Small Passerine Species Research Articles

First Records of Conspecific Brood Parasitism in Two Species of Small Passerines: Lesser Whitethroat and Common Linnet

We provide the first records of possible conspecific brood parasitism in the lesser whitethroat Sylvia curruca and the common linnet Linaria cannabina, two species of small passerines. In 2018 we found two unusually large clutches, one for each species (8 and 9 eggs, respectively), both containing two distinct egg morphs differing in coloration. Further detailed analysis of egg morphology and brood phenology (in the whitethroat) suggested that the eggs in each nest had been laid by different females. Surprisingly, two seemingly full sized clutches were laid in both nests, a pattern that is unusual in conspecific brood parasitism in passerines, whose nests are typically parasitized with single eggs. Alternatives to conspecific brood parasitism are therefore discussed. We argue that traditional field-based methods, when carefully used, may be sufficient to document brood parasitism recorded during occasional observations. We finally conclude that enlarged broods, resulting from conspecific brood parasitism, are probably more frequent than expected, but they may be often overlooked.

Insulation of Common Chaffinch Fringilla coelebs Nests is Largely Driven by Animal-Derived Materials in the Cup Lining

Incubation of eggs and nestlings is energetically costly and may be affected by the amount of thermal insulation the surrounding nest provides. In many small passerine species, animal-derived materials, i.e., feathers and hair, are often used in the nest lining where, presumably, their lower thermal conductance offers better insulation. A previous study that involved partial deconstruction of thrush nests revealed that different parts of the nest confer different levels of insulation. The present study examined the insulatory values of Common Chaffinch Fringilla coelebs nests because of the high proportion of animal-derived materials in their cup lining but not the outer nest. Insulatory values and cooling rates of temperature loggers inside the cup were determined for whole nests and then only the cup lining. There were no significant relationships between nest measurements and measures of thermal insulation. However, removal of the outer nest wall reduced the insulatory value by around 10% despite the cup lining being less than half the thickness of the complete nest wall and the cup lining being only a third of the total nest mass. Differential placement of animal-derived materials within the cup lining of Common Chaffinch nests means that the birds seem to be able to confer a high level of insulation without expending too much energy searching for a large mass of particular nest materials.

Comparing fall migration of three Catharus species using a radio-telemetry network

AbstractMigration routes vary greatly among small passerine species and populations. It is now possible to determine the routes over great distances and long periods of time with emerging monitoring networks. We tracked individual Swainson’s Thrush (Catharus ustulatus), Bicknell’s Thrush (Catharus bicknelli) and Gray-cheeked Thrush (Catharus minimus) in northeastern Quebec and compared their migration routes and paces across an array of radio-telelemetry stations in North America. Swainson’s Thrush migrated further inland than the other two species. Individuals from all three species slowed their migration pace in the southeastern United States, and Swainson’s Thrush was more likely to stopover than Bicknell’s Thrush. Although individuals were tagged in a small area within or close to their breeding range, the results document the variability of migration routes between species with similar ecological characteristics and provide detailed material to be used for migration studies with broader taxonomic or ecological scope.

Songbird presumed to be age‐limited learner may change repertoire size and composition throughout their life

AbstractSongbirds learn to sing by imitating their conspecific songs through social learning. It is commonly thought that in species with small repertoires, so‐called crystallization of the song repertoire takes place before the first breeding attempt and afterwards their repertoires remain unchanged. However, the number of studies in which individual song repertoires have been tracked longitudinally under natural conditions is still small. The ortolan bunting (Emberiza hortulana) is a small Eurasian passerine species. Studies on this species have shown that males have small song repertoires (usually 2–3), share the same final phrase within a local dialect area, and their repertoires remain unchanged during their lifetimes. We studied the whole, isolated Norwegian population of this species with 100–150 individually marked males. We compared repertoire sizes and contents using cross‐sectional and longitudinal approaches. We focused on marked males aged 2–10 years and recorded in up to five breeding seasons between 2001 and 2006. There was no local dialect because songs with different final phrases occurred both within and between males. Repertoire size varied between 1 and 24 (4.7 ± 3.4) song types per male. Longitudinal analysis showed an increase in repertoire size in 29% and a decrease in 21% of males. Males whose repertoires remained the same in size between years often substantially changed in contents. New song types appeared in almost 70% of males, and over 30% of males started singing new syllable types after the second calendar year. In almost 50% of males, new song types appeared that were built as new combinations of syllables shown in previous years. In 30% of males, the song complexity increased with age. Simultaneously, over 60% of males selectively ceased singing some song types. We suggest that these repertoire alterations are linked to the isolation and fragmentation of this population, which may affect song learning patterns through increased breeding dispersal and a strongly male‐biased sex ratio. Similar studies from abundant and continuous populations of the species are needed to test this idea.

Soft songs in male ortolan buntings are used in an aggressive context but are not an aggressive signal

AbstractMany bird species produce low‐amplitude acoustic signals that have been poorly studied in comparison with loud, broadcast songs used for mate attraction and repelling rivals. In some birds, these soft signals were found to be emitted in an antagonistic context and were the most reliable predictor of a subsequent physical attack. The function of this signal is poorly understood, and several hypotheses have been proposed to explain the mechanisms and possible functions of such low‐amplitude signals. The subject of this study is the ortolan bunting, a small passerine species that produces soft songs during territorial defence. In this study, we aim to study whether the soft songs of the ortolan bunting are a signal of increased aggressiveness by testing if they meet the context, prediction and response criteria of aggressive signals. We simulated stranger male intrusion into a focal male territory with three different playback experiments. We found no significant differences in the male responses to the taxidermic model regardless of whether they were or were not producing soft songs in response. The males responded more strongly to loud songs than to soft songs during the simulated intrusions, and the males did not treat soft songs as a predictor of conflict escalation. Although soft songs clearly appeared during territorial encounters and were not present during spontaneous singing before the intrusions, our results did not support the hypothesis that soft songs indicate aggressive character. We suggest that soft songs in the ortolan bunting are intentionally used by birds to modify their intentions or target‐specific individuals within a close range.

Associations between changing climate and body condition over decades in two southern hemisphere passerine birds

BackgroundClimate change presents considerable challenges for endotherms because they must maintain high, relatively constant body temperatures across a range of environmental conditions to ensure survival and optimise performance. Individuals exposed to changing weather must manage energy and water allocation to maintain thermal homeostasis, with consequences for body condition, and hence there is potential for selection because body condition is strongly linked to fitness. Understanding how weather drives changes in body condition is therefore fundamental to understanding how fitness is affected by climate change. Here we test for associations between weather and body condition and how this changes over time, in two co-existing species of small insectivorous passerines, the red-winged fairy-wren, Malurus elegans and white-browed scrubwren, Sericornis frontalis, that have been the subject of a ringing study for 39 years in temperate south-western Australia. The study populations have experienced increases in minimum temperatures in winter and summer as well as decreases in the frequencies of days with thermal minima < 5 °C, but the summer climate remains relatively mild with few days experiencing thermal maxima > 35 °C. Although, warming temperatures may reduce thermoregulatory costs, repeated exposure to hot conditions has been shown to have negative effects on body condition. Thus, we predict that the reduction over time in daily minima < 5 °C, along with the influence of increased maximum and minimum temperatures in summer and winter, will have positive effects on body condition.ResultsIn accordance with thermoregulatory predictions, colder daily minima in the range 1–19 °C prior to capture were associated with reduced body condition in winter in both species. Furthermore, in summer, in fairy-wrens but not scrubwrens, warmer daily maxima were associated with increasing body condition, and repeated exposure to temperatures > 30 °C over consecutive days was negatively associated with body condition. Body condition increased over the 39 years of the study for fairy-wrens but there was no change in scrubwrens, which is consistent with observed within-season associations between body condition and weather, and the change in climate over time.ConclusionsWe show that associations between body condition and weather variables are complex and dynamic, with seasonal trends in body condition resulting from a balance between multiple, competing weather variables. Moreover, temporal trends in body condition over years could be predicted from the relative strength of seasonal trends and the direction and magnitude of changing climate. Because body condition is predicted to be strongly tied to both reproduction and survival, changes in climate may be having complex and far reaching consequences for demography mediated through shifts in body condition. Finally, subtle differences in the sensitivities of the species to weather variables led to different trends in condition over time which may be associated with differences in the capacity for behavioural thermoregulation. Understanding the causes of such sensitivities is vital in improving capacity to predict species responses to climate change.

Wind farms affect the occurrence, abundance and population trends of small passerine birds: The case of the Dupont's lark

AbstractThe assessment of the effects of wind farms on bird populations is commonly based on collision fatality records. This could undervalue the effect of wind farms on small‐sized birds. We evaluate the effect of wind turbines on occurrence, abundance and population trends of a threatened small passerine species, the Dupont's larkChersophilus duponti. To our knowledge, this is one of the first studies addressing the effect of wind farms on population trends using time‐series data from multiple wind farms.We estimated population trends by fitting a switching linear trend model with the softwaretrim(Trend &amp; Indices for Monitoring data). We used multiannual data surveys of five populations in the presence of wind farms and nine in their absence (2008–2016 period). Furthermore, we fitted a logistic and a negative binomial regression model to test the effect of wind farm proximity on species occurrence and abundance in 2016, respectively. We incorporated local connectivity and habitat availability estimates in both models as predictors.Results showed a negative trend overall, but that was significantly more regressive in the presence of wind farms: 21.0% vs. 5.8% average annual decline in the absence of wind farms.Dupont's lark occurrence and abundance in 2016 were negatively affected by measures of population isolation and positively affected by the distance to wind farms.These results highlight the negative effect of isolation and wind farm proximity on Dupont's lark population parameters. Taking into account the metapopulation structure exhibited by the species in the study area, this work established a 4.5‐km threshold distance from wind farms, beyond which Dupont's lark populations should be unaffected.Synthesis and applications. This work highlights the negative impact of wind farms on small‐sized birds and provides a 4.5‐km threshold distance that should be taken into account in the design of future wind energy projects. Moreover, we suggest an analytical approach based on population trends, species abundance and occurrence variation in relation to wind farms, useful for the assessment of wind farm impacts on small‐sized birds.

Arionslugs as nest predators of small passerine species – a review

Arionid slugs have been reported to attack nestlings of some ground‐ or shrub‐nesting passerine birds, mainly in Europe. We review these reported cases and consider their effects. The slugs can cause grave or even fatal injuries to the nestlings. Surprisingly, no brood defence by the parents has been described. The information on the frequency of slug predation in bird populations is scanty, and the scale of the phenomenon is unknown. The expansion of the invasiveArion vulgarisMoquin‐Tandon, 1855 (synonymouslyA. lusitanicusorA. lusitanicusauct. non Mabille, 1868) in Europe may result in an increase of the negative influence of slugs on the breeding success of some passerines in the near future.

Relationships between interspecific differences in the mass of internal organs, biochemical markers of metabolic activity, and the thermogenic properties of three small passerines

The capacity for thermogenesis is considered part of an animal’s adaptive strategy for survival, and basal metabolic rate (BMR) is one of the fundamental physiological standards for assessing the energy cost of thermoregulation in endotherms. BMR has been shown to be a highly flexible phenotypic trait both between, and within, species, but the metabolic mechanisms involved in the regulation of BMR, which range from variation in organ mass to biochemical adjustments, remain unclear. In this study, we investigated the relationship between organ mass, biochemical markers of metabolic tissue activity, and thermogenesis, in three species of small passerines: wild Bramblings (Fringilla montifringilla), Little Buntings (Emberiza pusilla) and Eurasian Tree Sparrows (Passer montanus), caught in Wenzhou, southeastern China. Oxygen consumption was measured using an open-circuit respirometry system. Mitochondrial state-4 respiration and cytochrome c oxidase (COX) activity in liver and pectoral muscle were measured with a Clark electrode. Our results show that Eurasian Tree Sparrows had significantly higher BMR, digestive organ mass, mitochondrial state-4 respiration capacity and COX activity in liver and muscle, than Bramblings and Little Buntings. Furthermore, interspecific differences in BMR were strongly correlated with those indigestive tract mass, state-4 respiration and COX activity. Our findings suggest that the digestive organ mass, state-4 respiration and COX activity play an important role in determining interspecific differences in BMR.

Effects of breeding habitat (woodland versus urban) and metal pollution on the egg characteristics of great tits (Parus major)

In an urban environment, birds are exposed to metals, which may accumulate in their tissues and cause oxidative stress. Female birds may eliminate these pollutants through depositing them into eggs, thus eggs become suitable bioindicators of pollution. In this study, we aimed to analyse whether eggshell spotting pattern, egg volume, eggshell thickness and egg yolk antioxidant (lutein, tocopherol, retinol and selenium) levels were related to the breeding area (woodland versus urban) and the metal levels in the eggshell of a small passerine species, the great tit (Parus major). In the urban habitat, soil and eggshells contained higher concentrations of metals, and soil calcium level was also higher than that in the woodland. Eggshell spotting intensity and egg volume did not differ between eggs laid in the woodland and the urban park, and these traits were not related to the metal levels of the eggshell, suggesting that these egg characteristics are not sensitive indicators of metal pollution. A more aggregated eggshell spotting distribution indicated a higher Cu concentration of the eggshell. We found that eggshells were thinner in the less polluted woodland habitat, which is likely due to the limited Ca availability of the woodland area. Great tit eggs laid in the urban environment had lower yolk lutein, retinol and selenium concentrations, however, as a possible compensation for these lower antioxidant levels, urban females deposited more tocopherol into the egg yolk. It appears that females from different breeding habitats may provide similar antioxidant protection for their offspring against oxidative damage by depositing different specific dietary antioxidants. Egg yolk lutein and retinol levels showed a negative relationship with lead concentration of the eggshell, which may suggest that lead had a negative impact on the amount of antioxidants available for embryos during development in great tits.

Birds and Mammals of Prince Leopold Island, Nunavut, 1975–2012

Prince Leopold Island is the most important marine bird colony in the Canadian High Arctic. An Environment Canada research camp on the island was occupied for varying periods (mean 37 days) during 18 summers from 1975 to 2012. Research concentrated on the biology of the marine bird colonies, but incidental notes were kept on other sightings of birds and mammals. Forty-seven species of birds, of which 12 bred, six species of terrestrial mammals, four seals, and three whales were recorded on or from the island. Sightings of Ivory Gull and Brant decreased over the period considered, while sightings of Peregrine Falcons and breeding records of Baird’s Sandpipers increased. Collared lemmings invaded the island in 2009, and extensive evidence of their presence was found by 2012. Arctic fox presence has become more frequent. Some or all of these changes may be related to recent climate warming and increased precipitation in the area. Eleven species of small passerines that normally do not breed north of the tree line were recorded, most often in June, suggesting that their appearance was due to migration overshoot. The regular appearance of southern passerines suggests that colonization of the Arctic Archipelago by sub-Arctic species may occur rapidly if climate and vegetation become more suitable.

Foraging Patch Selection in Winter: A Balance between Predation Risk and Thermoregulation Benefit

In winter, foraging activity is intended to optimize food search while minimizing both thermoregulation costs and predation risk. Here we quantify the relative importance of thermoregulation and predation in foraging patch selection of woodland birds wintering in a Mediterranean montane forest. Specifically, we account for thermoregulation benefits related to temperature, and predation risk associated with both illumination of the feeding patch and distance to the nearest refuge provided by vegetation. We measured the amount of time that 38 marked individual birds belonging to five small passerine species spent foraging at artificial feeders. Feeders were located in forest patches that vary in distance to protective cover and exposure to sun radiation; temperature and illumination were registered locally by data loggers. Our results support the influence of both thermoregulation benefits and predation costs on feeding patch choice. The influence of distance to refuge (negative relationship) was nearly three times higher than that of temperature (positive relationship) in determining total foraging time spent at a patch. Light intensity had a negligible and no significant effect. This pattern was generalizable among species and individuals within species, and highlights the preponderance of latent predation risk over thermoregulation benefits on foraging decisions of birds wintering in temperate Mediterranean forests.

Oxidative status in nestlings of three small passerine species exposed to metal pollution

Antioxidant defense has an important role in the protection of organisms against oxidative stress caused by reactive oxygen species (ROS). Many metals are capable of generating ROS and inducing oxidative damage, and may therefore lead to changes in oxidative regulation. We studied species-specific variation in the oxidative status of great tit (Parus major), blue tit (Cyanistes caeruleus) and pied flycatcher (Ficedula hypoleuca) nestlings in a vicinity of a non-ferrous smelter. Non-enzymatic (glutathione [tGSH], GSH:GSSG ratio, and carotenoids) and enzymatic (glutathione peroxidase [GP], glutathione-S-transferase [GST], superoxide dismutase [SOD], and catalase [CAT]) antioxidants were evaluated to determine the effects of metal exposure on the oxidative status of the birds. We found strong evidence of interspecific variation in CAT and SOD activities, whereas less variation was observed in parameters related to glutathione metabolism. Oxidative state (in terms of tGSH and GSH:GSSG) did not vary between species, suggesting that different species may employ different antioxidant pathways to achieve the same oxidative state. Oxidative status was only weakly related to metal exposure, and these associations were further obscured by species-specific environmental effects. Our results indicate that effects on oxidative status observed in one species cannot be generalized to other ones. Future work should attempt to incorporate species-specific biology and environmental context into assessments of contaminant impacts on oxidative regulation of passerine birds.

Do miners (Manorina spp.) affect bird assemblages in continuous savanna woodlands in north‐eastern Australia?

AbstractOverabundant native species can have a significant cascading effect on other components of wildlife, and those that deplete other species, often promoted by anthropogenic change to vegetation cover and habitat, are called reverse keystone species. Birds in the genus Manorina are widely reported as being such species, and in highly disturbed or fragmented environments, and some intact environments, noisy miners Manorina melanocephala can have a strong negative effect on small passerine species via hyper‐aggressive mobbing. The tropical savannas of northern Australia consist of largely unmodified woodlands, and two species of Manorina occur naturally in this region: the noisy miner and the yellow‐throated miner Manorina flavigula. Therefore, what effect do these species have on bird assemblage in predominantly continuous habitats, relative to other typical determinants of avifauna assemblage such as vegetation structure? We used data collected from bird surveys at 511 sites across northern Queensland (179 noisy miner M. melanocephala sites, 332 yellow‐throated miner M. flavigula sites) between 1998 and 2010. We examined the variation in bird composition at each site due to increasing abundance of Manorina spp. using uni‐ and multivariate techniques. We found total bird richness was significantly lower in sites where noisy and yellow‐throated miner abundances were highest, and passerine species seemed most affected. For species, 45 species varied significantly in abundance with increasing miner numbers, and the overall effect of yellow‐throated miners on other birds seemed more pronounced. However, vegetation structure was generally an equal or more important predictor of avifauna richness and abundance. We conclude that despite the superficially intact nature of northern Australian woodlands, pastoral intensification or poor land management might create disturbances that facilitate increases in the abundance of Manorina, causing localized overabundance and a compounding negative effect on other native bird species.

The communicative significance of song frequency and song length in territorial chiffchaffs

Spectral and temporal measures of vocalizations have been found to correlate with physical parameters that affect the fighting ability in various species of frogs, mammals, and birds. This correlation could play a role in communication for intersexual mate attraction, as well as intrasexual competition. In this study, we investigated whether the frequency and length of territorial songs reflects the body size (tarsus length, weight) of males in a small passerine species, the chiffchaff Phylloscopus collybita. We found a tendency for a negative correlation between song frequency and tarsus length, but no significant links with song length. Furthermore, we carried out playback experiments to see whether the variation in song frequency and length is meaningful to receiving males and found that both parameters affected the males’ responses. We found that the response strength was related to the frequency difference between the songs of the tested male and the playback stimulus, rather than only to the stimulus frequency manipulation (increased/decreased frequency). Males showed a mixed strategy of moderate attack response, combined with a low approach response, when relatively low-frequency song stimuli were played back. In contrast, manipulation of the stimulus song length (shortened/elongated) was a better predictor of response strength than the relative differences in song length. Males attacked more and approached closer in response to elongated stimuli. Our data show how multiple messages can be encoded in different signal components; song frequency most likely conveys information about some aspect of fighting ability, whereas song length probably signals motivation to escalate into a fight among male chiffchaffs. Key wor ds: acoustic com munication, fighting ability, motivational signaling, Phylloscopus collybita, playback experiment. [Behav Ecol]

A reverse keystone species affects the landscape distribution of woodland avifauna: a case study using the Noisy Miner (Manorina melanocephala) and other Australian birds

We explored the effects of a purported ‘reverse keystone species’, the Noisy Miner (Manorina melanocephala) using a long-term, large-scale dataset. Specifically, we identify whether this aggressive bird affects the landscape distribution patterns of other avifauna, by displacing them into, or restricting their distribution to, less productive areas, and in so doing, adheres to ‘isoleg theory’. We sought to determine the effect of abundance of the Noisy Miner on the abundance of other birds (individual species and groups), and determine whether that effect was consistent with varying site productivity, using a negative binomial distribution with a logarithmic link function, and an offset variable to account for variations in search effort. Relationships between abundance of Noisy Miners and habitat variables were examined using a Poisson distribution with a logarithmic link function scaled for extra-variation (quasi-Poisson regression). We demonstrate that when Noisy Miner abundance is low, many small passerine species are more abundant on high productivity sites. However, as Noisy Miner abundance increases, small passerine abundance decreases, with this decrease most apparent on productive sites. The same patterns were not evident for birds considered ‘non-competitors’ of the Noisy Miner. We identify that both site productivity and vegetation structure influence the abundance of the Noisy Miner. We reveal that the species increasingly tolerates ‘less desirable’ habitat attributes with increasing site productivity. The preference of the Noisy Miner for productive areas is likely to have deleterious impacts on the long-term survival and reproductive success of other Australian woodland bird species, many of which have already undergone severe declines.

PATHOLOGY AND VIRUS DETECTION IN TISSUES OF NESTLING HOUSE SPARROWS NATURALLY INFECTED WITH BUGGY CREEK VIRUS (TOGAVIRIDAE)

Alphaviruses (Togaviridae) infect wild birds, but clinical illness and death attributable to virus in naturally infected birds is rarely reported, particularly for small passerine species or nestlings. Buggy Creek virus is a unique alphavirus in the Western equine encephalomyelitis virus (WEEV) complex that is vectored by the cimicid swallow bug (Oeciacus vicarius), an ectoparasite of the colonially nesting Cliff Swallow (Petrochelidon pyrrhonota) and the introduced House Sparrow (Passer domesticus). While sampling birds for Buggy Creek virus (BCRV) during the summers of 2007 and 2008, we discovered large numbers of clinically ill or dead House Sparrow nestlings. Ill nestlings exhibited ataxia, torticollis, paresis, and lethargy. Histologic examination revealed that encephalitis was the most common finding, followed by myositis, myocarditis, and hepatic changes, but pathology was highly variable. We isolated BCRV from brain tissue in most of the ill or dead nestlings, and from blood, liver, kidney, spleen, lung, feather pulp, and skin in some birds. To our knowledge, this is the first report of clinical illness, gross pathology, and histopathology for a WEEV-complex alphavirus in a field-collected passerine species.

Mercury, Lead and Copper in Feathers and Excreta of Small Passerine Species in Relation to Foraging Guilds and Age of Feathers

In the present study excreta and feathers of five species of adult passerine birds from Montepulciano wetland (Siena, Italy) were assayed for trace elements between January and August 2006. Lead concentrations varied from 16.31 to 26.50 mg/kg and were found strictly related to the age of feathers. Copper levels were found to be high mainly in insectivorous birds (9.68 mg/kg) and were probably influenced by local use of copper-based agricultural fungicides. Mercury accumulation in feathers varied between species from 0.08 to 0.73 mg/kg. The role offeeding habits on trace elements levels in feathers and excreta is discussed.

Impacts of grazing, selective logging and hyper‐aggressors on diurnal bird fauna in intact forest landscapes of the Brigalow Belt, Queensland

AbstractThe impact of forest management on diurnal bird assemblages and abundance was investigated in contiguous tracts of eucalypt forest in the Brigalow Belt Bioregion, south central Queensland. Sites were located across three levels of livestock grazing intensity and three levels of selective logging intensity within the most extensive habitat type, Corymbia citriodora‐dominant forest. We recorded a high rate of incidence and large numbers of the hyper‐aggressive noisy miner Manorina melanocephala (Passeriformes: Meliphagidae) at the majority of our survey sites, a phenomenon rarely reported in non‐cleared landscapes. As shown by numerous studies in fragmented landscapes, the distribution of this species in our study had a substantial negative effect upon the distribution of small passerine species. Noisy miners exerted the strongest influence upon small passerine abundance, and masked any forest management effects. However, key habitat features important for small passerines were identified, including a relatively high density of large trees and stems in the midstorey. Selective logging appeared to exert a minimal effect upon noisy miner abundance, whereas grazing intensity had a profound, positive influence. Noisy miners were most abundant in intensively grazed forest with minimal midstorey and a low volume of coarse woody debris. Higher road density in the forest landscape also corresponded with increased numbers of noisy miners. Reduction in grazing pressure in Brigalow Belt forests has the potential to benefit small passerine assemblages across large areas through moderating noisy miner abundance. The strong relationship between noisy miners and small passerines suggests that noisy miner abundance could act as an easily measured indicator of forest condition, potentially contributing to monitoring of forest management outcomes.

Interspecific competition and small bird diversity in an urbanizing landscape

Throughout eastern Australia, fragmentation and modification of eucalypt woodlands are causing declines in populations of woodland-dependent small passerines. Although agriculture is a major factor in these land use changes, development of peri-urban areas is also driving the simplification of habitat structure through removal of both native and weedy understorey species and the subdivision of remnant habitat. This study investigated the influence of habitat modification and fragmentation on birds in an urbanizing area of south east Queensland, Australia. The influence of spatial factors, such as surrounding vegetation cover, was considered alongside that of site-level habitat factors (vegetation structure) including interspecific competition from the noisy miner ( Manorina melanocephala). Spatial factors did not influence the abundance and species richness of small passerines, a group of conservation concern. However, site-level factors, specifically shrub density and interspecific competition from the noisy miner, had a substantial influence on small passerine species richness and abundance. The density of shrubs (which consisted mainly of the introduced weed Lantana camara) had a strong positive relationship with small passerines while the abundance of noisy miners had a strong negative influence. Consequently, protection of vegetation with an intact shrub layer in this developing area is essential for many small birds of conservation significance. Removal of weedy understorey plants should be accompanied by replacement with native shrubs. The results of the study emphasize that factors other than the spatial distribution of vegetation in the landscape need to be considered in order to develop appropriate conservation strategies.