central Texas and Oklahoma, indicating that management guidelines need to be regi on-specific.

Seasonal variation in coastal marine habitat use by the European shag: Insights from fine scale habitat selection modeling and diet

Studies of habitat selection by higher trophic level species are necessary for using top predator species as indicators of ecosystem functioning. However, contrary to terrestrial ecosystems, few habitat selection studies have been conducted at a fine scale for coastal marine top predator species, and fewer have coupled diet data with habitat selection modeling to highlight a link between prey selection and habitat use.The aim of this study was to characterize spatially and oceanographically, at a fine scale, the habitats used by the European Shag Phalacrocorax aristotelis in the Special Protection Area (SPA) of Houat-Hœdic in the Mor Braz Bay during its foraging activity. Habitat selection models were built using in situ observation data of foraging shags (transect sampling) and spatially explicit environmental data to characterize marine benthic habitats. Observations were first adjusted for detectability biases and shag abundance was subsequently spatialized. The influence of habitat variables on shag abundance was tested using Generalized Linear Models (GLMs). Diet data were finally confronted to habitat selection models.Results showed that European shags breeding in the Mor Braz Bay changed foraging habitats according to the season and to the different environmental and energetic constraints. The proportion of the main preys also varied seasonally. Rocky and coarse sand habitats were clearly preferred compared to fine or muddy sand habitats. Shags appeared to be more selective in their foraging habitats during the breeding period and the rearing of chicks, using essentially rocky areas close to the colony and consuming preferentially fish from the Labridae family and three other fish families in lower proportions. During the post-breeding period shags used a broader range of habitats and mainly consumed Gadidae. Thus, European shags seem to adjust their feeding strategy to minimize energetic costs, to avoid intra-specific competition and to maximize access to suitable habitats and preys.

Habitat Selection by Burrowing OwlsAthene cuniculariain the Pampas of Argentina: A Multiple-Scale Assessment

Fil: Baladron Felix, Alejandro Victor. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

FLORISTIC COMPARISON BETWEEN TWO TREE COMMUNITIES ASSOCIATED WITH HABITAT DESCRIPTOR VARIABLES

ABSTRACT The knowledge about the influence of habitat variables is essential to understand the underlying ecological patterns in vegetation. This study compared the floristic composition of two forest communities located in different altitudes. Associated with this comparison, we used a methodology where habitat descriptor variables were scaled and interpreted by the biotic set sampled. We constructed one matrix with scores given to physical, biotic, vegetation, and anthropogenic variables in the field and one matrix with the species sampled and performed multivariate analyses. We found that the floristic communities differ between the different altitudes and that the methodology used showed significant variables for the ecological characterization of the sampled habitat.

Multilevel habitat preferences of Apodemus sylvaticus and Clethrionomys glareolus in an intensively cultivated agricultural landscape

Small mammals are considered good model species for assessing the global effects of habitat loss and fragmentation in agricultural landscapes. With the aim of investigating the composition and habitat preferences of the small mammal community in an intensively cultivated area, we sampled the three main “macro-habitats” (wood patches, poplar plantations and crops) available on the western plain of the River Po (North Italy). The influence of habitat variables on each species’ occurrence was assessed at three different scales of observation: “macro-habitat”, “micro-habitat” (i.e. vegetation layers at trap sites) and the landscape level (i.e. land cover in plots of 500 m radius centred on each trap line). Overall, 3344 trap-nights yielded 169 Apodemus sylvaticus, 28 Clethrionomys glareolus and two Sorex araneus. The first species was dominant in all macro-habitats, while the other two species were trapped only in residual wood patches. The thickness of the fine litter was the main micro-habitat factor affecting the occurrence of both C. glareolus and A. sylvaticus in woods, while sites with herbaceous vegetation cover were preferred by the latter species in poplar plantations. Intraclass correlation coefficients showed that sites with thick litter or high herb cover were neither exclusive nor predominant in wood patches and poplar plantations, respectively, suggesting that the choice for micro-habitat parameters is subordinate to that of macro-habitat characteristics, mainly tree and shrub cover. At the landscape scale, no habitat variable affected the occurrence of both species. At the macro-habitat level, the strong selection for wood patches by both wood mice and bank voles and the negligible occurrence of small mammals in cultivated plots pointed out the major role for conservation played by residual semi-natural habitats in agricultural landscapes.

Territory size and habitat selection of Cinnamon-breasted Rock Bunting Emberiza tahapisi in Nigeria

Most of our understanding of territorial behaviour in birds comes from studies of temperate species. Territoriality and factors influencing territory size of tropical birds are still poorly studied. In this study, 11 territories of the Cinnamon-breasted Rock Bunting Emberiza tahapisi were measured in the Amurum Forest Reserve and adjoining farmlands. Factors influencing the habitat choice of this species were also studied. Territory sizes ranged from 0.1–0.3 ha with a mean territory size of 0.19 ± 0.1ha. Territory size decreased with increasing food abundance and increased with tree height and number of saplings. The birds did not show signs of territoriality in farmlands but flocked in small groups (mean group size 6.88 ± 0.89). Flock size also increased with increasing number of seeds. In the forested land, birds showed a preference for rocky outcrops, whereas in farmlands, they appeared to prefer open and newly cultivated farmlands with little or no ground cover. Understanding the influence of habitat variables on territory size and habitat selection in a locally abundant and widely distributed tropical species such as the Cinnamon-breasted Rock Bunting thus offers unique opportunities for understanding how changes in landscape caused by land-use regimes may affect populations.

Woodpecker Nest Survival in Burned and Unburned Managed Ponderosa Pine Forests of the Northwestern United States

Abstract. Woodpeckers are particularly susceptible to habitat changes resulting from forest management because of their reliance on trees and snags for nesting and foraging. However, the influence of habitat variables on the reproductive success of woodpeckers has received less attention than it has in other avian taxonomic groups. We estimated nest-survival rates for the White-headed Woodpecker (Picoides albolarvatus), Hairy Woodpecker (P. villosus), and Northern Flicker (Colaptes auratus) in managed ponderosa pine (Pinus ponderosa) forests along the eastern slope of the Cascade Range in Washington, 2005–2010. Using a model-selection framework, we found that the most supported models included terms for a quadratic effect of date and habitat type for the Hairy Woodpecker, a negative effect of percent shrub cover for the White-headed Woodpecker, and a negative linear effect of date and habitat type, a negative linear effect of snag density, and a positive linear effect of tree density for the flicker. Surv...

Distribution of tadpoles of large wrinkled frog Nyctibatrachus major in central Western Ghats: influence of habitat variables

The relationship between habitat variables and the distribution and abundance of adults and tadpoles of Nyctibatrachus major (large wrinkled frog) in 35 forest streams in central Western Ghats is detailed in this paper. Tadpoles were not equally distributed among these streams. Adult frogs and tadpoles were absent from 19 streams. In the remaining 16 streams, adults were found throughout the study period but the density of tadpoles varied considerably. Analysis of habitat variables at streams showed significant relationship with canopy cover over the streams, presence of leaf litter and high relative humidity on the occurrence of tadpoles. Reduction in canopy cover increases light level and air and water temperature of the streams discouraging the occurrence of adult frogs and tadpoles. However, canopy cover in the study area is frequently altered by agriculture related human activities including removal of trees for fuel and timber, pruning of green leaves and twigs for making manure and conversion of forest into commercial plantations. The results suggest that disturbances to forest canopy near streams could have deleterious effects on the occurrence and distribution of tadpoles.

Progress in the use of remote sensing for coral reef biodiversity studies

Coral reefs are hotspots of marine biodiversity, and their global decline is a threat to our natural heritage. Conservation management of these precious ecosystems relies on accurate and up-to-date information about ecosystem health and the distribution of species and habitats, but such information can be costly to gather and interpret in the field. Remote sensing has proven capable of collecting information on geomorphologic zones and substrate types for coral reef environments, and is cost-effective when information is needed for large areas. Remote sensing-based mapping of coral habitat variables known to influence biodiversity has only recently been undertaken and new sensors and improved data processing show great potential in this area. This paper reviews coral reef biodiversity, the influence of habitat variables on its local spatial distribution, and the potential for remote sensing to produce maps of these habitat variables, thus indirectly mapping coral reef biodiversity and fulfilling information needs of coral reef managers.

Evaluating the potential of night spotlighting as a method for assessing species composition and brown trout abundance: a comparison with electrofishing in small streams

Direct counts of fish obtained by night spotlighting were compared with species composition and population estimates obtained from three‐pass electrofishing obtained across 29 sites along small clear streams in the Otago region of New Zealand. The influence of habitat variables on the relative efficiency of each method was also examined. The same seven species of fishes were identified by both methods. Juvenile brown trout Salmo trutta were the only species present in sufficient numbers to allow comparison of abundance estimates using the two methods. A total of 777 brown trout were counted by spotlight and 803 brown trout were caught using electrofishing. Estimates of abundance obtained by spotlighting reflected population estimates obtained by three‐pass electrofishing across most habitats. Electrofishing produced higher population estimates relative to spotlighting in fast‐flowing turbulent riffle habitats, whereas counts obtained by spotlighting tended to be higher relative to electrofishing in slow‐flowing pool habitats. The results suggest that spotlighting is an effective method for assessing fish composition and brown trout abundance in small clear water streams, although the extremes of water velocity may influence efficiency of both spotlighting and electrofishing.

The Influence of Habitat Variables on Bird Communities in Forest Remnants in Costa Rica

This study examined the effects of forest structure (tree species richness, canopy height, percent canopy cover, understory density, tree density and DBH) and avian species traits (nest type and indicator list status) on the diversity, abundance and dissimilarity of bird communities in forest remnants and reforestation areas adjacent to Costa Rican banana plantations. Bird species richness and abundance were significantly related to tree species richness, canopy height and canopy cover in multiple linear regressions, the latter two forest structure variables being the best statistical predictors. Stratification of analyses by bird species indicator categories improved fits of regressions, because correlations with environmental variables differed in sign for different guilds of birds, a result likely to hold for other avifaunas. Analysis of avifauna dissimilarities among sites demonstrated that the species composition of bird communities was highly correlated with forest structure and tree species composition. Logistic regressions indicated that birds making protected (cavity, burrow, pendant, sphere and covered) nests were 2–6 times more likely to be present in the study avifauna than birds making open (cup, saucer, platform and scrape) nests and indicators of disturbed habitats were 11 times more likely to be present than indicators of primary forest. The forest structure data used were simple and inexpensive to collect, and data on avian traits were drawn from the literature. Thus, these methods could easily be replicated at other locations and would be valuable management aids and biodiversity assessment tools for conservation planning.

The Importance of Spatial Scale for Conservation and Assessment of Anuran Populations in Coastal Wetlands of the Western Great Lakes, USA

Distributions of pond-breeding amphibians may be influenced by habitat factors at different spatial scales. We used anuran calling surveys to investigate the association between 5 anuran species and habitat variables measured within 100, 500, 1000, and 3000 m of sampling points at 63 coastal wetlands along the US shores of Lake Michigan and Lake Huron. Stepwise logistic regression was used to create predictive models for each species at each spatial scale. Our results confirm the view that habitat variables at multiple scales influence frog distributions, but the strength of predictive models was significantly affected by the spatial scale at which habitat variables were derived. Remotely sensed habitat variables within a 3000 m radius were among the most effective predictors of occurrence for American toad (Bufo americanus), eastern gray treefrog (Hyla versicolor), spring peeper (Pseudacris crucifer), and green frog (Rana clamitans melanota). The western chorus frog (Pseudacris triseriata) was predicted most effectively by variables derived within a 500 m radius. For the most part, these anurans exhibited species-specific responses to habitat variables; however the suite of landscape-scale variables associated with urban land use appeared in all species’ regression models. Associations with landscape-scale variables coupled with well-documented habitat needs at local breeding sites suggest that conservation and assessment of frogs and toads in coastal wetlands should consider the influence of habitat variables at multiple spatial scales.

Habitat selection by the red fox Vulpes vulpes (L. 1758) in an Alpine area

Habitat selection and the influence of habitat variables on red fox ranges were assessed in the Gran Paradiso National Park, Western Alps, Italy, all year round. Nine hundred twenty-two scats were mapped as “signs of presence” by monthly surveys of fixed transects in the main habitat types and altitude belts. Forested habitats and lower altitudes (1000–1500 m a.s.l.) were selected, whereas upper altitudes were avoided, during the cold season. This pattern was attributed to the availability of ungulate carrion, widely used as food by foxes, at low altitude, while upper altitudes provided poor resources in the cold season. During the warm season, no clear pattern of habitat selection could be detected. The selection for forested habitats could therefore be explained by the availability of resources other than food, e.g. resting and denning sites. The strong seasonality of an Alpine altitudinal succession, where resource availability varies over short distances, may lead to home ranges containing a variety of habitat types along the altitudinal gradient, providing resources throughout the year. Foxes possibly hold “vertical” home ranges, where certain habitat types became strategic, especially under limiting climatic conditions.

Effects of variable-intensity logging and the influence of habitat variables on the distribution of the Greater Glider Petauroides volans in montane forest, southeastern New South Wales

Populations of arboreal marsupials were assessed in forests before and after logging at different levels of logging intensity to determine the sensitivity of these species to habitat disturbance. The logging treatments imposed were unlogged controls and two intensities of integrated logging for sawlogs and woodchips. The mean basal area of trees retained in logged blocks ranged from 83% to 35% of pre-logging levels. The objective of the study was to develop better methods for managing arboreal marsupials within the wood production forests of southeastern New South Wales. Seven species of arboreal marsupials were recorded during the study, but the Greater Glider Petauroides volans was the only species recorded in sufficient numbers for analysis (86% of all records). No significant differences were observed between the treatments in counts of the Greater Glider before and after logging. However, given the observed trend and an a priori expectation of a decline in numbers of this species following intensive logging, a one-tailed statistical test was applied which resulted in a significant difference at P = 0.08 for the contrast between the unlogged controls and the most intensively logged treatment. The existence of a threshold in logging intensity within the range of 21 % to 39% retention of tree basal area, below which numbers of the Greater Glider suffer a marked decline, was inferred on the basis of comparisons with the results of other studies. Factors other than logging were important in determining the distribution of the Greater Glider. Elevation, in particular, was a significant environmental variable, with Greater Gliders more likely to occur in forests above 845 m a.s.1. The presence and absence of particular tree species also influenced the distribution of the Greater Glider. Forests containing Manna Gum E. viminalis and Mountain Gum E. dalrympleana were highly preferred compared to forests with a high proportion of E. obliqua. The presence of E. cypellocarpa appeared to improve the quality of habitat for the Greater Glider in forests dominated by E. obliqua. This study has shown that Greater Glider populations can be maintained at or near pre-logging levels when at least 40% of the original tree basal area is retained thoughout logged areas and when the usual practice of retaining unlogged forest in riparian strips is applied.