Sympatric Bird Species Research Articles

Life-History and Ecological Correlates of Egg and Clutch Mass Variation in Sympatric Bird Species at High Altitude.

The variation in egg and clutch mass in sympatric species at high altitudes is poorly understood, and the potential causes of variation are rarely investigated. This study aimed to describe the interspecific variation in avian egg and clutch mass among 22 sympatric bird species at an altitude of 3430 m. Our objective was to reduce potential confounding effects of biotic/abiotic factors and investigated hypotheses concerning allometry, clutch size, parental care, nest predation, and lifespan as possible correlates and explanations for the observed variation. Our findings indicated that both egg and clutch mass evolve with body mass across species. We found that egg mass variation was not explained by clutch size when controlling for allometric effects, which contrasts the "egg mass vs. clutch size trade-off" hypothesis. Additionally, we found that clutch mass was positively associated with parental care (reflected by development period) but negatively associated with predation rate. By substituting egg mass and clutch size into the models, we found that clutch size was significantly correlated with parental care, predation rate, and lifespan, while egg mass was only significantly associated with development period. Overall, these findings support life-history theories suggesting that reduced clutch size or mass is associated with a higher risk of predation, reduced parental care, but longer adult lifespan. Interestingly, our results indicate that clutch size has a greater influence on these factors compared to egg mass. This could be attributed to the fact that smaller clutch sizes result in a more notable decrease in energetic allocation, as they require a reduced effort in terms of offspring production, incubation, and feeding, as opposed to solely reducing egg size. These findings contribute to the growing evidence that life-history and ecological traits correlate with egg and clutch mass variation in sympatric species. However, further research is needed to explore the potential evolutionary causes underlying these patterns.

Density Estimates and Habitat Preferences of Two Sympatric Bird Species as Potential Bioindicators of Tropical Forest Alterations

Forestry management can shape the structure of habitat types and have important biological consequences on the composition of biodiversity. This study focused on Momotus lessonii and Eumomota superciliosa, two potential bioindicators of local and wide scale tropical forest alterations. The study took place in the Karen Mogensen Wildlife Refuge (Costa Rica), a protected area characterized by two main forest habitats where the two species coexist, i.e., primary moist and second-growth dry forest. A distance sampling method was used to obtain density estimates for each species. A spot mapping approach showed an apparent partitioning of the two species at the site. The Kilometric Abundance Index (KAI) and statistical analyses revealed significant differences between the two habitats, i.e., E. superciliosa tended to be more abundant and preferred the dry forest, whilst M. lessonii favored moist environments. The development of arid and semi-arid environments characterized by open areas will probably lead to a numerical increase in E. superciliosa with a consequent expansion, while the decline of moister and homogeneously forested environments will likely affect negatively M. lessonii. We argue that these birds will act as bioindicators of local and global environmental changes, and their monitoring will enable appropriate forest management decisions for conservation purposes.

Habitat alteration and fecal deposition by geese alter tundra invertebrate communities: Implications for diets of sympatric birds.

Over the last 60 years, Arctic goose populations have increased while many sympatric tundra nesting bird populations have declined. Hyperabundant geese have well-documented effects on tundra habitats, which can alter habitat use by sympatric bird species. These habitat changes may also alter invertebrate communities and abundances, with potentially important, but as of yet, undocumented effects on insectivorous birds such as shorebirds. Here, we determined the effects of goose-induced habitat alteration on invertebrate communities and relate the observed changes to shorebird diet. At sites and habitat types representing a gradient of goose influence, we identified goose-related changes in ground cover and linked these factors to variation in invertebrate communities. We then used DNA metabarcoding to characterize the diet of six shorebird species across sites and identify inter-site variation in abundance, biomass, and timing of emergence of dominant shorebird prey items. Invertebrate diversity and richness did not vary either among sites or habitat types. However, for prey items identified as part of the shorebird diet, we found significantly higher abundances and biomasses at a moderately goose-influenced site than at either low or high goose-influenced sites. Biomass of Tipulidae, the dominant prey taxon for shorebirds at the study sites, was 7.5 times higher at the moderately goose-influenced site compared to the site where goose influence was minor. We attribute this enhancement of prey biomass to both the fertilizing effect of goose fecal pellets and the moderate grazing pressure. Many studies have documented adverse effects of overabundant geese, but here we show that a moderate degree of goose grazing can lead to enhanced biomass of invertebrates, with the potential for improved shorebird foraging success and chick growth. These benefits, however, might be outweighed by negative effects of goose-induced habitat alteration and predation pressure.

Dear-enemy effect between two sympatric bird species

Although interspecific interactions appear to be less competitive than intraspecific ones, interspecific territoriality is much more frequent and more stable than is commonly believed. When territorial interactions between competing species are repeated, discrimination between heterospecifics can allow for a more precise allocation of resources and risk. An example of such a strategic approach is the dear-enemy effect, according to which individuals are less aggressive to familiar than unfamiliar individuals. We investigated the occurrence of the dear-enemy effect in territorial interactions between two nonpasserine bird species: water rail, Rallus aquaticus , and little crake, Zapornia parva , which compete for food and nest site resources. We used a cross-species playback experiment where water rails received calls of strangers and neighbouring little crakes, while little crakes received calls of water rails in the same manner. In addition, each focal pair was exposed to control calls of little grebes, Tachybaptus ruficollis . In both species, territory holders produced more calls in response to heterospecific strangers than heterospecific neighbours, and the response to control stimuli was the weakest. Furthermore, little crakes often approached and attacked the loudspeakers and mostly when they heard the calls of stranger water rails. Our results indicate that both species were able to distinguish not only each other from the control species, but also specific individuals of the second species. In line with the dear-enemy effect, water rails and little crakes adjusted their territorial response according to the intruder's status, being most aggressive to heterospecific strangers. These findings suggest an adaptive territorial response to resource competition that is commonly confirmed among conspecifics but rarely between individuals of different species. • We studied the dear-enemy effect between two competing bird species. • Water rails and little crakes recognized specific individuals of the other species. • Both species responded with lower vocal intensity to heterospecific neighbours. • Stronger nonvocal response to stranger calls was observed only in little crakes.

Nest concealment is associated with reproductive traits across sympatric bird species.

Nest‐site characteristics are thought to play an important role in reproductive performance in birds (e.g., influencing reproductive success and predation risk). Nest‐site characteristics such as concealment may be particularly critical at high elevation where nests are exposed to challenging environmental conditions. In this study, we conducted both conventional and phylogenetically controlled analyses to investigate whether nest concealment affected several reproductive traits across 21 sympatric bird species living on Tibet Plateau (3,400 m altitude). Qualitatively equivalent results were reached in analyses, regardless of phylogenetic controls. We found that clutch size, incubation period, nestling period, and nest success were strongly and positively associated with nest concealment across species. Our study addressed such a high‐elevation bird community that is lacking in the previous studies. This study adds to theory that while there are a few exceptions, overall evidence supports a positive effect of nest concealment on reproductive performance across coexisting alpine species.

Evidence of endozoochory in upland geese Chloephaga picta and white-bellied seedsnipes Attagis malouinus in sub-Antarctic Chile.

Birds are known to act as potential vectors for the exogenous dispersal of bryophyte diaspores. Given the totipotency of vegetative tissue of many bryophytes, birds could also contribute to endozoochorous bryophyte dispersal. Research has shown that fecal samples of the upland goose (Chloephaga picta) and white‐bellied seedsnipe (Attagis malouinus) contain bryophyte fragments. Although few fragments from bird feces have been known to regenerate, the evidence for the viability of diaspores following passage through the bird intestinal tract remains ambiguous. We evaluated the role of endozoochory in these same herbivorous and sympatric bird species in sub‐Antarctic Chile. We hypothesized that fragments of bryophyte gametophytes retrieved from their feces are viable and capable of regenerating new plant tissue. Eleven feces disk samples containing undetermined moss fragments from C. picta (N = 6) and A. malouinus (N = 5) and six moss fragment samples from wild‐collected mosses (Conostomum tetragonum, Syntrichia robusta, and Polytrichum strictum) were grown ex situ in peat soil and in vitro using a agar Gamborg medium. After 91 days, 20% of fragments from A. malouinus feces, 50% of fragments from C. picta feces, and 67% of propagules from wild mosses produced new growth. The fact that moss diaspores remained viable and can regenerate under experimental conditions following the passage through the intestinal tracts of these robust fliers and altitudinal and latitudinal migrants suggests that sub‐Antarctic birds might play a role in bryophyte dispersal. This relationship may have important implications in the way bryophytes disperse and colonize habitats facing climate change.

Seasonal metabolic flexibility is correlated with microclimate variation in horned larks and house sparrows.

Maximum and minimum metabolic rates in birds are flexible traits and such flexibility can be advantageous in variable climates. The climatic variability hypothesis (CVH) posits that more variable climates should result in greater metabolic flexibility for geographically distinct populations. Whether the CVH applies to sympatric species occupying microclimates differing in variability is unknown. Microclimates of open habitats are likely more variable than those of sheltered habitats. If the CVH extends to microclimates, we expect birds from open habitats to show greater flexibility than those from sheltered habitats. To test this extension of the CVH, we compared seasonal variation in microclimates and metabolic rates for sympatric horned larks Eremophila alpestris, which occupy open habitats, and house sparrows Passer domesticus, which occupy sheltered habitats. We measured operative temperature (Te, an integrative measure of the thermal environment), summit metabolic rate (Msum, maximal cold-induced metabolic rate), and basal metabolic rate (BMR, minimal maintenance metabolic rate) in summer and winter. For both winter and summer, daily minimum Te was similar between open and sheltered habitats but maximum Te was higher for open habitats. Winter microclimates, however, were colder for open than for sheltered habitats after accounting for convective differences. Both species increased Msum in winter, but seasonal Msum flexibility was greater for larks (43%) than for sparrows (31%). Winter increases in BMR were 92.5% and 11% for larks and sparrows, respectively, with only the former attaining statistical significance. Moreover, species * season interactions in general linear models for whole-organism metabolic rates were significant for BMR and showed a similar, although not significant, pattern for Msum, with greater seasonal metabolic flexibility in horned larks than in house sparrows. These results suggest that extending the CVH to sympatric bird species occupying different microclimates may be valid.

Parasites of the Shiny Cowbird, Molothrus bonariensis, and the Austral Blackbird, Curaeus curaeus, (Passeriformes: Icteridae) in Chile.

Comparative studies of parasites in sympatric bird species have been generally scarce. Parasitic infection/transmission can be spread in a number of ways that suggests possible direct and indirect, horizontal transmission between avian hosts. In order to determine whether two sympatric icterids from Central and Southern Chile share their parasite fauna (ecto- and endoparasites), we examined parasites of 27 Shiny Cowbirds, Molothrus bonariensis, and 28 Austral Blackbirds, Curaeus curaeus, including individuals captured in the wild and carcasses. We found that Shiny Cowbirds were infected with the chewing lice Brueelia bonariensis, Philopterus sp. 1, the feather mites Amerodectes molothrus, Proctophyllodes spp. (species 1 and 2), and the helminths Mediorhynchus papillosus, Plagiorhynchus sp., Dispharynx nasuta and Tetrameres paucispina, while Austral Blackbirds had the chewing lice Myrsidea sp., Philopterus sp. 2, the feather mites Proctophyllodes sp. 3, Amerodectes sp., and three helminths: Anonchotaenia sp., Capillaria sp. and M. papillosus. The flea Dasypsyllus (Neornipsyllus) cteniopus was found only on the Austral Blackbird. The only parasite species shared by both icterids was the acanthocephalan M. papillosus, possibly due to their feeding on the same intermediate insect hosts. With the exception of B. bonariensis and Philopterus sp. 1 found on the Shiny Cowbird, all species reported in this study represent new parasite-host associations and new records of parasite diversity in Chile.

CHLAMYDIA PSITTACI IN FERAL ROSY-FACED LOVEBIRDS ( AGAPORNIS ROSEICOLLIS) AND OTHER BACKYARD BIRDS IN MARICOPA COUNTY, ARIZONA, USA.

In 2013, a mortality event of nonnative, feral Rosy-faced Lovebirds ( Agapornis roseicollis) in residential backyards in Maricopa County, Arizona, US was attributed to infection with Chlamydia psittaci. In June 2014, additional mortality occurred in the same region. Accordingly, in August 2014 we sampled live lovebirds and sympatric bird species visiting backyard bird feeders to determine the prevalence of DNA and the seroprevalence of antibodies to C. psittaci using real-time PCR-based testing and elementary body agglutination, respectively. Chlamydia psittaci DNA was present in conjunctival-choanal or cloacal swabs in 93% (43/46) of lovebirds and 10% (14/142) of sympatric birds. Antibodies to C. psittaci were detected in 76% (31/41) of lovebirds and 7% (7/102) of sympatric birds. Among the sympatric birds, Rock Doves ( Columba livia) had the highest prevalence of C. psittaci DNA (75%; 6/8) and seroprevalence (25%; 2/8). Psittacine circovirus 1 DNA was also identified, using real-time PCR-based testing, from the same swab samples in 69% (11/16) of species sampled, with a prevalence of 80% (37/46) in lovebirds and 27% (38/142) in sympatric species. The presence of either Rosy-faced Lovebirds or Rock Doves at residential bird feeders may be cause for concern for epizootic and zoonotic transmission of C. psittaci in this region.

Parental care mitigates carry-over effects of poor early conditions on offspring growth

Poor developmental conditions can have long-lasting negative effects on offspring phenotypes, but impacts often differ among species. Contrasting responses may reflect disparities in experimental protocols among single-species studies or inherent differences among species in their sensitivity to early conditions and/or ability to mitigate negative impacts. We used a common experimental protocol to assess and compare the role of parental care in mitigating effects of poor early conditions on offspring among 4 sympatric bird species in the wild. We experimentally induced low incubation temperatures and examined effects on embryonic developmental rates, hatching success, nestling growth rates, and parental responses. We examined the generality of these effects across 4 species that differ in their phylogenetic history, breeding ecology, and life histories. We found that cooling led to delayed hatching in all species, but carry-over effects on offspring differed among species. Parents of some but not all species increased their offspring provisioning rates in response to experimental cooling with critical benefits for offspring growth rates. Our study shows for the first time that species exhibit clear differences in the degree to which they are affected by poor early conditions. Observed differences among species demonstrate that parental care is a critical mechanism for mitigating potential negative effects on offspring and suggest that parental responses may be constrained to varying degrees by ecology and life histories.

Using Next-Generation Sequencing to Contrast the Diet and Explore Pest-Reduction Services of Sympatric Bird Species in Macadamia Orchards in Australia.

Worldwide, avian communities inhabiting agro-ecosystems are threatened as a consequence of agricultural intensification. Unravelling their ecological role is essential to focus conservation efforts. Dietary analysis can elucidate bird-insect interactions and expose avian pest-reduction services, thus supporting avian conservation. In this study, we used next-generation sequencing to analyse the dietary arthropod contents of 11 sympatric bird species foraging in macadamia orchards in eastern Australia. Across all species and based on arthropod DNA sequence similarities ≥98% with records in the Barcode of Life Database, 257 operational taxonomy units were assigned to 8 orders, 40 families, 90 genera and 89 species. These taxa included 15 insect pests, 5 of which were macadamia pests. Among the latter group, Nezara viridula (Pentatomidae; green vegetable bug), considered a major pest, was present in 23% of all faecal samples collected. Results also showed that resource partitioning in this system is low, as most bird species shared large proportion of their diets by feeding primarily on lepidopteran, dipteran and arachnids. Dietary composition differed between some species, most likely because of differences in foraging behaviour. Overall, this study reached a level of taxonomic resolution never achieved before in the studied species, thus contributing to a significant improvement in the avian ecological knowledge. Our results showed that bird communities prey upon economically important pests in macadamia orchards. This study set a precedent by exploring avian pest-reduction services using next-generation sequencing, which could contribute to the conservation of avian communities and their natural habitats in agricultural systems.

Differential heat tolerance in nestlings suggests sympatric species may face different climate change risks

For endotherms, a major threat of climate change will be the increasing frequency of extreme climate events, including heat waves. Thus, the ability of different species to tolerate high environmental temperatures is likely to have important consequences for ecology and population dynamics. We investigated the impacts of exposure to high temperatures on survival, mass gain and physiological stress of nestlings of 2 sympatric bird species subjected to the same climatic conditions in the Mediterranean basin. Results showed species-specific responses to high temperatures. Whilst hyperthermia or acute dehydration caused 36% mortality among lesser kestrels Falco naumanni, none occurred among European rollers Coracias garrulus. Within survivors, high maximum daily temperatures significantly reduced mass gain, especially among kestrels. Moreover, mass loss during heat events was shown to result in carry-over fitness costs only for lesser kestrels, by decreasing fledging condition and likely impacting post-fledging survival. High nest temperatures strongly elevated physiological stress levels of kestrels. Overall, rollers exhibited greater resilience to heat than kestrels, surviving nest temperatures up to 50°C and recovering from mass losses, suggesting that nestling development is flexible enough to cope with the constraints imposed by occasional heat waves. Although predicted increases in the frequency of extreme temperatures can accentuate lethal and sublethal fitness costs for both species, the higher thermal tolerance of rollers makes them more resilient. Our results highlight that sympatric species are not equally at risk when facing climate change and suggest that successfully predicting species response to global warming will require a better understanding of species-specific thermal tolerance.

The usefulness of top predators as biodiversity surrogates indicated by the relationship between the reproductive outputs of raptors and other bird species

Given the global reduction in biodiversity, conservation actions must occur even with only a partial understanding of the distribution and abundance of species in various locales. The concept of surrogate species, those whose protection affords the protection of other species, is considered a conservation short-cut. Although surrogate species have been used as practical conservation tools, whether they serve as indicators of the reproductive output of other species is still unknown. We hypothesized that the reproductive output of the eastern marsh harrier (Circus spilonotus) can serve as a surrogate for both the adult abundance and reproductive output of sympatric birds. In a fragmented wetland landscape (approximately 211.60km2), we measured the reproductive output of harriers for 3years and conducted replicated counts of the adults and juveniles of other wetland bird species in wetland patches that varied in harrier reproductive output. We used playbacks of mobbing calls in replicated counts and accounted for imperfect detection using an N-mixture model. We modeled adult and juvenile abundances for 10 and 7 species, respectively, and showed that the reproduction-based habitat quality of the marsh harrier (cumulative numbers of both years occupying the habitat and chicks produced) was positively associated with adult abundances in four species and with juvenile abundances in five species. We suggest that areas with high reproductive output of several sympatric bird species could be selected based on the reproduction-based habitat quality of the marsh harrier. Furthermore, the approach combining the playback of mobbing calls and N-mixture models enabled us to estimate juvenile abundances for many bird species on a landscape scale over a short period of time.

Do birds of a feather disperse plants together?

Summary 1. Dispersal of propagules by waterbirds is thought to be important for wetland plants because of the abundance of birds and their frequent movements among aquatic habitats. Differences in bird characteristics (size, movement, feeding ecology) were expected to lead to different outcomes for plant dispersal. 2. We investigated heterogeneity in plant dispersal by ducks (Anas superciliosa, Anas gracilis, Anas castanea). We calculated the probability of transport of viable seeds by germinating propagules retrieved from feathers and feet (epizoochory) and the contents of the oesophagus, gizzard and lower gut (endozoochory). 3. The abundance and richness of seeds carried internally and externally did not differ among sympatric bird species. We used estimates from the literature of movements of Anas species to approximate dispersal kernels for the transport of plant propagules. 4. Heterogeneity in the abundance and movement ecology of disperser species will result in differing patterns and degrees of connectivity for wetland plant metacommunities. Sedentary waterfowl are likely to have an important role in replenishing propagules and connecting aquatic metacommunities over small distances. Nomadic waterfowl may facilitate long-distance dispersal. We discuss the implications of differences between duck species in movement patterns for connectivity of aquatic plant metacommunities across landscapes.

Avian Host-Selection by Culex pipiens in Experimental Trials

Evidence from field studies suggests that Culex pipiens, the primary mosquito vector of West Nile virus (WNV) in the northeastern and north central United States, feeds preferentially on American robins (Turdus migratorius). To determine the contribution of innate preferences to observed preference patterns in the field, we conducted host preference trials with a known number of adult female C. pipiens in outdoor cages comparing the relative attractiveness of American robins with two common sympatric bird species, European starling, Sternus vulgaris and house sparrow, Passer domesticus. Host seeking C. pipiens were three times more likely to enter robin-baited traps when with the alternate host was a European starling (n = 4 trials; OR = 3.06; CI [1.42–6.46]) and almost twice more likely when the alternative was a house sparrow (n = 8 trials; OR = 1.80; CI = [1.22–2.90]). There was no difference in the probability of trap entry when two robins were offered (n = 8 trials). Logistic regression analysis determined that the age, sex and weight of the birds, the date of the trial, starting-time, temperature, humidity, wind-speed and age of the mosquitoes had no effect on the probability of a choosing a robin over an alternate bird. Findings indicate that preferential feeding by C. pipiens mosquitoes on certain avian hosts is likely to be inherent, and we discuss the implications innate host preferences may have on enzootic WNV transmission.

Red Squirrels (Sciurus vulgaris) Respond to Alarm Calls of Eurasian Jays (Garrulus glandarius)

AbstractRecognition of heterospecific (interspecific) alarm calls has been demonstrated in birds and mammals, but bird–mammal interactions have rarely been studied. Here, I tested the hypothesis that red squirrels (Sciurus vulgaris) are able to recognize alarm calls of a sympatric bird species, the Eurasian jay (Garrulus glandarius), and respond adequately with anti‐predator behaviour. Both animals are preyed upon by the same predators. To test whether squirrels would react to heterospecific alarm calls, I recorded squirrels behaviour during playbacks of jay alarm calls, control playbacks (territorial songs of sympatric songbirds) and during silence. Differences between the control treatment (songbirds) and silence were not significant. Seven of the 13 squirrels responded with escape after broadcasting alarm calls of jays. Further, squirrels spent less time in the patch, expressed a higher vigilance, and showed more rapid head and body movements. These results suggest that squirrels recognize heterospecific alarm vocalizations of jays and discriminate them from equally loud non‐threatening sounds.

Implications of waterbird ecology for the dispersal of aquatic organisms

In this paper, we review some potential implications of waterbird ecology for their role as dispersers of aquatic plants and invertebrates. We focus particularly on internal transport (endozoochory) by the Anatidae (mainly ducks) and shorebirds, groups especially important for dispersal processes owing to their abundance, migratory habitats and diets. We conduct a literature review to assess the seasonal patterns shown by Anatidae in consumption of seeds and plankton, the interspecific patterns in such consumption (including the effects of body size, bill morphology, etc.), and differences in habitat use (e.g., shoreline vs. open water specialists) and migration patterns between species (e.g., true migrants vs. nomads). We show that many shorebirds are important consumers of seeds as well as plankton, and suggest that their role in plant dispersal has been underestimated. This review confirms that Anatidae, shorebirds and other waterbirds have great potential as dispersers of aquatic organisms, but illustrates how closely related, sympatric bird species can have very different roles in dispersal of specific aquatic organisms. Furthermore, great spatial and temporal variation is likely in dispersal patterns realized by a given bird population. We present evidence suggesting that northbound dispersal of aquatic propagules by endozoochory during spring migration is a frequent process in the northern hemisphere. Much more systematic fieldwork and reanalysis of the existing data sets (e.g., from diet studies) are needed before the relative roles of various waterbird species as dispersers can be fully assessed.

Aversion of the feral pigeon and the house sparrow to pellets and sprouts treated with commercial formulations of methyl anthranilate.

Two methyl anthranilate formulations, ReJex-iT TP-40 and AG-36, were tested as bird-repelling agents for animal feed and vegetable sprouts, respectively. Feral pigeons (Columbia livia) and house sparrows (Passer domesticus) are important pests of animal husbandry and field crops in Israel. In each 4-day experiment, four birds were held together in an aviary, and were offered four trays or dishes with animal feed or cauliflower sprouts in four corners of the cage. The trays and dishes were transposed daily in a Latin square sequence. Pigeons consumed significantly more untreated feed than treated feed. When no alternative untreated food was offered, there was no significant repellency. Treatment of animal feed with TP-40 to give 2.0 ml methyl anthranilate kg-1 or less had no repellent effect on sparrows. Concentrations of 4.0 ml kg-1 or more repelled the sparrows significantly. When no untreated feed was presented, pigeons and sparrows preferred the lowest concentration of methyl anthranilate presented. When AG-36 was tested on vegetable sprouts, the sparrows tended significantly to avoid the highest concentration used--14.5 ml methyl anthranilate litre-1 spray. The inter-specific differences between the birds indicate that the efficacy of methyl anthranilate formulations as a repellent has to be specified for every species. This study did not determine (1) the possibility of developing habituation, (2) the behaviour of birds under natural conditions in the field, or (3) the influence of the feeding behaviour of a sympatric bird species on the repellency of methyl anthranilate to other species.

Courts and courtship behaviour of Archbold's Bowerbird Archboldia papuensis in Papua New Guinea

Twelve bowers of Archbold's Bowerbird Archboldia papuensis in the Tari Gap, Southern Highlands, Papua New Guinea, are described. Incomplete courtship displays at four bowers were observed directly and videotaped, and 13 courtship displays culminating in copulation at five bowers were videotaped automatically. Bowers and male advertisement and courtship vocalizations and visual displays are described. Vocalizations included the mimicry of numerous sympatric bird species, calls like those of other bowerbird genera found elsewhere and inanimate sounds of the habitat. Courtships involved two phases. In the first, the male repeatedly chased the female while moving low, close to the surface of the display court. In the second phase, the male prostrated himself below the female and the yellow crest of adult males was presented to females as the male shook and repeatedly raised and lowered his head. Contrary to a previous report, the courtship display of the male Archbold's Bowerbird was assertive and the low position of the male appeared to function in threat reduction.

The Effect of a Single Species of Avian Predator on the Arthropods of Aerial Leaf Litter

Recent studies have shown that insectivorous birds can have an effect on their arthropod prey populations. Holmes et al. (1979) found that enclosures in the understory of a temperate deciduous forest had a pronounced effect on Lepidoptera larvae. Solomon et al. (1976) showed that codling moth larvae had higher survivorship inside cages in an apple orchard in England. Dahlston and Copper (1979) found that birds reduced the population of overwintering tussock moth pupal egg masses, and Askenmo et al. (1977) reported the impact of birds on spider populations in a spruce forest. In all of these studies, many sympatric bird species may have been responsible for the observed increased mortality of arthropods. Here we report on an exclosure experiment conducted in moist tropical forest understory in Panama. The results indicate that predation by one species of insectivorous bird, Myrmotherula fulviventris (Checker-throated Antwren, Formicariidae), had a pronounced effect upon the arthropod prey populations in a single, easily sampled microhabitat. On our study area Myrmotherulafulviventris spends 98% of its foraging time searching aerial leaf litter for arthropods. Aerial leaf litter consists of dead leaves that fall from canopy trees and get caught in vegetation and vine tangles. As the leaves dry and curl they are colonized by many types of arthropods. These arthropods are abundant and many species appear to be unique to aerial leaf litter (J. A. Gradwohl, personal observation). While two or more species of aerial leaf litter foragers often occur in lowland Neotropical forests (Ridgely 1976, Munn and Terborgh 1979, Wiley 1980), on our study site there is only one, M. fulviventris. We have observed two species of antbird that usually forage by gleaning live foliage, checking dead leaves on our study site (Myrmotherula axillaris and Thamnophilus punctatus, Greenberg and Gradwohl 1980), but this behavior is very rare (<5% of total foraging repertoire). Myrmotherula fulviventris lives in pairs or small family groups on small (: 1.5-3 ha) territories which are co-defended with Microrhopias quixensis (Formicariidae). These areas are traversed several times daily, and areas of high use correspond with the presence of dense vine tangles (Gradwohl and Greenberg 1980). The density of aerial leaf litter is greater in vine tangles because tangles catch more falling leaves than vegetation in the open understory. In this study we exclosed vine tangles for 6 wk and found that aerial leaf litter arthropods were nearly twice as common inside the enclosures as outside. Because they experience heavy use by antwrens and contain high densities of dead leaves, we made vine tangles the focus of our exclosure experiment.