Status and population trends of Starling Sturnus vulgaris in Great Britain

Capsule Starling populations have declined markedly since 1964, with the greatest declines in pastoral areas in the south and west of Britain.

Aims To establish the size of the Starling population and its recent decline in different habitats and regions.

Methods We use distance-based transect sampling to establish, for the first time, robust estimates of population size in different habitats and regions. We then analyse long-term trend data from two extensive monitoring schemes using generalized additive models to find correlates of the population decline.

Results The mean national breeding population of Starling over the period 1994–2000 was estimated at about 8.5 million birds, with a 95% confidence interval of 8.1–10.8 million. Most Starlings (36%) occur in southern Britain and densities are greatest in suburban habitats. Populations in both suburban areas and the wider countryside declined by over 50% between 1964 and 2000, being greatest in the south and west of Britain and in areas of livestock farming.

Conclusions Changes in pastoral farming practices are likely to account for at least some of the decline in the wider countryside, probably related to changes in food resources, though these are largely unquantified.     

The starvation–predation risk trade-off, body mass and population status in the Common Starling Sturnus vulgaris

It is theoretically and empirically well established that body mass variation in small birds reflects a trade-off between starvation risk and predation risk. This occurs because carrying increased fat reserves reduces starvation risk but also results in a higher predation risk due to reduced escape flight performance and/or the increased foraging exposure needed to maintain a higher body mass. In principle, therefore, the theory of mass-dependent predation risk could be used to understand how a bird perceives and responds to the risks in its environment, because its mass will reflect the predictability of foraging opportunities and predation risk. Mass in birds may then provide a relatively straightforward way of assessing the foraging environment of birds and so the potential conservation problems a species faces. This study tests, for the first time for any species, how body mass changes in response to changing starvation risk, changing predation risk and changing population status. Common Starling Sturnus vulgaris mass varies as predicted by starvation–predation risk trade-off theory: mass is lower when foraging conditions are more favourable and when predation risk is increased. The populations that are declining the most strongly have higher mass, which is most likely indicative of a poor foraging environment, leading to lower relative survival. The results suggest that increased mass in Starlings, and possibly in other species, may provide an indication of the poor quality of the foraging environment and/or rapidly declining populations.     

Seasonal variation in the whistles of the Starling Sturnus vulgaris

Observations of sedentary male Starlings at two sites in Brittany from December 1979 to December 1980 showed that the amount of whistled song varies during the year, principally from March to July during the reproductive season. Whistles are not numerous in summer but increase from September. These results suggest a link between whistled songs and testosterone titers. The different whistle types present different evolutions of their relative frequencies. Some are abundant during the nest building phase, others during the feeding phase. The curves were similar at the two sites for a given theme, showing that each theme constitutes an entity and that the different themes are influenced differently by environmental factors. The significance to the learning process in young birds is discussed.     

Wingtip shape and flight performance in the European Starling Sturnus vulgaris

Although wingform is known to differ among individuals of the same species it is not known how intraspecific variation in wingtip shape is associated with flight performance. In this study, we have examined both among- and within-individual variation in wingtip shape in relation to changes in flight performance in the European Starling Sturnus vulgaris . We found that level flapping-flight speed and the ability to negotiate an aerial obstacle course were unrelated to wingtip shape. However, take-off parameters did vary with wingtip shape; birds with more rounded wingtips tended to take off from the ground at a steeper angle of ascent than those with relatively more pointed wingtips. The same relationships between wingtip morphology and flight were present in both the inter- and intra-individual experimental analyses. The evolutionary importance of this variation in take-off ability is discussed in terms of predator avoidance and enhancement of individual survival.     

Causes and consequences of egg-size variation in the European Starling Sturnus vulgaris

Variations in egg-size (weight, or an index of volume derived from the length and breadth of eggs) were analysed for four years' data from a colony of Starlings in southern England. Variation was much greater among clutches than within clutches. There were no consistent trends for egg-size to increase or decrease through the laying sequence, but the first- and last-laid eggs tended to be smaller than the clutch mean. Loss of single nestlings (perhaps by starvation) was more frequent if the smallest, or last-laid egg was particularly small. Effects of egg-size on the growth of surviving chicks were slight-most variation in development was attributable to factors such as clutch or brood size, and nestlings' relative weights fluctuated so that they continually changed ranks during the nestling period. In Starlings, egg-size was inversely correlated with clutch size, but three open-nesting species (Bullfinch, Song Thrush and Blackbird) showed the opposite pattern. These results are discussed in relation to their implications for understanding the adaptive aspects of egg-size variation.     

Intraspecific variation in reproductive physiology and egg quality in the European Starling Sturnus vulgaris

Egg mass shows large intraspecific variation in birds and is repeatable within individuals. The mechanisms underlying this variation are unknown. We hypothesized that measures of egg quality (the mass of yolk protein, yolk lipid, and albumen protein) would be positively correlated with the plasma pools of the yolk precursor vitellogenin, and the masses of the oviduct, metabolic machinery (liver, heart, lungs, kidneys, gizzard, small intestine and pancreas), and endogenous stores of protein and lipid. We tested these predictions in European Starlings Sturnus vulgaris collected at the peak of egg production effort. In contrast to our predictions, both yolk protein and yolk lipid were negatively correlated with plasma vitellogenin levels. Albumen protein was positively related to oviduct mass, but other aspects of body composition failed to explain variation in egg quality. Hence, while we observed correlations between egg composition and peripheral systems (circulating precursor pools and the oviduct), we found no evidence that egg quality is determined by more general processes, i.e., the supply and processing of nutrients.     

Diet of Starling Sturnus vulgaris nestlings on farmland: the importance of Tipulidae larvae

Capsule?Tipulidae larvae are a key resource for adult Starlings provisioning their young on lowland farmland.

Aims?(i) To describe Starling nestling diet on lowland farmland. (ii) To examine the effects of brood size variation and nestling age on Starling parental food provisioning.

Methods?Over 4 years, we observed parental food provisioning at 42 nests across 4 sites on lowland farmland in Oxfordshire, UK using nestbox video recorders.

Results?Tipulidae larvae were the most frequent prey item recorded in provisioning loads (52%), the next most frequent were winged insects (11%), then Coleoptera larvae (6%), Lepidoptera larvae (5%) and Lumbricidae (5%), with 21% of prey unidentified. Estimates of prey lengths, dry mass and total energy content also confirmed that Tipulidae larvae were the key prey source. Generalized linear mixed-effects models showed that larger broods received fewer Tipulidae larvae per nestling per day and that the proportion of Tipulidae larvae in the diet did not vary with brood size or nestling age.

Conclusion?Our results support the idea that Tipulidae larvae are the primary dietary item for nestling Starlings on lowland farmland.     

Stimulus Familiarity Affects Perceptual Restoration in the European Starling (Sturnus vulgaris)

Background

Humans can easily restore a speech signal that is temporally masked by an interfering sound (e.g., a cough masking parts of a word in a conversation), and listeners have the illusion that the speech continues through the interfering sound. This perceptual restoration for human speech is affected by prior experience. Here we provide evidence for perceptual restoration in complex vocalizations of a songbird that are acquired by vocal learning in a similar way as humans learn their language.

Methodology/Principal Findings

European starlings were trained in a same/different paradigm to report salient differences between successive sounds. The birds'' response latency for discriminating between a stimulus pair is an indicator for the salience of the difference, and these latencies can be used to evaluate perceptual distances using multi-dimensional scaling. For familiar motifs the birds showed a large perceptual distance if discriminating between song motifs that were muted for brief time periods and complete motifs. If the muted periods were filled with noise, the perceptual distance was reduced. For unfamiliar motifs no such difference was observed.

Conclusions/Significance

The results suggest that starlings are able to perceptually restore partly masked sounds and, similarly to humans, rely on prior experience. They may be a suitable model to study the mechanism underlying experience-dependent perceptual restoration.     

Estimation of Unsteady Aerodynamics in the Wake of a Freely Flying European Starling (Sturnus vulgaris)

Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight.     

Influence of habitat and season on foraging flock composition in the European Starling (Sturnus vulgaris)

Summary This study examines the relative importance of habitat and season in determining size and composition of foraging flocks of European Starlings (Sturnus vulgaris). We hypothesized that if season was the principal determinant of flock size, variation across seasons (within habitat) would be greater than variation across habitats (within season). The calendar year was divided into 6 seasons corresponding to major stages in the annual cycle of starlings. After measuring the availibility of 15 foraging habitats occurring within the study area, we drove a 184 km route weekly (over a 17 month period) to census starling flock size, species composition, habitat use, and activity.Although flock size was influenced by both season and habitat, it varied relatively less within seasons (across habitats). Only five of nine seasons showed significant habitat effects, and two (of the five) were significant mainly because of large aggregations in habitats with unusually abundant food (e.g. feedlots, cornfields). In contrast, eight of nine habitats showed significant seasonal effects. The only exception (hay) was little used (<1% of all birds observed). For starlings the activities associated with seasonal events of the annual cycle were a major influence on patterns of social foraging. Habitat factors were less important because of constraints imposed by seasonal factors, but under some conditions (e.g. drought, clumped food supply) they became dominant.     

On the Estimation of Time Dependent Lift of a European Starling (Sturnus vulgaris) during Flapping Flight

We study the role of unsteady lift in the context of flapping wing bird flight. Both aerodynamicists and biologists have attempted to address this subject, yet it seems that the contribution of unsteady lift still holds many open questions. The current study deals with the estimation of unsteady aerodynamic forces on a freely flying bird through analysis of wingbeat kinematics and near wake flow measurements using time resolved particle image velocimetry. The aerodynamic forces are obtained through two approaches, the unsteady thin airfoil theory and using the momentum equation for viscous flows. The unsteady lift is comprised of circulatory and non-circulatory components. Both approaches are presented over the duration of wingbeat cycles. Using long-time sampling data, several wingbeat cycles have been analyzed in order to cover both the downstroke and upstroke phases. It appears that the unsteady lift varies over the wingbeat cycle emphasizing its contribution to the total lift and its role in power estimations. It is suggested that the circulatory lift component cannot assumed to be negligible and should be considered when estimating lift or power of birds in flapping motion.     

Habitat affects escape behaviour and alarm calling in Common Starlings Sturnus vulgaris

Animals should adapt their escape behaviour to both physical and social surroundings in order to maximize their probability of survival. Cover can be both obstructive, reducing the visibility of the surroundings and hindering escape, and protective, providing refuge. We investigated how the provision of cover (long grass) affected (1) the escape behaviour and (2) the alarm call behaviour of Common Starlings Sturnus vulgaris responding to a model hawk during a simulated attack. Starlings always retreated away from the predator and sometimes alarm-called. Their escape trajectory was close to the ground when escaping in long grass, which could be explained by either tall swards hindering take-off or such swards being used as protective cover. On short grass their escape trajectory was much steeper (> 45°). We also investigated the use of alarm calls in Starlings according to predictions arising from the costs and benefits to callers and receivers. Callers could benefit from using alarm calls through dilution or confusion if their use initiates flock departures, thus reducing their probability of being targeted. If there is no cost to the producer of alarm calls we predicted that detectors should call at all times to gain these benefits (i.e. irrespective of grass length), but if their use is costly we predicted that they would be used only when the benefits outstrip the costs. In this case we would predict that alarm calls would be given when other (visual) signals were impaired on long grass but not when they were effective on short grass. Starlings used alarm calls on long grass when visibility was reduced more frequently than on short grass, suggesting that calling has a cost to the producer. The contrasting escape strategies of Starlings in relation to a relatively small (10 cm) change in grass height demonstrates the potential importance of habitat structure in determining predation risk.     

A detailed analysis of primary feather moult in the Common Starling Sturnus vulgaris– new feather mass increases at a constant rate

During moult, the rate that protein can be synthesized and used to grow new feathers must be a critical factor influencing the quality of new plumage. However, the rate that new feather mass accrues during moult has not been assessed in detail. To estimate this, the increase in length of each of the nine primary feathers (P1–P9) in 16 captive Common Starlings Sturnus vulgaris was measured at weekly intervals throughout moult. The rate of increase in length was similar for all primary feathers except P9, which increased more slowly. After completion of moult, these feathers were plucked, accurately measured and weighed. The distribution of mass along the length of each primary was assessed. Using these data, I estimated the rate that mass had increased for each feather during moult. For each individual primary, mass increased at a steady rate until almost fully grown. The rate of increase in mass was least for P1 and greatest for P9. The number of feathers growing concurrently decreased as moult progressed. The net result was that total new primary feather mass increased at a steady rate throughout most of moult (linear regression between start of growth of P2 and end of growth of P8; r ² = 0.991). Retrospective conversion of feather lengths into moult score showed that the increase in score was not linear. It was greatest early in moult and decreased as moult progressed. A scoring system that factors in distribution of mass within and between feathers may provide a more physiologically relevant measure of the progress of moult.     

Song Differentiation and Population Structure: the Example of the Whistled Songs in an Introduced Population of European Starlings Sturnus vulgaris in Australia

Whistled songs of male starlings were studied in Australia and results compared with previous ones in Europe. Starling whistle sonograms can be divided into general classes according to certain criteria. All or most males sing five whistled types (“species-specific” themes), plus other (“individual”) themes. The basic repertoire of species-specific themes is almost the same in Europe and Australia with the same characteristics and similar variation ranges. In both continents each male has a certain number of individual themes, but Australian repertoires tend to be smaller, with two species-specific themes less and fewer individual themes. In all study areas dialects were based on local variations in species-specific theme structure, but the Australian dialectal system is simpler than in Europe. Therefore basic characteristics seem to have been similarly transmitted across generations in both continents. But some of the differences (individual characteristics, repertoire size, frequencies) may stem from different habitat characteristics and also social structure, which could have greatly affected song differentiation.     

From population genetics to population genomics of forest trees: Integrated population genomics approach

Early works by Altukhov and his associates on pine and spruce laid the foundation for Russian population genetic studies on tree species with the use of molecular genetic markers. In recent years, these species have become especially popular as nontraditional eukaryotic models for population and evolutionary genome-wide research. Tree species with large, cross-pollinating native populations, high genetic and phenotypic variation, growing in diverse environments and affected by environmental changes during hundreds of years of their individual development, are an ideal model for studying the molecular genetic basis of adaptation. The great advance in this field is due to the rapid development of population genomics in the last few years. In the broad sense, population genomics is a novel, fast-developing discipline, combining traditional population genetic approaches with the genome-wide level of analysis. Thousands of genes with known function and sometimes known genome-wide localization can be simultaneously studied in many individuals. This opens new prospects for obtaining statistical estimates for a great number of genes and segregating elements. Mating system, gene exchange, reproductive population size, population disequilibrium, interaction among populations, and many other traditional problems of population genetics can be now studied using data on variation in many genes. Moreover, population genome-wide analysis allows one to distinguish factors that affect individual genes, allelles, or nucleotides (such as, for example, natural selection) from factors affecting the entire genome (e.g., demography). This paper presents a brief review of traditional methods of studying genetic variation in forest tree species and introduces a new, integrated population genomics approach. The main stages of the latter are: (1) selection of genes, which are tentatively involved in variation of adaptive traits, by means of a detailed examination of the regulation and the expression of individual genes and genotypes, with subsequent determination of their complete allelic composition by direct nucleotide sequencing; (2) examination of the phenotypic effects of individual alleles by, e.g., association mapping; and (3) determining the frequencies of the selected alleles in natural population for identification of the adaptive variation pattern in the heterogeneous environment. Through decoding the phenotypic effects of individual alleles and identification of adaptive variation patterns at the population level, population genomics in the future will serve as a very helpful, efficient, and economical tool, essential for developing a correct strategy for conserving and increasing forests and other commercially valuable plant and animal species.