Area Sensitivity in Grassland Passerines: Effects of Patch Size, Patch Shape, and Vegetation Structure on Bird Abundance and Occurrence in Southern Saskatchewan

The Auk ◽  
2004 ◽  
Vol 121 (4) ◽  
pp. 1130-1145 ◽  
Author(s):  
Stephen K. Davis
Keyword(s):  
Vegetation Structure ◽  
Patch Size ◽  
Bird Abundance ◽  
Patch Shape ◽  
Area Sensitivity

scholarly journals Area Sensitivity in Grassland Passerines: Effects of Patch Size, Patch Shape, and Vegetation Structure on Bird Abundance and Occurrence in Southern Saskatchewan

The Auk ◽  
2004 ◽  
Vol 121 (4) ◽  
pp. 1130-1145 ◽  
Author(s):  
Stephen K. Davis
Keyword(s):  
Habitat Fragmentation ◽  
Tallgrass Prairie ◽  
Vegetation Structure ◽  
Native Species ◽  
Patch Size ◽  
Grassland Birds ◽  
Bird Abundance ◽  
Mixed Grass Prairie ◽  
Mixed Grass ◽  
Area Sensitivity

Abstract Information on area sensitivity and effects of habitat fragmentation has come largely from forest and tallgrass-prairie habitats. Research from other ecosystems is required to determine whether the fragmentation paradigm derived from those studies is applicable to passerine communities elsewhere. I examined the effects of habitat fragmentation on abundance and occurrence of nine species of mixed-grass prairie passerines in southern Saskatchewan. I conducted 190 point-counts in 1996 and 1997 on 89 pastures ranging in size from 8 to 6,475 ha. Sprague's Pipit (Anthus spragueii), Baird's Sparrow (Ammodramus bairdii), Grasshopper Sparrow (A. savannarum), and Chestnut-collared Longspur (Calcarius ornatus) were found to be area-sensitive, in that they were more abundant or occurred more frequently, or both, in larger patches of mixed-grass prairie. However, the ratio of edge to interior habitat was a better predictor of area sensitivity than patch size in most cases. Horned Lark (Eremophila alpestris), Savannah Sparrow (Passerculus sandwichensis), Clay-colored Sparrow (Spizella pallida), Western Meadowlark (Sturnella neglecta), and Brown-headed Cowbird (Molothrus ater) were insensitive to patch size, though occurrence of Clay-colored Sparrow and Western Meadowlark tended to be greater in smaller pastures. Vegetation structure was also found to be an important predictor of grassland songbird abundance and occurrence, in that it explained additional variation not accounted for by patch size or the ratio of edge to interior habitat. Although protection of large contiguous tracts of habitat is essential to conservation of native species, small native-prairie patches with minimal edge habitat also play a vital role in conservation of grassland birds.

scholarly journals Bird diversity and abundance on two different shade coffee plantations in Guatemala

1998 ◽  
Vol 8 (3) ◽  
pp. 297-308 ◽  
Author(s):  
Lorena Calvo ◽  
John Blake
Keyword(s):  
Vegetation Structure ◽  
Management Practices ◽  
Bird Diversity ◽  
Bird Abundance ◽  
Shade Coffee ◽  
Coffee Plantations ◽  
Bird Populations ◽  
Migrant Birds ◽  
Abundance And Diversity ◽  
Fertilizer Regimes

SummaryMany studies have examined differences in bird communities between shade and sun coffee plantations but less is known about how different management practices within shade coffee plantations affect bird populations. This study compares diversity and abundance of resident and migrant birds in two shade coffee plantations located in Palajunoj, Quetzaltenango, Guatemala, that differ in their farming practices (e.g. pruning schedules and fertilizer regimes) and, consequently, in vegetation structure. One plantation represents a traditional, polyculture shade system whereas the second represents a more modernized, monoculture shade system. Both plantations supported many resident and migrant birds. Bird abundance and diversity were significantly greater during both wet and dry seasons on the traditional farm, due largely to the vegetation structure resulting from the different management practices. All plantations typically classified as ‘shade coffee’ are not equivalent, much of their conservation value coming from the more diverse and structurally complex traditional polycultures rather than from the newer, monocultural systems. Coffee production techniques that affect the structural and floristic diversity of the vegetation (e.g. pruning, application of chemicals) have important consequences for birds.

Winter habitat selection by a montane forest bird assemblage: the effects of solar radiation

2001 ◽  
Vol 79 (2) ◽  
pp. 279-284 ◽  
Author(s):  
Daniel L Huertas ◽  
José A Díaz
Keyword(s):  
Solar Radiation ◽  
Vegetation Structure ◽  
Prey Availability ◽  
Bird Species ◽  
Principal Component ◽  
Interspecific Variation ◽  
Montane Forest ◽  
Bird Abundance ◽  
Winter Habitat ◽  
Movement Rates

A relationship between sunlight and bird abundance in cold climates may seem intuitive and perhaps obvious. However, there is, surprisingly, little or no evidence to support it. We investigated the effects of solar radiation on the winter abundance of insectivorous birds inhabiting a Mediterranean montane forest with a high frequency of cold, cloudless days. We censused birds by ear in 20 different forest tracts in which we simultaneously quantified a number of variables related to the availability of solar radiation, vegetation structure, arthropod abundance, and altitude. All variables related to solar radiation were reduced to a single principal component that attained high scores for south-facing transects, where many tree trunks received direct sunlight for a long period daily. The abundance of all bird species was positively related to the scores of transects on this component after the effects of vegetation structure, altitude, and prey availability were controlled for. Solar radiation was the main predictor of overall abundance and species richness of bird assemblages. Body mass and diet (insectivorous vs. mixed) explained 94.6% of interspecific variation in the strength of the relationship between solar radiation and bird abundance. We hypothesize that selecting forest sectors with a higher availability of sunlit patches allows birds to improve their winter survival by reducing the metabolic costs of thermoregulation, decreasing movement rates, and (or) increasing the time spent motionless in safe locations.

Riparian edge effects on boreal balsam fir bird communities

1995 ◽  
Vol 25 (4) ◽  
pp. 555-566 ◽  
Author(s):  
Pierre Larue ◽  
Louis Bélanger ◽  
Jean Huot
Keyword(s):  
Edge Effect ◽  
Vegetation Structure ◽  
Riparian Forest ◽  
Close Association ◽  
Bird Communities ◽  
Riparian Forests ◽  
Balsam Fir ◽  
Bird Abundance ◽  
Vegetation Diversity ◽  
Bird Richness

Riparian forests are often identified as prime habitat for wildlife because of the presence of particular plant communities and edges creating a highly developed and diversified vegetation structure. However, in the northeastern boreal forests of Canada, where narrow land–water ecotones with abrupt edges are quite common, the relative habitat value of riparian forests remains to be demonstrated. We compared bird communities of eight pairs of riparian and nonriparian plots, similar in vegetation structure and composition, to verify the relative value for breeding birds of typical coniferous riparian forest stands of the southern boreal region of eastern Quebec. Bird abundance (P = 0.02), richness (P = 0.03), and diversity (P = 0.02) were significantly higher in the riparian stands, where the spatial sequence of three distinct habitats (a balsam fir (Abiesbalsamea (L.) Mill.)–northern white cedar (Thujaoccidentalis L.) forest, a narrow alder (Alnusrugosa (Du Roi) Spreng.) - grass wetland, and water) created high horizontal vegetation diversity. In riparian stands median bird richness and density were, respectively, 23.5 species and 437.5 territories/km2 compared with 19.0 species and 348.2 territories/km2 for interior stands. Nine species were observed exclusively in riparian plots. In addition to the species usually found in the studied nonriparian forests, the riparian plots were used by species typically related to the water edge such as the Northern Waterthrush (Seiurusnoveboracensis Gmelin) and Rusty Blackbird (Euphaguscarolinus Miiller) as well as species associated with the shrub and grass wetland such as the American Robin (Turdusmigratorius L.), the Veery (Catharusfuscescens Stephens), and the Common Yellowthroat (Geothlypistrichas L.). The shrub-foraging guild showed higher abundance in riparian stands. The tree-foraging and tree-bole foraging guilds, however, were comparable in both groups of stands. In this study, the natural conditions prevailing along he riparian sites appeared mostly positive for the breeding-bird community; it created what is perceived as being an "edge effect." The edge effect can be defined, in this case, as being the additional density and number of species induced by the added horizontal vegetation diversity created by the close association of three extremely different ecosystems: a forest stand, an aquatic ecosystem, and a narrow but distinct shrub-grass wetland. This also confirms the necessity of distinguishing natural edges that are permanent features of the landscape from induced edges created by human activity.

Birds in patches of old-growth ash forest, in a matrix of younger forest

1998 ◽  
Vol 4 (2) ◽  
pp. 111 ◽  
Author(s):  
Richard H. Loyn
Keyword(s):  
Forest Structure ◽  
Patch Size ◽  
Forest Birds ◽  
Old Growth ◽  
Forest Patches ◽  
Bird Abundance ◽  
Old Growth Forest ◽  
Generalized Linear Modelling ◽  
Mountain Ash ◽  
Context Variables

Birds were studied at 57 sites in Mountain Ash forests in the Central Highlands of Victoria, Australia in spring and summer 1995/96. The sites represented 41 patches of old-growth forest (up to 390 ha in size) in a matrix of regrowth mostly from severe fires in 1939 (57 years previously), with multiple sites in the four largest patches of old-growth and eight sites in 1939 regrowth. Relative bird abundance was assessed by an area-search technique. Generalized linear modelling was used to develop predictive models by regressing abundance of groups of bird species against patch size, isolation and some basic habitat and context variables. Total bird abundance (of all species combined) tended to be higher in old-growth patches than in 1939 regrowth, but not significantly. There was no trend in total abundance with patch size or isolation. Fruit-eating birds tended to be commonest in small patches. Bark-foragers and uncommon birds favoured large patches, though the latter were most common in 1939 regrowth. More variation was explained by habitat and context variables such as aspect, altitude and forest structure. Unevenaged forest structure was often associated with small patches. It was concluded that old-growth forest patches can have similar values per hectare for forest birds whether they are large or small. The regrowth forest matrix appears to protect small patches from factors which reduce densities of forest birds in small forest patches in farmland. The data support the current policy of retaining all old-growth ash forest patches. A range of factors should be considered in selecting regrowth stands of various sizes to regrow as old forest of the future, including their intrinsic potential to develop particular habitats and produce a mix of forest stuctures in the landscape.

scholarly journals Patch size and vegetation structure drive changes to mixed-species flock diversity and composition across a gradient of fragment sizes in the Western Andes of Colombia

The Condor ◽  
2020 ◽  
Vol 122 (2) ◽  
Author(s):  
Harrison H Jones ◽  
Scott K Robinson
Keyword(s):  
Species Richness ◽  
Functional Diversity ◽  
Edge Effects ◽  
Vegetation Structure ◽  
Phylogenetic Diversity ◽  
Patch Size ◽  
Forest Edge ◽  
Mixed Species ◽  
Functional And Phylogenetic Diversity ◽  
Diversity Metrics

Abstract Forest fragmentation is a leading driver of biodiversity loss, yet its effects on positive species interactions remain poorly known. We examined the effects of fragmentation on mixed-species bird flocks in the Western Andes of Colombia. Using 500-m transect surveys (n = 14 transects), we sampled flocks in 8 fragments (range: 10–173 ha) and an unfragmented reference site within the same altitudinal band (1,900–2,200 m.a.s.l.) and matrix type (cattle pasture). We evaluated the relative contributions of 9 predictor variables, including patch size, distance from edge, and selective aspects of vegetation structure on the composition, size, species richness, functional diversity, and phylogenetic diversity of flocks. We found effects of both patch size and vegetation structure on flock species richness, size, and functional diversity, but no support for edge effects. Generally, flock richness and size responded differently to fragmentation than did functional and phylogenetic diversity metrics. Both flock size and richness increased with patch size, but this variable had no effect on functional and phylogenetic diversity. Flock richness and size increased in high-canopy forests with greater foliage height diversity, whereas unlogged, old-growth primary forests with large-diameter trees had lower flock richness and size, but significantly greater functional diversity. Phylogenetic diversity was not affected by patch size, edge effects, or vegetation structure. We found differences in flock composition in response to fragmentation. Richness of Furnariidae in flocks increased with increasing distance from edge and foliage height diversity, whereas that of Thraupidae and boreal migrant species increased in early successional and forest edge flocks, respectively. All flock diversity metrics differed significantly seasonally, with smaller, less diverse flocks observed in January–March than in June–August. Flocking behavior persisted in 10-ha fragments, likely because Andean flocks are “open membership” in nature, but there was extensive species turnover as forest edge and generalist species replaced forest-interior species in smaller fragments.

Vegetation structure drives mixed-species flock interaction strength and nuclear species roles

2020 ◽  
Author(s):  
Harrison H Jones ◽  
Scott K Robinson
Keyword(s):  
Vegetation Structure ◽  
Patch Size ◽  
Species Turnover ◽  
Interaction Strength ◽  
Global Network ◽  
Edge Density ◽  
Mixed Species ◽  
Network Measures ◽  
Old Growth Forest ◽  
Nuclear Species

Abstract Mixed-species flocks are a key facilitative interaction for tropical birds. Forest fragmentation leads to species loss and spatial turnover in these flocks, yet it is unknown how these changes to composition influence within-flock species interactions. We used network analysis to characterize flocking interactions along a fragment-size gradient in the Colombian Western Andes. We asked 1) how patch size, edge density, and vegetation structure explained network measures indicative of flock cohesion, 2) whether changes were driven by flocking species turnover or changes to the frequency of species co-occurrence, and 3) whether nuclear species, those that maintain flock stability and cohesion, changed in importance across the gradient. We constructed weighted social networks from flock compositions observed on 500-m transects, and then calculated global network measures and the centrality of six nuclear species. Patch size and edge density did not correlate with interspecific co-occurrence patterns, but interaction strength increased with canopy height. Flocks contained numerous, weak interactions, and there were no flock subtypes, suggesting flock composition was dynamic and unstructured. Several redundant nuclear species were present and varied in importance based on ecological conditions. A chlorospingus (Passerellidae) was most central in old-growth forest, whereas several tanager (Thraupidae) species became more central in smaller fragments and disturbed forest. When partitioning network dissimilarity, we found that 66% of dissimilarity resulted from species turnover, whereas only 34% resulted from changes to species co-occurrence. This finding suggests that coherence of flocking behavior itself is maintained even as extensive species turnover occurs from continuous forest to small fragments.

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