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There is not much information on avifauna especially Pycnonotidae at Padang Chong Forest Reserve (PCFR). Therefore, the main objective of this study is to identify and document species from Pycnonotidae family at PCFR. A total of five sampling sessions were carried out from June to November 2022. Surveys were carried out at two plots along the gradient from the border of PCFR namely Plot 1 (500 m) and Plot 2 (1 km) each plot consist of transect line 100 m x 100 m (1 ha). Ten mist nets were deployed at each plot for five consecutive days per sampling session. Binoculars and cameras were aided for observation purposes. As a result, a total of 25 individuals from 9 species were recorded where 10 individuals (Plot 1) and 15 individuals (Plot 2) respectively. Species, Grey-bellied Bulbul were mostly recorded (8 individuals), followed by Spectacled Bulbul and Hairy-backed Bulbul (5 individuals), Grey-cheeked Bulbul (2 individuals), and Buff-vented Bulbul, Stripe-throated Bulbul, Cream-vented Bulbul, Black-headed Bulbul, and Olive-winged Bulbul are recorded one individual. Based on the species accumulative curve, the species composition is not reaching the plateau which indicates more sampling sessions are needed for Pycnonotidae at PCFR. In Plot 1, two bulbul species were recorded namely Spectacled Bulbul (LC) and the Grey-cheeked Bulbul (VU). In Plot 2 recorded the presence of Buff-vented Bulbul (NT), Stripe-throated Bulbul (LC), Cream-vented Bulbul (LC), and Hairy-backed Bulbul (LC). PCFR plays its role in providing a habitat for avifauna and resources to survive. Therefore, conservation efforts must be taken immediately to ensure this reserve is preserved and conserved.

Vocal communication plays a critical role in understanding animal behavior, evolution, and cognition. We developed an automated system combining audio signal processing and machine learning (supervised and unsupervised) to characterize the vocal repertoire of the White Spectacled Bulbul (Pycnonotus xanthopygos), a widespread passerine in Israel known for its complex year‐round vocal activity. Analyzing hundreds of field recordings using passive acoustic monitoring (PAM), our system identified thousands of calls, revealing a hierarchically structured vocal repertoire composed of distinct complex vocalizations (motifs) and base units (syllables). Our results show that different populations possess unique motif repertoires, primarily consisting of population‐specific motifs built from syllables that are similar across genetically distinct populations. This study enhances our understanding of this understudied species and highlights the White Spectacled Bulbul's potential as a model organism for investigating vocal communication and social learning in animals. How do birds develop their unique vocal repertoires, and how do these vary across populations? Using machine learning and bioacoustics, we analyzed the vocalizations of the White Spectacled Bulbul, revealing population‐specific motifs built from shared syllables. Our findings suggest that while syllable production may be constrained, their arrangement is flexible, shaping distinct local repertoires. This study provides new insights into vocal communication and highlights the potential of automated methods for studying complex animal vocalizations.

Seasonal variation in innate immunity is often attributed to either temporal environmental variation or to life‐history trade‐offs that arise from specific annual cycle stages but decoupling them is difficult in natural populations. Here, we effectively decouple seasonal environmental variation from annual cycle stage effects by exploiting cross‐seasonal breeding and moult in the tropical Common Bulbul Pycnonotus barbatus. We test how annual cycle stage interacts with a key seasonal environmental variable, rainfall, to determine immunity at population and individual level. If immune challenge varies with precipitation, we might expect immune function to be higher in the wet season due to increased environmental productivity. If breeding or moult imposes resource constraints on birds, depending on or independent of precipitation, we might expect lower immune indices during breeding or moult. We sampled blood from 818 birds in four annual cycle stage categories: breeding, moult, simultaneous breeding and moulting, or neither. We quantified indices of innate immunity (haptoglobin, nitric oxide (NOx) and ovotransferrin concentrations, and haemagglutination and haemolysis titres) over two annual cycles of wet and dry seasons. Environment (but not annual cycle stage or interactions between both) explained variation in all immune indices, except NOx. NOx concentration differed between annual cycle stages but not between seasons. However, within the wet season, haptoglobin, NOx, ovotransferrin and haemolysis differed significantly between breeding and non‐breeding females. Aside from some recorded inconsistencies, population level results were largely similar to results within individuals that were measured repeatedly. Unexpectedly, most immune indices were higher in the dry season and during breeding. Higher immune indices may be explained if fewer or poorer quality resources force birds to increase social contact, thereby exposing individuals to novel antigens and increased infection risk, independently of environmental productivity. Breeding birds may also show higher immunity if less immune‐competent and/or infected females omit breeding. We conclude that seasonal environmental variation impacts immunity more directly in natural animal populations than via resource trade‐offs. In addition, immune indices were more often variable within than among individuals, but some indices are characteristic of individuals, and so may offer selective advantages if heritable. Tropical environments are considered highly immune‐challenging for animals because of their relative higher organic productivity. However, this study from a seasonally arid tropical environment where annual cycle stages are decoupled from seasonal environmental variation, provides evidence that variation in innate immune function does not follow differences in annual cycle stages or simple environmental productivity pattern but may arise from interactions between individuals and their environment, and this may apply to variation in disease risk.

Animal vocal communication is a broad and multi-disciplinary field of research. Studying various aspects of communication can provide key elements for understanding animal behavior, evolution, and cognition. Given the large amount of acoustic data accumulated from automated recorders, for which manual annotation and analysis is impractical, there is a growing need to develop algorithms and automatic methods for analyzing and identifying animal sounds. In this study we developed an automatic detection and analysis system based on audio signal processing algorithms and deep learning that is capable of processing and analyzing large volumes of data without human bias. We selected the White Spectacled Bulbul (Pycnonotus xanthopygos) as our bird model because it has a complex vocal communication system with a large repertoire which is used by both sexes, year-round. It is a common, widespread passerine in Israel, which is relatively easy to locate and record in a broad range of habitats. Like many passerines, the bulbul's vocal communication consists of two primary hierarchies of utterances, syllables and words. To extract each of these units’ characteristics, the fundamental frequency contour was modeled using a low degree Legendre polynomial, enabling it to capture the different patterns of variation from different vocalizations, so that each pattern could be effectively expressed using very few coefficients. In addition, a mel-spectrogram was computed for each unit, and several features were extracted both in the time-domain (e.g. zero-crossing rate and energy) and frequency-domain (e.g. spectral centroid and spectral flatness). We applied both linear and non-linear dimensionality reduction algorithms on feature vectors and validated the findings that were obtained manually, namely by listening and examining the spectrograms visually. Using these algorithms, we show that the Bulbul has a complex vocabulary of more than 30 words, that there are multiple syllables that are combined in different words, and that a particular syllable can appear in several words. Using our system, researchers will be able to analyze hundreds of hours of audio recordings, to obtain objective evaluation of repertoires, and to identify different vocal units and distinguish between them, thus gaining a broad perspective on bird vocal communication.

The net consequence of nectar robbing on reproductive success of plants is usually negative and the positive effect is rarely produced. We evaluated the influence of nectar robbing on the behaviour of pollinators and the reproductive success of Tecomella undulata (Bignoniaceae) in a natural population. Experimental pollinations showed that the trees were strictly self-incompatible. The three types of floral colour morphs of the tree viz. red, orange and yellow, lacked compatibility barriers. The pollinators (Pycnonotus cafer and Pycnonotus leucotis) and the robber (Nectarinia asiatica) showed equal preference for all the morphs, as they visited each morph with nearly equal frequency and flower-handling time. The sunbirds caused up to 60% nectar robbing, mostly (99%) by piercing through the corolla tube. Although nectar is replenished at regular intervals, insufficient amount of nectar compelled the pollinators to visit additional trees in bloom. Data of manual nectar robbing from the entire tree showed that the pollinators covered lower number of flowers per tree (5 flowers/tree) and more trees per bout (7 trees/bout) than the unrobbed ones (19 flowers/tree and 2 trees bout). The robbed trees set a significantly greater amount of fruits than the unrobbed trees. However, the number of seeds in a fruit did not differ significantly. The study shows that plant-pollinator-robber interaction may benefit the self-incompatible plant species under conditions that increases the visits of pollinators among the compatible conspecifics in a population.

The bulbul family Pycnonotidae is an Old-World group of tropical birds that plays important roles in tree seed dispersal. The behavior and vocalization of bulbuls have been studied only in a few species. The objective of the present study is to describe, for the first time, the acoustic and social behavior of three species of bulbuls of the genus Pycnonotus : the sooty-headed bulbul ( P. aurigaster ), the streak-eared bulbul ( P. conradi ), and the stripe-throated bulbul ( P. finlaysoni ). Field studies were conducted from November 2021 to May 2022 in Cat Tien National Park, Dong Nai Province, Vietnam, where all three species are sympatric and tend to inhabit disturbed biotopes. We analyzed “observations,” that is, a single record of a bird or a group of birds of a given species. During each observation (about 800 in total), the behavior of the birds was described and, when possible, vocalizations were recorded. The total duration of phonograms of all three species amounted to about 227 min. The sooty-headed and streak-eared bulbuls are social birds that maintained pairs throughout the year, but often, especially during the nonbreeding season, gathered in larger groups. Pair members and individuals from neighboring pairs maintained acoustic contact with each other all the time. To do so, they used calls: broadband calls (noise sounds without clear structure, but with a wide continuous frequency spectrum) emitted by streak-eared bulbuls, and tonal calls (musical sounds showing one clearly defined frequency) by sooty-headed bulbuls. Both these species were only rarely observed singing, this possibly being due to reduced territorial behavior in these birds. The stripe-throated bulbul differs from the other two in singing more frequently, along with producing calls, and song could be used for territorial purposes. We assume that territorial behavior is better expressed in stripe-headed bulbuls than in the other two species. However, even stripe-throated bulbuls did not react to playback-simulated territorial intrusion in our experiments. We assume that vocalizations play important roles in the communication of the three species because we noted these sounds or others in almost all observations. Moreover, we observed a general increase in vocal activity at the beginning of the breeding season (February–March). In addition, during this time, bulbuls were most often those to sing.

Resource acquisition and allocation are central to life history theory, explaining the diversity of strategies among species as well as the distribution of events over the annual cycle. Moult is a major phase in the annual cycle of birds, but explanations for moult scheduling are heavily biased towards temperate systems with seasonal breeding patterns. Our research on a year‐round breeding tropical bird, the common bulbul Pycnonotus barbatus (bulbul), tests whether moult depends primarily on stored body reserves (capital) or on resources acquired throughout the moult period (income). Making this distinction elucidates trade‐offs between moult, and other annual cycle events, and responses to environmental change. We estimated moult start date and duration in captive bulbuls whose body condition we experimentally manipulated by feeding them fruits or invertebrates 6–3 and 3–0 months before moult, and fruits or a mixed diet during moult. We studied free‐living bulbuls as reference group. We found that moult onset is best predicted by diet‐manipulated condition just before moult, while moult duration is best predicted by diet‐manipulated condition during moult. Specifically, invertebrate‐fed bulbuls started moult 33 days later than fruit‐fed bulbuls. In addition, once invertebrate‐fed bulbuls were switched to a mixed diet, they moulted 52 days quicker than fruit‐fed bulbuls, albeit still 36 days slower than free‐living bulbuls on average. Males started moult 15 days earlier and had a more variable start of 20 days, but did not moult quicker than females on average. Our findings indicate that moult in bulbuls is both income‐ and capital‐dependent, with moult initiation determined by individual body reserves and feather growth still occurring on a fruit‐only‐diet, but is significantly improved by dietary proteins from a mixed diet and in field bulbuls. In this year‐round breeding bird, moult seasonality is maintained in the absence of breeding, but heavily influenced by foraging conditions.

The Straw-headed Bulbul Pycnonotus zeylanicus is one of South-East Asia’s most threatened songbirds due to relentless demand for the regional cage-bird trade. The species was recently uplisted from ‘Endangered’ to ‘Critically Endangered’ only two years after its previous uplisting. Intriguingly, populations in highly urbanised Singapore appear relatively secure. However, the last Singaporean density estimates, derived from traditional census methods, were obtained nearly two decades ago in 2001. A recent population estimate in 2016 was derived from the census work in 2001 coupled with relative abundance indices from population trends. We thus performed systematic field surveys using the distance sampling method, estimating 573 ± 185 individuals nation-wide, with a break-down of 217 ± 81 on the main island of Singapore and 356 ± 104 birds on the satellite of Pulau Ubin. Taken together, the total population estimate reported here comprises 22.9–57.3% of the global wild population, underscoring the importance of Singapore as a stronghold for the species. In spite of its apparently secure status in Singapore, the species remains susceptible to local and foreign trapping pressures. Based on our assessment, we propose a number of local and regional conservation measures to ensure the continued survival of populations in Singapore.

The Red-vented Bulbul (Pycnonotus cafer) is native to southern Asia and is an established invasive species in several tropical Pacific islands, parts of the Middle East, Spain, and Houston (Texas, USA), the focal region presented herein. Here, we assess recent range expansion, density, and population size. We used locality databases and the Map Maker program to measure bulbul range expansion. The range expanded from 589 km2 before June 2012 to 4,606 km2 during the following decade. By counties, there were 215 bulbul reports in Harris County before June 2012 (and none in surrounding counties), and 6,543 in the following decade, along with nearly 50 records in adjacent counties. Mean distance of outliers from the central population doubled from 27 km before June 2012 to 53 km during the following decade. To estimate minimum density and population size we conducted transect surveys for bulbuls January—March 2024 at four sites, repeating each transect 10 times. We estimated a mean population density of 8.77 bulbuls/km2 and a total population of 466 (range = 144–955) individuals within the 53.18 km2 core area. Although range size of the Houston bulbul is indeed expanding, it is not expanding rapidly, growing at approximately 400 km2/year. Additionally, recent outliers have appeared as far as 68 km from the center of the bulbul’s range, suggesting that expansion trajectories are continuing. Natural barriers (e.g. rivers, intracoastal waterways) and some highways appear to inhibit continued bulbul range expansion, as additional records are absent beyond these features.

Currently listed as Endangered on the IUCN Red List of Threatened Species, the Straw-headed Bulbul Pycnonotus zeylanicus is being driven towards extinction throughout most of its range by unregulated illegal trade supplying the demand for songbirds. We conducted surveys of bird markets in North and West Kalimantan, and Central, West and East Java between July 2014 and June 2015, and observed a total of 71 Straw-headed Bulbuls in 11 markets in eight cities. Comparing our data with the literature, we found that as numbers in markets are decreasing, prices are increasing to over 20 times the prices recorded in 1987, indicating that numbers in the wild are diminishing. This is corroborated by widespread extirpations throughout their range and reports from traders that Straw-headed Bulbuls are increasingly difficult to locate, while demand from consumers remains high. Concerted efforts from a variety of stakeholders are urgently needed to prevent the extinction of this species in the wild. We recommend that the Straw-headed Bulbul be included in Indonesia’s list of protected species, considered for uplisting to Critically Endangered on the IUCN Red List and listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). We also urge the Indonesian Government to effectively enforce existing laws, targeting the open bird markets to shut down the trade in this and other threatened species.