Turdus Torquatus Research Articles

Spatio-temporal patterns of earthworm abundance suggest time-limited food availability for a subalpine bird species

Changes in food availability may act as a major mechanism by which global change impacts populations of birds, especially in seasonal environments at high elevations or latitudes. Systematic sampling of invertebrates, which constitute the diet of many bird species during the breeding season, is however largely missing in mountain ecosystems and is overall very rare for soil-dwelling species or stages. Here, we repeatedly sampled earthworms (Lumbricidae), the staple prey of the Ring Ouzel Turdus torquatus, over a whole breeding season in a study area in the Swiss Alps. Our main goal was to finely characterise spatio-temporal patterns of food availability for this declining bird species, in relation to elevation, habitat type and snowmelt stage. In 24 sampling plots, we extracted two soil cores every week for 6–10 weeks and hand-sorted soil invertebrates separately for two 5-cm soil layers. We then analysed the abundance of earthworms in those two layers in relation to various environmental parameters. We show that within our study area, edaphic and topographical parameters are poor predictors of the mean abundance of earthworms over the breeding season. Ground vegetation cover and soil moisture, however, are suitable predictors for the number of earthworms within the soil profile at each sampling time, i.e., of their availability for Ring Ouzels. Moreover, we provide evidence for a clear seasonal peak in earthworm availability, which was more pronounced in open grasslands compared to forested areas and happened later in the season where snow lingered. This study, by improving our understanding of the factors driving food availability for a mountain bird species, provides insights into how shifts in land-use and climate might lead to altered predator-prey interactions.

Variation in Demography and Life-History Strategies Across the Range of a Declining Mountain Bird Species

Species- and population-specific responses to their environment may depend to a large extent on the spatial variation in life-history traits and in demographic processes of local population dynamics. Yet, those parameters and their variability remain largely unknown for many cold-adapted species, which are exposed to particularly rapid rates of environmental change. Here, we compared the demographic traits and dynamics for an emblematic bird species of European mountain ecosystems, the ring ouzel (Turdus torquatus). Using integrated population models fitted in a Bayesian framework, we estimated the survival probability, productivity and immigration of two populations from the Western European Alps, in France (over 11 years) and Switzerland (over 6 years). Juvenile apparent survival was lower and immigration rate higher in the Swiss compared to the French population, with the temporal variation in population growth rate driven by different demographic processes. Yet, when compared to populations in the northwestern part of the range, in Scotland, these two Alpine populations both showed a much lower productivity and higher adult survival, indicating a slower life-history strategy. Our results suggest that demographic characteristics can substantially vary across the discontinuous range of this passerine species, essentially due to contrasted, possibly locally evolved life-history strategies. This study therefore raises the question of whether flexibility in life-history traits is widespread among boreo-alpine species and if it might provide adaptive potential for coping with current environmental change.

Seasonal and daily movement patterns of an alpine passerine suggest high flexibility in relation to environmental conditions

Mountains naturally offer variable habitat conditions, but their biodiversity is currently facing the extra challenge of adapting to rapid environmental shifts that are much more pronounced than in the lowlands. Among adaptive responses, intra‐ and inter‐seasonal movements represent potentially important coping strategies for wildlife that remain largely unexplored. We investigated the seasonal and daily movements of the ring ouzel Turdus torquatus, a European mountain bird species that is declining in many parts of its distribution. We tracked individuals breeding in the Swiss Alps using light‐level geolocators and multi‐sensor loggers. Of the birds traced to their non‐breeding grounds, two‐thirds reached the Atlas Mountains while one‐third stayed in Spain, a region potentially more significant for overwintering than previously thought. The birds remained mostly above 1000 m throughout the annual cycle, highlighting a strict association of ring ouzels with mountain habitats. We also evidenced flexible daily elevational movements, especially upon spring arrival on the breeding grounds in relation to date and snowfall occurrence, suggesting adaptive potential in response to environmental variation. This study shows how modern technology can deliver deeper and valuable insights into movements, behavioural patterns and life‐history strategies for relatively little‐studied animal species. By doing so, it paves the way for refined assessments of species' vulnerability to ongoing global change while providing basic conservation guidance.

The Ring Ouzel: A View from the North York Moors

The Ring Ouzel: A View from the North York Moors

Climate and land‐use change drive habitat loss in a mountain bird species

Mountain areas still feature remnants of traditional land use and consequently constitute a large proportion of the remaining species‐rich habitats in Central Europe. However, their biodiversity is increasingly threatened by changes in climate and land use. The Alpine Ring Ouzel Turdus torquatus alpestris is a typical mountain bird that has recently declined in most of its breeding range. In this study we compared the historical (1986–1987) and recent (2017) distribution of breeding Ring Ouzels in 62 randomly selected 750 × 750 ‐m plots and analysed local colonization and extinction patterns in 558 subunits (= ‘grid cells’) in the southern Black Forest (south‐western Germany). Our study revealed that habitat occupancy has decreased by about one‐third, mainly at lower elevations and in depressed landforms, during the past three decades. Local colonization amounted to 25% and extinction to 66% of the previously vacant or occupied grid cells, respectively. Habitat occupancy and local colonization and extinction were driven by climate and habitat parameters. The Ring Ouzel preferred convex landscape formations such as mountain peaks and ridges with long snow‐cover duration for breeding. Sites with high proportions of deciduous forest and abandoned pasture were avoided. Local colonization was higher at convex landscape formations and by high coniferous forest coverage and forest‐edge length. Local extinction, on the other hand, was lower at convex landscape formations and high‐elevation sites. Our results suggest that shorter persistence of snow fields caused by climate change and degradation of feeding grounds through land‐use abandonment might severely deteriorate food availability for the species, which is likely to have contributed to the observed decline. For conservation of the Alpine Ring Ouzel, we recommend adopting measures to mitigate the negative effects of climate warming and improve habitat quality. The creation of small‐scale mosaics of sparse conifer forests and regularly grazed pastures, especially on north‐ and east‐facing slopes on the lee sides of hills, mountain peaks or ridges, should be supported.

Predictive models of distribution and abundance of a threatened mountain species show that impacts of climate change overrule those of land use change

AbstractAimClimate is often the sole focus of global change research in mountain ecosystems although concomitant changes in land use might represent an equally important threat. As mountain species typically depend on fine‐scale environmental characteristics, integrating land use change in predictive models is crucial to properly assess their vulnerability. Here, we present a modelling framework that aims at providing more comprehensive projections of both species’ distribution and abundance under realistic scenarios of land use and climate change, and at disentangling their relative effects.LocationSwitzerland.MethodsWe used the ring ouzel (Turdus torquatus), a red‐listed and declining mountain bird species, as a study model. Based on standardized monitoring data collected across the whole country, we fitted high‐resolution ensemble species distribution models to predict current occurrence probability, while spatially explicit density estimates were obtained from N‐mixture models. We then tested for the effects of realistic scenarios of land use (land abandonment versus farming intensification) and climate change on future species distribution and abundance.ResultsOccurrence probability was mostly explained by climatic conditions, so that climate change was predicted to have larger impacts on distribution and abundance than any scenarios of land use change. In the mid‐term (2030–2050), predicted effects of environmental change show a high spatial heterogeneity due to regional differences in climate and dominant land use, with farming intensification identified as an important threat locally. In the long term (2080–2100), climate models forecast a marked upward range shift (up to +560 m) and further population decline (up to −35%).Main conclusionsOur innovative approach highlights the spatio‐temporal heterogeneity in the relative effects of different environmental drivers on species distribution and abundance. The proposed framework thus provides a useful tool not only for better assessing species’ vulnerability in the face of global change, but also for identifying key areas for conservation interventions at a meaningful scale.

Nestling diet and parental food provisioning in a declining mountain passerine reveal high sensitivity to climate change

Mountain ecosystems naturally experience strong seasonal weather variations leading to a brief peak in food availability that constrains bird reproduction. Climate change accentuates both the intra‐ and interannual weather variability, which in turn can reduce the predictability of food resources and hence impact population demography. Yet, relatively little is known about the influence of environmental factors on the breeding ecology of mountain birds. Here, we quantified the nestling diet and provisioning behaviour of the Alpine ring ouzel Turdus torquatus alpestris, an emblematic and declining thrush species typical of central European treeline ecotones, and relate these parameters to local weather conditions. Nests were monitored with camcorders to assess prey provisioning frequency and identify items delivered by parents to nestlings, as well as to estimate prey biomass. Our results indicate the prominence of earthworms (Lumbricidae) in the nestling diet, both in terms of abundance (80%) and biomass (90%). Elevated ambient temperatures negatively impacted both prey provisioning rates and biomass delivered to chicks by parents, while rainfall had a positive effect on the delivered biomass. The mean prey item biomass decreased throughout the breeding season, as did the proportion of earthworms in nestlings' diet. These findings highlight the key role played by local weather in parental provisioning behaviour, probably reflecting the low availability of the staple food source, earthworms, in warm and dry weather contexts. In particular, they underpin how climate alterations, notably increasing ambient temperatures and changing precipitation regimes, could impact mountain birds. Although effects on reproductive performance and population dynamics still ought to be studied, these results further our understanding of the ecological mechanisms potentially at play in the decline of wildlife inhabiting high‐elevation, climate‐sensitive ecosystems.

The importance of seasonal environmental factors in the foraging habitat selection of Alpine Ring Ouzels Turdus torquatus alpestris

Species inhabiting mountain ecosystems are expected to be particularly vulnerable to environmental change, yet information on their basic ecology is often lacking. Knowledge from field‐based empirical studies remains essential to refine our understanding of the impact of current habitat alterations and for the consequential development of meaningful conservation management strategies. This study focuses on a poorly investigated and vulnerable mountain bird species in Europe, the Ring Ouzel Turdus torquatus. Our aim was to identify the species’ key ecological requirements during the crucial period of nestling provisioning in the context of environmental change. We radiotracked and observed Alpine Ring Ouzels in a high‐density population, investigating their pattern of foraging habitat selection in 2015 and 2017, and evaluated the transferability of these results over a wider geographical range across the SW Swiss Alps. Foraging birds selected, consistently in space and time, short grass swards (< 10 cm) with interspersed patches of accessible and penetrable soils, at intermediate moisture levels (around 40–65% volumetric water content). In Alpine ecosystems, this microhabitat configuration is typically widespread during the spring snowmelt, but extremely seasonal, with a rapid decrease in its availability over the course of the breeding season. This underlines the high vulnerability of the Ring Ouzel to environmental change: an earlier snowmelt could generate a temporal mismatch between the peak of the breeding effort and optimal foraging conditions; however, abandoning grazing activities on semi‐wooded Alpine pastures may further decrease foraging habitat suitability through taller and denser grass swards, and subsequent woody vegetation encroachment. This study provides a mechanistic appraisal of the challenges Ring Ouzels will face in the future, as well as initial guidelines for targeted habitat management within timberline ecotones.

The status of the Ring Ouzel Turdus torquatus in the UK in 2012

ABSTRACTCapsule: There were up to 6348 Ring Ouzel territories in the UK in 2012.Aims: To produce estimates of the size of the Ring Ouzel breeding population in the UK and its constituent countries.Methods: A stratified random selection of tetrads was surveyed within the known breeding range, except for the remaining breeding areas on Dartmoor and historical sites elsewhere, which were surveyed in their entirety. The methods followed those devised for the first UK-wide survey in 1999, using playback of song at specific points along tetrad transect lines.Results: The UK population estimate in 2012 was 5332 (95% confidence limits (CL), 4096–6875) territories, a non-significant decline of 29% since 1999. There were no significant differences in the population changes in England, Scotland and Wales between the two surveys. An estimation of survey efficiency found that 84% of territories were located by the national survey methods, suggesting that the UK population in 2012 could have been as many as 6348 (95% CL, 4825–8198) territories.Conclusion: The results suggest that the UK Ring Ouzel population has continued to decline since 1999. Ongoing and future research should determine where the main threats to the population are: on the breeding or wintering grounds, or during migration.

Geolocators reveal new insights into Ring Ouzel Turdus torquatus migration routes and non-breeding areas

Capsule The first details of the migration pattern of a male Ring Ouzel Turdus torquatus, fitted with a geolocator on its Scottish breeding grounds, showed that it wintered in the Algerian Atlas Mountains, substantially east of the suspected main wintering area.

Soil pH and organic matter content add explanatory power to Northern LapwingVanellus vanellusdistribution models and suggest soil amendment as a conservation measure on upland farmland

Habitat associations of farmland birds are well studied, yet few have considered relationships between species distribution and soil properties. Charadriiform waders (shorebirds) depend upon penetrable soils, rich in invertebrate prey. Many species, such as the Northern Lapwing Vanellus vanellus, have undergone severe declines across Europe, despite being targeted by agri-environment measures. This study assessed whether there were additive effects of soil variables (depth, pH and organic matter content) in explaining Lapwing distribution, after controlling for known habitat relationships, at 89 farmland sites across Scotland. The addition of these soil variables and their association with elevation improved model fit by 55%, in comparison with models containing only previously established habitat relationships. Lapwing density was greatest at sites at higher elevation, but only those with less peaty and less acidic soil. Lapwing distribution is being constrained between intensively managed lowland farmland with favourable soil conditions and upland sites where lower management intensity favours Lapwings but edaphic conditions limit their distribution. Trials of soil amendments such as liming are needed on higher elevation grassland sites to test whether they could contribute to conservation management for breeding Lapwings and other species of conservation concern that depend upon soil-dwelling invertebrates in grassland soils, such as Eurasian Curlew Numenius arquata, Common Starling Sturnus vulgaris and Ring Ouzel Turdus torquatus. Results from such trials could support improvement and targeting of agri-environment schemes and other conservation measures in upland grassland systems.

Food supplementation does not increase demographic rates in a passerine species of conservation concern

Numerous studies have examined the effects of the provision of supplementary food on aspects of avian reproductive success, but far fewer have gone on to examine the potential positive effects of food supplementation on the demographic rates which are key for population growth rate. Testing for potential effects of food shortage on vital rates is likely to be particularly important in species of high conservation concern, where populations are particularly small, isolated or decreasing rapidly. Here we test the effects of the provision of supplementary food on reproductive success, body condition at fledging and post-fledging survival of ring ouzels (Turdus torquatus), a species of high conservation concern in the UK. However, food supplementation had no detectable effect on any of these parameters. There was no significant difference in return rates of fed and unfed fledglings in the year following hatching, and most post-fledging mortality was apparently caused by predation by raptors and mustelids. We conclude that the supply of invertebrate food sources for nestlings was not a major limiting factor in our study area, at least during this two-year study. Further studies are required to quantify the precise mix of habitats used by ring ouzels, at the appropriate scale, which provide concealment from predators and access to food supplies throughout the spring and summer months.

Newly Discovered Seed Dispersal System of Juniperus cedrus Questions the Pristine Nature of the High Elevation Scrub of El Teide (Tenerife, Canary Islands)

As a working hypothesis, we examined evidence for the former presence of a climacic woodland of Juniperus cedrus above the pine forest in the high elevation area of Tenerife (Canary Islands), which would indicate that the current dominant vegetation (endemic Spartocytisus supranubius scrub) may not be pristine. The main causes of the great regression of this woodland were caused by human activities (timber harvesting, herbivory by goats, and fires). The main support for this hypothesis is the survival of a presumably relict seed dispersal system of the endangered endemic J. cedrus, which relies mainly on the wintering thrush Turdus torquatus. The fact that genetic factors are directly involved in the control of bird migration routes strongly supports the idea that this interaction could be remnant of an older system, probably more widespread in the past. To test this hypothesis, we propose that a paleoecological approach could reconstruct the vegetation dynamics in the Teide National Park (Tenerife) and the past presence of this seed disperser migratory thrush. The analysis of plant microfossils in sediments (e.g., pollen, spores, phytoliths, coprolites, and charcoal) would allow us to evaluate whether the current vegetation is the same as that which naturally existed in the past, and assess the impact of the anthropogenic and natural factors to which it has been subjected during history. The results of these analyses will be useful for future management policies and practices aimed at restoring the pristine landscape and biotic interactions of the Teide National Park. To our knowledge, the case presented in this contribution, based on the high dependence of the seed dispersal of an endemic tree (J. cedrus) on a migratory bird, is the only reported in the context of oceanic islands.

Effects of variation in breeding habitat on Ring Ouzel Turdus torquatus productivity and chick condition

Capsule Territory habitat influenced clutch size and within-brood variability of chick condition in Ring Ouzel Turdus torquatus.Aims To assess the relationship of Ring Ouzel productivity and chick condition with territory habitat, in order to improve understanding of the importance of breeding habitat for population change.Methods Productivity and chick condition were recorded for Ring Ouzel pairs in a small area of upland Scotland and these were related to vegetation and physical characteristics for all breeding territories using General Linear Models.Results We found that clutch size and variability of chick condition varied with Ring Ouzel breeding habitat.Clutch size was related to variation in territory habitat, broadly increasing with territory grass, sedge and rush cover. The best-supported models for within-brood variability of chick condition included fledgling number and territory habitat, with chick condition broadly becoming more variable with territory bracken cover. Relationships between breeding habitat and brood size, fledgling number or mean chick condition were not supported by the data, although statistical power was low.Conclusion Breeding habitat may be a driver of demographic rates of Ring Ouzel, with the effects of poor habitat being passed on indirectly through chick condition. The population-level importance of these effects is unclear, but this study highlights a possible link between recent observed habitat changes and first-year survival, the demographic parameter contributing most to variation in population growth rate in UK Ring Ouzels.

Habitat selection of the Ring Ouzel Turdus torquatus in the Western Carpathians: the role of the landscape mosaic

Capsule The Ring Ouzel in central Europe occurs in a mosaic of mountain forests and open areas. Aims To determine the habitat selection of the Ring Ouzel on a landscape scale in the western Carpathians. It was hypothesized that occurrence of the Ring Ouzel is associated with upper subalpine Carpathian forests and the presence of anthropogenic open habitats. Methods The study compared habitat characteristics of Ring Ouzel breeding areas and randomly selected control plots. Results The Ring Ouzel occurred between 685 and 1316 m asl, preferring middle and upper subalpine Carpathian forests. Significant differences between the Ring Ouzel breeding areas and randomly selected control plots were found for five of the landscape-scale habitat variables: altitude; distance to built-up areas; distance to roads; distance to small mountain meadows; and distance to clear-cut areas. A logistic regression model indicated that the important parameters influencing the occurrence of the Ring Ouzel were altitude and distance to the nearest clear-cut and small mountain meadow. Conclusion The Ring Ouzel preferred higher altitudes and the proximity of clear-cuts, which presumably are a physionomical substitute for the timberline and alpine meadows. However, this species avoids the presence of small mountain meadows, presumably because of succession of a dense layer of vegetation on former mountain pastures. The presence of a cultural landscape in the Carpathians may have allowed the Ring Ouzel to colonize the lower mountain areas.

Postfledging survival, movements, and dispersal of Ring Ouzels (Turdus torquatus)

ABSTRACT. Recent evidence suggests that avian population growth rates may be constrained by low postfledging survival. Therefore, quantifying postfledging mortality and understanding the ecological factors that influence it are fundamental for assessing the relative importance of this life-history stage for population growth and identifying the ecological drivers of population dynamics. We radiotracked 110 juvenile Ring Ouzels (Turdus torquatus), a species of high conservation concern in the United Kingdom, to test hypotheses regarding the timing and causes of postfledging mortality and to quantify the timing and magnitude of local movements and dispersal. Juveniles fledged from early-season broods had higher survival during each 4-day period over 116 days postfledging (0.952 ± 0.011 [SE]) than juveniles fledged from late-season broods (0.837 ± 0.021). Most mortality occurred within the first 3 weeks postfledging, and predation by raptors and mammals was the main apparent cause of mortality, accounting fo...

Seasonal variation in foraging conditions for Ring Ouzels Turdus torquatus in upland habitats and their effects on juvenile habitat selection

Recent studies indicate that variation in juvenile survival may be particularly important in driving avian population dynamics. The quality of habitats available to inexperienced juveniles of migrant species is critical to their survival because they must obtain enough food to build up fat reserves for migration, while avoiding predation. We radiotracked 110 juvenile Ring Ouzels Turdus torquatus, a species of high conservation concern in the UK, to quantify for the first time seasonal patterns in foraging habitat and food abundance during this potentially key life‐history period. Key attributes of foraging plots were compared with those on control plots (representing the broad habitat types selected by foraging juveniles) during 2007–08. Birds foraged on invertebrates in grass‐rich plots during June to mid‐July and then shifted to foraging mainly on moorland berries in higher‐altitude, heather‐rich plots during mid‐July to early‐September. Juveniles selected invertebrate foraging plots with low soil acidity, and increasingly selected plots with high earthworm (an important food) biomass and grass cover, but low grass and all vegetation height as the season progressed. In contrast, earthworm biomass and grass cover remained constant, and grass and all vegetation height increased, on control plots. Juveniles selected berry foraging plots with higher abundance of ripe Bilberries Vaccinium myrtillus and Crowberries Empetrum nigrum than found on control plots. Juvenile Ring Ouzels thus appear to require access to short, grass‐ and invertebrate‐rich habitat during early summer, and taller, heather‐dominated and berry‐rich areas in late summer. The use of two distinct habitat types during the pre‐migratory period illustrates the need for a detailed understanding of the requirements of juvenile birds.

Are Ring Ouzel (Turdus torquatus) populations of the low mountain ranges remnants of a broader distribution in the past?

The Ring Ouzel (Turdus torquatus) has an arctic-alpine distribution, with small populations also occurring at the higher altitudes of the low mountain ranges north of the Alps. The populations of the Alps and mountain ranges are classified as the subspecies T. torqu- atus alpestris, and those of the northern populations as T. torquatus torquatus. Since birds are mobile when, e.g., compared to mammals of the same size, it is likely that the populations in the low mountain ranges originated from dispersal events after the last ice age. We analyzed an mtDNA fragment of Ring Ouzel museum specimens from across Europe. We found a shallow gene tree with little differentiation between the subspecies and therefore incomplete lineage sorting. However, both, subspecies as well as low mountain range populations were characterized by private alleles respectively. Furthermore, when we grouped sequenced specimens according to their origin in an alpine group, a group from the low mountain ranges, and two northern groups, we found significant differentia- tion between the alpine and the low mountain range group, similar to the difference between the alpine and the two northern groups. This suggests an origin of populations on the low mountain ranges similar to that of the arctic-alpine disjunction, and that these populations are remnants of a broader distribution in the past.

Frequency of multiple brooding in Ring Ouzels, including first documented cases of triple brooding

Capsule The majority of female Ring Ouzels made two successful breeding attempts in a single season, but triple brooding was much less common.

Differential seed dispersal systems of endemic junipers in two oceanic Macaronesian archipelagos: the influence of biogeographic and biological characteristics

This article evaluates the seed dispersal systems of two congeneric and endemic fleshy-fruited plants in the context of two relatively close oceanic archipelagos. For this purpose, representative populations of the endangered junipers Juniperus cedrus in the Canary Islands and Madeira, and Juniperus brevifolia in the Azores were studied. Despite both species sharing the same biogeographic region, we set out to test whether different conditions of the islands and biological characteristics of each juniper species determine the distinctive guilds of seed dispersers involved. We assessed the quantitative and qualitative role of the potential frugivores, showing that the wintering Turdus torquatus and the native Turdus merula were the main seed dispersers for J. cedrus and J. brevifolia, respectively (Frequency of occurrence: 74.9%, 80.2%; germination increase with respect to controls: 11.6%, 15.5%; for J. cedrus and J. brevifolia, respectively). The endemic lizard Gallotia galloti was quantitatively outstanding as seed disperser of J. cedrus, although its qualitative effect does not appear to be beneficial. The introduced rabbit Oryctolagus cuniculus acts as a disruptor in both natural seed dispersal systems, as inferred from the high percentage of damaged seeds found in their droppings. Our results indicate that J. cedrus and J. brevifolia are primarily adapted to ornithochory processes, T. torquatus and T. merula being their respective legitimate long-distance dispersers. Although these birds should be playing a key role in the connectivity of fragmented populations, the dependence of J. cedrus on a migrant bird involves a notable fragility of the system.