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.     

Pheasant release in Great Britain: long-term and large-scale changes in the survival of a managed bird

The release of artificially reared pheasants is a widespread practice in Great Britain, used to increase the number of birds available for hunting. We examined the spatial and temporal patterns of release and shooting between 1960 and 2014 using data from a self-selected sample of 1195 sites. We examined changes in the efficiency of release, the contribution of birds that were not released that year to the numbers shot, and the form of these relationships through time. An annual estimate of the efficiency by which releasing increased the numbers shot was 50% over the period 1960–1990 declining rapidly to 35% by 2005 and reducing more slowly thereafter. There was no obvious regional pattern to this relationship. It has been hypothesised that the efficiency of releasing is lower on sites that release higher densities of pheasants; this study does not support this hypothesis. Annual variation in the density of birds shot in the absence of releasing (1960–1990) was closely correlated with a measure of annual gamebird chick survival. After this date, the relationship was no longer significant, consistent with a decline in wild pheasant stocks and coinciding with the declines in other farmland birds. We highlight increased fox abundance, genetic and behavioural changes arising from the rearing process, and increased shooting in late winter as possible causes for the observed decline in releasing efficiency. We consider the general increase in rearing, habitat changes, increased disease or losses to protected predators as unlikely to have been important causes of the changes in releasing efficiency. Pheasant releasing results in increased numbers for shooting, but has not prevented the wide-scale decline of wild pheasant numbers.     

Analysing Population Numbers of the House Sparrow in the Netherlands With a Matrix Model and Suggestions for Conservation Measures

The House Sparrow (Passer domesticus), formerly a common bird species, has shown a rapid decline in Western Europe over recent decades. In The Netherlands, its decline is apparent from 1990 onwards. Many causes for this decline have been suggested that all decrease the vital rates, i.e. survival and reproduction, but their actual impact remains unknown. Although the House Sparrow has been dominant in The Netherlands, data on life history characteristics for this bird species are scarce: data on reproduction are non-existent, and here we first present survival estimates based on live encounters and dead recoveries of marked individuals over the period 1976–2003, 14 years before and 14 years during the decline, reported to the Dutch Ringing Centre. We show that there is an indication that both juvenile and adult survival are lower during the period of decline. Secondly, to be able to analyse the relative impact of changes in the vital rates, we formulated a general matrix model based on a range of survival values between zero and one with a step size of 0.01 (both juvenile and adult yearly survival) and a range of realistic reproduction values (one, three or five fledglings per pair per year). With the matrix model, we calculated the finite rate of population change (λ) and applied elasticity analysis. To diagnose the cause of the decline in the Dutch House Sparrow, we parameterised the model with estimates of survival values before and during the decline and present the resulting λ. With the survival estimates from the declining period, λ < 1 only if reproduction is relatively low. We discuss this result within the light of available literature data on survival in the House Sparrow. Finally, we evaluate which of the suggested causes of population decline should be reversed to mitigate the decline and how this can be achieved.     

Survival of Gunnison sage‐grouse Centrocercus minimus in Colorado,USA

Gunnison sage‐grouse Centrocercus minimus has declined from their historic range and recent monitoring has provided evidence that some populations are continuing to decline. The evaluation of long‐term, population‐specific survival rates is important to assess population stability, and is necessary for conservation of this species of concern. We evaluated adult and yearling survival in two dynamically different populations of Gunnison sage‐grouse (a relatively large, more stable population and a small, declining population). Our goal was to examine the relationship between annual survival and population, and test hypotheses with regards to temporal effects (across years and within year) and individual effects (sex and age). We also evaluated the effects of snow depth on sage‐grouse survival. We tracked 214 radiomarked birds in the large population from 2005–2010 and 25 birds in the small population from 2007–2010. We found no evidence for a difference in survival between yearlings and adults nor did we find an influence of snow depth on survival. Males had the lowest survival during the lekking season (March–April); females had lower survival during the nesting and chick rearing season (May–July) and late‐summer and fall (August–October). The annual survival rate was 0.61 (SE 0.06) for females and 0.39 (SE 0.08) for males. Survival was constant across years and between the populations suggesting observed population changes during this time period are not a result of changes in adult survival.     

The effect of age and year on the survival of breeding adult Great Skuas Catharacta skua in Shetland

The survival rates of breeding adult Great Skuas Catharacta skua were examined at Foula, the largest colony in the world, where numbers have been declining since the late 1970s. Resightings of colour-ringed breeding adults over a 12-year period were analysed using Cormack-Jolly Seber models to estimate survival rates. Annual survival rates averaged 0.89 but varied among years between 0.82 and 0.93, with annual variations being temporally associated with variations in sandeel abundance during the breeding season. Most birds appeared to die outside the breeding season and so it is possible that nutritional stress and reproductive costs of breeding in years of poor food supply affect survivorship on migration or in the wintering range. Survival rates of adult Great Skuas were affected by their age according to a quadratic equation, with survival increasing significantly with age from 0.73 in 5-year-old-birds to between 0.85 and 0.96 in birds from 7 to 22 years old, with a sharp decline to between 0.75 and 0.87 in birds over 22 years old. Year effects were evident when controlling for age, indicating that annual variations in survival rates are not explained by changes in age-composition of the marked population among years.     

The decline of the Spotted Flycatcher Muscicapa striata in the UK: an integrated population model

The Spotted Flycatcher has become a species of great conservation concern in Europe and the UK following a period of prolonged and accelerating decline. We consider a range of population models for UK census data between 1965 and 1996, along with independent survey data designed to estimate demographic parameters. Population declines are similar in the major habitats and regions of the UK, indicating that a broad-scale factor has influenced the population. Nest record data show that changes in individual nest success are not the cause of the increasing decline. This is more likely the result of a fall in the survival rates of fledged birds prior to the next breeding season; we show by comparison with the recoveries of ringed birds that the most likely cause is an increased mortality rate of birds either shortly after fledging or within the subsequent first year of life.     

The timing of breeding and wing-moult of four African Sturnidae

Wing-moult of the Cape Glossy Starling, Red-winged Starling, Pale-winged Starling and Pied Starling was examined primarily from specimens in southern African museums. Breeding data were obtained from nest record cards.
The Cape Glossy Starling breeds from October to March, with the moult period from December to May. There is no evidence of moult-breeding overlap in individual birds. The Red-winged Starling breeds from September to March, while the moult takes place between November and April, overlapping with the second broods. The Pale-winged Starling breeds from October to April and moults between November and May. The Pied Starling moults between November and April, while breeding varies regionally, occurring concurrently with moulting in some areas.     

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.     

Reduced blood parasite prevalence with age in the Seychelles Warbler: selective mortality or suppression of infection?

Avian malaria can affect survival and reproduction of their hosts. Two patterns commonly observed in birds are that females have a higher prevalence of malaria than do males and that prevalence decreases with age. The mechanisms behind these patterns remain unclear. However, most studies on blood parasite infections are based on cross-sectional analyses of prevalence, ignoring malaria related mortality and individual changes in infection. Here, we analyse both within-individual changes in malaria prevalence and long-term survival consequences of infection in the Seychelles Warbler (Acrocephalus sechellensis). Adults were less likely to be infected than juveniles but, contrary to broad patterns previously reported in birds, females were less likely to be infected than males. We show by screening individual birds in two subsequent years that the decline with age is a result both of individual suppression of infection and selective mortality. Birds that were infected early in life had a lower survival rate compared to uninfected birds, but among those that survived to be screened twice the proportion of infected birds had also decreased. Uninfected birds did not become infected later in life. Males were found to be more infected than females in this species possibly because, unlike most birds, males are the dispersing sex and the cost of dispersal may have to be traded against immunity. Infected males took longer to suppress their infection than did females. We conclude that these infections are indeed costly, and that age-related patterns in blood parasite prevalence are influenced both by suppression and selective mortality.     

Individual condition,but not fledging phenology,carries over to affect post-fledging survival in a Neotropical migratory songbird

Migratory animals face severe time and energy constraints during their annual cycle. These constraints may be exacerbated in young animals by conditions experienced during development that can affect both phenotype and phenology. For young migratory songbirds, the period between fledging and autumn migration, the post-fledging period, is believed to represent a time of intense selective pressure. However, there has yet to be a study that has assessed post-fledging survival for the entirety of the post-fledging period, probably due to the challenge of following juveniles as they move broadly across the landscape (tens to hundreds of kilometres). To overcome this challenge, we used an automated radiotelemetry array spanning 60 000 km² in southern Ontario, Canada, and miniature digital radiotelemetry tags to track 216 juvenile Barn Swallows Hirundo rustica continuously from fledging to migration. We hypothesized that young that fledged in better condition and earlier in the breeding season would have higher survival relative to birds fledging in poorer condition, because they have more energy to deal with resource constraints, and that early-fledging birds would depart on migration earlier than late-fledging birds because there is probably a fixed period of time required post-fledging to prepare for migration. We found that average cumulative apparent survival was 42% and that condition in the nest was a strong positive predictor of post-fledging apparent survival. We also found that birds that fledged earlier in the season departed on migration earlier in the autumn relative to late-fledging birds. Contrary to our prediction, average apparent survival was equal for early- and late-fledging birds. Our results suggest that factors during development that promote better nestling condition are critical for predicting future apparent survival prior to migration. Differences in annual apparent survival between early- and late-fledging songbirds, as commonly observed, may be driven by events occurring at later stages of the annual cycle.     

The survival rate of Australian passerines

The Australian avifauna is composed largely of two groups–the 'old endemics', species that originated in Gondwana and radiated in Australia and New Guinea, and the 'new invaders', species that originated in Asia and invaded Australia during the Pleistocene. In addition, several species were introduced by Europeans during the last 200 years. The old endemics have clutch-sizes significantly smaller than those of the new invaders (Yom-Tov 1987). The aim of this paper was to study the survival rates of Australian passerines from the three groups.
The survival rates of 3 5 species of Australian passerines were calculated by using recapture data provided by the Australian Bird Banding Scheme for birds older than one year. Survival depends primarily on body-mass, with no difference between the old endemics and the new invaders. It is suggested that the survival rates of birds younger than one year is different between the two main groups.
Overall, the survival rates of Australian passerines is at least 1.2 greater than that of equal-sized British passerines. The survival rates of the introduced House Sparrow Passer domesticus and Blackbird Turdus merula were similar on the two continents, suggesting either that insufficient time had elapsed since their introduction to Australia for them to adapt to local conditions, or that the habitats occupied in Australia were so modified by human activities that selection did not favour long lives. The survival rate of the introduced Starling Sturnus vulgaris was lower in Australia, probably because it lives in natural habitats there.     

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.     

Biannual breeding and moult-breeding overlap of the Chestnut-bellied Starling Spreo pulcher

At Kano, Nigeria, the Chestnut-bellied Starling Spreo pulcher has two distinct breeding seasons, a long one from the late dry season to the early rains (February to June) and a short one in September, October and rarely November following the rains. Males have enlarged testes from February to October, so the breeding periods are probably determined by the reproductive condition of the females. Most individuals breed in both periods but some breed only in the pre-rains period. Adult wing-moult begins in March and April, overlapping with any breeding attempts in the latter half of the pre-rains session; some birds continue to moult into the post-rains session. Post-juvenal wing-moult is from August to January for birds reared in the previous pre-rains period and is simultaneous with adult moult for birds reared in the post-rains period. An increase in ambient temperature may be the most important proximate cue determining the pre-rains and also the post-rains breeding periods. A correlation between moult-breeding overlap and co-operative breeding for some tropical birds is suggested and discussed briefly.     

Survival of the African white‐backed vulture Gyps africanus in north‐eastern South Africa

Old World vultures are in decline across their entire range. Although critical for the formulation of effective conservation measures, neither survival nor movement patterns of African vultures are adequately known. This paper presents survival and movement data on the African white‐backed vultures (Gyps africanus) from South Africa. Survival estimates were modelled on resightings of tagged vultures. Birds were captured en masse and resighted between November 2005 and December 2010. A total of 93 adult and subadult birds were fitted with uniquely numbered patagial tags, which were resighted 3707 times(mean of 39.8 resightings per bird). The programme MARK was used to estimate survival. The best model was one where survival and recaptures varied only with time (e.g. year). However, owing to the fading (illegibility) of tags in later years, the relationship with time is probably spurious. The second best model was one where survival and recaptures varied with age and time. Annual survival estimates increased from 85.2% in second‐year birds to 99.9% in adults. This corresponds well with the survival of two other Gyps vultures that have been studied to date and underscores the point that additional mortality of adults in these long‐lived species will result in rapid population declines.     

Impaired flight ability--a cost of reproduction in female blue tits

When prey are attacked by predators, escape ability has an obvious influence on the probability of survival. Laboratory studieshave suggested that flight performance of female birds mightbe affected by egg production. This is the first study of changesin take-off ability, and thus potentially in predation risk,during reproduction in wild birds. We trapped individual maleand female blue tits repeatedly during the breeding season.Females were 14% heavier and flew 20% slower (probably as aconsequence of a lower ratio of flight muscle to body mass)during the egg-laying period than after the eggs had hatched.However, flight muscle size did not change to compensate for changes in body mass over this period. In contrast, males showedno changes in either body mass, muscle size, or flight abilityover the same period. Furthermore, the impairment of flightin females increased with the proportion of the clutch thathad been laid, an effect that was independent of body mass and muscle size. This indicates that egg production causes additional physiological changes in the female body that produce impairedlocomotor performance. We suggest that courtship feeding offemale blue tits by their mates might reduce predation riskduring the period when female take-off ability is impairedby reducing the time females have to spend foraging and thusreducing the time they are exposed to increased predation.     

Characterising demographic contributions to observed population change in a declining migrant bird

Populations of Afro‐Palearctic migrant birds have shown severe declines in recent decades. To identify the causes of these declines, accurate measures of both demographic rates (seasonal productivity, apparent survival, immigration) and environmental parameters will allow conservation and research actions to be targeted effectively. We used detailed observations of marked breeding birds from a ‘stronghold’ population of whinchats Saxicola rubetra in England (stable against the declining European trend) to reveal both on‐site and external mechanisms that contribute to population change. From field data, a population model was developed based on demographic rates from 2011 to 2014. Observed population trends were compared to the predicted population trends to assess model‐accuracy and the influence of outside factors, such as immigration. The sensitivity of the projected population growth rate to relative change in each demographic rate was also explored. Against expectations of high productivity, we identified low seasonal breeding success due to nocturnal predation and low apparent first‐year survival, which led to a projected population growth rate (λ) of 0.818, indicating a declining trend. However, this trend was not reflected in the census counts, suggesting that high immigration was probably responsible for buffering against this decline. Elasticity analysis indicated λ was most sensitive to changes in adult survival but with covariance between demographic rates accounted for, most temporal variation in λ was due to variation in productivity. Our study demonstrates that high quality breeding habitat can buffer against population decline but high immigration and low productivity will expose even such stronghold populations to potential decline or abandonment if either factor is unsustainable. First‐year survival also appeared low, however this result is potentially confounded by high natal dispersal. First‐year survival and/or dispersal remains a significant knowledge gap that potentially undermines local solutions aimed at counteracting low productivity.     

Integrated population monitoring of breeding birds in Britain and Ireland

Effective wildlife monitoring schemes identify changes in population variables that require conservation action. This must be based on an understanding of normal patterns of population variability. Monitoring schemes ideally provide data on the stages of the life cycle at which changes are taking place and indications of the probable causes of change.
The Integrated Population Monitoring Programme of the British Trust for Ornithology aims to fulfil these requirements for British birds. It encompasses existing BTO projects that measure population size, productivity and survival rates, principally the Common Birds Census, Waterways Bird Survey, Nest Record Scheme, Constant Effort (mist-netting) Sites Scheme and the Ringing Scheme. Integrated analyses of long-term BTO data are being used to study the population dynamics of individual species. Relationships established through such analyses will be used to construct models that will predict population performance, and against which observed performance can be compared.
A simple application of Integrated Population Monitoring is presented using data for the Song Thrush ( Turdus philomelos ), a species which has been declining throughout most of Britain since the mid 1970s. No reduction in reproductive performance was detected and the decline appears to have been brought about through reduced survival rates. Factors responsible for much of this decline were identified from a multiple regression model involving winter weather conditions.     

Heavy rainfall increases nestling mortality of an arctic top predator: experimental evidence and long-term trend in peregrine falcons

Although animal population dynamics have often been correlated with fluctuations in precipitation, causal relationships have rarely been demonstrated in wild birds. We combined nest observations with a field experiment to investigate the direct effect of rainfall on survival of peregrine falcon (Falco peregrinus) nestlings in the Canadian Arctic. We then used historical data to evaluate if recent changes in the precipitation regime could explain the long-term decline of falcon annual productivity. Rainfall directly caused more than one-third of the recorded nestling mortalities. Juveniles were especially affected by heavy rainstorms (≥8 mm/day). Nestlings sheltered from rainfall by a nest box had significantly higher survival rates. We found that the increase in the frequency of heavy rain over the last three decades is likely an important factor explaining the recent decline in falcon nestling survival rates, and hence the decrease in annual breeding productivity of the population. Our study is among the first experimental demonstrations of the direct link between rainfall and survival in wild birds, and clearly indicates that top arctic predators can be significantly impacted by changes in precipitation regime.     

Declining winter survival and fitness implications associated with latitudinal distribution in Norwegian Greylag Geese Anser anser

The Norwegian Greylag Goose Anser anser population has been increasing steadily over the past few decades, causing increasing nuisance in terms of agricultural crop damage. This, in combination with the importance of Greylags as a hunting target, has called for demographic estimates for the population to assist in management decisions. To this end, we analysed long-term mark–recapture data using Cormack–Jolly-Seber models embedded in program MARK to obtain survival estimates for the population. No sex-specific difference, or age effect on survival after juveniles had completed their first migration (3 months of age), was evident. Mean first-year survival was reported as 0.485 and annual survival of older birds as 0.700. On a monthly basis, survival in Greylags during summer and winter was very similar over the study period. A significant linear decline in winter survival from 0.909 to 0.807 was, however, apparent during the study period. Over the second half of the study (1994–2002), summer survival was about 3% lower than in the first half (1986–94) but no linear relationship was evident. We found a significant inverse relationship between Greylag survival during summer and latitudinal distribution in Norway. A similar relationship was evident between survival and annual bag numbers. The changes in adult survival observed in this study are likely to have had a substantial impact on the growth rate of the Norwegian Greylag population.     

Climate change affects populations of northern birds in boreal protected areas

Human land-use effects on species populations are minimized in protected areas and population changes can thus be more directly linked with changes in climate. In this study, bird population changes in 96 protected areas in Finland were compared using quantitative bird census data, between two time slices, 1981-1999 and 2000-2009, with the mean time span being 14 years. Bird species were categorized by distribution pattern and migratory strategy. Our results showed that northern bird species had declined by 21 per cent and southern species increased by 29 per cent in boreal protected areas during the study period, alongside a clear rise (0.7-0.8 °C) in mean temperatures. Distribution pattern was the main factor, with migratory strategy interacting in explaining population changes in boreal birds. Migration strategy interacted with distribution pattern so that, among northern birds, densities of both migratory and resident species declined, whereas among southern birds they both increased. The observed decline of northern species and increase in southern species are in line with the predictions of range shifts of these species groups under a warming climate, and suggest that the population dynamics of birds are already changing in natural boreal habitats in association with changing climate.