Basal metabolic rate in free-living tropical birds： the influence of phylogenetic, behavioral, and ecological factors

The majority of our knowledge of avian energetics is based on studies of birds from temperate and high latitudes. Using the largest existing sample of wild-caught Old World tropical species, we showed that birds from Southern Vietnam had lower basal metabolic rate （BMR） than temperate species. The strongest dissimilarity between tropical and temperate species was the low scaling exponent in the allometric relation between BMR and body mass in tropical birds （the regression slope was 0.573）. The passerine migrants to temperate and high latitudes had higher BMR than tropical sedentary passerines. Body mass alone accounted for 93% of the variation in BMR （body mass ranged from 5 to 252 g）. Contrary to some other studies, we did not find evidence besides the above mentioned that phylogeny, taxonomy, behavior, or ecology have a significant influence on BMR variation among tropical birds.

Nest-site fidelity and breeding dispersal by Common Tailorbirds in a tropical forest

Background:Information pertaining to nest-site fidelity and breeding dispersal over successive years can help to better our understanding of how birds respond to nest predation.Methods:By using mist nets and tracking the color banded individuals,we investigated nest-site fidelity and breeding dispersal by Common Tailorbirds(Orthotomus sutorius)throughout a year and between successive years in 2017–2018.Results:The present study showed that Common Tailorbirds could produce up to four clutches per breeding season.When multiple broods were produced within a year,breeding pairs remained together,and the nest rebuilding rate was up to 92.2%,with only four cases(7.8%)in which birds reused their old nests.The dispersal distance between the nests during multiple breeding was found to be 10.0±10.5 m,and nest-site fidelity within the same year was 90.0%.By the second year of breeding,76.2%of individuals remained in the original breeding pairs,while for those that did switch partners,the females remained in the nest from the previous year and paired with new males.The dispersal distance between years was 26.5±41.9 m,and nest-site fidelity between different years was 80.1%.There was no significant difference between within-year and between-year dispersal distances.Moreover,there was no significant difference in the dispersal distance of rebuilt nests between birds that had experienced nest predation and those that had not.Conclusions:Our findings suggest that Common Tailorbirds maintain a high degree of fidelity to mates and nestsites,and nest predation had no significant effect on territorial changes or breeding dispersal distance between each breeding attempt.

Local predation pressure predicts the strength of mobbing responses in tropical birds

Many birds join cooperative mobbing aggregations and collectively harass predators. Individuals participating in these ephemeral associations benefit by deterring the predator, but also incur energetic costs and increased risk of predation. Ex- plaining the evolution of mobbing is challenging because individuals could prevail by selfishly seeking safety while allowing others to mob. An important step in understanding the evolution of mobbing is to identify factors affecting its expression. The ecological constraints model suggests that animals are more likely to cooperate under adverse environmental conditions, such as when local predation pressure is high. We tested this prediction by comparing the mobbing responses of several species of birds to the local abundance of their primary predator, the ferruginous pygmy-owl Glaucidium brasilianum. We used acoustic playback to elicit mobbing responses in environments where owls were common, uncommon, or rare. Stimuli were either the song of a fer- ruginous pygmy-owl or the mobbing calls of three of the owl＇s common prey species. During each playback, we characterized mobbing responses by noting the number of species and individuals that approached the loudspeaker, as well as the closest ap- proach by any bird. Mobbing responses to both stimuli were strong in locations where Ferruginous Pygmy-owls were common, intermediate where owls were uncommon, and weak where they were rare. This pattern persisted even after controlling for dif- ferences in species richness and composition among the three environments. Results support the ecological constraints model and provide strong evidence that intense predation pressure increases the expression of cooperative mobbing in tropical birds [Cur- rent Zoology 58 （5）： 781-790, 2012].

Response of tropical avifauna to visitor recreational disturbances: a case study from the Sinharaja World Heritage Forest, Sri Lanka

Background: We investigated the impact of human recreational disturbances on the distribution of birds along a popular nature trail in Sinhararja World Heritage Forest, Sri Lanka. It was hypothesized that visual and noise stimuli caused by the presence of humans affect the distribution of avifauna associated with this nature trail.Methods: Nine circular plots of 25 m fixed-radius laid along the trail(0 m), and 18 plots laid perpendicular to the trail at 75 and 150 m intervals, were studied from March 2013 to January 2014. The degree of human recreational disturbances was assessed in terms of visitor group size(visual disturbance) and their noise level(sound disturbance). These disturbances were categorized along a four-point scale(no human disturbance, low, medium and high disturbance). The relationship between disturbance levels and the abundance of birds was statistically tested.Results: ANOVA results revealed that the abundance of birds differed significantly under various intensities of recreational disturbances at each distance level. A significant negative correlation between abundance of birds and intensity of disturbance at 0 m distance suggests an avoidance of edge habitats by birds in the presence of humans. Abundance of birds increased at the 75 and 150 m distance levels with increasing disturbances occurring at the trail. Significant negative correlations were further observed between disturbance level and the abundance of birds in ground/understory and sub-canopy vertical strata of the forest at 0 m distance.Conclusions: Under high levels of recreational disturbance occurring at this trail, the abundance of birds near the trail declined significantly, while bird abundance in the interior of the forest increased. The sensitivity of individual bird species to visitor disturbances varied with the vertical stratum of the forest they usually occupy. Birds occupying the ground, understory and sub-canopy are particularly sensitive to recreational disturbances while bird species occupying the canopy and above are less vulnerable to recreational disturbances.

High-throughput sequencing reveals dietary segregation in Malaysian babblers

The coexistence of numerous species within a community results from how those species use available resources.Babblers are one of the major groups of Malaysian insectivorous birds,which frequently forage in dense vegetation cover and have a high level of sympatry.Therefore,examining the diet,prey selection,and niche segregation of babblers can be challenging.In this study,we used high-throughput sequencing to investigate potential dietary overlap or segregation among 10 babbler species of the 4 genera of the family Pellorneidae and Timaliidae:Pellorneum,Malacopteron,Stachyris,and Cyanoderma in central peninsular Malaysia.We tested the hypothesis that trophically similar species may differ in resource use to avoid competitive exclusion.We identified 81 distinct arthropod taxa from fecal samples,belonging to 71 families representing 13 orders,which were predominantly from 16 dipteran,13 lepidopteran,and 10 coleopteran families.Of all the prey taxa consumed,45%were found to be distinct across the 10 babbler species,and<35%were shared simultaneously by≥3 babbler species,indicating minimal dietary overlap.The black-throated babbler Stachyris nigricollis and moustached babbler Malacopteron magnirostre had the most generalist tendencies because they consumed a greater variety of prey taxa.Small dietary overlap values(Ojk)and a relatively wide range of food resources suggest that dietary segregation occurred among the studied babblers.The great diversity of prey consumed revealed the presence of dietary flexibility among the sympatric insectivorous birds,thus reducing any active dietary competition and facilitating the coexistence through niche partitioning.