Mixed-species Flocks Research Articles

Why Migrate? A Test of the Evolutionary Precursor Hypothesis

The question of why birds migrate is still poorly understood despite decades of debate. Previous studies have suggested that use of edge habitats and a frugivorous diet are precursors to the evolution of migration in Neotropical birds. However, these studies did not explore other ecological correlates of migration and did not control for phylogeny at the species level. We tested the evolutionary precursor hypothesis by examining the extent to which habitat and diet are associated with migratory behavior, using a species-level comparative analysis of the Tyranni. We used both migratory distance and sedentary versus migratory behavior as response variables. We also examined the influences of foraging group size, membership in mixed-species flocks, elevational range, and body mass on migratory behavior. Raw species analyses corroborated some results from studies that put forth the evolutionary precursor hypothesis, but phylogenetically independent contrast analyses highlighted an important interaction between habitat and diet and their roles as precursors to migration. Foraging group size was consistently associated with migratory behavior in both raw species and independent contrast analyses. Our results lead to a resource variability hypothesis that refines the evolutionary precursor hypothesis and reconciles the results of several studies examining precursors to migration in birds.

ARTHROPOD RESOURCE PARTITIONING AMONG OMNIVOROUS TANAGERS (TANGARA SPP.) IN WESTERN ECUADOR

The distribution and abundance of food are primary factors affecting resource-use patterns in birds. Many bird species eat several food types, which may differ in their distribution and overall abundance. I studied foraging ecology of seven sympatric species of Tangara at Mindo, Ecuador, to determine whether the patterns of resource use differed between two food types: arthropods and fruits. Interspecific differences in arthropod-foraging were manifested in the fine segregation of microhabitat preference combined with different habitat use. By contrast, interspecific differences in fruit-foraging were manifested in preferences for different plant genera, often associated with different habitats. No evidence was found for spatial partitioning of the same fruit species. Interspecific overlap in fruit-for- aging was 3× higher than that in arthropod-foraging, and species of Tangara that frequently joined the same mixed-species flocks differed largely in arthropod-foraging but overlapped greatly in fruit-foraging. The differences in patterns between arthropod and fruit-foraging may be explained by the different characteristics of arthropods and fruits as food resources. High sympatry of species of Tangara and other omnivorous tanagers, in general, appears to be maintained not because fruits are abundant, resulting in little competition for them, but because these tanagers specialize on different microhabitats for foraging arthropods. Segregación de Artrópodos como Recurso Alimenticio de Tangaras Omnívoras (Tangara spp.) en el Oeste de Ecuador

Arthropod Resource Partitioning Among Omnivorous Tanagers (Tangara SPP.) in Western Ecuador

AbstractThe distribution and abundance of food are primary factors affecting resource-use patterns in birds. Many bird species eat several food types, which may differ in their distribution and overall abundance. I studied foraging ecology of seven sympatric species of Tangara at Mindo, Ecuador, to determine whether the patterns of resource use differed between two food types: arthropods and fruits. Interspecific differences in arthropod-foraging were manifested in the fine segregation of microhabitat preference combined with different habitat use. By contrast, interspecific differences in fruit-foraging were manifested in preferences for different plant genera, often associated with different habitats. No evidence was found for spatial partitioning of the same fruit species. Interspecific overlap in fruit-for- aging was 3× higher than that in arthropod-foraging, and species of Tangara that frequently joined the same mixed-species flocks differed largely in arthropod-foraging but overlapped greatly in fruit-foraging. The differences in patterns between arthropod and fruit-foraging may be explained by the different characteristics of arthropods and fruits as food resources. High sympatry of species of Tangara and other omnivorous tanagers, in general, appears to be maintained not because fruits are abundant, resulting in little competition for them, but because these tanagers specialize on different microhabitats for foraging arthropods.Segregación de Artrópodos como Recurso Alimenticio de Tangaras Omnívoras (Tangara spp.) en el Oeste de Ecuador

Foraging Depth of Flamingos in Single-species and Mixed-species Flocks at Laguna de Pozuelos, Argentina

Habitat use by Chilean Flamingo (Phoenicopterus chilensis), Andean Flamingo (Phoenicoparrus andinus) and James Flamingo (Phoenicoparrus jamesi) in single-species and mixed-species flocks were studied at Laguna de Pozuelos, Argentina, by comparing the foraging pattern of each species in the presence and absence of the others. Spatial segregation among species within a flock was found. James Flamingo used the edge and the shallow foraging depth both in single-species and mixed-species flocks. Chilean Flamingo did not use the edge or the shallow depth either in single-species or mixed-species flocks, and used moderate and deep foraging depths. Andean Flamingo exhibited the most flexible foraging pattern, grouping either with Chilean Flamingo or with James Flamingo depending on which of these species predominated in the flock. Spatial difference in the feeding behavior among the three flamingo species may be principally attributed to the habitat of prey organisms. Chilean Flamingo feeds on planktonic organisms present mainly in the upper portion of the water column, and therefore this species can access a wider range of food items if foraging at deeper depths both in single-species or mixed-species flocks. The foraging pattern of James Flamingo was indicated by its main prey, benthic and aerophilic diatoms, largely found in shallow waters near the edge of the lake. Andean Flamingo feed on benthic diatoms common in the water-sediment interface of shallow and deep waters, thus favoring its grouping behavior with James or Chilean Flamingos in mixed-species flocks.

Vocal mimicry by a passerine bird attracts other species involved in mixed-species flocks

Little is known about how vocal mimicry affects the behaviour of members of other species. Such effects might, however, be especially likely in mixed-species flocks in which birds of some species directly benefit from the behaviour of members of other species. In mixed-species flocks in Sri Lanka, the greater racket-tailed drongo, Dicrurus paradiseus , mimics the songs and contact calls of other flock participants. We hypothesized that this mimicry attracts other species, as drongos are well known to increase their foraging efficiency in association with other species. Consistent with the predictions of this hypothesis, we recorded the most mimicked vocalizations during the rare occasions in which drongos were outside of flocks. In addition, we performed a playback experiment, which showed that taped drongo vocalizations that included song mimicry were more than twice as attractive to birds of other species as were taped vocalizations that lacked mimicry. We suggest that mimicry is a way in which drongos manage the behaviour of flockmates in what appears to be overall a mutualistic relationship.

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.

Diurnal Studies do not Predict Nocturnal Habitat Choice and Site Selection of European Golden-Plovers (Pluvialis Apricaria and Northern Lapwings (Vanellus Vanellus)

AbstractMany species, including shorebirds, feed during both day and night, yet little is known about how this affects behavior and habitat preferences. European Golden-Plovers (Pluvialis apricaria) and Northern Lapwings (Vanellus vanellus) feeding on arable farmland were more widely dispersed at night: nocturnal flocks were smaller, typically monospecific, and occurred in many more fields than diurnal mixed-species flocks. Diurnal numbers of European Golden-Plovers could not be used to predict nocturnal numbers; this indicates that ranging behavior differed between day and night. For both species, nocturnal feeding was recorded on almost all nights, irrespective of moon phase. Northern Lapwing nocturnal feeding activity decreased with increasing cloud cover and decreasing ground temperature, but no clear relationships were detected between European Golden-Plovers’ nocturnal feeding activity and environmental variables. Habitat selection differed between day and night, and between species at night. Diurnal studies of habitat choice and site selection may misrepresent the full requirements of such species.Los Estudios Diurnos no Predicen la Preferencia Nocturna de Hábitat ni la Selección Nocturna de Sitio en Pluvialis apricaria y Vanellus vanellus

Effects of feeding height and distance from protective cover on the foraging behavior of wintering birds

Foraging behavior that balances feeding efficiency with predation risk avoidance may be selected for; thus, foraging animals may choose among sites and achieve various giving-up densities under different feeding conditions. We compared the frequency and duration of visits and the feeding efficiency of a mixed-species wintering bird flock among feeders set up at three heights within woods, at the edge between woods and dense shrub, and in open fields to investigate the feeding height preference of birds and its relationship to the extent of openness of the sites. Carolina chickadees (Parus carolinensis Audubon, 1834) and tufted titmice (Parus bicolor L., 1766) accounted for 96% of the total number of visits to feeders and 95.9% of the total time spent on feeders. Birds tended to visit higher feeders and feeders in the woods and at edge sites more frequently than they visited lower feeders and feeders in open fields. Birds also spent more time on higher feeders and feeders in the woods and at edge sites than on lower feeders and feeders in open fields. However, the feeding height preference changed over the course of observations, and different patterns were observed at different sites. In the woods and at the edge, bird visits shifted to the lower feeders earlier; in contrast, birds preferred higher feeders throughout the period of observation in open fields. Feeding efficiency was lower at open sites than in woods and at edge sites, but birds spent the least time per seed on low feeders at open sites. Seeds on higher feeders and in woods or at edge sites were removed faster. Regardless of the height and locality of feeders, birds preferred energy-rich oil-type seeds over energy-poor striped seeds.

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.

Alarm Calling in Sri Lankan Mixed-Species Bird Flocks

AbstractVocal alarm calls are important to the vigilance and likely the organization of mixed-species flocks, but community-wide studies of alarm calling in flocks are lacking. We investigated which species alarm-call, and the characteristics of their calls, in a large flock system of a Sri Lankan rainforest. We recorded naturally elicited alarm calls during several attacks by Accipiter hawks and while following flocks for 10 h. We then artificially elicited alarms by throwing a stick to the side of the flock, in a total of 70 trials at 30 flock sites. The Orange-billed Babbler (Turdoides rufescens) was the most frequent caller to both the artificial and natural stimuli, followed by the Greater Racket-tailed Drongo (Dicrurus paradiseus). Several other species also called, and multiple species often called to the same stimulus (in 23 trials, and in all of the hawk attacks). The species differed in their rapidity of response and in their sensitivity to different natural stimuli. Calls of the gregarious babbler usually provided a first, unreliable warning of an incoming threat, whereas later calls of other species emphasized the seriousness of the threat. We suggest that birds in mixed-species flocks may be particularly aware of aerial predators for two reasons: (1) a “numbers effect,” whereby nongregarious species are more aware of predators when surrounded by large numbers of other species; and (2) an “information effect,” whereby species differ in the information available in their alarm calls, leading to an accumulation of information in a mixed-species flock.Llamadas de Alarma en Bandadas Mixtas de Aves en Sri Lanka

ALARM CALLING IN SRI LANKAN MIXED-SPECIES BIRD FLOCKS

Abstract Vocal alarm calls are important to the vigilance and likely the organization of mixed-species flocks, but community-wide studies of alarm calling in flocks are lacking. We investigated which species alarm-call, and the characteristics of their calls, in a large flock system of a Sri Lankan rainforest. We recorded naturally elicited alarm calls during several attacks by Accipiter hawks and while following flocks for 10 h. We then artificially elicited alarms by throwing a stick to the side of the flock, in a total of 70 trials at 30 flock sites. The Orange-billed Babbler (Turdoides rufescens) was the most frequent caller to both the artificial and natural stimuli, followed by the Greater Racket-tailed Drongo (Dicrurus paradiseus). Several other species also called, and multiple species often called to the same stimulus (in 23 trials, and in all of the hawk attacks). The species differed in their rapidity of response and in their sensitivity to different natural stimuli. Calls of the gregarious bab...

DIURNAL STUDIES DO NOT PREDICT NOCTURNAL HABITAT CHOICE AND SITE SELECTION OF EUROPEAN GOLDEN-PLOVERS (PLUVIALIS APRICARIA AND NORTHERN LAPWINGS (VANELLUS VANELLUS)

Abstract Many species, including shorebirds, feed during both day and night, yet little is known about how this affects behavior and habitat preferences. European Golden-Plovers (Pluvialis apricaria) and Northern Lapwings (Vanellus vanellus) feeding on arable farmland were more widely dispersed at night: nocturnal flocks were smaller, typically monospecific, and occurred in many more fields than diurnal mixed-species flocks. Diurnal numbers of European Golden-Plovers could not be used to predict nocturnal numbers; this indicates that ranging behavior differed between day and night. For both species, nocturnal feeding was recorded on almost all nights, irrespective of moon phase. Northern Lapwing nocturnal feeding activity decreased with increasing cloud cover and decreasing ground temperature, but no clear relationships were detected between European Golden-Plovers’ nocturnal feeding activity and environmental variables. Habitat selection differed between day and night, and between species at night. Diurn...

Effects of habitat disturbance on mixed species bird flocks in a tropical sub-montane rainforest

Despite their vulnerability to forest disturbances in the Neotropics, the consequences of forest perturbation on mixed species flocks are poorly understood in the threatened Southeast Asian rainforests. We examined the effects of local-scale habitat disturbance on mixed species flocks along an escalating gradient of anthropogenic modification (i.e., forest interior, forest edge, and urban) in a sub-montane tropical rainforest in Peninsular Malaysia that is presently experiencing low intensity development. Mixed species flocks in the forest interior and forest edge habitats (9.3 ± 2.3 and 8.4 ± 2.3, respectively) had significantly higher number of species than those observed in the urban habitat (5.1 ± 1.7). Flock participation was influenced by environmental characteristics (e.g., canopy cover). Flocking species sensitive to habitat disturbance were likely to be from the Families Corvidae, Nectariniidae, and Sylviidae; had narrow to restricted altitudinal ranges; and were exclusively dependent on primary forest and understory microhabitats. We conclude that sub-montane mixed species flocks are affected by even small scale urbanization and that they, particularly with species richness as a parameter, can be used as effective ecological indicators. With the looming development pressure on the sub-montane/montane habitats in Peninsular Malaysia and the Southeast Asian region, urgent conservation actions are needed for the preservation of their biotas.

Predator avoidance as a function of flocking in the sexually dichromatic Hawaii akepa

Hypotheses for joining a mixed-species bird flock consider each species as a single unit. In sexually dichromatic birds, differential conspicuousness between the sexes may result in differences in vigilance for predators. Aspects of the predator avoidance and foraging enhancement hypotheses for the selective value of joining a mixed-species flock were assessed for the strongly sexually dichromatic Hawaii akepa (Loxops coccineus coccineus). There was support for the primary predictions of the predator avoidance hypothesis: vigilance levels decreased with increasing group size, and with membership in a flock, but only for brightly colored adult males. There was little support for the hypothesis that the primary benefit of joining a mixed-species flock is to enhance foraging efficiency through “local enhancement”.

Mixed-Species Flocking and Foraging Behavior of Four Neotropical Warblers in Panamanian Shade Coffee Fields and Forests

Mixed-Species Flocking and Foraging Behavior of Four Neotropical Warblers in Panamanian Shade Coffee Fields and Forests

Mixed-Species Flocking and Foraging Behavior of Four Neotropical Warblers in Panamanian Shade Coffee Fields and Forests

Abstract We quantified foraging rates and foraging visibility metrics for four Neotropical warblers—Slate-throated Redstart (Myoborus miniatus), Golden-crowned Warbler (Basileuterus culicivorus), Wilson's Warbler (Wilsonia pusilla), and Black-and-White Warbler (Mniotilta varia)—under flocking and solitary conditions in western Panama to test hypotheses regarding the relative influences of predation pressure and social facilitation on foraging behavior. We also compared foraging behavior in primary forests and in traditionally managed shade coffee fields for two species (Slate-throated Redstart and Wilson's Warbler) to estimate spatial variation in foraging behavior and compare it to variation due to social situation (flocking or solitary). We then assessed the contribution of spatial variation in flocking propensity to the total spatial variation in foraging rates within species. We observed very little overall within-species variability in foraging behavior between social situations or study locations. Only Slate-throated Redstart's behavior was consistent with the hypothesis that flock membership reduces predation pressure and therefore reduces the amount of foraging time spent being vigilant against predators, allowing birds to forage more quickly and find more prey items per minute. No species' behavior supported the hypothesis that flocking birds forage more efficiently than solitary birds by obtaining useful information from flock mates about the location or suitability of foraging resources or techniques. The effort required to find prey items did not vary between study locations (forest and coffee field plots) for Wilson's Warbler. Because flocking also had no effect on foraging behavior of Wilson's Warbler, a reduction in flocking propensity in coffee habitat, relative to forest, did not cause further foraging behavior differences between study locations. Spatial variation in Slate-throated Redstart's foraging behavior independent of a flocking effect was minor; but flocking affected foraging rates, and flocking propensity was lower in coffee fields than in forest, so that location and flocking effects combined to widen foraging rate differences between locations. Thus, variations in flocking behavior and foraging behavior interacted differently for those two species.

Mixed-species bird flocks from Brazilian Atlantic forest: the effects of forest fragmentation and seasonality on their size, richness and stability

The effects of forest fragmentation on species richness, size and stability of bird mixed-species flocks were studied during rainy and dry seasons at nine Atlantic Forest fragments in Minas Gerais state, southeastern Brazil. Two distinct kinds of mixed-species flocks were identified at the study area: heterogeneous flock and understory flocks. The first type of association was observed in all forest fragments and was composed mainly of canopy and midstory species, but may include a few understory species. Understory flocks were composed mainly of understory species and were detected in only three forest fragments. Forest fragment area and season significantly affected species richness, size and stability of heterogeneous flocks. Moreover, species richness in heterogeneous flocks was correlated with total species pool in forest fragments. Species richness and size of understory flocks were different among the three forest fragments, but season influenced only flock size. Understory flock stability differed neither among forest fragments nor between seasons. The red-crowned ant-tanager Habia rubica was the nuclear and leader species of understory flocks, and determined the occurrence of this association in forest fragments. Our results show that forest fragmentation can affect species’ interactions in foraging associations, and that conservation plans for the region should preserve nuclear species of mixed-species flocks and their preferred habitats.

Home-range size, habitat use, and reproduction of the Ivory-billed Woodcreeper (Xiphorhynchus flavigaster) in dry forest of western Mexico

Abstract From March 1999 to August 2000, we used mist-netting, point counts, and radio-tracking to study habitat use, area requirements, and breeding of the Ivory-billed Woodcreeper Xiphorhynchus flavigaster in the tropical deciduous and semi-deciduous forest (arroyo forest) of the Chamela-Cuixmala Biosphere Reserve, western Mexico. The Ivory-billed Woodcreeper was a common, year-round resident. Breeding commenced at the end of the dry season (May) and continued during the rainy season through August. Our observations suggested that only the female builds the nest, incubates, and feeds nestlings. Ivory-billed Woodcreepers commonly foraged alone, but sometimes joined mixed-species flocks that passed through their territories, occasionally following army ant swarms. Home-range size varied from 6–36 ha, although most birds' home range was 15 ha or less. We did not find differences in home range size or mobility between the dry and rainy seasons, and we did not find a correlation between the size of the home ...

STRUCTURE AND DYNAMICS OF MIXED-SPECIES FLOCKS IN A HAWAIIAN RAIN FOREST

Abstract Mixed-species flocks of native and introduced birds were studied for four years in an upper elevation Hawaiian rain forest. Those flocks were characterized by strong seasonality, large size, low species richness, high intraspecific abundance, a lack of migrants, and a general lack of territoriality or any sort of dominance hierarchy. There was high variability among years in patterns of occurrence at the species level, and high variability within years at the individual level. These flocks are loosely structured social groupings with apparently open membership. The fluid, unstable movement patterns, high degree of variability in size and composition, and lack of positive interspecific associations are not consistent with the “foraging enhancement” hypothesis for flocking. Two resident, endangered insectivores, the Akepa (Loxops coccineus) and Hawaii Creeper (Oreomystis mana) served as “nuclear” species. Flock composition was compared between two study sites that differed significantly in density ...

Structure and Dynamics of Mixed-Species Flocks in a Hawaiian Rain Forest

Abstract Mixed-species flocks of native and introduced birds were studied for four years in an upper elevation Hawaiian rain forest. Those flocks were characterized by strong seasonality, large size, low species richness, high intraspecific abundance, a lack of migrants, and a general lack of territoriality or any sort of dominance hierarchy. There was high variability among years in patterns of occurrence at the species level, and high variability within years at the individual level. These flocks are loosely structured social groupings with apparently open membership. The fluid, unstable movement patterns, high degree of variability in size and composition, and lack of positive interspecific associations are not consistent with the “foraging enhancement” hypothesis for flocking. Two resident, endangered insectivores, the Akepa (Loxops coccineus) and Hawaii Creeper (Oreomystis mana) served as “nuclear” species. Flock composition was compared between two study sites that differed significantly in density of these two nuclear species. Flock size was similar at the two sites, primarily because the nuclear species were over-represented relative to their density. This observation suggests that birds are attempting to achieve a more optimal flock size at the lower density site.