Participation In Mixed-species Flocks Research Articles

The impacts of host traits on parasite infection of montane birds in southwestern China

Parasitic infections have the potential to impact the hosts’ body condition, elevate physiological responses, and ultimately lead to increased mortality. Host-parasite interactions are tied to the ecological and life-history traits of the hosts. While montane birds are susceptible to avian blood parasites, few studies have simultaneously assessed how inter- and intra-specific traits of hosts influence their probability of parasite infection. In this study, we screened for avian blood parasites across 214 individuals from 51 species at two sites, including a lowland farmland at 700 m and a highland forest at 2,500 m, in the Gaoligong Mountains in southwestern China. Overall blood parasite prevalence was 53.74%, with divergent species-specific prevalence ranging from 6.25% to 66.67%. We also measured traits indicative of body condition and physiological responses of each sampled individual. Using Bayesian phylogenetic logistic models, we assessed whether parasite infection probability is associated with ecological and life history traits of host species. Larger bird species were more likely to be infected than smaller bird species, and omnivore species showed lower susceptibility than those with other diets such as insectivores and herbivores. In contrast, foraging strata, nest type, and participation in mixed-species flocks of host species did not affect infection probability. We then used a reduced sample of eight species with more than five individuals, to assess the associations between intra-specific infection probability and host body condition, represented by fat and muscle reserves, and acute stress responses measured through breath rate. While infected individuals were likely to have more fat reserves than non-infected individuals, we did not find any association between infection probability and muscle reserve and body mass, nor with breath rate. Our results revealed that at the species level, specific traits (body mass and diet) of host species predict infection probability and implied a potential link at the individual level between enhanced body condition and increased resilience to parasite infection.

Effect of temperature on flocking propensity and species interactions in a subtropical mixed-species flocking system

Increased participation in mixed-species flocks is one hypothesized behavioral tactic used by forest birds to adjust to cold temperatures in winter. This phenomenon has been documented in temperate North America, but not at subtropical latitudes where temperatures are less extreme. To understand how temperature structures the size, richness, flocking propensity, and species interactions of subtropical mixed-species flocks, we performed paired mixed-species flock and point count surveys in upland hardwood forests in north-central Florida, USA. We described the composition of 92 mixed-species flocks across a ∼20 °C range of daytime temperatures, using linear mixed models and network analyses to test for effects of temperature. We found that both flock species richness and size were significantly smaller at higher temperatures while statistically controlling for effects of time of day, canopy height, and local site effects. Thirteen of 14 flocking species showed decreases in within-flock abundance with increasing temperature, although this effect was only significant for the nuclear Carolina Chickadee (Poecile carolinensis). Flock composition and species flocking propensities were less plastic than in temperate systems. By comparing metrics from 7 social networks corresponding to temperature ranges, we found that strength of flocking interactions was lower and that species were significantly less likely to co-occur with similarly foraging species at temperatures above 20 °C. Flocking propensities were lower for many species in the warmest temperature range. Thirteen of 14 species joined flocks in all 7 networks, and dissimilarity of social networks was consequently best explained by changes in species co-occurrence patterns rather than species turnover within flocks. In contrast to boreal flocking systems, changes to flocking behavior were prompted by unseasonably warm weather rather than cold spells, which suggests that warming winter temperatures could lead to breakdown of social behaviors in our system.

Trait-environment relationships differ between mixed-species flocking and nonflocking bird assemblages.

Hypotheses about the mechanisms of community assembly suggest that biotic and abiotic filters constrain species establishment through selection on their functional traits. It is unclear how differences in traits influence the niche dimensions of closely related bird species when they coexist in spatiotemporally heterogeneous environments. Further, it is necessary to take into account their participation in mixed-species flocks, social systems that can include both competition and facilitation. For 6 yr, we conducted counts of forest bird species and took measurements of environmental variables along an elevational gradient in the Nanling Mountains, China. To disentangle different deterministic and historical/stochastic processes between flocking and nonflocking bird assemblages, we first compared phylogenetic and functional structure, and community-weighted mean trait values (CWM). We further assessed elevational variations in trait-environment relationships. We found that the flocking and nonflocking bird assemblages were structured by environmental gradients in contrasting ways. The nonflocking assemblage showed a strong change from over-dispersed to clustered community structure with increasing elevations, consistent with the strong selective pressures of a harsh environment (i.e., environmental filtering). The nonflocking assemblage also displayed significant trait-environment relationships in bivariate correlations and multivariate ordination space, including specific morphological and foraging traits that are linked to vegetation characteristics (e.g., short trees at high elevations). By contrast, flocking birds were more resilient to habitat change with elevation, with relatively consistent community membership, and showed fewer trait-environment associations. CWM of traits that are known to be associated with species' propensity to join mixed-species flocks, including small body size and broad habitat specificity, were linked to the flocking assemblage consistently across the elevational gradient. Collectively, our trait-based analyses provide strong evidence that trait-environment relationships differ between flocking and nonflocking bird assemblages. Besides serving as bellwethers of changing environments, emergent properties of flock systems may increase the resilience of animal communities undergoing environmental change. Mixed-species flocks present an ideal model with which to explore cooccurrence of closely related species, because habitat filtering may be buffered, and the patterns observed are therefore the outcomes of species interactions including both competition and facilitation.

Mixed species flock, nest height, and elevation partially explain avian haemoparasite prevalence in Colombia.

The high avian biodiversity present in the Neotropical region offers a great opportunity to explore the ecology of host-parasite relationships. We present a survey of avian haemoparasites in a megadiverse country and explore how parasite prevalences are related to physical and ecological host characteristics. Using light microscopy, we documented the presence of haemoparasites in over 2000 individuals belonging to 246 species of wild birds, from nine localities and several ecosystems of Colombia. We analysed the prevalence of six avian haemoparasite taxa in relation to elevation and the following host traits: nest height, nest type, foraging strata, primary diet, sociality, migratory behaviour, and participation in mixed species flocks. Our analyses indicate significant associations between both mixed species flocks and nest height and Haemoproteus and Leucocytozoon prevalence. The prevalence of Leucocytozoon increased with elevation, whereas the prevalence of Trypanosoma and microfilariae decreased. Plasmodium and Haemoproteus prevalence did not vary significantly with elevation; in fact, both parasites were found up to 3300m above sea level. The distribution of parasite prevalence across the phylogeny of bird species included in this study showed little host phylogenetic signal indicating that infection rates in this system are evolutionarily labile. Vector distribution as well as the biology of transmission and the maintenance of populations of avian haemoparasites deserve more detailed study in this system.

Patterns of species participation across multiple mixed-species flock types in a tropical forest in northeastern India

We studied mixed-species bird flocks in northeastern India to (a) develop a framework for quantifying species participation in mixed-species flocks, (b) characterize the ecology and behaviour of participant species, and (c) explore mechanisms influencing the coexistence of different mixed-species flock types. To characterize participation in mixed-species flocks, we implement a new method incorporating species abundances, minimizing potential biases in measuring participation arising from differences in the availability of flocking species. There are at least three distinct flock types in the lowland forests of northeastern India; these flock types differ in the body mass and vertical stratum use of participant species. The “core” of mixed-species flocks was composed of a species group that differed much more in their foraging method in comparison with “attendant” species. The exchange of benefits and minimization of interspecific competition might lead to, and maintain, heterogeneity in foraging methods among core species of mixed-species flocks.

Characterizing complex mixed-species bird flocks using an objective method for determining species participation

We developed sampling methods to characterize the participation of bird species in foraging flocks led by the Eastern Tufted Titmouse (Baeolophus bicolor) in North-central Florida during winter, because standard field methods, developed primarily for permanent resident Neotropical flocks, were intractable in our system. During January–February 2004 and November 2004–March 2005, we observed 55 mixed-species flocks, recorded 40 potential flocking species [mean of 12.4 species (SD = 3.8; range 3–20), 26.3 individuals (SD = 12.2; range 8–60), and 3.1 titmice (SD = 1.4; range 1–7), per flock]. Twenty-six species were observed frequently enough (>10% of observations) to be included in analyses. We paired 60-min flock observations with 10-min point counts conducted in locations used by flocks, but after flocks had moved more than 100 m away. This method yielded a measure of flocking propensity: the ratio of the number of individuals observed in the flock versus during the point count for each species. We used regression tree (RT) analysis to classify species into groupings according to their levels of flock participation, and to investigate relationships between flocking propensity and various environmental and social factors that we measured. Our analysis identified three clear species groups; “Nuclear/Regular Associate” (12 spp.; high/moderate), “Occasional Associate” (four spp.; moderate/low), and “Non-joiner/Accidental” (ten spp.; low/no flocking propensity). Groupings were similar to schemes produced via more time-intensive field methods. In order to contextualize grouping categories, we conducted a review of flocking group definitions and relevant autecological information (e.g., interspecific sociality) about our study species. We found this method to be useful for geographically extensive sampling of species’ participation in mixed-species flocks, despite high inter-flock variability in species composition and limited labor.

Response to conspecific and heterospecific alarm calls in mixed-species bird flocks of a Sri Lankan rainforest

The flow of information about predators in mixed-species groups is likely to influence the structure and organization of these communities. To map this flow, it is necessary to demonstrate in a playback experiment that animals use the information provided in heterospecific calls. We investigated the response of birds to conspecific and heterospecific calls in a mixed-species flock system of a Sri Lankan rainforest. We played back the aerial alarm calls of the species that produce the most alarms, the Orange-billed Babbler (Turdoides rufescens) and the Greater Racket-tailed Drongo (Dicrurus paradiseus), as well as natural choruses of alarm calls of several species, to 4 species of birds. We found that babblers moved quickly away from the playback speaker after hearing either babbler or drongo alarm calls. Ashy-headed Laughingthrushes (Garrulax cinereifrons) responded similarly to drongo alarm calls. Response by other species was less clear: Malabar Trogons (Harpectes fasciatus) stayed perched for longer during alarms of several species; drongos showed no difference in response to any treatment. We conclude that birds are listening to heterospecifics and suggest that their response is influenced by several factors, including their foraging technique. The fact that the babbler, the gregarious leading species of the flocks, gains information from another species is one of the first indications that such a “nuclear” species can benefit from its participation in mixed-species flocks, and the response of at least 2 species to drongo alarms emphasizes the importance sentinel species such as drongos may play in flock communities.

Avian Community Response to Lowland Tropical Rainforest Isolation: 40 Years of Change at La Selva Biological Station, Costa Rica

Since 1960, most of the forest surrounding the La Selva Biological Station, an intensively studied tropical research facility in Costa Rica, has been converted to agricultural uses. We used quantitative censuses and analysis of previously published categorical abundances to assess changes in the bird community, and we evaluated potential causes of species-specific changes by assessing their association with habitat, diet, participation in mixed-species flocks, and nest type. Approximately the same percentage of species increased as decreased in abundance from 1960 to 1999 (10-20% of all species, depending on method of assessment). Diet was the single most important trait associated with declining species. At least 50% of the species that declined have insectivorous diets. Use of forest habitat and participation in mixed-species flocks were also significant factors associated with declines, but nest type was unrelated to change in abundance. The species that increased in abundance tended to occur in open habitats and have omnivorous diets. These results reinforce the importance of several population risk factors associated with tropical understory insectivory and mixed-species flocking: patchy spatial distribution, low population density, large home range, and dietary specialization. La Selva's protected area (1611 ha), despite a forested connection on one boundary with a higher elevation national park, is apparently too small to maintain at least one major guild (understory insectivores). This first quantitative assessment of bird community change at La Selva highlights the need to intensify study of the mechanisms and consequences of biological diversity change in tropical forest fragments.

Avian malaria in Brazilian passerine birds: parasitism detected by nested PCR using DNA from stained blood smears

The microscopical examination of Giemsa-stained thin blood smears and a nested PCR were performed to detect avian Plasmodium in 275 passerine birds from small and large fragments of Atlantic Forest, Minas Gerais, Brazil. The 275 blood smears were used both for the microscopical examination and nested PCR providing the DNA template used for the reactions. The sensitivity of the nested PCR assay was higher than that observed for blood smears through microscopical examination. High prevalence (39.6%) of Plasmodium infections was detected by nested PCR while the microscopical examination detected only 16.5 % positive birds. Poor agreement was observed between the results of the two different tests. The PCR data obtained were correlated to the forest fragment size of the Atlantic Forest and also correlated to the biological characteristics of the birds (nest type construction, diet, participation in mixed-species flocks, age and sex). Birds captured in the large forest areas were more infected than birds captured in the small areas (51.9 % and 28.5 %, respectively). Diet and participation in mixed-species flocks were correlated to the Plasmodium parasitism. The insectivorous birds and those that participated in mixed-species flocks were more frequently infected (47% and 41.5%, respectively) than the other groups.

The paradoxical social system of the DuskyBush-Tanager (Chlorospingus semifuscus): lekking in a nine-primaried oscine?

We studied the behavior of the Dusky Bush-Tanager (Chlorospingus semifuscus; Thraupinae) in southwestern Colombia, where it seems to exhibit singing assemblages resembling leks. A lek mating system would be paradoxical in a genus noted for its active participation in mixed-species flocks, largely insectivorous diet, and stable pair bond. We used the bird's behavior and the relations between fruit availability, its diet, and its participation in mixed flocks to try to explain the social system. We found males singing in dense linear assemblages, regularly spaced along ridgetops, during early morning and late afternoon hours during much of the year, with a peak from May through August. Singing males occupied small circular territories, which usually were reoccupied the next year by the same males. The critical resource is likely the males themselves, although fruit availability may permit them to remain on territories for long periods; nesting areas are apparently far from the ridgetops. Participation in flocks occured year-round but was somewhat reduced during the singing season and in the singing hours. The evidence of pair bonds in this species, in which males participate at least in nest-site selection and feeding of young, excludes the possibility of a lek mating system in the strict sense. Nevertheless, the system of singing linear assemblies appears to have been superimposed upon the typical social system of the genus. This social system is unique in the entire nine-primaried oscine assemblage.

Woodpecker Participation in Mixed Species Flocks in Peninsular Malaysia

Woodpeckers (family Picidae) are widely distributed and have been documented as participants in mixed species flocks in both temperate and tropical regions. However, they usually are not considered frequent flock participants, and the presence of multiple species of woodpeckers participating simultaneously in flocks is virtually undocumented. We determined the frequency of this association for the six most common woodpecker species at Pasoh Forest Reserve, West Malaysia. During the two-month study period, woodpeckers participated regularly in flocks with other woodpecker species, including congeners. Observations of multiple species of woodpeckers participating in foraging flocks in other parts of Malaysia, as well as Thailand and Indonesia, suggest that this might be a regular occurrence in Southeast Asia.

Winter Flocking of Insectivorous Birds in Montane Pine-Oak Forests in Middle America

Abstract We studied mixed-species insectivorous bird flocks in pine-oak forests in Middle America during three winter seasons to determine whether patterns of flock structure and dynamics were similar to those reported from other tropical sites. We also analyzed patterns of association among bird species, as well as their foraging behavior and the vegetation characteristics associated with birds in flocks. We encountered 333 flocks containing 144 species, of which 26 species had adequate sample sizes for analyses. The size and rate of movement of the flocks were similar to those reported from other Neotropical sites, however, the species richness of our flocks was lower than reported in most other studies, perhaps due to simpler vegetation structure or higher latitude. Only 3 of 50 significant correlations between species pairs were negative, indicating that species generally were not restricted in their participation in mixed-species flocks by other species. In only one instance did we observe correspondence between the association of species-pairs in flocks and their foraging behavior. For most species there was no relationship between association between species-pairs in flocks and vegetation parameters with which they were associated. Thus, additional factors besides foraging facilitation and mutual association with particular vegetation characteristics must be responsible for many of the positive correlations among species pairs. We suggest that non-random association among species within flocks may result in part from enhanced vigilance for predator detection afforded by flock members using similar parts of the environment at the same time.

WINTER FLOCKING OF INSECTIVOROUS BIRDS IN MONTANE PINE-OAK FORESTS IN MIDDLE AMERICA

Abstract We studied mixed-species insectivorous bird flocks in pine-oak forests in Middle America during three winter seasons to determine whether patterns of flock structure and dynamics were similar to those reported from other tropical sites. We also analyzed patterns of association among bird species, as well as their foraging behavior and the vegetation characteristics associated with birds in flocks. We encountered 333 flocks containing 144 species, of which 26 species had adequate sample sizes for analyses. The size and rate of movement of the flocks were similar to those reported from other Neotropical sites, however, the species richness of our flocks was lower than reported in most other studies, perhaps due to simpler vegetation structure or higher latitude. Only 3 of 50 significant correlations between species pairs were negative, indicating that species generally were not restricted in their participation in mixed-species flocks by other species. In only one instance did we observe correspond...