Bird Density Research Articles

Freshwater diversity in Svalbard: providing baseline data for ecosystems in change

The high Arctic is in a rapid transition due to climate change, and both direct effects due to warming and an extended growing season, as well as an indirect effect caused by increased bird activity and density (notably geese), strongly affect ponds and lakes. Our study presents the hitherto most comprehensive data on invertebrate freshwater diversity at Svalbard and had three main purposes: to provide a current “baseline” of community composition, to compare current species distribution and occurrence with older data to identify changes that have already occurred, and finally to identify how diversity and community composition are related to the age of localities. To address these aims, we conducted a survey of freshwater invertebrates in 75 ponds and lakes at Svalbard in August 2014 and 2015. We provide a full report of the species’ inventory data for zooplankton, benthos, and meiofauna. We also provide data for species that have likely colonized the sites over the previous decades. Finally, our study also clearly demonstrates a diversity gradient related to ecosystem age and/or parameters confounded with age (e.g., productivity), which may hint at the rate of colonization over the time span from the oldest to the youngest localities.

Complex behaviour in complex terrain - Modelling bird migration in a high resolution wind field across mountainous terrain to simulate observed patterns

Crossing of large ecological barriers, such as mountains, is in terms of energy considered to be a demanding and critical step during bird migration. Besides forming a geographical barrier, mountains have a profound impact on the resulting wind flow. We use a novel framework of mathematical models to investigate the influences of wind and topography on nocturnal passerine bird behaviour, and to assess the energy costs for different flight strategies for crossing the Jura Mountains. The mathematical models include three biological models of bird behaviour: i) wind drift compensation; ii) adaptation of flight height for favourable winds; and, iii) avoidance of obstacles (cross over and/or circumvention of an obstacle following a minimum energy expenditure strategy), which are assessed separately and in combination. Further, we use a mesoscale weather model for high-resolution predictions of the wind fields. We simulate the broad front nocturnal passerine migration for autumn nights with peak migration intensities. The bird densities retrieved from a weather radar are used as the initial intensities and to specify the vertical distributions of the simulated birds. It is shown that migration over complex terrain represents the most expensive flight option in terms of energy expenditure, and wind is seen to be the main factor that influences the energy expenditure in the bird's preferred flight direction. Further, the combined effects of wind and orography lead to a high concentration of migratory birds within the favourable wind conditions of the Swiss lowlands and north of the Jura Mountains.

Density and population estimates of Rose-bellied Bunting (Passerina rositae), Cinnamon-tailed Sparrow (Peucaea sumichrasti), and Orange-breasted Bunting (Passerina lechlancherii) in the Sierra Tolistoque, Oaxaca, Mexico

Micro-endemic species are at greater risk of extinction because of their small populations and limited distribution. We conducted a breeding population survey of 3 little-known Mexican endemic bird species: Rose-bellied Bunting (Passerina rositae), Cinnamon-tailed Sparrow (Peucaea sumichrasti), and Orange-breasted Bunting (Passerina lechlancherii) in Sierra Tolistoque, Oaxaca. The purpose of the survey was to (a) determine the population density and size of these 3 species in the Sierra Tolistoque, (b) estimate the relative importance of various landscape features for each species, and (c) provide more rigorous scientific information to aid in the conservation and management of these species. In the case of Rose-bellied Bunting, we aimed to assess whether it prefers ravines over other landscape types during the breeding seasons, as stated in previous studies. Between late May and June 2012, we conducted point counts (n = 209) throughout the southern slope of the Sierra Tolistoque on the Pacific slope of the Isthmus of Tehuantepec, in Oaxaca, Mexico. Overall bird density was 0.98 birds/ha for Rose-bellied Bunting, 0.547 birds/ha for Orange-breasted Bunting, and 0.514 birds/ha for Cinnamon-tailed Sparrow. The estimated population in each landscape category showed that despite the existence of subtle interspecific preferences, hillsides are the major reservoirs for the 3 species. Rose-bellied Bunting did not occur in greater density in ravines compared to hillsides, which comprised more than twice the area of ravines. The importance of the Sierra Tolistoque for the long-term conservation of the 2 micro-endemic species is crucial considering our population estimates suggest that ∼30% of the estimated world population of Rose-bellied Bunting and Cinnamon-tailed Sparrow are found within the range of the Sierra Tolistoque.

Paleoecology of seabirds at Nandao, Xisha Islands, South China Sea: Sub-fossil evidence for Ashmole's Halo during the Little Ice Age

Tropical seabirds play a key role in coral island ecosystems, but there are still many uncertainties regarding their paleoecology. Seabird paleoecology was investigated on Nandao Island, Xisha Islands, South China Sea, from sub-fossil remains spanning the past 800 years. Ornithogenic sediments were collected beneath seabird-inhabited shrubs where a large number of seabird/fish sub-fossils were recovered. We used reflectance spectroscopy to show that seabird population size was overall higher during the Little Ice Age (LIA) compared to periods before and after this event. Nonetheless, the number of seabirds also fluctuated during the LIA. Seabird populations on Nandao reached their highest points at 1480–1550 and 1650–1800 CE, respectively, but the population remained low from 1550 to 1650 CE. A large migration of seabirds from Nandao Island to the adjacent Beidao Island, where the population size surged at that time, is hypothesized to explain the corresponding decrease in the seabirds at Nandao. Stable isotope (δ15N and δ13C) analyses also suggest a change in foraging behavior by seabirds at Nandao during the period 1550–1650 CE. Seabirds at low population size foraged near the island and preyed upon smaller flying fish as inferred from low δ15N and high δ13C values in fish scales, but fed upon larger flying fish farther from the island during times of high population. This shift in foraging behavior is in accordance with predictions for Ashmole's Halo in that islands with high densities of birds will cause a depletion of resources near the colonies and force more distant foraging away from the colony.

Altitudinal patterns in breeding bird species richness and density in relation to climate, habitat heterogeneity, and migration influence in a temperate montane forest (South Korea).

Altitudinal patterns in the population ecology of mountain bird species are useful for predicting species occurrence and behavior. Numerous hypotheses about the complex interactions among environmental factors have been proposed; however, these still remain controversial. This study aimed to identify the altitudinal patterns in breeding bird species richness or density and to test the hypotheses that climate, habitat heterogeneity (horizontal and vertical), and heterospecific attraction in a temperate forest, South Korea. We conducted a field survey of 142 plots at altitudes between 200 and 1,400 m a.s.l in the breeding season. A total of 2,771 individuals from 53 breeding bird species were recorded. Altitudinal patterns of species richness and density showed a hump-shaped pattern, indicating that the highest richness and density could be observed at moderate altitudes. Models constructed with 13 combinations of six variables demonstrated that species richness was positively correlated with vertical and horizontal habitat heterogeneity. Density was positively correlated with vertical, but not horizontal habitat heterogeneity, and negatively correlated with migratory bird ratio. No significant relationships were found between spring temperature and species richness or density. Therefore, the observed patterns in species richness support the hypothesis that habitat heterogeneity, rather than climate, is the main driver of species richness. Also, neither habitat heterogeneity nor climate hypotheses fully explains the observed patterns in density. However, vertical habitat heterogeneity does likely help explain observed patterns in density. The heterospecific attraction hypothesis did not apply to the distribution of birds along the altitudinal gradient. Appropriate management of vertical habitat heterogeneity, such as vegetation cover, should be maintained for the conservation of bird diversity in this area.

Long-term avian response to fire severity, repeated burning, and mechanical fuel reduction in upland hardwood forest

Forest restoration, fuel reduction, and wildlife conservation management requires understanding if, and how repeated prescribed fire, fire severity, or mechanical methods can promote goals. We examined breeding bird response to repeated fuel reduction treatments by mechanical understory reduction (twice; Mechanical-only), prescribed burning (four times; Burn-only), or mechanical understory reduction plus burning (then three subsequent burns; Mechanical + Burn). Initial burns were hotter in Mechanical + Burn than Burn-only resulting in heavy tree mortality, canopy openness, thick shrub density, and abundant snags lasting several years. Relative density and species richness of birds increased in Mechanical + Burn within three breeding seasons of high-severity burns, and remained greater throughout subsequent burns. Increases were due to an influx of species associated with young forest conditions, with little change in most mature forest species. Repeated burning in Mechanical + Burn likely impeded forest maturation, allowing many scrub-shrub bird species to persist. Species richness in Burn-only did not differ from any treatment, but modest increases over time were apparent as structural heterogeneity increased with delayed tree mortality. Cavity-nester density was highest in Mechanical + Burn, but remained high even as snags fell to pretreatment levels. Ground-nester density was lower in Mechanical + Burn than Control and Mechanical-only, but ground-nesting species responded differently. Open woodlands were not created by any treatment due to persistent re-sprouting of top-killed trees and shrubs. We note that breeding birds appear to respond similarly to high-severity burns and silvicultural treatments with heavy canopy reduction, offering possible alternatives in managing upland hardwood forests for diverse breeding bird communities.

Bird diversity and dissimilarity show contrasting patterns along heavy metal pollution gradients in the Urals, Russia.

The effects of industrial pollution on bird diversity have been widely studied using traditional diversity measures, which assume all species to be equivalent. We compared species richness and Shannon index with distance-based measures of taxonomic, functional, and phylogenetic diversity (the abundance-weighted mean nearest taxon distances), which describe within-community dissimilarity at terminal branches. Analysis of dissimilarity can shed light on the processes underlying community assembly, i.e., environmental filtering decreases dissimilarity whereas competitive exclusion increases it. In the 2-year study near Karabash and Revda copper smelters in Russia, point counts of nesting birds and habitat descriptions were taken at 10 sites (40 plots) along each pollution gradient. The abundance and diversity of birds showed good repeatability in both regions. The total density of birds, number of species per plot, and Shannon diversity decreased at high toxic load in both regions. The taxonomic, functional, and phylogenetic nearest taxon distances showed the same pattern within regions. Species dissimilarity within communities increased with pollution in Karabash (due to loss of functionally similar species), but did not change in Revda (due to mass replacement of forest species by species of open habitats). Pollution-induced changes in bird communities near Karabash were greater due to the stronger deterioration of the forest ecosystems and less favorable natural conditions (more arid climate, lower diversity and vitality of the tree stand and understorey) compared to Revda. This study emphasizes the need for a multi-level approach to the analysis of bird communities using traditional indices of diversity, functional, taxonomic, or phylogenetic distances between species and environmental variables.

Fall vegetative cover and summer precipitation predict abundance of wintering grassland birds across the Chihuahuan desert

Local winter abundance of grassland passerines is highly variable throughout the Chihuahuan Desert among years. The objective of this study is to determine if plant biomass in grasslands and precipitation are predictors of bird abundance in space and time through Chihuahuan Desert. We conducted avian surveys in 17 Grassland Priority Conservation Areas (GPCA) in northern Mexico and southwestern United States in the winters of 2007–2011. We used distance sampling on line transects to estimate annual winter bird density in all GPCAs. We used a hierarchical model of distance sampling to estimate the effect of summer precipitation and vegetative cover during the fall on bird density for 10 grassland species. We used the MODIS NDVI at a pixel resolution of 231.5 m as a measure of plant biomass. Grasshopper Sparrow, Baird's Sparrow, Savannah Sparrow, Vesper Sparrow, and Eastern Meadowlark showed a strict positive response to NDVI, while Horned Lark, Sprague's Pipit, Chestnut-collared Longspur and Lark Bunting did not show a strictly-positive response to NDVI. Our results provide a valuable tool for the conservation of declining migratory birds on their wintering grounds by identifying a wildlife-habitat relationship using a remotely-sensed and readily available index of vegetative growth.

A survey of avifauna and vegetation communities in Hadejia-Nguru Wetlands, Nigeria

An understanding of the ecological relationship between birds and vegetation is important for management and conservation of any wetland ecosystem. Despite the significant importance of the Hadejia-Nguru Ramsar site and an Important Bird Area, little is known about the ecological relationship between bird and vegetation communities. Bird diversity and density were examined and compared between Protected Areas (PAs) and Unprotected Areas (UPAs) with attention to vegetation diversity and density. Data were collected from October to December, 2015. A total of 14 wetland sites were surveyed (seven in PAs and seven in UPAs), and point count method was emp oyed. In total, 42, 255 bird individuals, 148 species, 23 orders, and 50 families were identified. Two globally threatened species namely, European Turtle Dove ( Streptopelia turtur ) and Pallid harrier ( Circus macrourus ) were also recorded. Results showed that neither vegetation diversity nor density correlated with bird diversity nor density in both PAs and UPAs (p > 0.05), suggesting that there could be other factors that influence the bird diversity and density in both areas. PAs and UPAs of the Hadejia-Nguru Wetlands are rich in avifaunal species, thus management of these areas will preserve large species diversity. Increase public awareness in the wetland on the importance of conserving birds and vegetation, as they play a vital role in the ecosystem is strongly recommended. The results presented here provide an overview of the relationship between bird and vegetation communities of the Hadeji -Nguru Wetlands, an important input for better understanding of its conservation. Keywords: Bird diversity, Density, Hadejia- Nguru Wetlands, Protected and unprotected areas, Vegetation

Implications of transformation to irregular silviculture for woodland birds: A stand wise comparison in an English broadleaf woodland

Woodland birds in Britain have undergone significant long term declines since the late 1960s, associated in particular with changes in woodland structure in general, and loss of early successional vegetation. Irregular, continuous canopy broadleaf management is a form of selective logging, very recently adopted in UK that produces woodlands with open canopies and substantial mid- and understorey growth. We examined spring and late winter bird densities, estimated using distance sampling, at 310 points in irregular, transitional (that being managed towards irregular), limited intervention, and coppice stands within a large working broad-leaf woodland in lowland southern Britain. Almost all understorey and canopy vegetation measures differed significantly across stand types. Ten of 20 species had highest spring abundance in irregular woodland, five in coppice, three in transitional, and just two in limited intervention. In winter, 5–6 species preferred each of limited intervention, irregular and transitional, while no species preferred coppice. Densities differed little across seasons except in Paridae where abundances increased in late winter during which limited intervention stands were used more by this group. Birds generally occupied similar niche positions and had similar niche breadths across seasons. Compared to under-managed woodlands, irregular silviculture in UK’s broadleaf woodlands is likely to enhance habitat quality for woodland birds, including several species of conservation concern e.g. marsh tit Poecile palustris which was twice as abundant in irregular stands as in any other stand type.

Importance of Old Forest Stands for Diversity of Birds in Managed Pine Forests – A Case Study from Augustów Forest (NE Poland)

We assessed the assemblages of birds inhabiting pine-dominated managed forest, aged between 1–5 years and above 140 years. Birds were counted on study plots representing eight different phases to the forest's development, with nesting, foraging and migratory guild categories recognised. Numbers of bird species and population densities, both increased markedly with stand age (respectively r = 0.988 and r = 0.936, P < 0.001). While numbers of ground-nesting bird species failed to correlate with stand age, successively older stands did support ever-greater proportions of species in the assemblage that nested in tree crowns (r = 0.976, P < 0.005) or tree holes (r = 0.833, P < 0.005). Raptors were most abundant in forest at the oldest stages of growth, and there was an age-gradient-related increase in the shares of both plant-eating species (r = 0.952, P < 0.005) and raptors (r = 0.764, P < 0.005). Resident birds were most numerous in the oldest forest. PCA for ten selected variables (relating to guild type) showed that the two principal components explained almost 98% of the variation among groups of bird guilds in relation to forest age. On the basis of their suitability for birds it was possible to distinguish three categories of stand by age group, of which the first encompasses the initial stage, the second a broad interval involving middle-aged stands of between 16 and 140 years, and the third forest more than 140 years old. The presence of the oldest stands of all can thus be seen to play a very important role in maintaining high-diversity populations of birds in managed forest.

Large decline of birds in Sahelian rangelands due to loss of woody cover and soil seed bank

The large and widespread decline of European migratory birds spending the northern winter in the Sahel suggests – on top of adverse changes in the breeding quarters ‒ pivotal changes in African overwintering areas. This paper attempts to answer three questions related to the sub-Saharan region: (1) can a change in the woody vegetation explain the decline of migratory birds feeding in trees, (2) ditto for the ground vegetation and bird species searching for food on the ground, and (3) are African bird species also in decline? The analysis is confined to the western Sahel (annual rainfall 100–400 mm, 15.5–18°N and 14.7–16°W), a region intensively used as rangeland but too dry for agriculture. The woody cover, largely stable before 1970, declined in the driest zone by 90% between the 1960s and 2000s, and by 40% in the more humid zone where the woody cover was already low in the 1960s. The woody vegetation changed in many places from an Acacia savanna into an open savanna with scattered bushes and few trees, concomitant with a shift in species composition. These changes took place during a prolonged drought (1969–1992), and were aggravated by increased grazing pressure after the construction of boreholes as evident from the loss of woody cover close to boreholes. A comparison of bird composition and densities in grazed and ungrazed areas and in three study sites intermittently surveyed between 1960 and 1994, with our surveys in the same sites in 2014–2015, revealed about 80% losses for birds feeding on the ground. The increased grazing pressure of livestock must have caused a large reduction of the soil seed bank and most likely also of insects. Between 15 and 16°W an estimated 8 million arboreal birds, mainly migrants, and 30 million ground-feeding birds, mainly granivorous residents, lost their habitat. Assuming that this zone is representative for the Sahelian rangelands as a whole, 1.5–2.0 billion birds have lost their habitat in half a century.

Simultaneous modelling of movement, measurement error, and observer dependence in mark-recapture distance sampling: An application to Arctic bird surveys

Mark-recapture distance sampling is a promising method for surveying bird populations from aircraft in open landscapes. However, commonly available distance sampling estimators require that distances to target animals are made without error and that animals are stationary while sampling is being conducted. Motivated by a recent bird survey where these requirements were routinely violated, we describe a marginal likelihood framework for estimating abundance from double-observer data that can accommodate movement and measurement error when observations are made consecutively (as with front and rear observers), when animals are uniformly distributed during detection by the first observer, and when detections consist of both moving and stationary animals. Assuming that all animals are subject to measurement error and that some animals can move between detections, we integrate over unknown animal locations to construct a marginal likelihood for detection, movement, and measurement error parameters. Estimates of animal abundance are then obtained using a modified Horvitz–Thompson-like estimator. In addition, unmodelled heterogeneity in detection probability can be accommodated through observer dependence parameters. Using simulation, we show that our approach yields low bias compared to approaches that ignore movement and/or measurement error, including in cases where there is considerable detection heterogeneity. Applying our approach to data from a double-observer waterfowl helicopter survey in northern Canada, we are able to estimate bird density accounting for movement and measurement error and corrected for observer heterogeneity. Our approach appears promising for generating unbiased estimates of bird abundance necessary for reliable conservation and management.

Effect of beach management policies on recreational water quality

When beach water monitoring programs identify poor water quality, the causes are frequently unknown. We hypothesize that management policies play an important role in the frequency of fecal indicator bacteria (FIB) exceedances (enterococci and fecal coliform) at recreational beaches. To test this hypothesis we implemented an innovative approach utilizing large amounts of monitoring data (n > 150,000 measurements per FIB) to determine associations between the frequency of contaminant exceedances and beach management practices. The large FIB database was augmented with results from a survey designed to assess management policies for 316 beaches throughout the state of Florida. The FIB and survey data were analyzed using t-tests, ANOVA, factor analysis, and linear regression. Results show that beach geomorphology (beach type) was highly associated with exceedance of regulatory standards. Low enterococci exceedances were associated with open coast beaches (n = 211) that have sparse human densities, no homeless populations, low densities of dogs and birds, bird management policies, low densities of seaweed, beach renourishment, charge access fees, employ lifeguards, without nearby marinas, and those that manage storm water. Factor analysis and a linear regression confirmed beach type as the predominant factor with secondary influences from grooming activities (including seaweed densities and beach renourishment) and beach access (including charging fees, employing lifeguards, and without nearby marinas). Our results were observable primarily because of the very large public FIB database available for analyses; similar approaches can be adopted at other beaches. The findings of this research have important policy implications because the selected beach management practices that were associated with low levels of FIB can be implemented in other parts of the US and around the world to improve recreational beach water quality.

Recent climate change has increased forest winter bird densities in East Europe

AbstractRecent studies on climate change have reported serious impacts on winter forest birds in Western Europe. However, in areas where climate change has caused milder winters and more stable conditions in summer, one would expect resident bird populations to increase, rather than to decrease in winter. The aim of this study was to investigate the impact of climate change on the population dynamics of ten species of Passeriformes in the Tartarstan Republic, Russia. Ravkin's transect method was used to census fixed randomly selected plots spread over a large geographic area at least once every month for the past 26 years. Observers remained the same over the whole period. The abundance of nine species in the first half of the winter and four species in the second half of the winter showed significant increases during the study period. Unlike studies from countries in Western Europe, there were no significant decreases in these species. Significant changes in winter conditions, as well as during the breeding season, and an overall increase in annual temperatures are likely reasons for a significant increase in the number of birds in winter. Greater winter survival, an increase in the survival rate of fledglings and juveniles during the summer, and later onset of winter, are very important determinants of the winter population. Our findings show that numbers of birds in late winter are related to the severity of winter conditions. Our data do not support conclusions that the populations of forest bird species have decreased due to climate change.

Food preferences determine habitat selection at multiple scales: implication for bird conservation in tropical forests

AbstractForest degradation and fragmentation of quality habitat across the tropics underpins an urgent need for the conservation of area‐sensitive species. Management strategies adopted for small‐scale landscape patches may not be suitable for conservation of different communities across large landscapes. In this context, we examined the relationship of bird community composition and different bird functional groups with tree cover and normalized difference vegetation index (NDVI) at multiple landscape scales and also tested the effect of forest degradation on bird community composition. This study demonstrates the importance of core forest habitat for the conservation of area sensitive species. Forest degradation had negative impact on the bird community composition though some functional groups were associated with degraded areas. At the community level, bird density and richness was best explained by a combination of both NDVI at the patch level (50 m scale) and tree cover at the landscape level (500 m scale) where the patch level character was found to be more important than landscape level character. Most of the functional groups which preferred insects as primary or secondary diet items were sensitive to differences at the patch level (NDVI), whereas large frugivorous species were sensitive to differences at the landscape level (tree cover). High vegetation complexity should be conserved at the patch level (at least up to 50 m) for the conservation of insectivorous, nectarivorous and small to medium size frugivorous groups and tree cover should be conserved at the landscape level (at least up to 500 m) for the conservation of large‐bodied frugivorous birds.

Fine-scale heterogeneity drives forest use by spring migrant landbirds across a broad, contiguous forest matrix

ABSTRACT Much of our understanding of en route landbird habitat use comes from research performed at local scales, ignoring effects at larger spatial scales. We used a multiscale approach to investigate stopover habitat use by landbirds using transect surveys in 68 forested sites in southwestern Michigan, USA, during the springs of 2002 and 2003. We modeled relationships of bird density and arthropod abundance with broad-scale spatiotemporal factors (year, day of year, geographic location) and local landscape (forest composition and structure, presence of open water) as well as site-scale factors (bird density and arthropod abundance, which exchanged roles as predictor and response variables). We found migrant densities to be most influenced by fine-scale factors, such as the abundance of other avian taxa and substrate arthropods, followed by broader-scale factors, such as forest structure and location, within the local and broader surrounding landscape. We found that migrant habitat associations either d...

Probiotics on performance, intestinal morphology and carcass characteristics of broiler chickens raised with lower or higher environmental challenge

ABSTRACT: This study aimed to evaluate the effect of probiotics on performance, intestinal morphology and carcass characteristics of broiler chickens housed on lower or higher environmental challenge. Three hundred male Cobb chicks were distributed into four groups in completely randomised design with treatments arranged in a 2 x 2 factorial scheme to evaluate effects of two diets (with or without probiotics) and two environmental conditions (lower or higher challenge), totaling four treatments with five replications with 15 birds per box. Probiotics were added on diets and were composed of Lactobacillus acidophilus, Bacillus subtilis, Bifidobacterium bifidum and Enterococcus faecium. The environment with lower challenge was made up of new wood shavings used as litter, low bird density (8 birds/m2) and daily-cleaned bell drinkers. The environment with higher challenge was made up of re-used wood shavings used as litter (after three broods of broilers), bird density of 16 birds/m2 with bell drinkers cleaned every two days. No significant interaction between diet and environmental challenge was found for any of the variables evaluated. Performance, slaughterhouse variables and chemical carcass composition were not affected by the use of probiotics. Chicks receiving diets without probiotics had lower intestinal crypt depth (267.1 vs. 316.6 pm, P=0.0068). Birds raised in the environment with higher challenge decreased feed intake (4,660 vs 5,020 g, P=0.0422), weight gain (2,610 vs 2,810 g, P= 0.0054), drumstick and thigh yield (21.98 vs 24.14 %, P=0.0354), and increased crypt depth (325.2 vs 258.5 pm P=0.0009). In conclusion, the probiotic does not promote satisfactory improvements, regardless of the environmental challenge.

Variations in pest bird density in Argentinean agroecosystems in relation to land use and/or cover, vegetation productivity and climate

Context Changes in environmental conditions may influence bird populations, including pest bird species, and their distribution. In Argentina, particularly in the Pampas region, agricultural expansion has resulted in important changes in agroecosystems, with impacts on bird species. Aims This study analysed the relationship between pest bird densities and the environmental variables associated with land use and/or cover, vegetation productivity and climate. The study focused on the most important pest bird species to grain crops in Argentina and Uruguay: the eared dove (Zenaida auriculata) and the monk parakeet (Myiopsitta monachus). Methods An area in Central Argentina was divided into three agro-productive regions, one predominantly agricultural and two with mixed production activities: agricultural rangeland and agricultural forested rangeland. Bird populations were sampled on a yearly basis between 2003 and 2011 in point-transects located along secondary roads (47 routes in total). Linear mixed models and a multi-model inference approach were used to compare the effects of individual predictive variables on bird densities. Key results Mean estimated density for the eared dove was 0.39 individuals per ha (±0.02), almost three times the density of the monk parakeet (0.10 individuals per ha±0.02). The spatial distribution of changes in density of the eared dove and monk parakeet showed irregular patterns across the study area. Density of eared dove was directly related to cover of native and exotic woodlots and inversely related to cover of fallow and weedy fields, and to temperature and rainfall. Monk parakeet density, in turn, was directly related to cover of woodlots. Conclusions The density of eared doves and monk parakeets changed mostly in relation to land use and/or cover and, to a lesser extent, to climatic conditions. Information of pest bird populations in a long-term period allowed us to understand spatial patterns in bird population distribution and to identify the main environmental factors explaining them. Implications The consideration of land use and/or cover, vegetation productivity and climate variables at regional scale, measured during a long-term period, would be critical for anticipating population increases and, possibly, increases in crop damage.

A Review on Influence of Heat Stress in Poultry Production and Approaches to Combat it

Temperature and moisture of air are two major environmental factors controlling the heat stress of livestock. The general signs of heat stress in poultry includes open mouth panting while spreading their wings and squatting close to the ground, gasping, lethargic and droopy acting, closed eyes, lying down, decreased appetite, increased thirst, drop in egg production, reduced body weight, increased cannibalism etc. Heat stress during the growth period of broilers has been associated with undesirable meat characteristics and quality loss. Ventilation, bird density and nutrition are a few areas that play a role in controlling heat accumulation. Nutritional manipulations, such as addition of fat and reduction of excess protein along with vitamin, minerals and electrolyte supplementations have been reported to reduce mortality due to heat stress.