Thrushes now largely restricted to the built environment in eastern England

Abstract.  I studied the distribution and density of three thrush populations, blackbird Turdus merula , song thrush T. philomelos and mistle thrush T. viscivorus , in an urban and contiguous rural area, totalling 2636 ha, in eastern England. Populations of these species are declining and I found 826, 85 and 30 territories of blackbird, song thrush and mistle thrush, respectively. Significantly more territories of all species than expected were within the urban boundary. Significantly more territories than expected were found of all three species in the built environment (residential housing, factories, schools, etc. with their associated gardens and green-space), urban and rural areas combined. Farmland occupied 67% of the study area but held significantly fewer blackbird and mistle thrush territories than expected, associated mainly with the small amount of grass; song thrushes were not recorded on farmland. Rural woodland and scrub held more blackbird and song thrush territories than expected. Song thrush was significantly associated with scrub within the urban boundary. With all three species largely absent from farmland, residential habitats can be considered as habitat refuges. The consequences of this for conservation and planning are discussed.     

Large-scale spatial variation in the breeding performance of song thrushes Turdus philomelos and blackbirds T. merula in Britain

1.  Spatial variation in breeding performance is of critical importance in understanding the large-scale distribution and abundance of living species, and in understanding species conservation. We studied the large-scale spatial variation in reproductive output of two species of declining British bird, the song thrush Turdus philomelos and the blackbird Turdus merula .
2.  We developed a method to predict spatial variation in reproductive output. Brood size and nest failure rates during the incubation and nestling periods were related to environmental factors using generalized linear models. Predicted values obtained from these models were combined to give values of number of fledglings produced per nesting attempt for 10-km squares throughout Britain.
3.  We observed substantial spatial variation in reproductive output for both species; the component that varied most was nest failure rate during incubation. We were more successful in relating environmental factors to spatial variation in reproductive output for song thrush than for blackbird.
4.  Reproductive output in both species was affected mainly by factors that vary on a small spatial scale. Nest failure rate during incubation increased significantly where corvids were more abundant, suggesting a role for avian nest predators in determining spatial variation in reproductive output.
5.  Our approach can be extended readily to other species of birds, to other taxonomic groups and to finer spatial scales. Such models could be used to evaluate the implications of current and proposed wider countryside management for spatial variation in breeding performance. Evaluations based on breeding success as well as numbers are likely to be more robust than those based solely on abundance.     

Breeding bird communities on Scottish farms

The Common Birds Census, begun by the British Trust for Ornithology has now been monitoring bird population levels on a nationwide basis since 1962. Separate indices were constructed for Scotland and the rest of Great Britain for 12 of the commonest species. Of the species examined blue tit (Parus caeruleus), wren (Troglodytes troglodytes), song thrush (Turdus philomelos), lapwing (Vanellus vanellus), chaffinch (Fringilla coelebs) and skylark (Alauda arvensis) have increased since 1963 and show very similar population trends to the rest of Great Britain. Whitethroat (Sylvia communis), willow warbler (Phylloscopus trochilus) and swallow (Hirundo rustica) have all declined nationally, the decline in the swallow appears to have begun earlier in Scotland. The blackbird (Turdus merula) and dunnock (Prunella modularis) showed similar upward trends until 1972 when the Scottish population started to decline; a much more noticeable decline in the Scottish robin (Erithacus rubecula) population began in 1966. The total density of territory-holding males has not increased but the biomass has and this is due to more, bigger birds but fewer passerines. The species diversity measured by the Shannon Wiener index (H.) has improved a little since 1971 and it is concluded that during the study period the farmland plots censused in Scotland have on average not shown evidence of deterioration as habitats for territory-holding birds.     

Complex Responses of Songbirds to Soil Acidification of Managed Beech Forests in Central Europe

Abstract Many forest ecosystems have been extensively degraded by acidifying pollutants over the last decades. There is also widespread concern about population decline of a number of songbirds due to acidification-driven calcium limitation. We hypothesize that the carrying capacity of forests decreases with reduced soil calcium content. We analyzed songbird assemblage/habitat relationships by territory mapping at 30 sites in a total of five managed beech forests. The sites harbored 38 songbird species. A canonical correspondence analysis showed that soil acidification, represented by soil calcium content, had a significant influence on the species assemblages of the 14 most frequent songbirds. The vertical complexity of the canopy additionally influenced the assemblages. Multiple regressions revealed that the density of the territories of song thrush (Turdus philomelos) and nuthatch (Sitta europaea) were positively correlated to calcium content. Blackbirds (Turdus merula) seemed to compensate for the negative effect of acidification by selecting breeding sites close to forest edges to forage in less acidified agricultural habitats. In contrast, the territorial density of robin (Erithacus rubecula), chaffinch (Phylloscopus collybita) and coal tit (Parus ater) increased with increasing soil acidification. Contrary to our hypothesis, the overall carrying capacity of songbird was not reduced in forests with acidified soils. However, the nesting success of song thrush and blackbird, as determined by the number of fledglings, was higher in the forest with the highest calcium content when compared to the forest with the lowest calcium content. We conclude that some species are severely affected by acidification, whereas others seem to have evolved successful strategies to meet their calcium demand even in acidified habitats. Electronic supplementary material: The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nestling cuckoos,Cuculus canorus,exploit hosts with begging calls that mimic a brood

Nestling cuckoos, Cuculus canorus, eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus, as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula, or song thrush, T. philomelos, chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick''s rapid begging call (''si, si, si, si ...''), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.     

Synchrony of woodland bird populations: the effect of landscape structure

The influence of environmental stochasticity and dispersal in producing patterns in population synchrony was examined for 53 woods censused annually from 1990 to 1999 for nine resident bird species (wren Troglodytes troglodytes , dunnock Prunella modularis , robin Erithacus rubecula , blackbird Turdus merula , song thrush Turdus philomelos , long-tailed tit Aegithalos caudatus , blue tit Parus caeruleus , great tit Parus major , and chaffinch Fringilla coelebs ) and four migrant bird species (garden warbler Sylvia borin , blackcap Sylvia atricapilla , chiffchaff Phylloscopus collybita and willow warbler Phylloscopus trochilus ). Twelve species showed global synchrony of population counts due to regional population trends and widespread annual population fluctuations. There was a clear link between population fluctuations and winter weather for wren, and three other species showed their largest population declines after the coldest winters. Eight species showed a decline in synchrony with distance between woods, and there was evidence for dispersal causing this pattern in three species. Landscape structure affected patterns of synchrony in several species, with lower synchrony in landscapes with less woodland. For three species, this difference in synchrony across a landscape gradient of decreasing woodland cover accounted for the decline in synchrony over distance. Three species showed greater synchrony between woods with similar amounts of hedgerow in the surrounding landscape, suggesting that the surroundings of a wood influence the population dynamics of some species breeding in the wood. Habitat fragmentation can alter the processes contributing to population synchrony. Loss of woodland reduces the relative abundance of woodland bird species. The remaining patches of habitat are smaller, more isolated and are set in a more hostile landscape, all of which may disrupt dispersal between patches and alter the population dynamics within woods.     

Local extinctions and recolonisations of passerine bird populations in small woods

This paper considers, for eight species of woodland bird, the factors that influenced both local extinctions and recolonisations in 145 woods over 3 years. In all species, probability of local extinction was inversely related to population size; most local extinctions occurred in woods containing one to three breeding pairs. However, considerable variation in extinction probabilities occurred between species and between years. In addition, the suitability of habitat within a wood (more extinctions in less suitable woods) was important for wren Troglodytes troglodytes, song thrush Turdus philomelos and blue tit Parus caeruleus; also, the structure of the surrounding landscape was important for blue tit, great tit Parus major, and chaffinch Fringilla coelebs (more extinctions in localities with less woodland). In only two species was the probability of recolonisation related to any of the measured variables. Wrens were more likely to recolonise larger woods, whereas song thrushes were more likely to recolonise woods with a high habitat suitability rating and those which are more isolated from other woodland     

Propagation of bird acoustic signals: comparative study of starling and blackbird distress calls

Previous works have demonstrated that the information supported by a bird distress call is encoded both by the energy distribution among harmonics and the temporal evolution of the frequency modulation. In the present study, using these parameters, we compared long-range information transfer in a dense vegetatian environment between the starling Sturnus vulgaris and the blackbird Turdus merula distress calls. It appears that excess attenuation of high frequencies (higher than 4 kHz) after a longrange propagation is responsible for modifications in distress call spectra. The energy of propagated signals tends to be concentrated in a 1.5-4-kHz bandwidth whatever the initial spectrum. Owing to its broad spectrum (0.8-7 kHz), the starling distress call is greatly modified. On the contrary, owing to a narrower spectrum (2–5.5 kHz), the blackbird distress call is relatively preserved. The blackbird distress call appears to be well-adapted to long-range transmission in an environment with dense vegetation. In contrast, the starling distress call is far more easily degraded by propagation. Nevertheless, frequency modulation of the starling call is preserved and message decoding remains possible even if message reliability may diminish. This result is examined from an etho-ecological point of view, taking into account both habitat and social structure of both birds.     

Enhanced niche opportunities: can they explain the success of New Zealand's introduced bird species?

Aim  The niche hypothesis could explain why some species introduced to new locations reach higher densities than in their native range: it posits that the new environment provides more abundant or higher quality resources or habitat, a more suitable physical environment or both. We investigate whether 11 bird species occur at higher densities in their introduced range than in their native range and whether the differences can be explained by the availability of preferred habitat or the suitability of climatic conditions in their introduced range relative to their native range.
Location  South Island, New Zealand (the introduced range); UK (the native range).
Methods  We first develop a series of models that accurately predict the density of 11 bird species at 54 UK farmland sites, which are closely matched to our New Zealand sites, from habitat and climatic variables. We then use these models to predict the density of the 11 species at 54 New Zealand farmland sites and compare the predicted and observed values.
Results  Actual densities at New Zealand sites were on average (median) 22 times (range: 1–6361) higher than predicted from the UK models and similarly higher than actually observed at comparable UK sites. Habitat and climatic variables can accurately predict bird densities in the UK but grossly underestimate densities for all species except Turdus merula in New Zealand.
Main conclusions  These findings indicate that factors other than the measured habitat and climatic variables must differ between the two regions and explain the much higher densities of New Zealand birds. We suggest that introduced birds, other than T. merula , in New Zealand may still experience enhanced niche opportunities due to greater availability of higher quality resources within habitats, release from natural enemy regulation, less exposure to extreme weather events, particularly during winter, or some combination of these processes.     

Intraspecific abundance–occupancy relationships: case studies of six bird species in Britain

Although acknowledged to be common, intraspecific relationships between local abundance and site occupancy have been examined in detail for few species. Here we report such analyses for six widespread species of breeding birds in Britain, using data from the Common Birds Census. These exhibit a range of temporal trends, including different combinations of increase and decrease in abundance and occupancy. Overall, two species have a statistically significant positive abundance–occupancy relationship on farmland but no relationship in woodland (collared dove, tree sparrow), one a significant positive relationship on farmland and in woodland (magpie), two a significant positive relationship on farmland and a negative one in woodland (redstart, song thrush), and one a significant negative abundance–occupancy relationship on farmland but no relationship in woodland (sparrowhawk). The population dynamics associated with these patterns are used to discern their underlying mechanisms.     

Where in Europe should we look for sources of the cutaneous trematode Collyriclum faba infections in migrating birds?

Cutaneous cysts with trematodes of Collyriclum faba have been found in birds during their spring and post-breeding migrations in the Czech Republic. During spring migrations, C. faba was found in one dunnock Prunella modularis, two European robins Erithacus rubecula, three common nightingales Luscinia megarhynchos, one song thrush Turdus philomelos and one great reed warbler Acrocephalus arundinaceus. During post-breeding migration, the same parasite was found in one garden warbler Sylvia borin, one whitehroat S. communis, three goldcrests Regulus regulus and one Eurasian treecreeper Certhia familiaris. The newly identified hosts of C. faba are dunnock, common nightingale, song thrush, great reed warbler and Eurasian treecreeper. Geographical areas of the birds' infection were identified from an analysis of reports on ringed birds of the same species, the time necessary for the development of cutaneous cysts with C. faba and the time of their survival, and hitherto known geographical areas of endemic occurrence of C. faba. It is presumed that birds trapped during spring migrations were infected in some montane and submontane regions in south-western Europe (the Alps, the Apennines). Birds infected during autumn migration or post-breeding vagrancy could have been infected in the Central European Carpathians, the region of C. faba endemic occurrence. For migrating birds, the impact of C. faba infections has not been hitherto assessed.     

Response of introduced European birds in New Zealand to experimental brood parasitism

The loss of anti-parasite adaptations against the European cuckoo Cuculus canorus was studied in three European passerine species, song thrush Turdus philomelos , blackbird T. merula , and chaffinch Fringilla coelebs , introduced to New Zealand in the 19th century. Chaffinches in New Zealand ejected non-mimetic eggs at a rate similar to their source population in the United Kingdom, but both song thrushes and blackbirds in New Zealand rejected non-mimetic eggs at a higher rate than the United Kingdom. It is not clear if this difference reflects variation among hosts in their response to brood parasitism or if it is an artefact of subtle differences in the types of non-mimetic eggs tested. In contrast, all three introduced species showed little aggression to a taxidermic model of a European cuckoo presented at their nests. This differs from European populations of these species, where model cuckoos are typically attacked. Our results suggest that in the∼130 years since their release in New Zealand, introduced birds have lost recognition of the European cuckoo but not their ability to discriminate non-mimetic eggs. The differential loss of anti-parasite adaptations by introduced birds in New Zealand suggests that cyclical models of host/parasite co-evolution may need to take into account the differing rates at which different host adaptations are lost and gained.     

Does Gray Squirrel (Sciurus carolinensis) Response to Heterospecific Alarm Calls Depend on Familiarity or Acoustic Similarity?

In habitats in which multiple species are prey to the same predators, individuals can greatly benefit from recognizing information regarding predators that is provided by other species. Past studies have demonstrated that various mammals respond to familiar heterospecific alarm calls, but whether acoustic similarity to a familiar call can prompt a mammal's recognition of an unfamiliar call has yet to be shown. We presented alarm calls to free‐ranging eastern gray squirrels (Sciurus carolinensis) and recorded behavioral changes in vigilance and antipredatory response. Playbacks included alarm calls of a sympatric bird (American robin, Turdus migratorius), an allopatric bird with a call structure similar to that of the robin (common blackbird, Turdus merula), and an allopatric bird with a distinct call structure (New Holland honeyeater, Phylidonyris novaehollandiae). Squirrels responded significantly more frequently to squirrel alarm calls (positive control) than to robin song (negative control) or honeyeater calls. Squirrel response to robin and blackbird alarm calls was statistically similar to their response to squirrel alarm calls, indicating that squirrels responded to those alarm calls as if they provided information about the presence of predators. However, squirrel response to robin song was not statistically different from response to any of the other avian calls, including the robin and blackbird alarms, suggesting that squirrels neither respond to blackbird alarms as if they clearly signify danger, nor as if they clearly do not signify danger, perhaps reflecting some ambiguity in interpretation of the calls. These results suggest that squirrel responses to alarm calls are generally based on call familiarity, but that acoustic similarity of an unfamiliar allopatric call to a familiar call also can elicit antipredator behavior. The lack of response to honeyeater alarm calls also supports the hypothesis that call recognition by gray squirrels is dependent on familiarity, rather than simply detection of an acoustic feature common to alarm calls across a variety of avian species.     

Common and rare Swedish vertebrates — distribution and habitat preferences

Data have been compiled on the distribution, habitat preferences and population sizes of 348 vertebrates reproducing in Sweden (excluding fish) and their species richness in different habitats and regions was investigated. Furthermore, we compared the habitat preferences and distribution of rare and common vertebrates. The relative species number (corrected for area) increases from the north (the hemiarctic/boreal zone) to the south (the temperate/hemiboreal zone). The relative number of species in major habitats is highest in farmland, lakes and running waters, and possibly also in the sea. However, the absolute number of species is highest in woodland, the dominant habitat in Sweden (56% of the land area excluding sea). Within woodlands, a large proportion of species occur in southern deciduous forests, in other deciduous forests and in mixed forests, while coniferous forests are less species-rich when the habitat area is taken into account. In farmland, the most species-rich habitats are meadows and forest edges, while marshes are the most species-rich habitats amongst lakes and running waters. Nationally rare species (<1000 individuals) have a smaller European range than common species, and they also have their European distribution centres further to the south than the common species. Of the species occurring in large parts of Sweden (that is, both in the north and the south) a low proportion (4.7%) are classified as rare compared with species occurring mainly in the north (20.6% rare) or mainly in the south (31.6% rare) of Sweden. There is a positive correlation between the number of rare species and the total species number in 41 subcategory habitats, and the proportion of rare species is similar in most habitats. A more detailed analysis (including effects of both regions and habitats) suggests that the proportion of rare species in a region is a result of differences between latitudes, but also of different habitats (when corrected for latitude effects). There are differences in the proportion of rare species between the nine most species-rich orders (for example, there is a high proportion of rare species in the order Carnivora and a low proportion in the order Rodentia), but the proportion of rare species in these orders is not independent of the habitats in which they occur, making it difficult to separate the effects of habitat preferences and taxonomy on rarity. The focusing of conservation work on relatively species-rich habitats in southern and middle Sweden — such as some farmland habitats (that is, meadows and forest edges), marshes (in connection with lakes and running waters) and forests with a relatively high proportion of deciduous trees — is of high priority if the conservation of biodiversity is a main goal. These are also the habitats with a high number of rare and red-listed species.     

Avian eggshell pigments are not consistently correlated with colour measurements or egg constituents in two Turdus thrushes

The colourful appearance of avian eggshells is a prominent aspect of maternal reproductive effort in birds. Some differences in eggshell coloration have been reported to co‐vary with various measures of maternal condition and these patterns support the hypothesis that, in some bird species, several aspects of eggshell colour (i.e. primary chroma and brightness) function as a signal of maternal and offspring quality to induce greater paternal investment. We directly quantified eggshell pigment concentrations of blackbird Turdus merula and song thrush T. philomelos eggshells and tested how the two key pigments (protoporphyrin IX and biliverdin) co‐varied with other eggshell traits and egg constituents as measures of maternal reproductive investment, including total yolk carotenoid concentration, total lipid concentration, yolk mass, and shell thickness. Contrary to predictions, we detected few statistical patterns overall. We found that protoporphyrin IX concentration was negatively associated with blue‐green chroma in blackbirds but not in song thrush. The concentration of protoporphyrin IX was significantly greater in blackbirds and also showed different patterns of association with total yolk lipids and yolk carotenoid concentrations between these two species (significant species interaction terms). Our results reveal that it is not appropriate to simply assume in these two avian species that reflectance‐based eggshell colour measures are a suitable proxy for eggshell pigment concentrations or can be used as consistent predictors of maternal reproductive investment. These results highlight the need to assess and validate the strength and direction of the statistical relationships between eggshell colour measures, pigment concentrations, and maternal resource deposition in the egg for other species of birds.     

BIRDS ON TENERIFE

.1. A visit was paid to Tenerife in March 1948.
2. Of 16 species common to Tenerife and Britain, all showed detectable differences in song or call-notes. The differences were in some cases slight but in others very marked.
3. Various species occupy broader habitats on Tenerife than in Western Europe, and this can in most cases be correlated with the absence of a related species which fills part of the habitat in Western Europe. For instance, on Tenerife Parus cceruleus breeds in conifers as well as broad-leaved woods, and Phylloscopus collybita breeds in low scrub as well as woods.
4. Fringilla ccelebs is more restricted in habitat on Tenerife than in Western Europe. a fact which can be correlated with the presence of the related F. teydea.
5. The bird fauna of the Canary Islands is recommended as a profitable field for ai detailed ecological study.     

Seasonal Abundance and Species Richness of Birds in Common Reed Habitats in Lake Erie

Abstract: Common reed (Phragmites australis) forms dense stands with deep layers of residual organic matter that negatively affects plant diversity and possibly habitat use by wetland birds. We sought to determine whether seasonal relative abundance and species richness of birds varied among 3 habitat types in Great Lakes coastal wetland complexes recently invaded by common reed. We used fixed-distance point counts to determine species relative abundances and species richness in edge and interior locales within common reed, cattail (Typha spp.), and meadow marsh habitats of various sizes during 2 summers (2001 and 2002) and 1 autumn (2001) at Long Point, Lake Erie, Ontario, Canada. We found that total relative abundance and species richness of birds were greater in common reed habitat compared to cattail or meadow marsh habitats. However, we also found that relative abundance of marsh-nesting birds was greater in meadow marsh habitat than in cattail and common reed during summer. Lastly, we found that, irrespective of habitat type, habitat edges had higher total relative abundance and species richness of birds than did habitat interiors. Our results show that common reed provides suitable habitat for a diversity of landbirds during summer and autumn but only limited habitat for many marsh-nesting birds during summer. Based on these results, we recommend restoration of meadow marsh habitat through reduction of common reed in Great Lakes wetlands where providing habitat for breeding marsh-nesting birds is an objective. Managers also might consider reducing the size of nonnative common reed stands to increase edge effect and use by birds, possibly including wetland birds.     

A host-race difference in begging calls of nestling cuckoos Cuculus canorus develops through experience and increases host provisioning

The structure of common cuckoo nestling begging calls differs between the two host-races parasitizing reed warblers (reed warbler-cuckoos) and dunnocks (dunnock-cuckoos; longer syllable duration, lower peak and maximum frequency, narrower bandwidth). Cross-fostering experiments demonstrated that this difference is not genetically fixed but develops through experience. When newly hatched reed warbler-cuckoos were transferred to dunnock nests, they developed begging calls more like those of dunnock-cuckoos, whereas controls transferred to the nests of robins or left to be raised by reed warblers developed calls more typical of reed warbler-cuckoos. We tested the effectiveness of these different calls in stimulating host provisioning by placing in host nests a single blackbird or song thrush nestling (of similar size to a young cuckoo, but lacking its exuberant begging calls); when it begged we broadcast, from a small loudspeaker on the nest rim, recordings of either dunnock-cuckoo or reed warbler-cuckoo begging calls. Playback of dunnock-cuckoo begging calls induced higher levels of provisioning by dunnocks, whereas playback of reed warbler-cuckoo begging calls did so for both reed warblers and robins. We suggest that the young cuckoo (which ejects the host's eggs/chicks and so is raised alone) learns by experience which calls best stimulate host provisioning.     

The relevance of non-farmland habitats, uncropped areas and habitat diversity to the conservation of farmland birds

Use of non-farmland habitats by species generally perceived as 'farmland birds' is common, yet these habitats are not always considered in conservation strategies aimed at population recovery. At the national scale, many farmland species occur in landscapes not dominated by farmland. An analysis of distribution atlas data coupled with remotely sensed habitat data showed that for 16 out of 28 farmland species, less than half of the breeding range was associated with high cover of lowland farmland. However, with a few exceptions, populations breeding in non-farmland habitats are likely to depend on farmland at some time in the year. Within farmland landscapes, uncropped areas and patches of non-farmland habitat can provide nesting, foraging or roosting resources. Habitats that are scarce on farmland and that provide potential supplementary or complementary resources to those available within the productive areas of farmland include ruderal vegetation, rough grassland and scrub. Enhancing habitat diversity through provision of modest quantities of these habitats will benefit farmland birds. Complete knowledge of year-round habitat requirements and patterns of resource use at all scales is needed if robust national conservation plans are to be developed for farmland species. Similarly, interactions between the farmland and non-farmland sections of populations need to be determined.     

Fruit tracking between sites and years by birds in Mediterranean wintering grounds

Knowledge of the ability of birds to track spatiotemporal variation in fruit distribution is essential for understanding plant-frugivore interactions. Arguably, although total fruit availability sets an upper limit to the number of birds that can exploit a habitat patch, not all species can equally distribute abundance according to variation in fruit resources. To explore this, we studied bird and fruit abundance in 1999–2005 in Mediterranean scrublands and woodlands of southern Spain. We analysed whether changes of fruit abundance in eight different sites during six winters could predict numerical changes of a set of frugivorous passerines of the area (blackcap Sylvia atricapilla , Sardinian warbler S. melanocephala , robin Erithacus rubecula , song thrush Turdus philomelos and blackbird T. merula ). We also investigated if all frugivores together tracked fruits better than individual species, thereby supporting a shared use of resources. Results showed strong inter-specific differences. Only the most abundant species (blackcaps and robins) tracked the spatial patterning of food despite strong differences in the use of space (vagrant and territorial, respectively). This suggests plastic behaviour of territorial robins, with individuals changing from strictly territorial to wandering, a flexibility that would favour between-site numerical arrangements according to food resources. Annual changes in bird numbers were independent of the availability of fruits, except for blackcaps, an abundant vagrant bird that tracked inter-winter changes in fruit abundance. The abundance of blackcaps fitted the spatiotemporal patterning of fruit resources better than the whole guild of frugivorous birds, inconsistent with the idea that these species track together the changing availability of fruit resources.