Using bioacoustics to examine shifts in songbird phenology

Monitoring patterns in biodiversity and phenology have become increasingly important given accelerating levels of anthropogenic change. Long‐term monitoring programs have reported earlier occurrence of spring activity, reflecting species response to climate change. Although tracking shifts in spring migration represents a valuable approach to monitoring community‐level consequences of climate change, robust long‐term observations are challenging and costly. Audio recordings and metrics of bioacoustic activity could provide an effective method for monitoring changes in songbird activity and broader biotic interactions. We used 3 years of spring and fall recordings at six sites in Glacier Bay National Park, Alaska, an area experiencing rapid warming and glacial retreat, to examine the utility of bioacoustics to detect changes in songbird phenology. We calculated the Acoustic Complexity Index (ACI), an algorithm representing an index of bird community complexity. Abrupt changes in ACI values from winter to spring corresponded to spring transition, suggesting that ACI may be an effective, albeit coarse metric to detect the arrival of migrating songbirds. The first peak in ACI shifted from April 16 to April 11 from 2012 to 2014. Changes in ACI were less abrupt in the fall due to weather events, suggesting spring recordings are better suited to indicate phenology. To ensure changes in ACI values were detecting real changes in songbird activity, we explored the relationship between ACI and song of three species: varied thrush   (Ixoreus naevius), Pacific wren (Troglodytes pacificus), and ruby‐crowned kinglet (Regulus calendula). ACI was positively related to counts of all species, but most markedly with song of the varied thrush, the most common species in our recordings and a known indicator of forest ecosystem health. We conclude that acoustic recordings paired with bioacoustic indices may be a useful method of monitoring shifts in songbird communities due to climate change and other sources of anthropogenic disturbance.     

Failure to detect seasonal changes in the song system nuclei of the black‐capped chickadee (Poecile atricapillus)

Most temperate songbird species sing seasonally, and the brain areas involved in producing song (the song system) vary in size alongside the changes in behavior. Black‐capped chickadees (Poecile atricapillus) also sing seasonally, and we find that there are changes in the stereotypy and the length of the fee‐bee song from the nonbreeding to the breeding season. Yet despite these changes, we fail to find any evidence of seasonal changes in the song system. The song system of males is larger than that of females, as is typical in songbirds, but the ratio between the sexes is small compared to other species. We suggest three hypotheses to explain our failure to find seasonal variation in the chickadee song system. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Local habitat complexity correlates with song complexity in a vocally elaborate honeyeater

Song complexity is an important behavioural trait in songbirds, subject to sexual selection. Elucidation of intraspecific variation in song complexity can provide insights into its evolution. In this study, we investigated song complexity variation in tūī (Prosthemadera novaeseelandiae), a vocally complex songbird endemic to New Zealand. At two separate nature reserves, we recorded male songs in two habitat types: forest remnants with high habitat complexity, and open habitats with lower habitat complexity. Analyses indicated strong evidence that song complexity was higher in forest habitats. Possible explanations for this divergence include: (i) competition between individuals results in higher quality, dominant males with more complex songs occupying forest habitats, and less competitive males occupying open habitat zones; (ii) forest habitats provide more abundant resources therefore higher tūī density, resulting in more complex songs; and (iii) a higher abundance of food in dense forest habitats may reduce nutritional stress during development resulting in full development of song nuclei. However, these hypotheses on the drivers of habitat effects on tūī song complexity remain to be tested.     

Soil Calcium and Forest Birds: Indirect Links Between Nutrient Availability and Community Composition

Calcium is an important nutrient that can be limiting in many forest ecosystems, where acid deposition and other natural and anthropogenic activities have resulted in significant soil calcium depletion. Calcium’s critical role in physiological and structural processes and its limited mobility and storage in many organisms, make it a potential driver of ecosystem structure and function, but little is known about how changes in soil calcium affect community composition, especially in terrestrial vertebrates. The aim of this study was to establish relationships between the abundances of forest songbird species and soil calcium and to elucidate linking mechanisms by establishing simultaneous relationships with trophic and habitat variables. We measured soil calcium and pH, calcium-rich invertebrate abundances, vegetation, and songbird abundances at 14 interior forest sites across central Pennsylvania representing a range of soil calcium levels. Bird community composition varied with soil calcium and pH, with 10 bird species having the highest abundances in forests with high calcium soils, and five species having the highest abundances with low calcium soils. Bird species associated with low-calcium soils were associated with high densities of mountain laurel (Kalmia latifolia), an acid-loving shrub, whereas bird species associated with high-calcium soils were associated with high densities of saplings and high basal area of acid-sensitive tree species. Homogenization of soil conditions through land-use patterns and soil calcium depletion pose the risk of reducing the beta diversity of bird species across forest areas because community composition varied with soil calcium.     

Changes in the land mollusc fauna and soil chemistry in an inland district in southern Sweden

The land mollusc fauna and some abiotic soil variables were investigated at 20 forest sites SW of Vaxjo, southern Sweden, in 1964-66 and again in 1987-88 to evaluate possible effects of soil acidification, base cation leaching and nitrogen deposition The number of snail individuals decreased on average by 60% in herb-rich deciduous forests and by 80% in spruce and herb-poor oak forests Nesovitrea petronella, N hammonis, Euconulus fulvus, Vertigo substriata, Cochlicopa lubrica and Clausilia bidentata were most affected The calcium content in litter and surface layer of soil had decreased on average by 31%
The snail number decrease is negatively correlated to base saturation In the lower range of calcium content the change is in good accordance with a significant regression line of abundance on calcium from 1964–66
The snail abundance is positively correlated to base saturation, to soil moisture and probably also to nitrogen content
The soil chemistry and the snail fauna of the coniferous forest sites are so severely affected that a continued acidification and base cation leaching might lead to extinction of the snail fauna in this kind of forest Problems, possibilities and use of results from retrospective studies on the soil fauna are discussed     

Growth,net photosynthesis and leaf nutrient status of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings grown in brown forest soil acidified with H<Subscript>2</Subscript>SO<Subscript>4</Subscript> or HNO<Subscript>3</Subscript> solution

To obtain basic information for evaluating critical loads of acid deposition for protecting Japanese beech forests, growth, net photosynthesis and leaf nutrient status of Fagus crenata seedlings grown for two growing seasons in brown forest soil acidified with H₂SO₄ or HNO₃ solution were investigated. The whole-plant dry mass of the seedlings grown in the soil acidified by the addition of H₂SO₄ or HNO₃ solution was significantly less than that of the seedlings grown in the control soil not supplemented with H⁺ as H₂SO₄ or HNO₃ solution. However, the degrees of reduction in the whole-plant dry mass and net photosynthetic rate of the seedlings grown in the soil acidified by the addition of H⁺ as H₂SO₄ solution at 100 mg l^–1 on the basis of air-dried soil volume (S-100 treatment) were greater than those of the seedlings grown in the soil acidified by the addition of H⁺ as HNO₃ solution at 100 mg l^–1 (N-100 treatment). The concentrations of Al and Mn in the leaves of the seedlings grown in the S-100 treatment were significantly higher than those in the N-100 treatment. A positive correlation was obtained between the molar ratio of (Ca+Mg+K)/(Al+Mn) in the soil solution and the relative whole-plant dry mass of the seedlings grown in the acidified soils to that of the seedlings grown in the control soil. Based on the results, we concluded that the negative effects of soil acidification due to sulfate deposition are greater than those of soil acidification due to nitrate deposition on growth, net photosynthesis and leaf nutrient status of F. crenata, and that the molar ratio of (Ca+Mg+K)/(Al+Mn) in soil solution is a suitable soil parameter for evaluating critical loads of acid deposition in efforts to protect F. crenata forests in Japan.     

Toward a recovery time: forest herbs insight related to anthropogenic acidification

Atmospheric deposition is a global concern contributing to soil acidification and biodiversity changes in forest ecosystems. Although acidifying deposition has decreased in the last decades in Europe, few evidence of ecosystem recovery from acidification has been reported until now. The objective of this study was to reconstruct spatiotemporal changes in soil pH across the entire French forest territory over the last 100‐year period through herb species assemblages. Data were collected from floristic databases resulting in a total of 120 216 plots covering French forests and spanning from 1910 to 2010. To define acidity figures, pH values were inferred from herb assemblages for each plot of the prediction dataset based on a weighted averaging partial least squares (WA‐PLS) model (R² = 0.80, SD = 0.59 for the validation dataset). Spatiotemporal trends of mean pH changes were obtained by comparing plots with respect to the period (mean year of the period = 1933, 1966, 1984, 1997, 2007) and substrate (acidic and nonacidic forest areas). Bioindicated pH highlighted a decrease in soil pH in both acidic and nonacidic forest areas. The sharpest and most significant pH decrease occurred before 1984 in acidic areas, reaching 0.34 pH units. Subsequently, no significant changes were observed, with a tendency toward stabilization. By contrast, the pH decrease reached 0.19 pH units in nonacidic areas, only reaching significance between 1984 and 1997. Thereafter, we observed a slight and significant pH increase. Spatially, pH trends revealed a regionalized character of acidification regarding the substrate, which could not be related to the extent of deposition modeled by the European Monitoring and Evaluation Programme. Both temporal and spatial trends highlight the lagged responses of nonacidic areas compared with acidic areas. Hence, floristic reconstructed pH trends demonstrate a gradual cessation and recovery from acidification of French forests after a period of intense atmospheric pollution.     

华西雨屏区植被恢复对紫色土酸化的影响

退耕还林是控制水土流失、恢复森林植被和改善生态环境的重要举措。植被恢复进程中会发生土壤酸化,进而影响植物生长,厘清不同还林树种对土壤酸化的影响程度及作用机制有助于更好地评估退耕还林工程的整体生态效益。以华西雨屏区紫色土坡耕地(玉米)为对照,分析了退耕20a后柳杉纯林、柳杉-光皮桦混交林、慈竹林和茶园土壤pH的变化及其垂直分异。结果表明：玉米地、慈竹林、茶园、混交林和柳杉纯林0—50 cm土壤pH平均值分别为5.66、5.55、5.12、5.03和5.00,相较于玉米地,柳杉纯林、混交林和茶园土壤pH值显著下降(P<0.01),土壤酸化严重。相较于玉米地土壤pH值的均匀分布,植被恢复不同类型人工林pH值随土壤深度的增加而增加,10—50 cm土壤pH值(4.89—5.90)显著高于0—10 cm土壤pH值(4.72—5.21)(P<0.01),表层土壤酸化最明显。土壤pH值与土壤有机质含量呈极显著负相关,而与风化指数Na/K比值呈显著正相关,有机质含量和Na/K比值共同解释了土壤pH值变化的53.9%,表明植被恢复引起的土壤有机质积累与长石类矿物风化是驱动紫色土酸化的重要过程...     

A role for migration‐linked genes and genomic islands in divergence of a songbird

Next‐generation sequencing has made it possible to begin asking questions about the process of divergence at the level of the genome. For example, recently, there has been a debate around the role of ‘genomic islands of divergence’ (i.e. blocks of outlier loci) in facilitating the process of speciation‐with‐gene‐flow. The Swainson's thrush, Catharus ustulatus, is a migratory songbird with two genetically distinct subspecies that differ in a number of traits known to be involved in reproductive isolation in birds (plumage coloration, song and migratory behaviour), despite contemporary gene flow along a secondary contact zone. Here, we use RAD‐PE sequencing to test emerging hypotheses about the process of divergence at the level of the genome and identify genes and gene regions involved in differentiation in this migratory songbird. Our analyses revealed distinct genomic islands on 15 of the 23 chromosomes and an accelerated rate of divergence on the Z chromosome, one of the avian sex chromosomes. Further, an analysis of loci linked to traits known to be involved in reproductive isolation in songbirds showed that genes linked to migration are significantly more differentiated than expected by chance, but that these genes lie primarily outside the genomic islands. Overall, our analysis supports the idea that genes linked to migration play an important role in divergence in migratory songbirds, but we find no compelling evidence that the observed genomic islands are facilitating adaptive divergence in migratory behaviour.     

Forest/environment relationships in Yosemite National Park,California, USA

Forest compositional patterns in Yosemite National Park, California, were related to environmental factors through numerical classification of forest types, arrangement of forest types along elevational and topographic gradients, and development of regression models relating basal area of common tree species to environmental variables. The eight forest types are differentiated primarily by elevation zone and secondarily by topographic setting. Lower montane forests (1200–1900 m) were divided into the Abies concolor/Calocedrus type occurring primarily on mesic sites and the Pinus ponderosa/Calocedrus type predominantly on xeric sites. Upper montane forests (1900–2500 m) included the Abies concolor/Abies magnifica type on mesic sites, the Abies magnifica/Pinus type on somewhat more xeric sites, and Juniperus occidentalis/Pinus jeffreyi woodlands on granitic domes. Subalpine forests (2500–3300 m) embraced three types: Tsuga mertensiana/Pinus forests on mesic sites, monotypic Pinus contorta forests on drier sites, and Pinus albicaulis/Pinus contorta groves at treeline. Regression models consistently included elevation and soil magnesium content as explanatory variables of species basal area totals. The two Abies spp. were negatively correlated with soil magnesium levels, whereas other montane species (e.g. Calocedrus decurrens, Pinus lambertiana, and Pinus ponderosa) exhibited positive correlation with soil magnesium. Topography and soil physical properties were only infrequently incorporated into species regression models.Abbreviations DBH= diameter at breast height (1.4 m) - DCA= detrended correspondence analysis - TWINSPAN= two-way indicator species analysis     

Diversity of understory birds in old stands of native and Eucalyptus plantations

We compared the vegetation structure between old (>70 year) stands of planted diversified native forests and stands of Eucalyptus tereticornis embedded in a mosaic of Eucalyptus stands. We then tested for differences in the abundance, species richness, species composition, and ecological traits (forest dependence, sensitivity to forest fragmentation, and diet) of the understory bird assemblages inhabiting both kinds of stands. We expected differences in the structure of the bird assemblages because of the different origins and management strategies (contrary to native stands, Eucalyptus stands were selectively logged in the past). Three stands of each habitat (native and Eucalyptus) were sampled with mist nets during 11 months. Eucalyptus stands had a denser understory, whereas native plantations had a more developed vertical structure and a greater density of native trees. The abundance distribution of bird species was more homogeneous in Eucalyptus than in native stands. Eucalyptus had slightly higher species richness (36 species) than native stands (32 species). The composition of species and the occurrence of the diet, forest dependence, and sensitivity to forest fragmentation categories were similar between habitats. Some bird species (e.g. Turdus leucomelas), however, were more abundant in one habitat over the other. Old stands of Eucalyptus and planted native forest can harbor a diverse bird community similar in structure but not exactly equivalent for individual bird species. Planting native diversified forests and keeping set‐aside stands of the exotic tree should be viewed as complementary rather than alternative strategies for maintaining bird diversity within plantations.     

Social cues facilitate habitat selection: American redstarts establish breeding territories in response to song

For migratory songbirds nesting in northern temperate forests, a short breeding season demands that males rapidly establish territories. Because critical insect and vegetation resources are unavailable during spring arrival, we suggest that conspecifics serve as settlement cues for males new to a local population. To test conspecific attraction, we conducted playback experiments with American redstarts Setophaga ruticilla. Experimental results demonstrate that song playbacks strongly attract conspecifics, recruiting an average of 4.2 additional males per plot; adult males new to our sites increased, while yearling males failed to respond. Yearlings arrived 6 to 10 days later than adults, raising the possibility that yearlings responded to songs of early arriving adults rather than to playbacks. Our work indicates that conspecific attraction is an important mechanism for breeding habitat selection in an established population of a migratory forest songbird, but the effect is moderated by age, reproductive experience and arrival timing.     

Acidification: its impact on the environment and mitigation strategies

The effect of acidification on ecosystems is reviewed. About 30% of the world land area is acidified mostly by natural processes. Only a small part of it is acidified from pollution which leads to extensive forest and surface water deterioration in Europe and North America. The damage is especially visible in areas of poor soil quality. The acid deposition pattern is characterized, with a special emphasis on Poland. It was shown that strategies for mitigation of ecosystem acidification lead to a decrease of SO₂ emissions due to the use of lower sulphur content fuels and application of desulphurisation methods. Also, a decrease in NO_x emissions is observed due to use of catalysts and application of NO_x removal technologies. However, since about 50% of NO_x emission is from vehicles, this improvement is offset by a continuously increasing vehicle population. The application of liming, forest fertilisation and suitable land use for mitigation of ecosystem acidification is also reviewed.     

Early singers attend to conspecific but not heterospecific behavioural cues at dawn

During the dawn chorus songbirds initiate singing activities just prior to sunrise. Environmental factors affect the timing of the dawn chorus, but relatively little is known about how behavioural cues influence chorus timing. We assessed whether early playback of conspecific and heterospecific song influenced chorus start times in two early‐singing temperate species, hermit thrush Catharus guttatus and veery C. fuscescens. We used arrays of GPS time‐synchronized recorders to record the dawn chorus at 30 locations. In each location, thirty minutes prior to natural chorus initiation, we broadcast: 1) an early singing species (hermit thrush or veery), 2) a late singing species (black‐throated green warbler Setophaga virens or Nashville warbler Oreothlypis ruficapilla), 3) a noise control, and 4) also recorded without playback (silent control). Playback treatments were separated by two‐three days at each location. Both hermit thrush and veery sang significantly earlier in response to conspecific playback compared to noise or silent controls. Both species also sang earlier in response to conspecific playback compared to the day before or the day after playback. Neither species sang earlier in response to heterospecific playback (regardless of whether the broadcast species was a naturally early or late song initiator) compared to noise or silent controls. Our results support the theory that the dawn chorus is a communication network where individuals attend primarily to conspecific cues; heterospecific song appears to have minimal impacts on the chorus start times of the two early‐singing species we investigated.     

Effects of European Earthworm Invasion on Soil Characteristics in Northern Hardwood Forests of Minnesota, USA

European earthworms are colonizing worm-free hardwood forests across North America. Leading edges of earthworm invasion in forests of northern Minnesota provide a rare opportunity to document changes in soil characteristics as earthworm invasions are occurring. Across leading edges of earthworm invasion in four northern hardwood stands, increasing total earthworm biomass was associated with rapid disappearance of the O horizon. Concurrently, the thickness, bulk density and total soil organic matter content of the A horizon increased, and it’s percent organic matter and fine root density decreased. Different earthworm species assemblages influenced the magnitude and type of change in these soil parameters. Soil N and P availability were lower in plots with high earthworm biomass compared to plots with low worm biomass. Decreases in soil nitrogen availability associated with high earthworm biomass were reflected in decreased foliar nitrogen content for Carex pensylvanica, Acer saccharum and Asarum canadense but increased foliar N for Athyrium felix-femina. Overall, high earthworm biomass resulted in increased foliar carbon to nitrogen ratios. The effects of earthworm species assemblages on forest soil properties are related to their feeding and burrowing habits in addition to effects related to total biomass. The potential for large ecosystem consequences following exotic earthworm invasion has only recently been recognized by forest ecologists. In the face of rapid change and multiple pressures on native forest ecosystems, the impacts of earthworm invasion on forest soil structure and function must be considered.     

Molecular characterization and distribution of Haemoproteus minutus (Haemosporida,Haemoproteidae): A pathogenic avian parasite

Recently, the lineage hTURDUS2 of Haemoproteus minutus (Haemosporida, Haemoproteidae) was reported to cause mortality in captive parrots. This parasite lineage is widespread and prevalent in the blackbird Turdus merula throughout its entire distribution range. Species identity of other closely related lineages recently reported in dead parrots remains unclear, but will be important to determine for a better understanding of the epidemiology of haemoproteosis. Using polymerase chain reaction (PCR)-based and microscopic methods, we analyzed 265 blood samples collected from 52 species of wild birds in Eurasia (23 samples from Kamchatka Peninsula, 73 from Sakhalin Island, 150 from Ekaterinburg and 19 from Irkutsk regions of Russia). Single infections of the lineages hTURDUS2 (hosts are redwing Turdus iliacus and fieldfare Turdus pilaris), hTUPHI1 (song thrush Turdus philomelos) and hTUCHR01 (fieldfare, redwing, song thrush and brown-headed thrush Turdus chysolaus) were detected. We identified species of these haemoproteids based on morphology of their blood stages and conclude that these lineages belong to H. minutus, a widespread parasite of different species of thrushes (genus Turdus), which serve as reservoir hosts of this haemoproteid infection. Phylogenetic analysis shows that the lineages hTURDUS2, hTUCHR01 and hTUPHI1 of H. minutus are closely related to Haemoproteus pallidus (lineages hPFC1 and hCOLL2), Haemoproteus pallidulus (hSYAT03), and Haemoproteus sp. (hMEUND3); genetic distance among their mitochondrial cytochrome b (cyt b) lineages is small (< 1% or < 4 nucleotides). All these blood parasites are different in many morphological characters, but are similar due to one feature, which is the pale staining of their macrogametocytes' cytoplasm with Giemsa. Because of the recent publications about mortality caused by the lineages hTUPHI1 and hTURDUS2 of H. minutus in captive parrots in Europe, H. minutus and the closely related H. pallidus and H. pallidulus are worth more attention as these are possible agents of haemoproteosis in exotic birds. The present study provides barcodes for molecular detection of different lineages of H. minutus, and extends information about the distribution of this blood parasite.     

Decline in snail abundance due to soil acidification causes eggshell defects in forest passerines

On poor soils in the Netherlands an increasing number of great tits, Parus major, and of other forest passerines produce eggs with defective shells and have low reproductive success as a result of calcium deficiency. A similar increase in eggshell defects has been observed in Germany and Sweden. Snail shells are the main calcium source for tits in forests where defective eggshells do not occur, but are very little taken in forests where tits often have eggshell defects. We investigated whether a decrease in snail abundance on poor soils could be responsible for the decline in eggshell quality, and if so, what caused this decrease. Snail density in forests where tits have eggshell defects was much lower than in forests where tits do not have such defects. Snail density correlated with the calcium content and to a lesser extent with pH of the litter layer. Liming of a calciumpoor forest soil with few snails resulted in snail densities comparable to those on calcium-rich soils after 4 years. Snail density has declined on calcium-poor soils over the last two decades, but not on calcium-rich soils. Acid deposition has caused a decline of soil calcium on poor soils. We conclude, therefore, that anthropogenic acidification has caused a decline in snail populations, resulting in an increase in eggshell defects in birds in forests on poor soils.     

Influence of forest structure on density and nest success of mature forest birds in managed landscapes

Managing for forest wildlife requires attention not only to quantity but quality of forests within the landscape. We examined the extent to which local structural attributes and landscape context of forest stands explained variation in density and reproductive success of mature forest birds across 12 sites in southeast Ohio, USA, 2004–2006. Results suggest that several structural characteristics influenced bird–habitat relationships in our study. Densities of 3 songbird species (i.e., ovenbird [Seiurus aurocapilla], cerulean warbler [Setophaga cerulea], and scarlet tanager [Piranga olivacea]) were positively related to canopy openness, which is usually a function of canopy gaps. Habitat attributes described by ground litter, understory density, and canopy height were positively associated with densities of ground (i.e., worm-eating warbler [Helmitheros vermivorum]), or shrub nesting species (i.e., Kentucky and hooded warblers [Geothlypis formosa and Setophaga citrina], respectively). Furthermore, the number of small trees likely drove the positive relationship between density of wood thrush (Hylocichla mustelina), a subcanopy nester. After accounting for temporal variability in daily nest survival rates, the odds of nest survival for all species increased 10.5% for every 1% increase in canopy openness and decreased 1.4% for each 5% increase in understory vegetation density. Habitat–nest survival relationships were not apparent at the level of the individual species. Our results suggest that structural attributes produced by increasing habitat heterogeneity may be necessary for conservation of forest bird communities. © 2012 The Wildlife Society.     

Research on acidification in forest soil driven by atmospheric nitrogen deposition

Soil acidification is defined as the process in which exchangeable cations are leaching and soil H⁺ concentration is raising thereby increases soil acidity. Changes in soil pH value and acid neutralizing capacity are mainly indicators of soil acidification. Soil acidification is considered to be a serious ecological and environmental issue, which not only reduces soil quality, but also decreases biodiversity of forest ecosystem and induces forest decline. With nitrogen (N) deposition rapidly increasing, its contribution to soil acidification becomes a major concern in the world. However, the impact of increased N deposition on soil acidification is not well addressed highlighting the need for further attention to the issue. In this paper, the studies on forest soil acidification induced by N deposition were reviewed. The factors related to soil acidification driven by N deposition were classified and discussed, which included soil acidic buffering capacity, N components in atmospheric N deposition, climate, plant species in forests, and N status in ecosystem. Iron (Fe) buffering phase and the consequent Fe toxicity occurring to the acidified soil caused by high N deposition were concerned. The scarcity of phosphorus (P) element induced by soil acidification was particularly emphasized. The research methods used to study soil acidification driven by N deposition were also evaluated. In the end we stressed the importance of the study on soil acidification especially in tropical and subtropical regions driven by N deposition and its mechanisms. This paper can serve for maintaining sustainable forest and agricultural ecosystems.     

Fighting talk: complex song elicits more aggressive responses in a vocally complex songbird

Song complexity in many songbirds is a trait subject to sexual selection. It is often associated with male territorial defence. Empirical studies testing differential male responses to rival song in vocally complex songbirds have, however, been scarce. We conducted playback experiments of the endemic New Zealand Tui Prosthemadera novaeseelandiae to test the aggressive response of territorial male Tui to rival songs with differing complexity levels. Overall, complex songs evoked significantly stronger responses from territorial males than did simple songs. Following playback of complex songs, focal males approached the playback more closely and rapidly, and responded with songs of higher complexity than they did to playback of simple songs. This suggests males could both distinguish between different levels of complexity within the Tui repertoire, and perceive a more complex song as a greater territorial threat. Our study is one of the first to demonstrate strong aggressive responses to increased levels of song complexity in a songbird species with highly complex vocalizations.