Reed Warbler Research Articles

Factors Shaping Breeding Phenology in Birds: An Assessment of Two Sympatric Acrocephalus Warblers with Different Life Histories

Timing of reproduction is a critical life-history trait and implies major fitness consequences. Differences in life history strategies can lead to different responses to the same environmental conditions even among closely related species. Investigating the factors affecting the timing of reproduction in closely related and sympatric species may help understanding the relationship between different life history traits and species-specific responses to ecological factors. We investigated the effects of season (photoperiod), local climatic variability and prey abundance on the breeding season of two sympatric insectivorous birds that differ in the timing of reproduction and moult and have different migration strategies: the Moustached Warbler Acrocephalus melanopogon and the Eurasian Reed-warbler Acrocephalus scirpaceus. During a five-year period, breeding phenology was determined by examining bird incubation patches during standardised captures and food availability was assessed by invertebrate sampling. Time, mean temperatures and the abundance of some prey taxa were inter-correlated and all contributed to influence the breeding phenology of both species according to partial least squares regression analysis. Besides some interspecific differences in the effect of environmental factors on the breeding phenology, we found strong similarities between the patterns observed in the two warblers. This suggests that, in spite of interspecific differences in life history, the ecological mechanisms shaping reproduction phenology are similar in the two warblers and the same environmental factors are involved in determining the timing of their reproduction.—Ceresa, F., Belda, E.J., Brambilla, M., Gómez, J., Mompó, C. & Monrós, J.S. (2020). Factors shaping breeding phenology in birds: an assessment of two sympatric Acrocephalus warblers with different life histories. Ardeola, 67: 371-385.

Characterization of the complete mitochondrial genome of Oriental reed warbler, Acrocephalus orientalis (Aves: Passeriformes), and a comparative analysis with other Sylviidae species

The complete mitochondrial genome of the Oriental reed warbler, Acrocephalus orientalis, which belongs to the family Sylviidae was determined. The complete mitochondrial genome has a length of 16,971 bp and consists of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region. A. orientalis has a mitochondrial gene arrangement that is typical of vertebrates. Phylogenetic analysis using mitochondrial genomes of 11 related species revealed that A. orientalis is clustered with Acrocephalus scirpaceus and rooted with the other Sylviidae species. This mitochondrial genome provides an important resource for addressing taxonomic issues and studying molecular evolution.

No evidence for the use of magnetic declination for migratory navigation in two songbird species

Determining the East-West position was a classical problem in human sea navigation until accurate clocks were manufactured and sailors were able to measure the difference between local time and a fixed reference to determine longitude. Experienced night-migratory songbirds can correct for East-West physical and virtual magnetic displacements to unknown locations. Migratory birds do not appear to possess a time-different clock sense; therefore, they must solve the longitude problem in a different way. We showed earlier that experienced adult (but not juvenile) Eurasian reed warblers (Acrocephalus scirpaceus) can use magnetic declination (the difference in direction between geographic and magnetic North) to solve this problem when they were virtually displaced from Rybachy on the eastern Baltic coast to Scotland. In this study, we aimed to test how general this effect was. Adult and juvenile European robins (Erithacus rubecula) and adult garden warblers (Sylvia borin) under the same experimental conditions did not respond to this virtual magnetic displacement, suggesting significant variation in how navigational maps are organised in different songbird migrants.

Nestlings of the common cuckoo do not mimic begging calls of two closely related Acrocephalus hosts

Nestlings of the obligate brood-parasitic common cuckoo, Cuculus canorus, use diverse signals to manipulate host parents into feeding them. Begging calls, one of the most prominent parent–offspring communication signals, have been suggested to differ between cuckoos parasitizing different host species but the call characteristics involved differ between studies. We studied nestling begging calls of the cuckoo and two closely related cuckoo hosts breeding in sympatry, the great reed warbler, Acrocephalus arundinaceus, and the reed warbler, Acrocephalus scirpaceus, to determine whether cuckoo nestlings adjust their begging calls according to the host species and if these calls vary with cuckoo age and sex. We found that begging calls of host nestlings differed markedly between species but there was no difference in the begging calls of cuckoo nestlings raised by great reed warblers and those raised by reed warblers. These results suggest that cuckoo nestlings do not adjust begging vocalizations to match host species but rather use general begging call features to solicit food. However, their call frequency band narrowed, syllable duration shortened and call rate tended to increase with increasing age. None of the begging call characteristics differed between the sexes. The rapid development of cuckoo begging call parameters during ontogeny suggests that any comparisons of begging calls of cuckoo nestlings raised by different host species must control for nestling age. Finally, some discordant conclusions of this and other studies emphasize how little we understand parasite–host communication.

The complete mitochondrial genome sequence of Alcippe ruficapilla (Passeriformes: Timaliidae) and phylogenetic position

In this work, we first reported the complete mitochondrial genome (mitogenome) sequence of Alcippe ruficapilla by next-generation sequencing (NGS). The complete mitogenome of A. ruficapilla was 16,941 bp in length and contained the typical structure of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes (tRNAs) and 2 no-coding control regions (D-loop). Nucleotide composition of the whole mitogenome was 29.2% A, 24.2% T, 31.87% C, and 14.8% G, respectively. Phylogenetic analysis indicated that Alcippe ruficapilla gathered into a single branch with Montifrigilla henrici and Acrocephalus scirpaceus with strong support.

First record of Common Blackbird Turdus merula nests built in a reedbed

ABSTRACT In May 2020, during our study on the breeding ecology of the Eurasian Reed Warbler Acrocephalus scirpaceus, we found two nests of Common Blackbird built within an unmanaged reedbed. The distance between the nests and dry land, overgrown by deciduous forest, was about 25 m. One of the nesting attempts was successful while the second was deserted during the incubation stage. To our knowledge this is the first record of Blackbirds nesting in reeds. This observation supports the notion of great flexibility of nest-site selection in this species. We conclude that Blackbirds use reedbeds as a nesting site more often, but such nests may be easily overlooked.

Bird ringing and nest recording in Britain and Ireland in 2018

ABSTRACT This is the 82nd annual report of the British Trust for Ornithology’s Ringing Scheme, incorporating the report of the Nest Record Scheme and covering work carried out and data processed in 2018. We reviewed the literature on tracking devices to assess the impact of their use on individual birds. More than 3400 studies were identified, the first dating back to the early 1960s. The ecological questions being studied varied, with migration being the most common study subject. The frequency of effects was significantly related to attachment type and the likelihood of adverse effects was related to device weight. The proportion of studies reporting adverse effects has declined over time and the research highlighted the need for systematic documentation of potential effects. NRS and CES data were used in a collaborative study which investigated mismatches between the timing of breeding for 21 British songbirds and the availability of food for their chicks. Results indicate that birds did breed later in warmer springs relative to the timing of spring; however, this did not have a significant impact on long-term breeding success. In 2018, 135 CE sites submitted data. Long-term (1984–2017) declines in abundance were observed in six migrant, one partial migrant and three resident species while long-term increases in abundance continue to be recorded in two short-distance migrants and four resident species. Seven species are exhibiting significant long-term declines in productivity; only two species, Reed Warbler Acrocephalus scirpaceus and Chaffinch Fringilla coelebs, are exhibiting a significant long-term increase in productivity. Long-term trends in survival indicate increases for 12 species and declines for eight. Compared to the five-year mean (2013–17), the abundance of 14 species decreased significantly in 2018 with five species being recorded in lower numbers than in any previous year since CES monitoring began. No significant increases in abundance were recorded. Productivity increased significantly for six migrant and four resident species in 2018 and decreased for only two species (both residents). Significant declines in survival rates were observed in 10 species in 2018 compared to the five-year mean. The number of Retrapping Adults for Survival submissions fell slightly in 2018 to 190; eight projects ran for the first time. In total, 58 species were monitored, with Pied Flycatcher Ficedula hypoleuca (23 projects), House Sparrow Passer domesticus (18), Starling Sturnus vulgaris (17), Sand Martin Riparia riparia (13) and Reed Warbler (10) the most-studied species. A total of 982 858 birds were ringed during the year, comprising 170 619 nestlings, 465 610 first-year birds, 319 955 adults (birds in their second calendar year or older) and 26 674 birds whose age could not be determined. In addition, there were 236 314 recaptures of ringed birds at or near the ringing site. In total, 54 324 recoveries (birds found dead, recaptured or resighted at least 5 km from the place of ringing) of BTO-ringed birds were reported in 2018. The Appendix highlights a selection of recoveries that have extended our knowledge of movements, as well as longevity records established during the year. A total of 38 269 NRS submissions were received in 2018, the lowest total since 2009. Mean laying dates for four species were significantly earlier than the five-year mean (2013–17) with eight of the 52 species analysed laying significantly later. Eight species displayed a significant increase in breeding success (fledglings per breeding attempt) in 2018 compared to the five-year mean, with one decreasing significantly. Permits or licences to disturb breeding birds on Schedule 1 of the Wildlife and Countryside Act 1981 (as amended), were prepared and issued to 502 ringers and nest recorders in 2018. During 2018, the use of special methods was authorised for 557 marking projects, 66 trapping projects and 52 sampling projects.

Autumn migration strategy of juvenile great reed warblers Acrocephalus arundinaceus on the eastern European flyway: a spatiotemporal pattern of accumulation and utilisation of energy stores

The great reed warbler Acrocephalus arundinaceus is a common migrant through the Western Palearctic. However, its migration strategy, especially the spatiotemporal pattern of accumulation and utilisation of energy stores en route, is poorly known. Using ringing data collected at distant stopover sites located from Central Europe to Asia Minor, we observed that pattern in juvenile great reed warblers migrating along the eastern European flyway in autumn. We analysed body condition and stopover duration and estimated potential flight ranges for this species, taking into account two large ecological barriers – the Mediterranean Sea and the Sahara Desert – which it crosses during its southward migration. In Central and South-Eastern Europe the seasonal trends in body condition were similar and non-linear, with low values in August (i.e., during intensive migration of Acrocephalidae), and then a significant increase from the beginning of September until the end of the month. Estimated potential flight ranges showed that individuals migrating through Central and South-Eastern Europe might generally reach only the northern coast of the Mediterranean Sea. On the other hand, those flying from Asia Minor were able to reach the northern edge of the Sahel zone, crossing two large ecological barriers without refuelling. Therefore, it seems that great reed warblers change their autumn strategy en route: first, they migrate in short steps with low energy reserves through continental Europe; and then, after intensive refuelling before the Mediterranean Sea, they reach sub-Saharan Africa in a long flight. Based on the analysis of ringing data from several stopover sites, we show the complex pattern of how a long-distance migratory species accumulates and utilises its energy stores en route.

Wing-size related habitat choice of Great Reed Warbler females: the role of habitat quality and management

Wing-size related habitat choice of Great Reed Warbler females: the role of habitat quality and management

Orientation of Trans-Saharan Passerine Migrants in Southwestern Spain – Revisited

Abstract At the end of the 1980s, a relatively large data set was collected from orientation cage tests of nocturnal migrants caught in one locality in south-western Spain. It was published in The Auk in 1989. At the time of publication, the use of orientation cages was a major advance in detailed studies on passerine migration patterns. The basic evaluation procedure was to calculate the average vector of all numbers representing bird activity in a number of sectors of the full wind-rose and to use the Rayleigh test to determine the statistical significance of the distribution. However, due to hidden assumptions in the procedure used at that time, the resulting heading patterns could be called into question in light of further methodological development. The paper revisits the original set of orientation data collected in the last century in the reported study. The new results from the multimodal distribution accepting procedure are compared with the older pictures and are found to be much better at explaining the migration pattern there. In particular, the Garden Warbler and Reed Warbler, which were claimed to be ‘disoriented’, now show acceptable directionality patterns which do not differ in shape from those of other species.

Host alarm calls attract the unwanted attention of the brood parasitic common cuckoo

It is well known that avian brood parasites lay their eggs in the nests of other bird species, called hosts. It remains less clear, however, just how parasites are able to recognize their hosts and identify the exact location of the appropriate nests to lay their eggs in. While previous studies attributed high importance to visual signals in finding the hosts’ nests (e.g. nest building activity or the distance and direct sight of the nest from vantage points used by the brood parasites), the role of host acoustic signals during the nest searching stage has been largely neglected. We present experimental evidence that both female and male common cuckoos Cuculus canorus pay attention to their host’s, the great reed warbler’s Acrocephalus arundinaceus alarm calls, relative to the calls of an unparasitized species used as controls. Parallel to this, we found no difference between the visibility of parasitized and unparasitized nests during drone flights, but great reed warblers that alarmed more frequently experienced higher rates of parasitism. We conclude that alarm calls might be advantageous for the hosts when used against enemies or for alerting conspecifics, but can act in a detrimental manner by providing important nest location cues for eavesdropping brood parasites. Our results suggest that host alarm calls may constitute a suitable trait on which cuckoo nestlings can imprint on to recognize their primary host species later in life. Our study contributes to the growing body of knowledge regarding the context-dependency of animal signals, by providing a novel example of a beneficial acoustic trait intercepted by a heterospecific and used against the emitter.

Departure Decisions of a Migratory Passerine, the Common Reed-Warbler Acrocephalus scirpaceus, in Relation to Fuel Load and Geographical Barrier Proximity

Research on the stopover ecology of migrant birds has examined the role of multiple factors, both intrinsic and extrinsic, on departure decisions. However, a single factor may influence stopover decisions differentially, depending on the relative geographic location of a stopover site within the flyway and the expectation of ecological challenges ahead. For instance, actual fuel load may have a decisive influence on departure decisions before a crossing of major geographical barriers, such as seas or deserts, but may be less important when crossing vast continental areas offering plenty of opportunities to refuel. The aim here was to test whether the relative influence of fuel load on departure decisions of the Common Reed-warbler Acrocephalus scirpaceus, a long-distance migrant songbird, varies in relation to proximity to a geographical barrier: the sea expanse between Iberia and Africa. We expected that departure from southern Iberian stopover sites would be highly influenced by fuel load, since migrants would not fly to Africa until they had sufficient fuel to cross the sea. We used Cormack-Jolly-Seber (CJS) models to test for the effect of fuel load on emigration (departure) probability from a number of stopover sites situated in northern and southern Iberia during the autumn migration period. Reed-warblers stopping over for longer than one day were more likely to depart if they were in northern Iberia than in southern sites. Moreover, large fuel loads promoted emigration from stopover sites in northern, but not in southern, Iberia. Therefore, we found no evidence supporting the hypothesis that Reed-warblers wait until they acquire large fuel loads before leaving their stopover sites near the edge of the barrier. This study shows that the same parameters may not act in the same way along migration route, in particular in relation to geographical barrier proximity.—Andueza, M., Barba, E., Cuenca, D., Laso, M., Unamuno, E., Unanue, A.,Valkenburg, T., Genovart, M. & Arizaga, J. (2020). Departure decisions of a migratory passerine, the Common Reed-warbler Acrocephalus scirpaceus, in relation to fuel load and geographical barrier proximity.

Testing for the effect of meteorological conditions on transient dynamics of a reed warbler Acrocephalus scirpaceus population breeding in northern Iberia

Transients can have a severe impact on demographic parameter estimates. For instance, the use of visual counts or number of captures at a ringing station to assess indices of abundance may result in biased over-estimates due to the presence of transients. With the aim of contributing to understand transient dynamics within the Eurasian breeding passerines, we used data collected at a ringing station (2010–2018) in a reed bed area of northern Spain designed to sample breeding reed warblers Acrocephalus scirpaceus. Specifically, we tested for the effect of season on the proportion of transients and explored for correlations of rainfall regimens at both the winter and breeding quarters on annual fluctuations of the proportion of transients. The proportion of transients was not constant across the season; it showed relatively small values until mid-June, coinciding with arrivals from Africa and the peak of the breeding period, and then increased very steeply (means > 60%) already in July, with even ca. 90% of transients captured during the second half of July, coinciding with an influx of birds that would be already passing through the area en route to winter quarters in Africa. Analyses to estimate population trends of breeding reed warblers should take this circumstance into account; otherwise, models may show odd patterns, due to a mixture of local and non-local population that might show dissimilar demographic trends. Limiting data analyses to the breeding sub-period having a lesser amount of transients is recommended. Annual fluctuations in the proportion of transients did not correlate with any of the rainfall values in Africa (winter quarters) or meteorological conditions in Europe (NAO index; rainfall values at a local level), though it might be that we did not choose the appropriate variable/period/location combination. Our data set was relatively small; hence, this may hamper us to detect weak linear trends. Future research should contribute to answer this question and deep into the factors driving transience dynamics in bird populations.

No Evidence for an Effect of Vegetation Productivity on the Structure and Diversity of a Reed-Bed Associated Passerine Assemblage during Autumn Migration

The structure of a species assemblage at given sites constitutes a key ecological parameter to understand the dynamics of bird assemblages. The aim of this paper is to (1) quantify how variable is a passerine assemblage associated with an inter-tidal reedbed area at a main stopover site in the Atlantic flyway in northern Iberia and to explore potential factors explaining the variation, with emphasis on the vegetation productivity, and (2) to test whether inter-annual fluctuations reflect possible demographic trends. Migratory birds, especially those species which show high flexibility to stop over in some places or others using an opportunistic strategy, should be expected to land in larger numbers and stay for longer periods at given stopover sites in years with higher vegetation productivity, thus with a higher amount of insect prey, since this would permit achieving higher fuel deposition rates. We used ringing data collected at Txingudi marshlands during the autumn migration of 2007–2016. The assemblage had a relatively simple structure, because few species dominated in number over the rest. Reed Warblers Acrocephalus scirpaceus dominated the assemblage in nine out of ten study years, supporting the importance of the site for the species. As compared with the other two most abundant passerines (the Sedge and Willow Warblers, A. schoenobaenus and Phylloscopus trochilus, respectively), the ratio between these three warblers varied from year to year, with the Willow Warblers having much higher annual fluctuations than the other two species. This is likely linked to an opportunistic exploitation of the reed bed by this species, but we did not find significant effect of vegetation productivity (quantified by Normalized Difference Vegetation Index, NDVI) on the structure and diversity of the bird assemblage. Annual fluctuations in species' contribution to the assemblage did not vary linearly, except for the Bluethroat Luscinia svecica. Only for Bluethroats the proportion of captures and the mean number of captures declined from year to year. The structure and diversity of the assemblage did not seem to be affected by local conditions hence factors working at larger spatial scales or at the origin region of the migrants captured at Txingudi apparently may be more relevant at explaining the structural traits of the assemblage.

Anosmic migrating songbirds demonstrate a compensatory response following long-distance translocation: a radio-tracking study

A number of studies have shown that migrating birds can navigate to their destinations even when displaced to unfamiliar territory. It has been demonstrated that adult Eurasian Reed Warblers (Acrocephalus scirpaceus) captured in spring in the Eastern Baltic, displaced 1000 km eastward to the Moscow region and tested in orientation cages, show a clear orientation tendency towards their breeding grounds. This response requires the ability to determine a new geographic position relative to the goal. The natural cues that are used as coordinates for this behaviour remain controversial. Among other natural cues, both magnetic and olfactory sources of information have received the most experimental attention. More recently, virtual displacement experiments have shown that the geomagnetic information alone is sufficient for Reed Warblers to find their geographic position. However, the role of olfaction was not explicitly examined. In the present study, we displaced anosmic Reed Warblers together with untreated controls between the same capture and displacement sites where the Emlen funnel tests were previously performed. Following release, we radio-tracked birds for the first few kilometres using an array of automated radio-tracking towers. The results strongly suggest a navigational response of both anosmic and intact birds (anticlockwise re-orientation), unlike some other experiments showing impaired navigational abilities of anosmic migrating birds. This data supports the hypothesis that, at least in this songbird species, the olfactory system is not crucial for determining geographic position, and that the zinc sulfate anosmia treatment is unlikely to have any non-specific effects on navigational abilities.

Effects of extreme habitat loss on a local population of Reed Warblers Acrocephalus scirpaceus

ABSTRACT Total habitat loss might lead to local extinction of populations, whereas habitat loss that is extreme but partial leaves some chance for their survival. Einot Gibton, a small nature reserve in Israel, has gone through a major structural change, involving the uprooting of much of its reedbed. In an attempt to maintain the local breeding population of Reed Warblers Acrocephalus scirpaceus in the reserve, conservationists retained 10% of the original 7.55 ha of reedbed habitat in the outskirts of the reserve. The Reed Warbler population was monitored in the year before and in the three years following the structural change, to investigate how a local bird population adapts to extreme reduction of its breeding habitat. Management operations occurred mainly while the Reed Warblers were wintering in Africa. After returning in spring their density in the remnant fragments of reedbed was six times higher than before the structural changes. Despite a 47% decline in their breeding success in the first breeding season after the work, site fidelity remained high. The 75% recovery of their habitat three years after its destruction was accompanied by recovery of their breeding success. Faced with planned, accidental or natural loss of habitat, conservationists should try to ensure that parts of the habitat persist, to maintain local populations.

Wintering areas on the move in the face of warmer winters

For several decades, there have been changes in the distance of bird migration. The Eurasian Reed Warbler Acrocephalus scirpaceus is a Trans-Saharan migratory species, which, as recent records suggest, is increasingly wintering in the Iberian Peninsula. This study investigated the strength of the influence of climate on the wintering of this insectivorous species in the Iberian Peninsula, and also used geospatial modelling to identify the most favourable areas. The model was constructed to identify the most relevant explanatory factors of this distribution and it was assessed by applying calibration and discrimination criteria, and the influence of each factor was analysed using variation partitioning. The minimum winter temperature is the most relevant factor affecting sites suitable for the wintering of this species in Europe.

Unusual Nests in the Great Reed Warbler Acrocephalus arundinaceus: Reuse of Nests in the Same Season and Unusual Forms of Nest Construction

Although previous studies have reported on rare nesting behaviour such as nest reuse and/or unusual nest construction in open nesting passerines, very little is known about these rare phenomena. We found and monitored 1224 Great Reed Warbler nests between 2008 and 2017. In three nests, we found reuse of nests in the same season; two nests were reused after a Cuckoo chick had disappeared and one nest was reused after a damaged egg had been ejected. In two other nests, we observed that replacement nests were built directly under the original nest, using the same reed stems. These observations suggest that there may be cases when breeding Great Reed Warblers benefit from performing unusual yet adaptive behaviour, such as conserving energy and time when nests are reused, or recognizing the advantages of original nests, e.g. they may serve as cover and/or concealment.

Confirmation of Acrocephalus scirpaceus avicenniae (Aves: Acrocephalidae) from mangroves on the Red Sea coast near Jazan, southwest Saudi Arabia

Members of the Eurasian (or Common) Reed Warbler complex, Acrocephalus scirpaceus, are widespread across much of Europe, Africa, the Middle East and Central Asia. With its relatively complex taxonomy, the identity of several local (and sometimes remote) populations remains somewhat unresolved. In Saudi Arabia, populations of reed warblers were first identified in mangroves at Yanbu’ on the Red Sea coast in 1984, with several subsequent records up to 900 km further south toward the Yemen border. We took morphological data from 51 individuals and genetic material from three individuals captured near Jazan in southwest Saudi Arabia. Both genetic and morphometric data confirmed that these birds belong to the taxon A. scirpaceus avicenniae, sometimes referred to as the Mangrove or Red Sea Reed Warbler.

Reed warblers in the Marquesas Islands: song divergence and plumage convergence of two distinct lineages

ABSTRACTThe Pacific Ocean is the site of the most important diversification of insular reed warblers (Acrocephalus). In the Marquesas Islands (Eastern Polynesia), reed warblers belong to two distinct lineages that have reached the archipelago independently. We used mitochondrial sequences and microsatellite markers and found evidence of gene flow between the two lineages. One island in particular, Nuku Hiva, seems to act as the main contact zone between the two taxa. We then used reflectance spectrometry to evaluate the variation of carotenoid colouration among all populations. Marquesan reed warblers exhibit convergent evolution in carotenoid-based plumage colouration, but variation among islands was important. Having two different phylogenetic origins, the two lineages acquired their yellow colour independently and there is stochastic variation in plumage among islands. Finally, we analysed the songs of reed warblers from the main islands. Multifactorial analysis showed that vocalisations of Marquesan reed warblers differ slightly between species, significant differences between islands leading to different dialects. Vocal characteristics may act as the main pre-zygotic barriers when birds from different lineages come into contact. This study provides another example of convergence in plumage evolution in insular bird species. Furthermore, it highlights the importance of integrative analyses, using both genetic and phenotypical characters, for the study of the evolutionary history of the Pacific Ocean avifauna.