Silvereyes Research Articles

Mosquito Communities and Avian Malaria Prevalence in Silvereyes (Zosterops lateralis) Within Forest Edge and Interior Habitats in a New Zealand Regional Park.

Forest fragmentation and agricultural development are important anthropogenic landscape alterations affecting the disease dynamics of malarial parasites (Plasmodium spp.), largely through their effects on vector communities. We compared vector abundance and species composition at two forest edge sites abutting pastureland and two forest interior sites in New Zealand, while simultaneously assessing avian malaria prevalence in silvereyes (Zosterops lateralis). Twenty-two of 240 (9.2%) individual silvereyes captured across all sites tested positive for avian malaria, and Plasmodium prevalence was nearly identical in edge and interior habitats. A total of 580 mosquito specimens were trapped across all sites. These comprised five different species: the introduced Aedes notoscriptus and Culex quinquefasciatus; the native A. antipodeus, C. asteliae and C. pervigilans. The known avian malaria vector C. quinquefasciatus was only recorded in the forest edge (mostly at ground level). In contrast, the probable vector C. pervigilans was abundant and widespread in both edge and interior sites. Although frequently caught in ground traps, more C. pervigilans specimens were captured in the canopy. This study shows that avian malaria prevalence among silvereyes appeared to be unaffected by forest fragmentation, at least at the scale assessed. Introduced mosquito species were almost completely absent from the forest interior, and thus our study provides further circumstantial evidence that native mosquito species (in particular C. pervigilans) play an important role in avian malaria transmission in New Zealand.

The relative roles of cultural drift and acoustic adaptation in shaping syllable repertoires of island bird populations change with time since colonization.

In birds, song divergence often precedes and facilitates divergence of other traits. We assessed the relative roles of cultural drift, innovation, and acoustic adaptation in divergence of island bird dialects, using silvereyes (Zosterops lateralis). In recently colonized populations, syllable diversity was not significantly lower than source populations, shared syllables between populations decreased with increasing number of founder events, and dialect variation displayed contributions from both habitat features and drift. The breadth of multivariate space occupied by recently colonized Z. l. lateralis populations was comparable to evolutionarily old forms that have diverged over thousands to hundreds of thousands of years. In evolutionarily old subspecies, syllable diversity was comparable to the mainland and the amount of variation in syllable composition explained by habitat features increased by two- to threefold compared to recently colonized populations. Together these results suggest that cultural drift influences syllable repertoires in recently colonized populations, but innovation likely counters syllable loss from colonization. In evolutionarily older populations, the influence of acoustic adaptation increases, possibly favoring a high diversity of syllables. These results suggest that the relative importance of cultural drift and acoustic adaptation changes with time since colonization in island bird populations, highlighting the value of considering multiple mechanisms and timescale of divergence when investigating island song divergence.

A Bronze Hellenistic Dwarf in the Metropolitan Museum

A Bronze Hellenistic Dwarf in the Metropolitan Museum

The influence of vagrant hosts and weather patterns on the colonization and persistence of blood parasites in an island bird

AbstractAimColonization and extinction are important drivers of island biogeography, but they are difficult to study. We used a long‐term dataset to determine the mechanisms that contribute to colonization and persistence for vector‐borne blood parasites in an island population of birds that regularly receives infected vagrant conspecifics and wind‐assisted potential vectors from the mainland.LocationHeron Island (Australia) and the Australian mainland.MethodsWe determined the prevalence, temporal stability and host‐specificity of Haemoproteus and Plasmodium parasites in resident and mainland‐vagrant silvereyes (Zosterops lateralis) on Heron Island over seven years (1999–2003 and 2012–2013). We carried out simulations using mainland infection data and vagrant arrival scenarios to test whether transmission from vagrants influences infection patterns in island residents. We tested whether variation in island parasite prevalence was predicted by abiotic factors associated with vector breeding and dispersal.ResultsParasite prevalence and composition on the island varied considerably across years. Host‐specialist Haemoproteus species exhibited lower prevalence than expected and frequent absence despite a high probability of arriving via vagrants. In contrast, host‐generalist Plasmodium species exhibited a low probability of arriving via vagrants but were temporally persistent in island silvereyes. Increases in prevalence and diversity of Plasmodium species were associated with episodes of offshore winds.Main conclusionsThis study shows that parasites that are abundant in source populations do not necessarily exhibit increased colonization success via vagrant host movement. Vagrant silvereyes are not likely to shape infection patterns in island‐resident silvereyes. Instead, indirect evidence of associations between weather patterns and parasite dynamics suggests that the insular parasite community may be limited by vector establishment. Our results support the hypothesis that host‐specificity is important in determining a parasite's ability to persist on islands, with host‐specialists at greater risk of failing to establish after their initial arrival.

Avian biodiversity in the coastal wetlands of the Okahukura Peninsula

The Tapora Landcare Group, operating on the Okahukura Peninsula, has the long-term goal of making this region predator fenced. The aim of this study was to obtain information on the current status of avian biodiversity and the bird community across the band of coastal wetlands on the Okahukura Peninsula. Bird counts were conducted and playback lures used to detect three cryptic wetland species: fernbirds (Bowdleria punctata); spotless crakes (Porzana tabuensis); and banded rails (Gallirallus philippensis). Fernbirds and banded rails were detected at seven of the eight wetland sites sampled whereas spotless crakes were detected at two sites. The native species with the highest relative abundance across the eight sites were silvereyes (Zosterops lateralis) and South Island pied oystercatchers (Haematopus finschi). Changes in avian biodiversity over time in the region can now be monitored, and comprehensive long-term data on the status of avian biodiversity over time obtained.

Silvereyes decrease acoustic frequency but increase efficacy of alarm calls in urban noise

Many passerines adjust song attributes to avoid potential masking by anthropogenic noise. The costs of masking should be particularly high for vocalizations important for survival (e.g. alarm calls), but few studies have investigated how such calls are affected. We compared urban and rural silvereye, Zosterops lateralis, alarm calls across southeastern Australia, and found that urban calls had lower average, peak and maximum frequencies than rural calls. The average, peak and maximum frequency of alarm calls also decreased linearly with increasing background noise. The direction of this frequency shift runs contrary to expectations and previous findings of higher-pitched avian vocal signals in urban habitats, including higher-pitched song and contact calls in urban silvereyes. However, assuming no change in call amplitude, acoustic modelling indicates that the observed frequency shift would lead to a 20% increase in the predicted active space of alarm calls (i.e. the distance over which the calls can be detected by a conspecific bird) in urban noise, and therefore may be potentially adaptive. Our findings highlight the importance of considering behavioural and ecological contexts in urban acoustic-adaptation studies.

Geographical surrogates of genetic variation for selecting island populations for conservation

AbstractAimThreatened species often exist in small numbers in isolated populations. Limited financial resources usually constrain conservationists to allocate funds to a subset of these populations. Because obtaining information required to maximize the amount of genetic and phenotypic variation protected can be costly and time‐consuming, the utility of surrogates should be explored. This study tests the efficacy of three simple and cost‐effective geographical measures in capturing genetic and phenotypic variation in fragmented populations when setting conservation priorities.LocationVanuatu archipelago.MethodsWe used neutral genetic data (mtDNA and microsatellites) and morphometric data (a proxy for functional variation) for two bird species displaying different patterns of regional population genetic structure: Zosterops flavifrons and Zosterops lateralis. We tested the performance of three geographical surrogates (maximizing: geographical distance between islands; area of islands; geographical representation of islands), in representing divergence between and diversity within populations, constrained to the number of islands being protected.ResultsMaximizing geographical separation of sites provided the best surrogate for a constrained budget (< 50% of the populations) for both species. For a larger protected area system (> 50% of the populations), the spatially most representative sites were often more effective. Selecting islands based on size retained about half of within‐population genetic diversity; however, this was not much higher than selecting the islands randomly.Main conclusionsThe ability of surrogates to capture genetic or phenotypic variation varied depending on the species, genetic markers and number of islands selected. While imperfect, selection of populations based on simple geographical surrogates for genetic and phenotypic variation will generally be better than random selection for conserving the evolutionary potential of threatened populations when time and money limit a more thorough and direct analyses of genetic and phenotypic variation.

Mice feeding on Sarracenia secretion

This story started a couple of years back when I arrived at my New Zealand greenhouse and found a pair of native nectar feeding birds we call wax eyes (Zosterops lateralis) flying along the inside of the greenhouse and hanging around a group of autumn Sarracenia leucophylla pitchers. I managed to take a couple of very average photos of the wax eyes feeding from the mouths of the S. leucophylla.

Sugar Preferences of Avian Nectarivores Are Correlated with Intestinal Sucrase Activity

Nectar-feeding birds generally demonstrate preference for hexose solutions at low sugar concentrations, switching to sucrose/no preference at higher concentrations. Species vary in the concentration at which the switch from hexose preference occurs; this could reflect physiological constraints that would also influence nectar selection when foraging. We recorded concentration-dependent sugar type preferences in three opportunistic/generalist Australian nectarivorous species: Dicaeum hirundinaceum, Zosterops lateralis, and Lichenostomus virescens. All three preferred hexoses up to sugar concentrations of 0.25 mol L(-1) and switched to sucrose/no preference for higher concentrations. Using these and literature records, we investigated physiological mechanisms that may explain the concentration dependence of sugar type preferences and compared diet preference data with foraging records. We measured sucrase activity in Z. lateralis and L. virescens as well as three specialized nectarivorous species (Anthochaera carunculata, Phylidonyris novaehollandiae, and Trichoglossus haematodus) for comparison with published concentration-dependent sugar preference data. Sucrase activity varied between these species ([Formula: see text]). The minimum diet concentration at which birds show no sugar preference was significantly correlated with sucrase activity for the 11 species analyzed ([Formula: see text]). Birds with the lowest sucrase activity showed hexose preference at higher diet concentrations, and birds with the greatest sucrase activity showed either no hexose preference or hexose preference on only the most dilute diets. Foraging data compiled from the literature also support the laboratory analyses; for example, T. haematodus (preference for hexose over a wide range of diet concentrations, low sucrase activity) also feed primarily on hexose nectars in the wild. Intestinal sucrase activity is likely to contribute to diet selectivity in nectarivorous bird species.

Immediate, independent adjustment of call pitch and amplitude in response to varying background noise by silvereyes (Zosterops lateralis)

Many birds raise the pitch of their vocalizations in urban environments, a shift generally attributed to avoidance of low frequencies vulnerable to masking by anthropogenic noise (acoustic adaptation hypothesis [AAH]). However, high frequencies could just be an incidental byproduct of singing more loudly (Lombard hypothesis). If birds cope with background noise by singing more loudly and increases in frequency are byproducts of increased amplitudes, they should respond with louder songs (and increased pitch) to either high- (HFN) or low-frequency noise (LFN) of similar amplitude. However, if birds adaptively adjust frequency to minimize interference, they should increase frequency in response to LFN but decrease it in response to HFN. We exposed silvereyes (Zosterops lateralis), which use higher songs and calls in urban areas, to high- and low-frequency background noise of standardized amplitude. Silvereyes from both rural and urban areas exposed to HFN responded by lowering the minimum frequencies of their calls, and this shift was independent of call amplitude, which increased in all noise treatments. These findings support the AAH. Calls during HFN treatments were also longer than those made during quiet treatments. Our results suggest that silvereyes are capable of flexible adjustments of call frequency, amplitude, and duration to maximize signal-to-noise ratio in noisy environments.

Coccidia species in endemic and native New Zealand passerines

New Zealand native passerines are hosts to a large variety of gastrointestinal parasites, including coccidia. Coccidian parasites are generally host-specific, obligate intracellular protozoan parasites. In passerine birds, members of the genus Isospora are most common. Under natural conditions, these parasites seldom pose a threat, but stressors such as quarantine for translocation, overcrowding, or habitat changes may cause an infection outbreak that can severely affect wild populations. Although coccidia are important pathogens and have caused mortalities in kiwi (Apteryx spp.) and hihi (Notiomystis cincta), their prevalence, epidemiology, life cycles, and taxonomic relationships are still widely unknown in native New Zealand songbirds. Over a period of 3years (2007-2009), we examined 330 fecal samples of six native passerine species: tui (Prosthemadera novaeseelandiae), North Island saddleback (Philesturnus carunculatus rufusater), North Island robin (Petroica longipes), silvereye (Zosterops lateralis), and fantail (Rhipidura fuliginosa). The overall prevalence by flotation of coccidian infection in the New Zealand bird species examined was 21-38%, 21% in North Island robin, 38% in tui, and 25% in saddleback. Similar to prior studies in other countries, preliminary sequencing results suggest that coccidia in passerines in New Zealand are members of the family Eimeriidae, unlike the phenotypically similar genus Cystisospora of mammals. Using molecular methods, we identified at least five new genetically distinct Isospora species in the examined birds (three in tui and one each in saddlebacks and North Island robins).

Resource availability and foraging of Silvereyes (Zosterops lateralis) in urban trees

Whereas the changes in avian community composition resulting from urban development are well described, the specific factors that allow certain species to thrive in urban areas remain poorly understood. However, the availability of arthropod prey is emerging as a potentially important factor in shaping urban bird communities. Silvereyes (Zosterops lateralis) are common in urban areas and so provide a useful study organism to test the factors that allow some birds to become urban ‘winners’. We here present the results of an observational study on the foraging frequency of Silvereyes and arthropod prey availability in native and exotic urban trees in Dunedin, New Zealand. Silvereyes more frequently used individual trees, native or exotic, that supported the highest level of arthropod abundance. Silvereye foraging also varied greatly on a seasonal scale. Silvereyes were able to adjust their seasonal foraging to incorporate exotic vegetation with high arthropod abundances. We conclude that the flexibility of Silvereyes with regards to foraging and their use of exotic plant species are important factors in their success in surviving urban development.

Larger body size on islands affects silvereye Zosterops lateralis song and call frequency

Differences in song repertoires and characteristics of island and mainland populations of the same avian species are usually explained by dispersal, cultural evolution and/or habitat differences. The influence of morphology is often overlooked, even though island populations are frequently morphologically distinct from mainland populations, and morphology could affect vocalizations. I compared morphological features, songs, contact calls and alarm calls of six isolated island populations of silvereye Zosterops lateralis with those of two mainland populations to examine whether differences between mainland and island vocalizations were consistent across vocalization types, and whether these differences could be linked to morphological differences. Vocalizations were lower in frequency on islands. Island individuals were larger (both in mass and body structure), and body mass was an important predictor of frequency in contact and alarm calls. I argue that this strong association results from the island rule (islands promote larger body sizes) and cascading effects of morphology on vocalization frequency in this species.

Night-Migratory Songbirds Possess a Magnetic Compass in Both Eyes

Previous studies on European robins, Erithacus rubecula, and Australian silvereyes, Zosterops lateralis, had suggested that magnetic compass information is being processed only in the right eye and left brain hemisphere of migratory birds. However, recently it was demonstrated that both garden warblers, Sylvia borin, and European robins have a magnetic compass in both eyes. These results raise the question if the strong lateralization effect observed in earlier experiments might have arisen from artifacts or from differences in experimental conditions rather than reflecting a true all-or-none lateralization of the magnetic compass in European robins. Here we show that (1) European robins having only their left eye open can orient in their seasonally appropriate direction both during autumn and spring, i.e. there are no strong lateralization differences between the outward journey and the way home, that (2) their directional choices are based on the standard inclination compass as they are turned 180° when the inclination is reversed, and that (3) the capability to use the magnetic compass does not depend on monocular learning or intraocular transfer as it is already present in the first tests of the birds with only one eye open.

Song convergence in multiple urban populations of silvereyes (Zosterops lateralis).

Recent studies have revealed differences between urban and rural vocalizations of numerous bird species. These differences include frequency shifts, amplitude shifts, altered song speed, and selective meme use. If particular memes sung by urban populations are adapted to the urban soundscape, “urban-typical” calls, memes, or repertoires should be consistently used in multiple urban populations of the same species, regardless of geographic location. We tested whether songs or contact calls of silvereyes (Zosterops lateralis) might be subject to such convergent cultural evolution by comparing syllable repertoires of geographically dispersed urban and rural population pairs throughout southeastern Australia. Despite frequency and tempo differences between urban and rural calls, call repertoires were similar between habitat types. However, certain song syllables were used more frequently by birds from urban than rural populations. Partial redundancy analysis revealed that both geographic location and habitat characteristics were important predictors of syllable repertoire composition. These findings suggest convergent cultural evolution: urban populations modify both song and call syllables from their local repertoire in response to noise.

Limited genetic differentiation between acoustically divergent populations of urban and rural silvereyes (Zosterops lateralis)

The bioacoustic attributes of vocalisations made by birds in urban environments often differ markedly from those of rural conspecifics. Whether such differences are result from genetic divergence between urban and rural populations, or from plasticity or cultural evolution of song remains poorly understood. Silvereyes (Zosterops lateralis) show evidence of acoustic adaptation to urban noise, modifying both their songs and calls in cities when compared to rural areas. We investigated whether these differences were associated with corresponding morphological and neutral genetic differences. Across six pairs of geographically separate urban and rural populations, all morphological traits measured were similar. Furthermore, genetic analyses of variation at nine microsatellite loci revealed high levels of genetic connectivity between populations, and similar levels of heterozygosity in both habitat types. Consistent directional shifts in song attributes of city birds across large geographic areas thus do not appear to be accompanied by associated morphological or neutral genetic divergence.

Severe pollen limitation in populations of the New Zealand shrub Alseuosmia macrophylla (Alseuosmiaceae) can be attributed to the loss of pollinating bird species

AbstractThe loss of bird species following human colonization of New Zealand has raised concerns about the consequences for crucial ecosystem functions such as pollination. The understorey shrub Alseuosmia macrophylla (Alseuosmiaceae) exhibits characteristics typical of a bird pollination syndrome, but populations still persist in northern North Island forest remnants despite the local extinction of most endemic bird pollinators, leading to the suggestion that moths – rather than birds – may be the primary pollinators. The aim of this study was to quantify the importance of endemic birds as pollinators of A. macrophylla over several years by comparing plants on Little Barrier Island (LBI), where all extant endemic bird pollinators still occur, to plants at sites on the adjacent North Island in the Waitakere Ranges (WTK), where only one of these species remains common. Flowers on LBI were visited by endemic bellbirds (Anthornis melanura) and stitchbirds (Notiomystis cincta), while at WTK sites the most common visitors were the recently arrived silvereye (Zosterops lateralis) and the introduced honeybee (Apis mellifera), both of which acted principally as nectar robbers. Caged flowers on LBI had significantly lower fruit set than open flowers, and plants at WTK were significantly more pollen‐limited than plants on LBI. This provides evidence that the loss of endemic pollinating birds is the most likely reason for the high pollen limitation found in some North Island A. macrophylla populations, and the very low seed set of these populations could have serious implications for the long‐term persistence of this species.

An invasive tree alters the structure of seed dispersal networks between birds and plants in French Polynesia

AbstractAim We studied how the abundance of the highly invasive fruit‐bearing tree Miconia calvescens DC. influences seed dispersal networks and the foraging patterns of three avian frugivores.Location Tahiti and Moorea, French Polynesia.Methods Our study was conducted at six sites which vary in the abundance of M. calvescens. We used dietary data from three frugivores (two introduced, one endemic) to determine whether patterns of fruit consumption are related to invasive tree abundance. We constructed seed dispersal networks for each island to evaluate how patterns of interaction between frugivores and plants shift at highly invaded sites.Results Two frugivores increased consumption of M. calvescens fruit at highly invaded sites and decreased consumption of other dietary items. The endemic fruit dove, Ptilinopus purpuratus, consumed more native fruit than either of the two introduced frugivores (the red‐vented bulbul, Pycnonotus cafer, and the silvereye, Zosterops lateralis), and introduced frugivores showed a low potential to act as dispersers of native plants. Network patterns on the highly invaded island of Tahiti were dominated by introduced plants and birds, which were responsible for the majority of plant–frugivore interactions.Main conclusions Shifts in the diet of introduced birds, coupled with reduced populations of endemic frugivores, caused differences in properties of the seed dispersal network on the island of Tahiti compared to the less invaded island of Moorea. These results demonstrate that the presence of invasive fruit‐bearing plants and introduced frugivores can alter seed dispersal networks, and that the patterns of alteration depend both on the frugivore community and on the relative abundance of available fruit.

Invasive rats and recent colonist birds partially compensate for the loss of endemic New Zealand pollinators

Reported declines of pollinator populations around the world have led to increasing concerns about the consequences for pollination as a critical ecosystem function and service. Pollination could be maintained through compensation if remaining pollinators increase their contribution or if novel species are recruited as pollinators, but empirical evidence of this compensation is so far lacking. Using a natural experiment in New Zealand where endemic vertebrate pollinators still occur on one offshore island reserve despite their local extinction on the adjacent North Island, we investigated whether compensation could maintain pollination in the face of pollinator extinctions. We show that two recently arrived species in New Zealand, the invasive ship rat (Rattus rattus) and the recent colonist silvereye (Zosterops lateralis; a passerine bird), at least partly maintain pollination for three forest plant species in northern New Zealand, and without this compensation, these plants would be significantly more pollen-limited. This study provides empirical evidence that widespread non-native species can play an important role in maintaining ecosystem functions, a role that needs to be assessed when planning invasive species control or eradication programmes.

Identification of nest predators using continuous time-lapse recording in a New Zealand city

Predation of eggs and/or chicks is the main cause of nesting failure in birds. Nest predation has been studied in many habitats in New Zealand, but few studies have been conducted in urban ecosystems. Twenty-one nests of four bird species (blackbird [Turdus merula], song thrush [Turdus philomelos], fantail [Rhipidura fuliginosa], and silvereye [Zosterops lateralis]) were monitored over one breeding season in Hamilton using time-lapse recordings. Five predation events were filmed (two by cats [Felis catus], and three by ship rats [Rattus rattus]), 10 nests successfully fledged chicks and 6 nests failed owing to poor weather, desertion, or unknown events. Although the sample size was small, our data suggest that nesting success may be higher in urban Hamilton than in other unmanaged habitats where predation rates can exceed 80%. We recommend that future studies of nesting success in urban birds should also focus on the fates of fledglings, as anecdotal evidence suggested that predation rates may have been highest at this stage.