Modeling the flocking propensity of passerine birds in two Neotropical habitats

We examined the importance of mixed-species flock abundance, individual bird home range size, foraging height, and foraging patch characteristics in predicting the propensity for five Neotropical passerine bird species (Slaty Antwren, Myrmotherula schisticolor; Golden-crowned Warbler, Basileuterus culicivorus; Slate-throated Redstart, Myioborus miniatus; Wilson’s Warbler, Wilsonia pusilla; and Black-and-white Warbler, Mniotilta varia) to forage within flocks, rather than solitarily. We used study plots in primary mid-elevation forest and in shade coffee fields in western Panama. We expected that all species would spend as much time as possible flocking, but that the social and environmental factors listed above would limit compatibility between flock movements and individual bird movements, explaining variability in flocking propensity both within and among species. Flocking propensity was well predicted by home range size and flock abundance together, for four of the five species. While flock abundance was uniform across plots, home range sizes varied among species and plots, so that home range size appeared to be the principle factor limiting flocking propensity. Estimates of flock abundance were still required, however, for calculating flocking propensity values. Foraging height and patch characteristics slightly improved predictive ability for the remaining species, M. miniatus. In general, individual birds tended to join flocks whenever one was available inside their home range, regardless of a flock’s specific location within the home range. Flocking propensities of individual species were lower in shade coffee fields than in forests, and probably vary across landscapes with variations in habitat. This variability affects the stability and species composition of flocks, and may affect survival rates of individual species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relationships between frequency of mixed-species flocks, weather and insect activity in a montane cloud forest in Ecuador

The frequency of mixed-species flocks of birds, weather and insect activity were studied in a high-altitude cloud forest in Ecuador. It is generally accepted that participation in mixed-species flocks improves foraging efficiency. If this is true, more flock activity may be expected when food is less available, which may happen during long-lasting periods of rain and otherwise adverse weather conditions. The total number and mean size of flying insects decreased as rainfall increased. The number of flocks observed increased with decreasing number and biomass of insects. Relatively more flocks were seen during rain than during dry weather. No flocks stopped foraging during rain. The flock activity pattern appeared to be the opposite of that found in humid lowlands, probably because of different weather regimes in the two zones. In the lowlands, heavy rain is typically of short duration. In high-altitude cloud forest, the rainfall is often less intense but persists for prolonged periods. Hence, from an energy point of view, cloud forest birds cannot afford to stop foraging during adverse weather conditions when insect availability is low. The results suggest that some mixed feeding parties have evolved in response to low tropical insect availability, necessitating long feeding excursions outside the territory.     

Phylogenetic and ecological determinants of the neotropical dawn chorus

The concentration of avian song at first light (i.e. the dawn chorus) is widely appreciated, but has an enigmatic functional significance. One widely accepted explanation is that birds are active at dawn, but light levels are not yet adequate for foraging. In forest communities, the onset to singing should thus be predictable from the species' foraging strata, which is ultimately related to ambient light level. To test this, we collected data from a tropical forest of Ecuador involving 57 species from 27 families of birds. Time of first song was a repeatable, species-specific trait, and the majority of resident birds, including non-passerines, sang in the dawn chorus. For passerine birds, foraging height was the best predictor of time of first song, with canopy birds singing earlier than birds foraging closer to the forest floor. A weak and opposite result was observed for non-passerines. For passerine birds, eye size also predicted time of first song, with larger eyed birds singing earlier, after controlling for body mass, taxonomic group and foraging height. This is the first comparative study of the dawn chorus in the Neotropics, and it provides the first evidence for foraging strata as the primary determinant of scheduling participation in the dawn chorus of birds.     

Phylogenetics and biogeography of eastern Asian-North American disjunct genus Pachysandra （Buxaceae） inferred from nucleotide sequences

Pachysandra is an eastern Asian-North American disjtunct genus with three species, two in eastern Asia （Pachysandra axillaris and Pachysandra terminalis） and one in eastern North America （Pachysandra procurnbens）. Although morphological and cytological studies suggest a close affinity of Pprocumbens with P axillaris, molecular data from nuclear and chloroplast DNA regions have provided conflicting signals. In this study, we tested previous phylogenetic hypotheses using sequences of nuclear ribosomal DNA internal transcribed spacers and chloroplast ndhF gene from multiple individuals of each of the three species. We also estimated the time of divergence between eastem Asia and eastern North America. Our results support the morphological and cytological conclusion that P procumbens is more closely related to P axillaris than to P terminalis. The estimated time of divergence of P axillaris and P procumbens was 14.6±5.5 mya, consistent with estimates from many other eastern Asian-North American disjunct genera. The migration of Pachysandra populations from eastern Asia to North America might have occurred by way of the North Atlantic land bridge.     

Species importance in a heterospecific foraging association network

There is a growing recognition of the need to integrate non‐trophic interactions into ecological networks for a better understanding of whole‐community organization. To achieve this, the first step is to build networks of individual non‐trophic interactions. In this study, we analyzed a network of interdependencies among bird species that participated in heterospecific foraging associations (flocks) in an evergreen forest site in the Western Ghats, India. We found the flock network to contain a small core of highly important species that other species are strongly dependent on, a pattern seen in many other biological networks. Further, we found that structural importance of species in the network was strongly correlated to functional importance of species at the individual flock level. Finally, comparisons with flock networks from other Asian forests showed that the same taxonomic groups were important in general, suggesting that species importance was an intrinsic trait and not dependent on local ecological conditions. Hence, given a list of species in an area, it may be possible to predict which ones are likely to be important. Our study provides a framework for the investigation of other heterospecific foraging associations and associations among species in other non‐trophic contexts.     

The Acoustic Properties of Low Intensity Vocalizations Match Hearing Sensitivity in the Webbed-Toed Gecko,Gekko subpalmatus

The design of acoustic signals and hearing sensitivity in socially communicating species would normally be expected to closely match in order to minimize signal degradation and attenuation during signal propagation. Nevertheless, other factors such as sensory biases as well as morphological and physiological constraints may affect strict correspondence between signal features and hearing sensitivity. Thus study of the relationships between sender and receiver characteristics in species utilizing acoustic communication can provide information about how acoustic communication systems evolve. The genus Gekko includes species emitting high-amplitude vocalizations for long-range communication (loud callers) as well as species producing only low-amplitude vocalizations when in close contact with conspecifics (quiet callers) which have rarely been investigated. In order to investigate relationships between auditory physiology and the frequency characteristics of acoustic signals in a quiet caller, Gekko subpalmatus we measured the subjects’ vocal signal characteristics as well as auditory brainstem responses (ABRs) to assess auditory sensitivity. The results show that G. subpalmatus males emit low amplitude calls when encountering females, ranging in dominant frequency from 2.47 to 4.17 kHz with an average at 3.35 kHz. The auditory range with highest sensitivity closely matches the dominant frequency of the vocalizations. This correspondence is consistent with the notion that quiet and loud calling species are under similar selection pressures for matching auditory sensitivity with spectral characteristics of vocalizations.     

A preliminary study of the wild siamang gibbon (Hylobates syndactylus) at Fraser's Hill,Malaysia

The wild siamang gibbon was studied at Fraser's Hill, Malaysia. The study area was covered with a well developed forest and offered a suitable habitat for siamang gibbons. Other primates living in this area were the white-handed gibbon, the duskey leafmonkey, the banded leaf-monkey, and the pig-tailed monkey. The siamang gibbon groups observed have a monogamous structure consisting of one pair of adult individuals and one or more subadults which are assumed to be the offspring of the adults. The adult male showed behavior typical of a group leader. As subadults become older, they tend to become spatially separated from the mother group. Each group was observed to range freely within an exclusive area of the forest into which no other group was observed to intrude. Each group emitted loud vocalizations which seemed to maintain the spacing between the groups.     

STRUCTURE AND FORAGING PATTERNS OF FLOCKS OF TITS AND ASSOCIATED SPECIES IN AN ENGLISH WOODLAND DURING THE WINTER

Blue Tits were the commonest and most frequent members of mixed-species insectivorous flocks during the winter at Wytham Wood, Oxford. Six common flocking species (Blue Tit, Longtailed Tit, Great Tit, Coal Tit, Marsh Tit and Golderest) made up nearly two-thirds of the birds in the study area. A tentative interspecific social dominance hierarehy was constructed: Great Tit > Blue Tit > Marsh Tit > Coal Tit > Long-tailed Tit and Goldcrest. Blue Tits permitted conspecifics to approach them more closely than did other flock members. Blue Tits most frequently led the flocks, but no more than would be predicted by their abundance. Great Tits, and Marsh Tits and Coal Tits to a lesser extent, defended territories during the winter. Two of the six common species frequented the inner parts of branches (Great Tit, Coal Tit), two the outer parts of branches (Blue Tit, Marsh Tit), and two the twigs (Long-tailed Tit, Goldcrest). Members of each of these species-pairs showed marked differences in height of foraging and/or species of tree frequented. Because of their abundance, the impact of Blue Tits outside of their most highly frequented foraging zones may exceed that of species concentrating in these other zones (e. g., twigs high in trees). The Coal Tit foraged most diversely, the Great Tit least diversely. Species that foraged diversely in one of the three foraging categories (species of tree, substrate, height) usually foraged less diversely than most other species in the other dimensions. Species usually overlapped least in the zones exploited (inner parts of branches, etc.). Great Tits overlapped with other species less than did any other common flock member, and Coal Tits were the next lowest in this regard.     

Decay of interspecific avian flock networks along a disturbance gradient in Amazonia

Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.     

Foraging patterns of breeding birds in eucalypt forest and woodland of southeastern Australia

The foraging ecology of eucalypt forest and woodland birds was studied on three 10 ha plots in southeastern Australia. Quantitative data were obtained for 41 species of which 31 were insectivorous, eight were nectar-feeders, and two were parrots that fed primarily on eucalypt seeds. Birds-of-prey, large omnivores and frugivores were uncommon. Insectivorous birds differed in foraging behaviour, the substrates on which they found prey, and foraging height. Nectar- feeders exploited a variety of carbohydrates including nectar, honeydew, lerp, manna and sap. Nectarivorous birds were separated by foraging behaviour, substrate, height and by the extent to which they used the different types of carbohydrates. Carbohydrates were also an important food resource for some insectivores. By understanding how birds exploit food resources within forest and woodland environments, the features of the environment which need to be conserved or manipulated to manage forest avifaunas can be identified. For example, in addition to the substrates such as foliage and bark, usually associated with the foraging of forest birds, carbohydrates and loose bark were identified as important resources for birds in eucalypt forests and woodlands. The broad importance of these two resources to the avifauna had not been previously appreciated, yet both may be sensitive to environmental changes associated with logging and other forest management practices which alter the composition or age-class structure of forests.     

Edge effect and structure of mixed-species bird flocks in an Afrotropical lowland forest

Avian mixed-species flocks are a dominant feature of tropical moist forests, yet their cost–benefit balance and habitat dependence in Africa are not fully documented. We recorded the composition of mixed-species bird flocks in a pristine Afrotropical lowland forest site in Salonga NP, DRC. Our data showed that at least four types of flock existed, one of which specialized on edge habitats. We used multivariate analyses to further characterize edge effect on the most documented mixed-species flock type and found a significant effect on flock composition. While neither species guild nor preferential foraging stratum played an important role in flock participation, the nucleus role was played by a different species at the edge and in the interior, and both species abundance and associations were habitat-dependant, suggesting “domino effects” on the structure of mixed-species flocks.     

Seasonal effects on foraging behaviour of two sympatric species of couas in the western dry forest of Madagascar

Coquerel's Coua ( Coua coquereli ) and Red-capped Coua ( Coua ruficeps ) occur in the western dry forest of Ankarafantsika in northwest Madagascar. This kind of forest is characterized by an alternating of a dry and a rainy season. Although they belong to the same genus, the two species differ in appearance, with Red-capped Coua being slender than Coquerel's Coua. We analyse their respective foraging strategies, according to the seasonal variation. The foraging behaviour of both species was different and was also influenced by the seasonal variations. They tended to use the same main substrates but differed in the proportion of foraging techniques according to the season. Seasonal variations probably have an important effect on the prey availability (estimated by the rate of prey capture), the nature of prey and also alternative foraging substrates used, forcing the two species to use different techniques and probably to capture different prey. These different foraging strategies could maintain the coexistence between these two species.     

Variations in flocking behaviour from core to peripheral regions of a bird species’ distribution range

Flocking behaviour in birds reflects the outcome of a momentary trade-off between increased foraging efficiency and improved predator avoidance. However, these changing patterns remain poorly known at any spatial or temporal scale. The aim of the present study was first to investigate seasonal fluctuations of flocking behaviour throughout the entire distribution range of a species and secondly to explore behavioural responses to daily temperature variations. From 2000 to 2010, sightings of Peruvian Thick-knees (Burhinus superciliaris) were collected throughout Ecuador, Peru and Chile. There were strong differences in flocking behaviour between Chilean and Peruvian populations. While Thick-knees occurred into few large year-round flocks in Chile, flock occurrence was highly seasonal in Peru, where group size grew gradually from loose flocks at the end of the breeding season to a few large ones by the middle of the year. Time of day seemed not to affect the species detectability but was negatively related to flock size. Variations in the flocking behaviour of Peruvian Thick-knees throughout its distribution range suggest that aggregation patterns might indicate individuals responding to seasonally fluctuating ecological pressures, such as those derived from predation, foraging or climate.     

Multicontinental community phylogenetics of avian mixed‐species flocks reveal the role of the stability of associations and of kleptoparasitism

If understood as a way to forage socially without incurring intra‐specific competition for mates or other resources, mixed‐species foraging flocks are predicted to be composed of functionally similar species. In the most intensively studied mixed‐species foraging system, understory forest birds, relevant functional traits are however extremely difficult to measure and best replaced by phylogenetic relatedness. A multicontinental analysis of flock phylogenetic structure revealed departures from the expected phylogenetic clustering. Long‐lasting associations (> one day) were phylogenetically overdispersed, indicating that these associations are affected by competitive exclusion or by mutualistic interactions. However, where kleptoparasites occurred, this effect disappeared completely, as expected if the dilution of kleptoparasitism risk compensated competition between related species. Mixed‐species flocks should not be analyzed as a homogeneous phenomenon.     

青羊湖林场不同林分物种多样性与水源涵养能力的研究

通过群落调查和林下土壤及枯落物特性的分析,研究了青羊湖林场南酸枣（Choerospondias axillaris）林、未抚育马尾松（Pinus massoniana）林、抚育马尾松林、马尾松-南酸枣混交林4种林分的物种多样性及水源涵养能力。结果表明：（1）4种林分共有维管束植物135种,隶属58科97属,其中南酸枣林物种相对较丰富(88种),混交林次之(76种),抚育马尾松林较少(64种),未抚育马尾松林则相对最少(55种);（2）林分类型对物种多样性有重要影响,南酸枣林和混交林草本物种多样性较两种针叶林高,而灌木物种多样性则较低;（3）DCA排序结果显示,南酸枣林和混交林物种相似性程度较高,两种马尾松林与南酸枣林、混交林差异明显;（4）林分类型对水源涵养能力有重要影响,相比两种马尾松林,南酸枣林和混交林的林下枯落物蓄积量分别降低10.1%和15.2%,最大持水量降低34.1%和44.7%,而且0～10 cm土壤容重降低14.7%和7.4%,10～20 cm土壤容重降低14.1%和4.0%,20～30 cm土壤容重降低8.7%和4.9%,但总储水量增加15.8%和4.5%,即南酸枣林和混交林具有较高的水源涵养能力。研究认为,生态抚育增加了马尾松林的水源涵养能力。     

Time Allocation Patterns of Lowland Woolly Monkeys (Lagothrix lagotricha poeppigii) in a Neotropical Terra Firma Forest

We investigated the time allocation decisions of lowland woolly monkeys (Lagothrix lagotricha poeppigii) in a terra firma forest in eastern Ecuador where they occur sympatrically with 9 other primate species. Woolly monkeys spent considerable amounts of time searching for and attempting to procure animal prey—roughly as much time as they spent consuming plant material: ripe fruits, leaves, and flowers. The amount of time spent foraging for animal prey is positively related to the habitat-wide availability of ripe fruits (the predominant component of the woolly monkey diet), and negatively related to both ambient temperature and the abundance of potential prey items in the habitat. Time spent resting showed exactly the opposite pattern with respect to these ecological variables. These results suggest that woolly monkeys follow an energy-maximizing strategy of food acquisition during times of fruit abundance—focusing on animal foods and perhaps laying down fat reserves to utilize when ecological conditions worsen—and follow an energy-minimizing strategy when fruit resources are scarce. Such a strong and seasonal commitment to animal prey foraging is unique among the ateline primates and is not ubiquitous even among lowland woolly monkeys. We suggest that this foraging strategy, and the greater intragroup cohesion that characterizes some populations of Lagothrix, are both opportunistic responses to regional differences in habitat quality. Identifying and accounting for such intraspecific variation should be a goal of any analysis of comparative socioecology.     

Seeing without being seen: a removal experiment with mixed flocks of Willow and Crested Tits Parus montanus and cristatus

This paper tests the hypothesis that foraging site selection reflects a trade-off between the various needs for concealment from predators, to find food, and for the individual to maintain some view of its surroundings. After removal of Crested Tits Parus cristatus (the dominant species in mixed flocks), Willow Tits P. montanus did not decrease their foraging heights as expected but remained in the most exposed parts of young pines. In contrast, after removal of Willow Tits, Crested Tits increased their foraging height from the sheltered lower canopy to sites previously occupied by Willow Tits. When flock size was reduced, the birds maintained the same high levels of vigilance without concealing themselves in dense vegetation. I suggest that flock members may benefit from foraging in sites that afford good anti-predator vigilance.     

Rodaucea, a new genus of the Laboulbeniales

The new genus Rodaucea is created for a new species of Laboulbeniales parasitic on carrion beetles from Ecuador. The new genus is characterized by the presence of two unequal secondary receptacles flanking cell II on opposite sides. The perithecia have the wall cells arranged in four tiers distinctly unequal in height and the antheridia are phialid-like structures borne terminally on branches of primary and secondary appendages.     

Vocal Coordination of Group Movement by Green Woodhoopoes (Phoeniculus purpureus)

Communication signals are used by many species to maintain group cohesion when moving over larger areas. Groups of green woodhoopoes (Phoeniculus purpureus) generally move around their territory as a close‐knit unit. Dominant individuals were more likely than subordinates to initiate movement to a new foraging site, but there was no intersexual difference. Dominants were also more likely than subordinates to be followed immediately. Vocalizations were shown to play an important role in mobilization: in the thick forests inhabited by woodhoopoes, visual cues to coordinate movement are likely to be less successful. When responding to the rallying call of a neighboring group, dominants and subordinates were equally likely to lead, as were males and females. As other group members followed immediately on most of these occasions, vocalizations were less important in this context than when moving to a new foraging site.     

Bird mixed‐species flock formation is driven by low temperatures between and within seasons in a Subtropical Andean‐foothill forest

According to both the predation avoidance and foraging efficiency hypotheses, birds within mixed flocks increase their foraging efficiency and/or can spend more time feeding and less time looking out for predators. These hypotheses predict that birds in mixed flocks obtain benefits. Thus, mixed flock formation could serve as a strategy to cope with difficult conditions imposed on birds such as climatic conditions that ultimately result in a change in predation pressure or food resources. We evaluate the hypotheses that forming part of a flock confers benefits to its members and the associated prediction that birds will take advantage of these benefits and flock more often under cold and dry weather conditions between and within seasons to cope with such conditions. We surveyed the presence of mixed flocks, flocking propensity, number of species and individuals in mixed flocks in the Subtropical Yungas foothill of Argentina, to examine seasonality, flocking behavior of birds and their responses to two climatic variables: temperature and humidity. Bird species presented a higher flocking propensity and mixed flocks occurred more frequently during the dry and cold seasons than during the more benign seasons, and lower values of temperature within seasons triggered the flocking behavior. Although effects between seasons were expected, birds also showed a short‐term response to small changes in temperature within seasons. These results strengthen the ideas proposed by the foraging hypothesis. Although benefits derived from flocking have yet to be determined, whatever they are should be understood in the context of seasonal variation in life‐history traits.