Passerine Populations Research Articles

Patterns in avian malaria at founder and source populations of an endemic New Zealand passerine

Significant progress in our understanding of disease transmission in the wild can be made by examining variation in host-parasite-vector interactions after founder events of the host. This study is the first to document patterns in avian malaria, Plasmodium spp., infecting an endemic New Zealand passerine, Anthornis melanura, at multiple-host subpopulations simultaneously. We assess the Beaudoin hypothesis of bimodal seasonality and use AIC model selection to determine host factors associated with disease prevalence. We had the rare opportunity to test the enemy release hypothesis (ERH) after a recent colonisation event of the bellbird host. Four Plasmodium species were found to infect bellbirds. Temporal patterns of three exotic parasite lineages, including GRW06 Plasmodium (Huffia) elongatum, SYAT05 Plasmodium (Novyella) vaughani and a Plasmodium (Haemamoeba) relictum, were sporadic with low prevalence year round. The fourth species was an endemic parasite, an unresolved Plasmodium (Novyella) sp. here called ANME01, which exhibited a strong winter peak at the source subpopulations possibly indicating greater immune stressors at the densely populated source site. At the colonies, we observed bimodal seasonality in the prevalence of ANME01 with autumn and spring peaks. These infection peaks were male-biased, and the amplitude of sex bias was more pronounced at the newer colony perhaps due to increased seasonal competition resulting from territory instability. We observed a decrease in parasite species diversity and increase in body condition from source to founder sites, but statistical differences in the direct relationship between body condition and malaria prevalence between source and colony were weak and significant only during winter. Though our data did not strongly support the ERH, we highlight the benefits of 'conspecific release' associated with decreased population density and food competition. Our findings contribute to the identification of ecological and environmental drivers of variability in malaria transmission, which is valuable for predicting the consequences of both natural range expansions, as well as host re-introductions resulting from intensive conservation practices.

Evaluation of autumn mist‐netting data for monitoring passerine populations in interior Alaska

AbstractWe evaluated the data from 2 autumn mist‐netting stations for monitoring passerine population trends and measuring the timing of migration. Migration‐monitoring stations were operated during autumn from 1993 to 2009 at 2 interior Alaska locations: in Fairbanks (64°50′N, 147°50′W) by the Alaska Bird Observatory (ABO) and near the Tetlin National Wildlife Refuge (NWR), Alaska, USA (63°22′N, 143°13′W) by the U.S. Fish and Wildlife Service. The location of these 2 stations, near the north and western limits of the continental landmass, provides information from the initial stages of long‐distance migration. The timing of migrant passage through ABO and Tetlin NWR were similar when all 17 years were combined. Juveniles preceded adults in 10 of 14 species at ABO and in 13 of 14 species at Tetlin NWR. Relative capture rates (log of weather‐corrected capture rates) from the ABO and Tetlin NWR stations from 1996 to 2009 were correlated for 2 of 7 species: ruby‐crowned kinglet (Regulus calendula) and yellow warbler (Dendroica petechia). A high proportion of captured birds were juveniles; therefore, these stations are most useful for monitoring an index of productivity. Power calculations indicate that for 6 of 7 species, a 50% decline in relative capture rates could be detected in a 20‐year period. These stations provide a unique contribution for monitoring passerine populations by providing a large sample of the timing of migration and productivity indices at 2 interior‐Alaska locations. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Divergence between passerine populations from the Malvinas - Falkland Islands and their continental counterparts: a comparative phylogeographical study

Bursts of speciation have followed colonization of remote oceanic islands by diverse taxa, a process evidenced by island endemics around the world. The present study explores whether the Malvinas – Falkland Islands (MFI), a relatively understudied archipelago off the South Atlantic coast of Patagonia, harbour endemic genetic lineages of passerine birds. Nine passerine species nest regularly in the MFI (Cinclodes antarcticus, Muscisaxicola maclovianus, Troglodytes cobbi, Cistothorus platensis, Turdus falcklandii, Anthus correndera, Melanodera melanodera, Sturnella loyca, and Carduelis barbata). Mitochondrial DNA (cytochrome c oxidase I sequences) are used to quantify and compare divergence between insular and continental populations, finding genetic patterns to vary across these nine species. Most MFI passerines do not show significant genetic differentiation from continental populations, whereas C. platensis, M. melanodera, and T. falcklandii are modestly diverged. Finally, T. cobbi differes markedly from its closest continental relative Troglodytes aedon, a result that is confirmed using nuclear and vocal data. The study also identifies broadly divergent lineages within continental populations of C. platensis and T. aedon. Taken together, these results suggest that the land bird populations of the MFI were established at different times. Troglodytes cobbi is the oldest MFI land bird, splitting from continental T. aedon during the Great Patagonian Glaciation of the Pleistocene. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

Genetic and morphological divergence in island and mainland birds: Informing conservation priorities

Evolutionary processes can complicate conservation efforts for species with uncertain taxonomic classifications and discrete geographic populations. Discordant morphological and genetic patterns across the geographic range of species further calls for the identification of evolutionary significant units for conservation. Using island and mainland populations of a small Australian passerine (the superb fairy-wren, Malurus cyaneus), we examine the relationship between morphological and genetic divergence among two subspecies, M. c. ashbyi (Kangaroo Island, South Australia) and M. c. leggei (South Australia, mainland), using eight microsatellite markers. Island birds showed clear evidence for morphological divergence, with a larger body size and thinner bill compared to mainland birds. Two genetic clusters were found using Bayesian methods, comprising mainland and island regions. Estimates of recent migration rates between all sites were very low (<2%). Morphological and genetic differentiation between island and mainland sites correlated significantly, but not when controlling for isolation by distance. Genetic and morphological substructure was evident with three distinct genetic clusters in each region. Males, the highly sedentary sex, appeared to drive correlations between morphological and genetic differentiation. Our study provides evidence that the subspecies classification of M. cyaneus in island and mainland regions encapsulates two independently diverging populations that can be recognised in conservation planning.

Warming climate advances breeding and improves synchrony of food demand and food availability in a boreal passerine

AbstractGlobal climate change affects ecosystems via several trophic levels. We investigated changes in the timing of breeding in the willow tit (Poecile montanus) and timing of its caterpillar food resource in relation to warming springs in a boreal forest. We used generalized linear mixed effect models to study the importance of synchrony between the timing of breeding in willow tits and the caterpillar food availability on the breeding success, measured as nestling survival rate and mean nestling weight. Both the timing of breeding and the timing of the caterpillar peak advanced during the last decades, and were well explained by spring temperatures. Unlike in most passerine populations studied, synchrony has improved with rising spring temperatures. However, it had only a modest although statistically significant positive influence on breeding success. Spring temperatures do not seem to be used as cues for the timing of caterpillar food availability by willow tits. We conclude that responses to climatic warming seem to be population, species and habitat specific, necessitating research in a wide range of taxa in different climatic zones.

Long‐term effects of agri‐environment schemes on breeding passerine populations in a lowland hay‐meadow system

Capsule Mowing postponement in 25% of a meadow system may lead to improved but instable population dynamics in meadow birds. Aim To monitor the long‐term effects of mowing postponement on the abundance and territory density of meadow passerines in 25% of a 3000‐ha hay‐meadow area in the Saône Valley (eastern France). Methods From 1993 to 2009, passerine abundance was measured annually in 78 plots using point counts and territory density was assessed in two study areas by Territory Mapping. Results The programme of mowing postponement led to substantially increased passerine abundance and territory density, with the highest increase detected in Whinchats Saxicola rubetra. No positive trend was observed in Corn Buntings Emberiza calandra. Immediately after the increase in abundance, bird distribution within the study area was not influenced by the timing of mowing. The hatching success, assessed by the systematic observation of food carrying, was negatively influenced by early mowing (<40% recorded when >60% of the meadow area was already harvested on 1 July) or, in late mown areas, by high meadow passerine territory density (<40% when territory density was >10 per 10 ha). Hatching rate was usually higher in Whinchats than in Corn Buntings. Conclusion By improving meadow passerine breeding outputs and density, mowing postponement led to instable population dynamics with dominance of certain species and density‐dependent breeding success.

Assessing the implications of the loss of set‐aside for farmland birds

Between 1988 and 2007, set‐aside, a European Commission production control measure, took an average of 10% of arable farmland in the EU out of production each year. In 2007, the set‐aside rate was set to 0% and the scheme was later abandoned altogether. By assessing associations of farmland birds with set‐aside and quantifying the extent of set‐aside loss, this study aims to assess the implications of set‐aside loss for farmland bird conservation. During the lifespan of set‐aside, a large number of studies assessed the biodiversity value of set‐aside and other agricultural crops and habitats. Where possible we considered measurable benefits of set‐aside. However, some studies did not specify the type of set‐aside and in some cases set‐aside fields were grouped with cereal stubble fields. In these cases, we took the pragmatic approach of assessing the value of generic stubble fields as a conservative minimum estimate of the value of set‐aside fields. A re‐analysis of data from 30 intensive studies demonstrates that farmland bird densities tended to be higher on set‐aside than on either cereal or oilseed rape crops. Without mitigation, these are the two crops likely to replace most set‐aside fields. We estimate that 26–52% of the farmland populations of key granivorous passerines were present on stubble fields, giving an indication of the proportion of birds likely to be present on set‐aside fields within this broader category. An extensive survey of lowland farmland during winters 1999/2000, 2000/2001 and 2002/2003, repeated in February 2008, showed a doubling of the number of 1‐km squares with no stubble and a halving of the number of squares with more than 10 ha of stubble. After set‐aside abandonment, 72% of squares had no stubble in the important late winter period, confirming that many of the former stubble fields were retained as set‐aside. A simple correlative model suggests that this could cause a small increase in the rate of decline of Skylark Alauda arvensis and Yellowhammer Emberiza citrinella populations, assuming causal links between stubble area and demography. However, even if this assumption cannot be supported, these results clearly indicate that a significant proportion of some farmland bird populations will need to find alternative breeding and foraging habitats.

Simple quantification of blood and plasma antimicrobial capacity using spectrophotometry

Summary Ecologists are becoming increasingly interested in characterizing immunological variation among and within species. However, many of the techniques available to immunologists are not viable for use in non‐model species, which limits the resolution and progress of ecoimmunological research. Recently, an assay was developed to quantify the capacity of blood or plasma to kill microorganisms in vitro. Such assays are ideal for ecologists because they provide holistic, integrated measures of immune function with minimal sample size and equipment. Although informative, the assay suffers from several shortcomings in its current form. Specifically, intra‐assay variation is often prohibitive, quantification of results is time consuming, sample volumes required are somewhat high (especially for small‐bodied species), and materials (e.g. Petri dishes for microbe culturing) are costly and generate excessive waste. Here, we describe a modified version of the assay for use against Gram‐negative, Gram‐positive, and fungal microbes using spectrophotometry. This assay decreases sample processing time, reduces blood/plasma volume (to 1·5 μL), and eliminates the need to score results manually. This technique was 3× more reliable than the alternative method when using house sparrow Passer domesticus plasma and Escherichia coli. We expect this assay will enable quantification of immune defence in a variety of contexts previously difficult to study (e.g. endangered species) because of the small volumes needed and the simplicity of the protocol. We also provide a list of pathogens that affect passerine populations as potential candidates in future studies. Anti‐microbial activity in other animal species should also be easy to characterize using our approach and the quantification of antimicrobial capacity of tissue and other body fluids should also be possible with only minor modifications of the assay.

Intraspecific basal metabolic rate varies with trophic level in rufous-collared sparrows

One of the most controversial hypotheses that associate basal metabolic rate (BMR) with food habits and habitat productivity is the food habit hypothesis (FHH). Here we examined the relationship between BMR, diet, and climate among populations of the omnivorous passerine, Zonotrichia capensis (Emberizidae). We used nitrogen stable isotopes to estimate each individual's relative trophic level. To tease apart the effect of climatic variables and diet on BMR, we also used structural equation modeling. After the effect of body mass and climatic variables was taken into account, a significant effect of trophic level as estimated by δ 15N on BMR was found. Our result seems to support the FHH at the intraspecific level, i.e., birds from the lower trophic levels – feeding on seeds and bud – had higher BMR than individuals from higher trophic levels.

Critical parameters for predicting population fluctuations of some British passerines

1. One of the greatest challenges in ecology is to develop tools that can give reliable projections of future population fluctuations as well as to quantity uncertainties. The population prediction interval (PPI), i.e. the stochastic interval that includes a given population size with a certain probability, is affected by changes in expected population size, e.g. due to density regulation, fluctuations in population size because of demographic and environmental stochasticity, uncertainties and biases in parameter estimates, and observation error in estimates of population size. 2. The aim of this study was to examine how PPI can be used to obtain reliable projections of future population fluctuations. Our approach is to split long time series into two parts: the first part is used for parameter estimation and the second part is used for comparing population predictions with actual population sizes after a certain period of time. 3. Here we use the Common Birds Census - data from the UK for several species of passerines. Unbiased predictions will give a uniform distribution of the recorded population sizes across the PPI when transformed to a scale defined by the quantiles of the PPI. However, deviations from a uniform distribution reveal biases in the predictions. For instance, if there is a predominance of recorded population sizes in the upper quantiles of the PPI, this shows that our predictions underestimate future population sizes. 4. Unbiased predictions required models that included both partitioning of stochastic influences into demographic and environmental stochasticity as well as observation error. 5. Precision in the population predictions was improved when including observation error as well as density dependence. 6. We recommend that predictions of future fluctuations of small passerine populations are based on models that include density dependence as well as observation error and estimates of the demographic variance that is obtained from individual-based demographic data or based on species-specific life-history characteristics. 7. These results show that constructing PPI by stochastic simulations may be a useful tool for obtaining reliable population projections.

VARIATIONS IN BIRD POPULATIONS IN A BROAD LEAFED WOODLAND: 1975 TO 1998

Variations in passerine populations were examined at a single Common Bird Census location over 24 years. Long term trends in the populations of Robin Erithacus rubecula , Blackbird Turdus merula , Wren Troglodytes troglodytes , Blue Tit Parus caeruleus and Great Tit Parus major were investigated. The statistical method proposed by Bulmer(1), which overcomes the problem of regressions to the mean, was used to investigate density-dependent variation (DDV). Little evidence of DDV was found and so long-term population trends could be evaluated. The commonest species seen were the Wren and Robin. Significant increases were seen in breeding pairs of Great Tit (p=<0.001) and Wren (p=0.048) whereas those of Blackbird decreased (p=0.006) and there was no significant change in breeding pairs of Blue Tit (p=0.090) or Robin (p=0.871). Selection pressures on the populations studied were probably reduced by the consistently mild winters and feeding at bird tables in the gardens near the study area in winter. The CBC technique is recognised as the most accurate method of estimating the size of breeding bird populations. This analysis shows that the CBC data collection method, combined with relatively simple statistical techniques, can be used to accurately interpret local trends in breeding bird populations.

Long‐term repeatability of winter basal metabolic rate and mass in a wild passerine

Summary Basal metabolic rate (BMR) is an important trait in the study of energy management of an individual, especially in small wintering passerines from the north which have one of the highest energy turnover rates in vertebrates. Laboratory studies have shown the trait to be repeatable and heritable, despite its plastic nature. However there is currently a lack of empirical data from wild passerine populations. We studied within‐ and between‐year repeatability of BMR, body mass and mass‐independent BMR from two populations of wintering great tits (Parus major) at the northern range of their distribution. We found body mass, BMR and mass‐independent BMR to be highly repeatable both within and between years. Our results provide the first evidence from a wild small passerine that, despite a large environmentally induced variation in metabolic rate, individuals show consistent metabolic strategies over periods even longer than a year. Homeotherm species exposed to new or changing environmental conditions may be able to evolve specific energetic strategies in the wild, as previously found in captive species.

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.

Extrapair paternity in an insular population of house sparrows after the experimental introduction of individuals from the mainland

Several studies have found that island populations of passerines exhibit lower levels of extrapair paternity (EPP) than mainland populations. An explanation proposing that lower levels of genetic diversity in isolated populations reduce the indirect genetic benefits of EPP to females has been supported by observational study but not tested experimentally. Here, we present the results of a manipulative study on an island population of house sparrows (Passer domesticus), which previously exhibited a significantly lower frequency of EPP than mainland populations. Fifty adults from a mainland population with significantly more genetic diversity than the island population (across 17 microsatellite loci) were introduced into the island population, and the incidence of EPP was subsequently monitored over 3 breeding seasons. In the year of the introduction, the incidence of EPP rose to approximately the level seen in mainland populations of house sparrows but dropped to an intermediate frequency in the following 2 years. Unexpectedly, parentage assignment showed that in the year of the introduction, all females producing extrapair offspring were native island birds, as were all the extrapair and cuckolded males. These results suggest that EPP in this experimental population was not driven by females trying to maximize the genetic diversity of their offspring. Key words: extrapair paternity, genetic variation, introduction experiment, island population, Passer domesticus. [Behav Ecol]

Estimation of Avian Population Sizes and Species Richness Across a Boreal Landscape in Alaska

We studied the distribution of birds breeding within five ecological landforms in Yukon-Charley Rivers National Preserve, a 10,194-km2 roadless conservation unit on the Alaska-Canada border in the boreal forest zone. Passerines dominated the avifauna numerically, comprising 97% of individuals surveyed but less than half of the 115 species recorded in the Preserve. We used distance-sampling and discrete-removal models to estimate detection probabilities, densities, and population sizes across the Preserve for 23 species of migrant passerines and five species of resident passerines. Yellow-rumped Warblers (Dendroica coronata) and Dark-eyed Juncos (Junco hyemalis) were the most abundant species, together accounting for 41% of the migrant passerine populations estimated. White-winged Crossbills (Loxia leucoptera), Boreal Chickadees (Poecile hudsonica), and Gray Jays (Perisoreus canadensis) were the most abundant residents. Species richness was greatest in the Floodplain/Terrace landform flanking the Yukon River but densities were highest in the Subalpine landform. Species composition was related to past glacial history and current physiography of the region and differed notably from other areas of the northwestern boreal forest. Point-transect surveys, augmented with auxiliary observations, were well suited to sampling the largely passerine avifauna across this rugged landscape and could be used across the boreal forest region to monitor changes in northern bird distribution and abundance.

The Potential Impact of Disease on the Migratory Structure of a Partially Migratory Passerine Population

Since its introduction into eastern North America in the 1940s, the eastern population of house finches (Carpodacus mexicanus) has become partially migratory, unlike its nonmigratory source population in southern California (Able and Belthoff in Proc. R. Soc. Lond. 265 (1410), 2063-2071, 1998; Belthoff and Gauthreaux in Condor 93, 374-382, 1991). The infectious disease mycoplasmal conjunctivitis (pathogen Mycoplasma gallisepticum or "MG"), which has been monitored in the house finch population since its appearance around 1993 (Dhondt et al. in J. Wild. Dis. 34 (2), 265-280, 1998), may induce higher mortality rates among populations in more northerly latitudes relative to more southerly populations. Here, we investigate the potential impact of this differential disease mortality on the migratory structure of the eastern house finch population using an epidemic modeling approach. Analytical and computational results suggest the ongoing MG epidemic in the eastern house finch could lead to increases in the percentage of and the total number of migrating individuals in a population despite overall population declines, assuming relatively high winter mortality rates in the north eastern part of their range. These results also suggest that empirical evidence of such a change in migratory structure would be most noticeable in northerly inland populations that showed significant declines following the initial outbreak of MG in the east.

Farmland birds and late winter food: does seed supply fail to meet demand?

Poor overwinter survival caused by low food availability represents the most likely mechanism behind the decline, and failure to recover, of many farmland passerine populations. Management to enhance food resources is now in place via agri‐environment schemes (AESs) such as Environmental Stewardship in England, but the measures concerned probably fail to provide a significant seed resource in late winter. Landscape‐scale experimental feeding over six winters was used to investigate the variation in demand for supplementary food from farmland birds between November and March. Quadratic modelling of the temporal variation in (semi‐)weekly bird‐use data from experimental feeding stations showed some evidence of curvilinear changes through the winter for all of the 11 granivorous or omnivorous species considered. For generalists and human‐associated granivores, peak use of supplementary food was found in January or earlier, suggesting that harsh weather is the principal influence. However, peaks occurred in February or later for Yellowhammer, Reed Bunting, Chaffinch and Dunnock, suggesting an effect of ambient food availability. These species depend on seed in farmland in winter and three of them have declined, probably because of reduced survival (rather than poor breeding success). It is likely that current farming practices, including existing agri‐environment prescriptions, do not provide enough food in late winter for such species and that the loss of set‐aside will exacerbate this problem. Revisions of management guidelines and crop content for AES stubble and sacrificial crop prescriptions are needed to ensure late winter seed availability for farmland birds.

Parasite assemblages distinguish populations of a migratory passerine on its breeding grounds

AbstractWe attempted to establish migratory connectivity patterns for American redstarts Setophaga ruticilla between their breeding and wintering grounds by characterizing the composition of their haematozoan parasite assemblages in different parts of their range. We detected significant but limited geographic structuring of haematozoan parasite lineages across the breeding range of the redstart. We found that redstarts from the south‐eastern (SE) region of the breeding range had a significantly different haematozoan parasite assemblage compared with populations sampled throughout the rest of the breeding range. Evidence using stable isotopes from feathers previously demonstrated that redstarts from the SE of the breeding range also have a unique and separate wintering range. Thus, although two methods of estimating migratory connectivity have now both shown the SE US breeding sub‐population of redstarts to be distinct from other populations on both the breeding and wintering grounds, conclusive migratory connectivity for this species as a whole could not be established.

Responses of Songbirds to Magpie Reduction in an Urban Habitat

ABSTRACT Bird communities change in response to urbanization, which poses a challenge for conservationists. We examined the consequences of the recent increase in European cities of black‐billed magpie (Pica pica), which has become the main bird nest predator in many urban parks, yet its impact remains disputed. We tested predator role in the limitation of postfledging and adult numbers of 10 common songbird species. We conducted before‐after, control‐treatment experimental magpie removal in the suburbs near Paris, France, during our 3‐year study. We also compared the productivity and the relative densities between urban and rural habitats for 14 songbirds. We found that magpies had very limited effect on songbird productivity, even for species sensitive to predation by corvids. In addition, impact of the magpie on population levels of passerines would also be minimized because we found no relationship between productivity of prey and their densities. Thus, the recent colonization of urban parks by magpies should not threaten persistence of local songbird populations. Yet, there was evidence that a small number of non‐territorial bird species were attracted to places where magpies were removed. Magpie densities may have modified habitat selection for foraging that might be explained by predator avoidance. But overall, characteristics of urban habitat explain variations of productivity and densities of songbirds better than did magpie predation. In France, conservationists widely use the control of predators, aiming at increasing levels of prey populations. Despite very high densities of magpies in urban parks, we gave evidence that removal of this predator was ineffective to preserve populations of common passerines. This would suggest that the risk induced by the presence of magpies is independent of its density, and conservationists must carefully assess its impact. In the future, we recommend management policies include long‐term monitoring of magpie‐prey interactions during breeding season to detect potential changes in songbird responses to magpie presence.

Weather‐dependent survival: implications of climate change for passerine population processes

Understanding demographic processes will be essential to construct robust models of population responses to climate change. We show that survival is related to the strength of the North Atlantic Oscillation in five out of ten British resident passerine species, and explore the importance of biologically more specific variables (duration of winter frosts and snow periods; occurrence of cold, wet days; spring temperature; and summer drought). The most important variables differed between species in relation to differences in foraging strategy. In almost all cases, first‐year survival was influenced by weather more than was the survival of adult birds. Particularly vulnerable species, such as the Wren Troglodytes troglodytes, may exhibit a 25% reduction in juvenile survival rates due to adverse weather within the range experienced in the last 30 years; variation in survival by 10% or more is commonplace in most species. Thus, climate influences on food availability may provide the mechanism by which populations will alter under changed climatic conditions, though the presence of density dependence may reduce the impact of this on long‐term population trajectories.