Tropical Forest Birds Research Articles

The Effects of Disturbance Intensity on Tropical Forest Bird Communities and Vegetation Structure after Two Decades of Recovery

The Effects of Disturbance Intensity on Tropical Forest Bird Communities and Vegetation Structure after Two Decades of Recovery

Black is the new orange: flight initiation distance of a tropical forest bird in relation to human clothing colour

ABSTRACT Avitourism has multiple conservation and economic benefits but can pose potential harm to some bird populations. To mitigate the potential impacts of avitourism on birds, researchers can use flight initiation distance (FID) to quantify the tolerance of animals to perceived threats, thereby informing management. This study focused on whether clothing colour used by avitourists (orange, camouflage, and black) affected the FIDs of White-rumped Shama Copsychus malabaricus (n = 123) in a protected area in northeastern Thailand. Camouflage clothing evoked significantly shorter FIDs than orange and black clothing, which elicited statistically similar FIDs. The results of this study aligned with the colour concealment hypothesis, which suggests that clothing colour resembling the forest environment reduces detectability, which results in shorter FIDs. As such, clothing colour may mediate disturbance caused by avitourists. Given that at least one species of Southeast Asian tropical forest bird adjusts its FID in relation to clothing colour, FID studies on additional Asian tropical bird species and clothing colours are encouraged.

Tropical forest birds after 20 years of the establishment of a reservoir: Extinction, colonization, and recolonization events

Reservoirs are fundamental for human well-being but can cause landscape changes (e.g., habitat fragmentation and loss), altering biodiversity and ecosystem services. However, we know little about reservoir long-term effects on bird communities of tropical rainforests at different temporal scales. We assessed species richness and composition changes in four consecutive periods in a reservoir area in the Colombian Tropical Andes. After 20 years of monitoring avifauna within the reservoir, we recorded 360 bird species along with 47 local extinction and 184 colonization events. We found that species richness increased by 42% during the first 11 years after reservoir establishment. After that, changes in species bird composition were largely explained by species turnover. Eighty-two percent of the expected species in the region were recorded within the reservoir area. Also, forests surrounding the reservoir are a habitat for several threatened bird species. Bird community changes observed can be explained by secondary succession, changes in vegetation cover (i.e., increase in forest area), the transformation of aquatic ecosystems, forest protection, and restoration programs focused on biodiversity conservation. Long-term systematic bird sampling in tropical forests is key to understanding biodiversity dynamics and the effectiveness of conservation actions.

Further notes on the Estimation of Biodiversity and the Influence of Land use and Climate Warming on European Heath Bird Populations

The present commentary elaborates on the question whether interspecies and niche interactions and long-distance interactions between hibernating and breeding habitats are important for maintaining biodiversity in a changing world. The study focusses on the abundance trends of five bird species that are typical for heathland in North- Western Europe. The sympatric species Saxicola rubetra and Saxicola torquata, the Whinchat and the Stonechat respectively, receive special interest because of their very divergent conservation status and habitat preferences. An important result is that conservation practices (especially in natural reserves) should take more notice of the species-specific niche requirements and adopt the timing and precautionary requirements for biodiversity protection instead of promoting a few species at the cost of many others. In this study also an old hypothesis (formulated for tropical forest birds) is re-examined with respect the influences of seasonal migration and flexible versus stereotypical habitat selection on the long-term species survival potential, now applied to heath bird species. Outline Introduction: about an old question of tropical forest birds and seasonal migration Recent trends in Dutch bird populations: the European Nightjar and other heath birds Comparison with European trends for two sympatric species: the Whinchat and Stonechat Impact of agriculture and grassland management in the Netherlands Ecological networks of flowering plants, insects and birds Conclusions and recommendations

The effects of habitat heterogeneity, as measured by satellite image texture, on tropical forest bird distributions

Global biodiversity loss is most pronounced in the tropics. Monitoring of broad-scale patterns of habitat is essential for biodiversity conservation. Image texture measures derived from satellite data are proxies for habitat heterogeneity, but have not been tested in tropical forests. Our goal was to evaluate image texture to predict tropical forest bird distributions across Thailand for different guilds. We calculated a suite of texture measures from cumulative productivity (1-km fPAR-MODIS data) for Thailand's forests, and assessed how well texture measures predicted distributions of 86 tropical forest bird species in relation to body size, and nesting guild. Finally, we compared the predictive performance of combining (a) satellite image texture measures, (b) habitat composition, and (c) habitat fragmentation. We found that texture measures predicted occurrences of tropical forest birds well (AUC = 0.801 ± 0.063). Second-order homogeneity was the most predictive texture measure. Our models based on texture were significantly better for birds with larger body size (p < 0.05), but did not differ among nesting guilds (p > 0.05). Models that combined texture with habitat composition measures (AUC = 0.928 ± 0.038) outperformed models that combined fragmentation with habitat composition measures (AUC = 0.905 ± 0.047) (p < 0.05). The incorporation of texture, composition, and fragmentation variables significantly improved model accuracy over texture-only models (AUC = 0.801 ± 0.063 to AUC = 0.938 ± 0.034; p < 0.05). We suggest that texture measures are a valuable tool to predict bird distributions at broad scales in tropical forests.

The standing dead: Importance of snags for cavity-nesting birds in tropical periurban forests

Las áreas boscosas periurbanas representan un activo importante para la conservación, ya que estos sitios podrían mitigar los efectos de la modificación del paisaje. Sin embargo, estos bosques se enfrentan a un manejo sin supervisión que afecta la disponibilidad de recursos como las cavidades utilizadas por los vertebrados que anidan en ellas. Evaluamos la importancia ecológica de los árboles muertos en pie para las aves que anidan en cavidades en 3 remanentes periurbanos de bosque de niebla con diferentes tipos de manejo, grado de protección y tamaño en Veracruz, México. Comparamos la disponibilidad y las características de las cavidades y árboles muertos en pie, además de la densidad de las aves anidadoras primarias y secundarias de cavidades en 3 sitios con diferentes tamaños y grado de perturbación. No encontramos árboles muertos en pie y hubo menor densidad de cavidades en los fragmentos más pequeños, además de menor riqueza y densidad de aves que anidan en cavidades. Las cavidades más adecuadas fueron excavadas por pájaros carpinteros en árboles muertos, y se encontraban en el sitio más grande, donde también registramos la mayor abundancia de árboles muertos, aves excavadoras y la mayor riqueza de anidadores secundarios de cavidad. Nuestros resultados sugieren una sinergia de disponibilidad de árboles muertos en pie, excavadores primarios y riqueza de anidadores secundarios de cavidad en fragmentos de bosque de niebla. Además, acciones simples, como la eliminación de árboles muertos y/o la extracción de leña, actividades comunes en pequeños fragmentos de bosque, pueden alterar la composición de los ensambles de anidadores de cavidad con futuros impactos ecológicos inciertos. Palabras clave: árboles muertos, extracción de madera, manejo de bosques, México, recursos de anidación.

High sensitivity of tropical forest birds to deforestation at lower altitudes.

Habitat conversion is a major driver of tropical biodiversity loss, but its effects are poorly understood in montane environments. While community-level responses to habitat loss display strong elevational dependencies, it is unclear whether these arise via elevational turnover in community composition and interspecific differences in sensitivity or elevational variation in environmental conditions and proximity to thermal thresholds. Here we assess the relative importance of inter- and intraspecific variation across the elevational gradient by quantifying how 243 forest-dependent bird species vary in sensitivity to landscape-scale forest loss across a 3000-m elevational gradient in the Colombian Andes. We find that species that live at lower elevations are strongly affected by loss of forest in the nearby landscape, while those at higher elevations appear relatively unperturbed, an effect that is independent of phylogeny. Conversely, we find limited evidence of intraspecific elevational gradients in sensitivity, with populations displaying similar sensitivities to forest loss, regardless of where they exist in a species' elevational range. Gradients in biodiversity response to habitat loss thus appear to arise via interspecific gradients in sensitivity rather than proximity to climatically limiting conditions.

Birds in Temperate and Tropical Forests: Introduction to the Special Issue

Globally, forests are the most threatened habitats, especially due to tree logging and other disturbances caused mainly by humans [...]

Repeated burning undermines the value of regenerating cattle pastures for tropical forest birds

Repeated burning undermines the value of regenerating cattle pastures for tropical forest birds

Effects of forest fragmentation on the weight of understory birds at the Biological Dynamics of Forest Fragments Project in Amazonia

AbstractDeforestation and habitat fragmentation are known as the chief drivers of biodiversity loss. Less is known about the condition of species and individuals that remain in disturbed habitats. Theory predicts that resources are more limited after compared with before fragment isolation. Thus, we assessed how body condition of individual birds' changes in response to forest fragment isolation. We compared weights of the same individually banded birds caught in mist nets within 5 years before and after fragment isolation and assessed the population‐level changes of three species at the Biological Dynamics of Forest Fragments Project in the Brazilian Amazon. We predicted that fragment isolation would result in reduced weight for all bird species. Out of the 3466 bird mist net captures before and after isolation in the 1980s and the 2150 birds captured before and after re‐isolation of fragments in the 2010s, only 73 adult individuals from 36 different species were recaptured, suggesting that few individuals stay in fragments. Contrary to predictions, insectivorous species that remained in fragments gained weight (3.43%) after fragment isolation while frugivorous birds maintained a stable weight. While recent studies report long‐term declines in body mass of birds in tropical unfragmented tropical forests, our results provide a novel analysis into how avian body mass responds to habitat fragmentation. Further studies on the body condition of individuals that remain in fragments and the ultimate consequences of fluctuations in body condition are needed to better understand why some individuals and species are more susceptible to forest fragmentation than others.Abstract in Portuguese is available with online material

Repeated burning undermines the value of regenerating cattle pastures for tropical forest birds

Forest restoration has become a central strategy to conserve biodiversity, especially in the global tropics, but many priority regions are increasingly threatened by anthropogenic stressors. Of particular concern is the growing frequency of fire in humid tropical systems due to agricultural expansion and regional drying. Yet little is known about how fire affects recovery of tropical biodiversity in restored lands, including forest-dependent and threatened species. Here we provide the first assessment of the impacts of burning within naturally regenerating cattle pastures on pasture use by Neotropical forest birds. Working within 1–11-year-old regenerating pastures in Guatemala’s Maya Biosphere Reserve, we asked how occupancy rates of forest-dependent and threatened bird species differ between repeatedly burned and unburned pasture. To better understand the effect of fire on pasture use, we examined how species’ opportunistic use of regenerating pastures is a function of vegetation succession at local scales. We found that 70 forest-dependent and 19 threatened species used unburned pastures, but fire reduced or eliminated pasture use for 56% of forest-dependent and 53% of threatened species. Local vegetation succession explained the likelihood of colonizing pastures for nearly half of forest species that used regenerating pastures. Species closely associated with closed-canopy vegetation were most likely to be partially or fully excluded from burned pasture, suggesting that fire excluded certain species by impeding forest regrowth. Our results clearly demonstrate that burning undermines the high value of regenerating pastures for forest-dependent and threatened species and highlight the critical importance of preventing human-caused fires in restored tropical landscapes.

Predicting population trends of birds worldwide with big data and machine learning

Birds are crucial for the functioning of Earth’s ecosystems but bird population declines have been documented worldwide in recent decades. A global assessment of potential causes of population declines is needed. Our goal here was to combine the power of big data and machine learning to identify predictors correlated with bird population declines and to predict population declines for species with unknown population trends on the IUCN Red List. From existing online databases, we gathered detailed species‐level data for 10 964 extant bird species around the world, featuring life history, ecology, distribution, taxonomy and categorical population trend information (i.e. decreasing or not decreasing). For the 10 163 species with known population trends, we split the data into a 75% training set to tune and train a machine‐learning model (Light Gradient Boosting Machine – ‘LightGBM’) and a 25% test set to evaluate the trained model. Our model predicted (i) bird population declines with an ROC AUC score of 0.828, F1 score of 0.748 and average accuracy of 0.747, and (ii) that 47% (n = 801) of bird species with currently unknown population trends are declining. Correlation analyses suggested that, globally, the top predictor associated with bird population declines was a severely fragmented population, with non‐migratory birds in South American and Southeast Asian tropical and subtropical forests being particularly vulnerable. Despite the lack of long‐term quantitative population trend data for all species worldwide, our study presents big data and machine learning as a useful tool for informing conservation priorities, lending insight, albeit imperfect, into bird population declines on the global scale for the first time.

Coccidial oocyst release: once a day or all day long? Tropical bird hosts shed new light on the adaptive significance of diurnal periodicity in parasite output.

Many parasites spend part of their life cycle as infectious forms released from an infected host in the external environment, where they may encounter and infect new hosts. The emergence of infectious life stages often occurs once a day to minimize mortality in adverse environments. In bird hosts, intestinal parasites such as coccidia are generally released with feces in the late afternoon. This dynamic is adaptive since it allows avoiding desiccation and ultraviolet (UV) radiation, thus reducing mortality of oocysts in the environment until transmission to the next host. If this circadian rhythm is the result of natural selection to increase oocyst survival, we may hypothesize that oocysts will appear in feces at different times depending on the environment where hosts live. Particularly, in an environment where UV radiation and desiccation are very low, we may expect oocyst circadian release to disappear since the main selective pressure would be relaxed. We sampled different species of birds in tropical and temperate forests in spring and investigated coccidian oocyst output. A strong circadian variation in the prevalence of hosts shedding coccidian oocyst was detected for species caught in the temperate forest with an increase in prevalence in the late afternoon, whereas prevalence of birds shedding oocysts was constant over the course of the day for most species sampled in the tropical rain forest. These results are consistent with the hypothesis that oocysts’ circadian output is maintained by natural selection to increase oocyst survival. We discuss the adaptive significance of diurnal periodicity in parasite output.

Timing Is Everything: Acoustic Niche Partitioning in Two Tropical Wet Forest Bird Communities

When acoustic signals sent from individuals overlap in frequency and time, acoustic interference and signal masking may occur. Under the acoustic niche hypothesis (ANH), signaling behavior has evolved to partition acoustic space and minimize overlap with other calling individuals through selection on signal structure and/or the sender’s ability to adjust the timing of signals. Alternately, under the acoustic clustering hypothesis, there is potential benefit to convergence and synchronization of the structural or temporal characteristics of signals in the avian community, and organisms produce signals that overlap more than would be expected by chance. Interactive communication networks may also occur, where species living together are more likely to have songs with convergent spectral and or temporal characteristics. In this study, we examine the fine-scale use of acoustic space in montane tropical wet forest bird communities in Costa Rica and Hawai‘i. At multiple recording stations in each community, we identified the species associated with each recorded signal, measured observed signal overlap, and used null models to generate random distributions of expected signal overlap. We then compared observed vs. expected signal overlap to test predictions of the acoustic niche and acoustic clustering hypotheses. We found a high degree of overlap in the signal characteristics (frequency range) of species in both Costa Rica and Hawai‘i, however, as predicted under ANH, species significantly reduced observed overlap relative to the random distribution through temporal partitioning. There was little support for acoustic clustering or the prediction of the network hypothesis that species segregate across the landscape based on the frequency range of their vocalizations. These findings constitute strong support that there is competition for acoustic space in these signaling communities, and this has resulted primarily in temporal partitioning of the soundscape.

Topography as a determinant of bird distribution in secondary Atlantic Forest fragments

AbstractThe spatial distribution of Neotropical birds at local scales is often associated with plant successional stages and unique microhabitats such as bamboo stands and treefall gaps. Only 15% of the Atlantic Forest remains, yet this habitat is home to more than 200 endemic birds. Understanding the distribution of bird species within the Atlantic Forest can improve the test of ecological hypotheses related to habitat use and habitat selection. This study analyses the distribution of birds among different types of relief (lowlands, ravines, hillsides, and hilltops) in 41 forest fragments of different sizes (1 to 384.5 ha) within the Atlantic Forest, south east Brazil. The presence and absence data were analysed with dynamic occupancy models to determine the influence of area and topography in the distribution of bird species. Of the 169 species detected, we were able to estimate an occupancy probability of 67. Among them, relief type was an important variable for 26 species (39%). Most species showed a preference for lowlands and ravines, and some showed an association of combinations of these two reliefs with hillsides and hilltops. These preferences might be related to distribution of preferred food, nesting microhabitats, and thermoregulation. For the endemic and threatened Atlantic Forest mountain birds, the ecological association with areas of relief is a strong, and previously unsuspected, spatial distribution pattern. Our results suggest that the ecology and distribution of birds in tropical forests across hilly regions could be better understood if topography is considered. This pattern should be better investigated among other taxa in tropical forests.

Optimizing tropical forest bird surveys using passive acoustic monitoring and high temporal resolution sampling

AbstractEstimation of avian biodiversity is a cornerstone measure of ecosystem condition. Surveys conducted using autonomous recorders are often more efficient at estimating diversity than traditional point‐count surveys. However, there is limited research into the optimal temporal resolution for sampling—the trade‐off between the number of samples and sample duration when sampling a survey window with a fixed survey effort—despite autonomous recorders allowing easy repeat sampling compared to traditional survey methods. We assess whether the additional temporal coverage from high temporal resolution (HTR) sampling, consisting of 240 15‐s samples spread randomly across a survey window detects higher alpha and gamma diversity than low temporal resolution (LTR) sampling of four 15‐min samples at the same locations. We do so using an acoustic dataset collected from 29 locations in a region of very high avian biodiversity—the eastern Brazilian Amazon. We find HTR sampling outperforms LTR sampling in every metric considered, with HTR sampling predicted to detect approximately 50% higher alpha diversity, and 10% higher gamma diversity. This effect is primarily driven by increased coverage of variation in detectability across the morning, with the earliest period containing a distinct community that is often under sampled using LTR sampling. LTR sampling produced almost four times as many false absences for species presence. Additionally, LTR sampling incorrectly found 70 species (34%) at only a single forest type when they were in fact present in multiple forest types, while the use of HTR sampling reduced this to just two species (0.9%). When considering multiple independent detections of species, HTR sampling detected three times more uncommon species than LTR sampling. We conclude that high temporal resolution sampling of passive‐acoustic monitoring‐based surveys should be considered the primary method for estimating the species richness of bird communities in tropical forests.

The El Niño – Southern Oscillation dramatically influences the probability of reproduction and reproductive rate of a tropical forest bird

Although climate change has been implicated in population declines of tropical forest birds, there is a critical lack of data on the mechanisms underlying these declines. Attempts to link climatic factors to variation in adult survival, fecundity or nest success have been largely inconclusive. Recent community‐scale analyses have suggested that tropical birds may be less likely to breed under adverse conditions, but long‐term data on individual reproduction are needed to test this hypothesis. Here we leverage 12 years of data on a lowland forest bird, the greater ani Crotophaga major, to investigate how demographic parameters vary with phase of the El Niño – Southern Oscillation (ENSO), a major driver of climatic conditions in tropical wet forest. The likelihood of breeding and annual reproductive rate both decreased dramatically in El Niño‐like years, with only 37.5% of adults attempting breeding in 2015 (a strong El Niño year). For birds that did breed, however, clutch size and daily nest predation rate were unaffected by climate. Of the local climate variables investigated, dry season length and the frequency of high temperatures were most closely associated with reproductive failure. These results indicate that El Niño conditions alter the demography of greater anis by reducing the likelihood of reproduction, a response that may be more widespread than currently recognized. We suggest that reduced reproduction under adverse conditions represents an important and understudied aspect of the life histories of tropical forest birds.

Selective logging reduces body size in omnivorous and frugivorous tropical forest birds

Selective logging is the main anthropogenic disturbance in tropical forests, driving shifts in species abundances. Body size and body condition are important metrics of fitness that may be affected by habitat degradation. We conducted a four-year study to investigate how selective logging impacted the body size and body condition index (BCI) of 55 Bornean bird species and whether changes in body metrics were associated with shifts in relative population abundance. Frugivorous and omnivorous birds had reduced body size in selectively logged versus unlogged forest, but we found no evidence for selective removal of individuals driven by sex differences or post-fledging body size, indicating different developmental conditions for frugivores and omnivores in logged forest. Change in body size between forest types showed no clear patterns for insectivorous birds, and did not differ between IUCN categories. BCI of birds was affected by study year, suggesting an effect of climatic conditions on food availability, but not by logging. At the community level, post-logging change in population abundance was not associated with reduced body size, although between species variation suggests that adverse environmental conditions and different coping strategies underlie body size reductions in logged forest. Our study suggests that body size is a valuable metric to assess how logging impacts forest birds, pointing towards potential functional consequences related to seed dispersal within logged forests and need for improved silvicultural practices.

The influence of egg presence and eggshell colour in the attraction of visually oriented predators to nests of a tropical forest bird

Several hypotheses have been proposed to account for the function of eggshell pigmentation. One predicts that patterns of colour and markings provide camouflage against visually oriented nest predators. However, the effectiveness of any anti‐predatory function of eggshell colour may be reduced if predators can use the nests per se as foraging cues (nest‐crypsis hypothesis). Here, we tested whether eggshell pigmentation, and a set of concurrent variables, could explain nest predation in natural nests of the Atlantic Forest endemic Blue Manakin Chiroxiphia caudata containing plasticine eggs. Nests were continuously monitored for predator identification using infra‐red camera traps, and we considered the nest‐crypsis hypothesis by testing the premise that if predators can use nests as visual cues, they would be recorded checking empty nests at rates similar to those containing eggs. Six bird species were identified as visually oriented predators of nest contents, and predation frequencies were low and not influenced by eggshell colour. Empty nests and nests containing eggs were visited by predators at similar frequencies, independently of eggshell colour, which provided the first direct support for the nest‐crypsis hypothesis. It suggests that for this tropical forest, open‐nesting passerine, selective forces driving nest concealment and nest camouflage may be stronger than selection for eggshell colour variation.

Acoustic monitors and direct observations provide similar but distinct perspectives on bird assemblages in a lowland forest of eastern Ecuador.

Bird communities in lowland Neotropical forests exhibit temporal and spatial variation in species composition and abundance at multiple scales. Detecting and explaining such variation requires adequate methods for sampling those bird communities but counting birds in highly diverse lowland forests of the Neotropics can be particularly challenging. Point counts are one of the most frequently used methods for counting birds in tropical forests but inter- and intra-observer variability in detecting and identifying sounds may cause problems. Acoustic monitors (passive acoustic monitors; autonomous recording units) provide an alternative and potentially effective method to sample bird communities by acting, in effect, as “point counts”, recording vocalizations at a given point for a set time. I used acoustic monitors to examine patterns of species richness, spatial distribution, and community composition of birds in a lowland forest in eastern Ecuador, one of the most diverse regions on earth. I deployed monitors at 25 locations, each separated by at least 200 m, on each of two 100-ha plots (Harpia, Puma) at Tiputini Biodiversity Station during January–February, 2013–2017. Monitors were set to record for 10 min followed by a 5-min break, from 0545 h to 0810 h (10 recording periods/morning). Recordings were later reviewed to identify species; no attempt was made to distinguish individuals or to estimate distance. Results were compared with contemporaneous direct observations along transects on the same plots. A total of 214 species were identified from recordings on both plots, combined, with slightly more on Harpia (208) than on Puma (188). Number per year ranged from 142 on Harpia in 2016 to 161 on Puma in 2015. Number per point was ~45 with an overall range of 29–68. Number of species detected in recordings was similar to but somewhat less than the number recorded during direct observations. Number of species recorded increased rapidly from the first period (0545–0555 h) to the third (0615–0625 h) but showed little subsequent change. Most species were recorded at relatively few points; the four most widely distributed species were the same on both plots (Patagioenas plumbea, Xiphorhynchus guttatus, Capito aurita, Ramphastos tucanus), all of which are relatively loud canopy or subcanopy species. Ordinations based on species composition illustrated differences between plots based on both recordings and direct observations; similarly, patterns of species composition differed between methods. Acoustic monitors can be an effective tool for sampling bird communities and may be particularly effective and efficient for sampling loud species with distinctive songs. Nonetheless, results from monitors may provide different perspectives on species composition when compared to direct observations. Which method is preferred likely will depend on the specific objectives of individual studies.