Letteratura scientifica selezionata sul tema "Silvereyes"

Abstract Frugivorous birds may be able to reduce the cost of processing seeds by discarding seeds, selecting fruits that have a high pulp-to-seed ratio, or by choosing fruit in which seeds are packaged in a way that the frugivore's gut can void them more rapidly. A preference for fruit based on pulp-to-seed ratio or seed composition within a fruit is likely to have important implications for plants and evolution of seed size. We tested whether captive Silvereyes (Zosterops lateralis) discriminate among artificial fruit on the basis of seed presence by presenting birds with artificial fruit with or without a seed. In the first experiment, fruit were translucent so that birds could see which fruit contained a seed. In the second experiment, the visual cue was removed. When Silvereyes were presented with a choice between translucent, artificial fruit with or without a seed, they showed a strong preference for fruit that did not contain a seed. However, when the visual cue to seed presence was removed, preference for seedless fruit was still significant, but markedly reduced. We also tested seed-size preference of Silvereyes in the field in Victoria, Australia. Seeds from a fruit commonly consumed by Silvereyes, fragrant saltbush (Rhagodia parabolica), were recovered from Silvereye faecal samples and their volumes measured. Comparisons were made between seed volumes of fruit consumed by Silvereyes and those within fruit available on the plant. Silvereyes consumed significantly smaller seeds than the mean size available on saltbush plants. When Silvereyes were presented with a cereal-based diet containing artificial seeds (designed to mimic large fruit containing many small seeds), they avoided seed ingestion and were able to consume proportionally more cereal than seeds, even when on a high seed-load diet (30%). Seed dispersal by Silvereyes may be inefficient for plant species with large fruit containing many small seeds, because Silvereyes in this experiment were able to avoid ingesting seeds.

The influence of accessibility on the fruit preferences of frugivorous silvereyes (Zosterops lateralis) was examined in three different contexts: for captive individuals, in a captive group and in a field situation. Individual silvereyes in small cages were presented with identical artificial fruit that differed only in their accessibility from a perch. The birds removed fruit that could be obtained by ‘picking’ rather than by ‘reaching up’ and avoided ‘hanging’ to remove fruit. A second experiment tested the response of silvereyes to fruit accessibility in a large aviary where birds fed in a group. The artificial fruit were presented at a larger and more natural scale on artificial trees. In this experiment, silvereyes again avoided ‘hanging’ to obtain fruit; however, these birds showed no preference for ‘picking’ over ‘reaching up’. Foraging observations of silvereyes were recorded for three different plant species in the field. Silvereyes generally avoided ‘hanging’ to remove fruit, although the foraging method used varied with the species of plant on which the bird was foraging. The foraging method used by avian frugivores to remove fruit is likely to be influenced by plant morphology, as well as the morphology of the bird. The strong preference shown by silvereyes for fruit that are more accessible suggests that when other fruit characteristics are equal, accessibility is important in influencing fruit-removal patterns. However, this may be affected by the context in which the fruit is presented. Properties of the fruiting plant, such as the branching pattern, perch stability and position of the fruit display, are likely to influence fruit preference. These aspects of plant structure should be considered when assessing foraging behaviour and resource use by frugivorous birds.

There are many secondary metabolites in ripe fruit that are toxic to vertebrate consumers. The most prevalent explanation for their presence in ripe fruit is to protect the fruit against consumers that do not disperse viable seeds. It has been hypothesised that seed dispersers are not deterred by, or can tolerate, the consumption of secondary metabolites in ripe fruit. We tested whether silvereyes (Zosterops lateralis), which are known seed dispersers, were deterred by quebracho (condensed tannins) presented in two different food types. In the first experiment, silvereyes were given artificial fruit containing either 0% or 5% quebracho and their fruit consumption was measured. A second experiment recorded consumption of a cereal-based, long-term maintenance diet containing either 0% or 5% quebracho. Silvereyes did not exhibit a significant preference for artificial fruit that did not contain quebracho: 39.9% of the fruit consumed did contain quebracho. However, silvereyes strongly avoided the cereal diet containing quebracho, consuming, on average, only 0.36 g (0.06 g) of cereal per 5 h compared with 17.3 g (0.23 g) of cereal that did not contain quebracho. We suggest that because the artificial fruit were swallowed whole by silvereyes, the quebracho may not have been detected as easily in the time available as it would have been in the aqueous cereal diet. Consumption of fruit containing secondary metabolites by wild silvereyes is likely to depend on factors such as food availability, nutrient content of the fruit and the degree of diet mixing.

AbstractSeed packaging is one fruit characteristic that may influence post-ingestional fruit processing in avian frugivores. We tested the response of a facultative frugivore, the Silvereye (Zosterops lateralis), to fruit containing different forms of seed packaging. Wild-caught, captive Silvereyes were presented with artificial fruit containing either one large seed or three small seeds of equivalent total volume, and their consumption rates were recorded over 90 min. In a second experiment, the seed transit times (ingestion to excretion) for similar large-seeded and small-seeded fruit consumed by Silvereyes were recorded. Silvereyes consumed significantly more large-seeded fruit than small-seeded fruit. The transit time of seeds was also significantly shorter for large-seeded (mean = 22 min) than for small-seeded fruit (mean = 29 min). Thus seed packaging had a significant influence on the rate at which fruit were processed. Silvereyes were able to consume more large-seeded than small-seeded fruit because the seeds in large-seeded fruit were defecated faster than those in small-seeded fruit. It is likely that Silvereyes can compensate for the costs of seed ingestion through having a rapid gut passage rate and hence an increased fruit consumption rate. The gut of Silvereyes showed morphological characters intermediate between insectivores and specialist frugivores. The dimensions of the intestine and gizzard were like those of insectivores and the gizzard was substantially larger than those of specialist frugivores. Facultative frugivores appear to have few morphological adaptations to frugivory and we argue that this facilitates plasticity in the diet and the processing of insects when fruit is not available.¿Influencia el Empaquetamiento de Semillas el Consumo de Frutos y el Tiempo de Tránsito en Aves Frugívoras?Resumen. El empaquetamiento de semillas es una característica que puede influenciar el procesamiento de frutos post ingestión en aves frugivoras. Pusimos a prueba la respuesta de un frugívoro facultativo (Zosterops lateralis) a frutos con distintas formas de empaquetamiento de semillas. Individuos de Z. lateralis silvestres fueron capturados y expuestos a frutos artificiales de volumen equivalente con una semilla grande o con tres semillas pequeñas y su tasa de consumo fue registrada durante 90 minutos. En un segundo experimento, se registró el tiempo de tránsito (de ingesta a defecación) de frutos similares con semillas grandes y pequeñas. Z. lateralis consumió una significativamente mayor cantidad de frutos con semillas grandes que de frutos con semillas pequeñas. El tiempo de tránsito de semillas grandes fué significativamente menor (promedio = 22 min) que el de semillas pequeñas (promedio = 29 min). Por lo tanto, el empaquetamiento de semillas tuvo una influencia significativa sobre la tasa a la que los frutos fueron procesados. Z. lateralis fue capaz de consumir más frutos con semillas grandes ya que sus semillas fueron defecadas más rápidamente que las de frutos con semillas pequeñas. Es probable que Z. lateralis pueda compensar el costo de la ingesta de semillas con un paso rápido a través del tracto digestivo lo que se traduce en un aumento en la tasa de consumo de frutos. El tracto digestivo de Z. lateralis muestra caracteres morfológicos intermedios entre los de insectívoros y frugívoros especialistas. Las dimensiones de los intestinos y la molleja son similares a las de insectívoros y la molleja es sustancialmente más grande que la de los frugívoros especialistas. Los frugívoros facultativos parecieran tener pocas adaptaciones morfológicas a la frugivoría. Sugerimos que esto facilita una mayor plasticidad en la dieta y en el procesamiento de insectos cuando existe poca disponibilidad de frutos.

Birds are important consumers and dispersers of the seeds of fleshy fruit and some have been shown to be selective in their choice of fruit. However, our knowledge of how birds respond to a variety of fruit characteristics is poor. Some birds are known to avoid green fruit or consume them less than fruit of other colours. The fruit of many plant species are green when they are unripe and contain low concentrations of sugars and high concentrations of secondary compounds. In this study, captive silvereyes (Zosterops lateralis) were presented with a choice of red, white and green artificial fruit. Half of them were given these fruit with equal sugar concentrations (15%) and the other half were given the choice but with the green fruit having a sugar concentration twice that of the other two colours (30%). Green fruit were not strongly avoided by silvereyes and were actually preferred when they had a higher sugar concentration than the other two fruit types (red and white). Sugar concentration was therefore a more important determinant of fruit choice than colour. Fruit size is also known to affect fruit choice in some bird species. Small fruit are easier to consume than larger fruit, but contain less pulp. To maximise energy gain, birds should consume fruit that are large, but not large enough to incur high handling costs. Silvereyes in this study were presented with a choice between 20 artificial fruit 4 mm in diameter (large fruit) and 20 artificial fruit 2 mm in diameter (small fruit), both of which they are able to consume. In this experiment, silvereyes exhibited a strong preference for large fruit over small fruit. In general, larger fruit contain more pulp and therefore more energy than smaller fruit. However, other fruit traits, such as seed load, are likely to influence fruit choice by silvereyes in the wild and result in a trait hierarchy.

The ability of migratory silvereyes to orient was tested in the geomagnetic field with one eye covered. Silvereyes using only their right eye were able to orient in migratory direction just as well as birds using both eyes. Using only their left eye, however, the birds did not show a significant directional preference. These data indicate that directional information from the magnetic field is mediated almost exclusively by the right eye and processed by the left hemisphere of the brain. Together with corresponding findings from European robins and indications for a similar phenomenon in homing pigeons, they suggest that a strong lateralisation of the magnetic compass is widespread among birds.

Recent studies in the Northern Hemisphere have shown that songbirds living in noisy urban environments sing at higher frequencies than their rural counterparts. However, several aspects of this phenomenon remain poorly understood. These include the geographical scale over which such patterns occur (most studies have compared local populations), and whether they involve phenotypic plasticity or microevolutionary change. We conducted a field study of silvereye ( Zosterops lateralis ) vocalizations over more than 1 million km 2 of urban and rural south-eastern Australia, and compared possible effects of urban noise on songs (which are learned) and contact calls (which are innate). Across 14 paired urban and rural populations, silvereyes consistently sang both songs and contact calls at higher frequencies in urban environments. Syllable rate (syllables per second) decreased in urban environments, consistent with the hypothesis that reflective structures degrade song and encourage longer intervals between syllables. This comprehensive study is, to our knowledge, the first to demonstrate varied adaptations of urban bird vocalizations over a vast geographical area, and to provide insight into the mechanism responsible for these changes.

The main objective of my investigation was to ascertain the prevalence and impact of avian pox in New Zealand silvereyes (Zosterops lateralis). Silvereyes were mist--‐netted between 2010 and 2012 in three locations of the South Island and were examined for external signs of avian pox. Of the 409 silvereyes captured over this time period, avian pox lesions were identified in 9 birds (2.2%) and were found in both sexes as well as in juveniles. The highest incidence of avian pox was seen on the west coast at Moana (7.2%) between late May and mid--‐June 2011. Overall prevalence for each location over the period of the survey ranged from 1% in Kaikoura, Christchurch 3.6% and Moana 3.5% suggesting only slight differences between populations. I next investigated the prevalence of avian pox in a community of forest passerines at Kowhai Bush Kaikoura in the spring of 2012. Pox lesions were observed in 2/492 of the birds caught. Both cases (3.8%, n=52) were in the introduced chaffinch (Fringilla coelebs). Pox occurred in < 1% of individuals of the introduced species (n=313) and was absent in all native and endemic species (n=189). No pox lesions were seen in silvereyes captured in the 2012 Kaikoura survey (0/69). White blood cell profiles, fat scores and mass where also compared between silvereyes with and without avian pox lesions but no differences were found, however, the small sample of individuals with pox meant the power to detect a difference was low. A review of the literature on avian pox revealed a similar low prevalence of avian pox to that seen in this study and the prevalence of avian pox seen in other populations of white--‐eyes in New Zealand and elsewhere. However, across a range of other passerine species, avian pox was significantly more prevalent in geographically isolated endemic species than other groups. My investigation suggests that avian pox needs to be monitored over extended periods to estimate its prevalence and how its epizootiology is influenced by a variety of biotic and abiotic factors. Furthermore, my investigation reveals the need for more information, including the identification of the type and virulence of strains present in New Zealand and the role that silvereyes and introduced birds may have on the dynamics of avian pox in rare endemic birds. The main objective of my investigation was to ascertain the prevalence and impact of avian pox in New Zealand silvereyes (Zosterops lateralis). Silvereyes were mist--‐netted between 2010 and 2012 in three locations of the South Island and were examined for external signs of avian pox. Of the 409 silvereyes captured over this time period, avian pox lesions were identified in 9 birds (2.2%) and were found in both sexes as well as in juveniles. The highest incidence of avian pox was seen on the west coast at Moana (7.2%) between late May and mid--‐June 2011. Overall prevalence for each location over the period of the survey ranged from 1% in Kaikoura, Christchurch 3.6% and Moana 3.5% suggesting only slight differences between populations. I next investigated the prevalence of avian pox in a community of forest passerines at Kowhai Bush Kaikoura in the spring of 2012. Pox lesions were observed in 2/492 of the birds caught. Both cases (3.8%, n=52) were in the introduced chaffinch (Fringilla coelebs). Pox occurred in < 1% of individuals of the introduced species (n=313) and was absent in all native and endemic species (n=189). No pox lesions were seen in silvereyes captured in the 2012 Kaikoura survey (0/69). White blood cell profiles, fat scores and mass where also compared between silvereyes with and without avian pox lesions but no differences were found, however, the small sample of individuals with pox meant the power to detect a difference was low. A review of the literature on avian pox revealed a similar low prevalence of avian pox to that seen in this study and the prevalence of avian pox seen in other populations of white--‐eyes in New Zealand and elsewhere. However, across a range of other passerine species, avian pox was significantly more prevalent in geographically isolated endemic species than other groups. My investigation suggests that avian pox needs to be monitored over extended periods to estimate its prevalence and how its epizootiology is influenced by a variety of biotic and abiotic factors. Furthermore, my investigation reveals the need for more information, including the identification of the type and virulence of strains present in New Zealand and the role that silvereyes and introduced birds may have on the dynamics of avian pox in rare endemic birds.

Vineyards in New Zealand suffer bird damage caused by several avian species, including blackbirds and silvereyes. The introduced European Blackbird takes whole grapes which reduces yield. The self-introduced Australasian Silvereye pecks on grapes, leaving them on the vine to be further attacked by fungi and bacteria, and the subsequent off-odours can cause grapes to be refused by the winery or to suffer a price-reduction. Bird control methods remain primitive and largely ineffective during the long ripening period of wine grapes. An ecologically sound method to manage and reduce bird pressure requires deeper understanding of why some birds eat grapes, especially since grapes are not particularly nutritious. This work investigated the extent to which blackbirds and silvereyes are attracted by various compounds in ripening grapes. Since in natural grapes these compounds develop and change simultaneously, I developed an artificial grape in which a single parameter could be investigated. Artificial grapes (and sometimes nectar) were presented on a bird feeder table and the responses of birds to hexose sugars, the aromas 2-3-isobutylmethoxypyrazine and geraniol, tartaric and malic acids, grape tannins, and purple and green colour were recorded on timelapse video and analysed.

Vineyards in New Zealand suffer bird damage caused by several avian species, including blackbirds and silvereyes. The introduced European Blackbird takes whole grapes which reduces yield. The self-introduced Australasian Silvereye pecks on grapes, leaving them on the vine to be further attacked by fungi and bacteria, and the subsequent off-odours can cause grapes to be refused by the winery or to suffer a price-reduction. Bird control methods remain primitive and largely ineffective during the long ripening period of wine grapes. An ecologically sound method to manage and reduce bird pressure requires deeper understanding of why some birds eat grapes, especially since grapes are not particularly nutritious. This work investigated the extent to which blackbirds and silvereyes are attracted by various compounds in ripening grapes. Since in natural grapes these compounds develop and change simultaneously, I developed an artificial grape in which a single parameter could be investigated. Artificial grapes (and sometimes nectar) were presented on a bird feeder table and the responses of birds to hexose sugars, the aromas 2-3-isobutylmethoxypyrazine and geraniol, tartaric and malic acids, grape tannins, and purple and green colour were recorded on timelapse video and analysed.

Birds are a major pest in vineyards both in New Zealand and overseas. There is a need for new behavioural research on birds' foraging habits and feeding preferences in vineyards, as much of the literature to date is anecdotal. Research on cues to birds' feeding will provide a basis on which new deterrent and control strategies can be devised. Spatial-and temporal bird damage in a small vineyard block was mapped to find if damage was correlated with grape maturity and environmental factors. Vineyard and field observations of bird behaviour using video technology combined with preference experiments aimed to establish the relative roles of grape sugar concentration and colour in avian selection. Proximity of vineyards to bird roosts affects damage levels, regardless of differing maturity between locations. The rate of damage tends to increase exponentially once grape maturity has passed a threshold of 13 °Brix. Bunches positioned closest to the ground receive more damage if blackbirds or song thrushes are the predominant pests. Both sugar concentration and grape colour were found to affect birds' feeding preference, but the importance of the two factors varied between years. Black and green grape varieties were differentially preferred by blackbirds (Turdus merula) and song thrushes (Turdus philomelos) while silvereyes (Zosterops lateralis) appeared to have no strong colour preference. It was apparent that there were other, not assessed, grape factors that also affect selection. In small unprotected vineyards that are adjacent to bird roosts the entire grape crop can be taken by bird pests. Besides removing the roosts, which can be beneficial shelterbelts in regions exposed to high winds, growers currently may have no alternative other than to use exclusion netting to keep crops intact. The differential preferences between bird species for variety characteristics suggest that any new deterrents and other strategies to deflect birds from grape crops may need to be species-specific.

Impact assessments increasingly rely on models to project the potential impacts of climate change on species distributions. Ecological niche models have become established as an efficient and widely used method for interpolating (and sometimes extrapolating) species’ distributions. They use statistical and machine-learning approaches to relate species’ observations to environmental predictor variables and identify the main environmental determinants of species’ ranges. Based on this estimated species–environment relationship, the species’ potential distribution can be mapped in space (and time). In this chapter, we explain the concept and underlying assumptions of ecological niche models, describe the basic modelling steps using the silvereye (Zosterops lateralis) as a simple real-world example, identify potential sources of uncertainty in underlying data and in the model, and discuss potential limitations as well as latest developments and future perspectives of ecological niche models in a global change context.