Aquatic Warbler Research Articles

Agonistic song rate positively correlates with male breeding success and avian malaria infection in Acrocephalus paludicola (Aquatic Warbler), a promiscuous songbird with female-only parental care

Abstract The link between male song and reproductive success has been explored at length in socially monogamous birds, but results were inconsistent and under-represented socially non-monogamous species with uniparental care. Here, we evaluated whether metrics of male song in Acrocephalus paludicola (Aquatic Warbler), a promiscuous songbird with female-only care and large repertoires, are associated with fitness- and quality-related traits. We showed that the number of 9-day-old nestlings fathered and probability of avian malaria infection increased with the rate of agonistic song, produced in male–male interactions, and that male-scaled mass index (proxy for energy reserves) positively correlated with the repertoire size. The male breeding success was not explained by repertoire size and song duty cycle. None of the song variables clearly explained the male return rate or change in the tarsus length (proxy for structural body size) and scaled mass index of the fathered chicks between days 2 and 9 post-hatch. No other relationships between the song characteristics and the inbreeding coefficient, scaled mass index, wing-length and Trypanosoma infection status of the males were supported, and Plasmodium infection was unrelated to the song duty cycle and repertoire size. We conclude that in male A. paludicola the repertoire size could be a signal of early developmental stress or current body condition, and the agonistic song rate could be shaped by sexual selection and signal to females a genetic makeup that enhances survival upon infection by Plasmodium.

Low genetic diversity and high gene flow in the Aquatic Warbler (Acrocephalus paludicola), a threatened marshland songbird with a fragmented breeding range

Breeding habitat loss and depletion of genetic diversity can have critically negative impacts on species, and especially so for habitat specialists. The Aquatic Warbler Acrocephalus paludicola is a threatened European songbird that breeds in fens, which have been lost and fragmented over centuries. We used microsatellite loci to perform a spatial and longitudinal comparison, comparing samples collected recently (contemporary) with those obtained about two decades earlier (historical) from c. 25% of the breeding range (Biebrza and Polesie) of the Aquatic Warbler. With these data we explored changes in genetic diversity, expansions and reductions of population size, population structure, and gene flow. Allelic richness, expected heterozygosity, the number of effective and private alleles, and effective population size (NE ≈ 200) were low and comparable across time and space. We detected a genetic bottleneck in contemporary Biebrza, and a less certain bottleneck in both historical and contemporary Polesie. Across space, Biebrza and Polesie were not genetically differentiated in either period. All the historical samples clustered together, but in the contemporary samples a small part of Polesie clustered separately (FST = 0.011). Across time, Biebrza and Polesie showed low but significant differentiation (FST = 0.026–0.064), and historical and contemporary groups clustered apart. A principal coordinate analysis on genetic distance detected three groups, which spanned sampling locations. In the temporal comparison, the contemporary group and contemporary Biebrza had elevated mean within‐group pairwise relatedness. We did not recover signals for sex‐biased dispersal, asymmetric gene flow or isolation‐by‐distance using the molecular data. Our results suggest that the studied populations show: (1) impoverished genetic diversity, (2) a change in allele frequencies over the two decades studied and (3) high gene flow between distant breeding sites, implying high resilience to habitat fragmentation that should facilitate the success of recolonising restored habitat patches by Aquatic Warblers.

Male song of the Aquatic Warbler, a promiscuous bird without paternal care, is more complex than previously thought

The Aquatic Warbler Acrocephalus paludicola is one of the rarest European passerines and is characterised by promiscuity, lack of pair-bonds and female-only parental care. This makes the species an important model for studying the function of avian courtship song. The song of the Aquatic Warbler consists of whistle and rattle phrases produced as discontinuous A-, B- and C-songs, which are built by a single rattle, a rattle and a whistle, and more than two phrases of both kinds, respectively. The A- and B-songs are thought to be aggressive signals in male-male interactions, while C-songs are thought to be important for female choice. Here, we analysed recordings of 40 individually marked males, and determined the phrase repertoire. The enumerated repertoire (males recorded for ≥ 10 min) ranged from 16 to 158 (mean 99), however, it did not capture the complete phrase repertoires. We then used models from species diversity ecology to estimate the actual phrase repertoire size, which ranged between 18 and 300 phrases (mean 155). The estimated repertoire was predicted by the number of C-songs. The rattle repertoire was larger than the whistle repertoire, and both positively correlated with the number of C-songs. Our study indicates that male Aquatic Warblers have highly complex phrase repertoires that vary widely in size. Their courtship song is flexible and efficient, enabling relative song complexity to be demonstrated in a short sample, thus facilitating both female attraction through the quick presentation of large phrase repertoires and rival deterrence through the production of many short and simple A- and B-songs.

Large fire initially reduces bird diversity in Poland’s largest wetland biodiversity hotspot

Freshwater wetlands are widely recognized as biodiversity hotspots for many organisms, including birds. Climate change and the projected increased risk of wetland fires may pose a major threat to wetland biodiversity in the future. There is urgent need to assess short- and long-term effect of fires on avian biodiversity and to establish relevant management implications. We analysed the short-term (first 3 months after fire) effect of a large (5 500 ha) spring wildfire on the community of breeding marshland birds in the best-preserved Polish local wetland biodiversity hotspot: Biebrza Valley. We compared the avian community structure and abundance of certain species before and after the fire on the 18 permanent transects located in both burned and unburned habitats. Within first breeding season post fire, fire significantly reduced pooled abundance and species richness of the whole bird community. Three bird species of special conservation concern (including aquatic warbler) temporarily disappeared from burned areas, and the numbers of 11 other species declined. In contrast, only 3 species benefited from the fire, none of which depended on marshes as their primary habitat. Although the reported strong initial fire effect is likely to fade away in subsequent years, its immediate detrimental effects on marshland birds should not be underestimated. We conclude that it is essential to temporarily provide the unburned adjacent refuge areas with additional protection and bird-friendly management and to focus on preventing further degradation of marshes to increase their resilience to fire.

Breeding Ecology of Aquatic Warblers Acrocephalus paludicola in their Key Habitats in SW Belarus

The breeding ecology of the Aquatic Warbler was studied on the three largest mires in Belarus in 1998–2004. Numbers of male Aquatic Warblers on these mires range from 6370 to 11500, which is more than 50% of the species world population. In years with favorable nesting conditions breeding success on the three mires varies from 36.3% to 54.1%. In years with significant water level fluctuations and irruptions of shrew populations the breeding success decreases sharply, varying from 2.9% to 27.7%. The main reason for the mortality of eggs and nestlings was predation, probably by small insectivorous mammals. The species is well adapted to the unstable nesting conditions in fen-mires; but in years with serious flooding, high water levels throughout the nesting season, disturbances to the vegetation structure after spring fires or in years with a high density of shrews, breeding success decreases significantly.

Conservation and Restoration of Coastal Reed Beds in the Context of Global Change: Potential Effects of Habitat Fragmentation for Specialist Marshland Passerines

In the context of coastal marshland reduction due to sea level rise, we evaluated the value of fragmented reed beds located within agricultural polders for the conservation of habitats exploited by marshland passerines characterized by different ecological requirements. Although our study was carried out within sites sampled over different years, analyses of body condition and diet of birds during the breeding period, as well as the local daily survival rate and the body mass evolution of birds during the post-breeding period, reveal trends illustrating that fragmented reed beds within inland meadows can: (i) generate habitats that may be significantly exploited by species with a large ecological plasticity, such as the Reed Warbler that could benefit from edge effects of habitat fragmentation; (ii) offer low attractiveness for specialised species such as the Aquatic Warbler, a migratory species apparently very sensitive to the effects of reed bed fragmentation. These results underline the reed beds fragmentation effects that may impact specialised marshland passerines and which should be taken into account in wetland conservation and restoration plans.

Autumn Migration Strategy and Stop-Over Sites of the Globally Threatened Aquatic Warbler Acrocephalus paludicola on the Atlantic Flyway Migration Route

Knowledge about migration strategy and availability of stop-over sites of globally threatened migratory birds is crucial for the implementation of efficient conservation plan. In this study, we investigated the refuelling strategy of the globally threatened Aquatic Warbler Acrocephalus paludicola at stop-over sites during the autumn migration in West Europe and Africa (40 and 72 sites, respectively, documented in published works about stop-over ecology and sites). Based on fuel reserves of captured birds we calculated potential maximal range of non-refuelling flight from stop-over sites located on the Atlantic flyway migration route. We tried to verify the hypothesis that Aquatic Warblers are able to cross the Sahara during one non-stop flight. We found that mean range of flights was affected significantly by the stopover geographic location but not by age of the birds and stop-over habitat. Individuals staging in France are able to cover smaller distances (mean 612.7 km) compared to individuals staging in Portugal and Spain (mean 857.5 km), i.e. closer to two important geographical barriers (the Gibraltar Strait and the Sahara desert). However, maximal ranges of the heaviest individuals were longer (2370 km in France and 1998 km in Portugal). Our study suggests that Aquatic Warblers are generally not able to cross the Sahara during one non-stop flight. Only some individuals with high fat loads starting from stop-overs in Portugal may be able to cross the Sahara without refuelling. However, due to diel air temperature pattern in the desert they need to stop at least once to rest and wait for nighttime drop in temperature to continue migration. Within the Sahara there are many small patches of suitable habitats which can facilitate resting and maybe even refuelling. Observed and predicted reduction of available area of stop-over habitats may have serious negative consequences for population dynamics of many land-bird species, including the globally threatened Aquatic Warbler.

Heterozygosity and fitness in a threatened songbird: blood parasite infection is explained by single-locus but not genome-wide effects

In non-pedigreed populations, insights into effects of inbreeding can be obtained by correlations between individual heterozygosity and fitness-related traits (HFCs). Using an information-theoretic approach, we explored whether heterozygosity of microsatellite markers, measured as internal relatedness (IR), is associated with infection by blood parasites (Plasmodium, Trypanosoma, or Leucocytozoon) in the threatened Aquatic Warbler (Acrocephalus paludicola). We also explored whether any of the markers is more influential than others, or than IR, in explaining blood parasitism (single-locus effects). While we observed that IR was a relatively important predictor of Plasmodium parasitism, we did not find strong evidence for IR to correlate with infection by the identified blood parasites, accounting for sex and population effects. Therefore, our data did not support negative inbreeding effects on blood parasite infection in the Aquatic Warbler. However, we found single-locus effects, such that individuals heterozygous at AW-03 and Ase19 had lower probability of infection by blood parasites pooled together and by Plasmodium, respectively. This indicates that these two markers are in linkage disequilibrium with unknown fitness loci which are related to resisting or clearing blood parasites, and which confer a heterozygote advantage in the Aquatic Warbler. Our results add to the growing evidence that single-locus effects contribute more to HFCs than formerly recognized and have implications for Aquatic Warbler conservation.

Effect of agri-environment measure for the aquatic warbler on bird biodiversity in the extensively managed landscape of Biebrza Marshes (Poland)

Farming intensification is one of the main factors responsible for bird populations declining in agricultural landscapes. Therefore, many countries implement agri-environment schemes (AES) to protect farmland biodiversity. However, recent studies showed that the effectiveness of AES varies between positive and negative.In this study we evaluated the effect an agri-environment measure, designed for aquatic warblers (AWM), has on bird biodiversity in a marginal, extensively managed landscape under strong succession pressure. We applied a point-count method to survey birds in areas within the AWM and outside the AWM and described habitat characteristics around these points.We found that AWM areas had a positive effect on the occurrence of aquatic warblers and six other bird species, meadow and Polish AES bird species richness; negatively affected the occurrence of three bird species and the all bird species richness, and was neutral for the occurrence of another ten bird species and for farmland bird species richness. We also show the diverse and sometimes mutually exclusive habitat preferences of the various species.The AWM implemented in extensively managed landscape successfully encouraged farmers to conduct extensive mowing of meadows and so stopped the habitat succession process. Simultaneously, if AWM is considered on a micro scale, it strongly supported some species but also eliminated others. Therefore, we suggest that management plans should be created at a landscape level. Such approach enables the determination of areas in which different species or groups of species are prioritised before others, allowing for the conservation of overall biodiversity.

Correlates of blood parasitism in a threatened marshland passerine: infection by kinetoplastids of the genus Trypanosoma is related to landscape metrics of habitat edge.

In birds, vector-borne parasites invading the bloodstream are important agents of disease, affect fitness and shape population viability, thus being of conservation interest. Here, we molecularly identified protozoan blood parasites in two populations of the threatened Aquatic Warbler Acrocephalus paludicola, a migratory passerine nesting in open marsh. We explored whether prevalence and lineage diversity of the parasites vary by population and whether infection status is explained by landscape metrics of habitat edge and individual traits (body mass, fat score, wing length and sex). Aquatic Warblers were infected by genera Plasmodium, Leucocytozoon and Trypanosoma, with seven, one and four lineages, and 29.9, 0.7 and 12.5% prevalence, respectively. No Haemoproteus infections were detected. Prevalence did not vary between the populations, but lineage diversity was higher in Polesie than in Biebrza for all the lineages pooled and for Plasmodium. Infection by Trypanosoma decreased with patch core area and increased with density of habitat edge. Infection status was not predicted by the individual traits. Our study is the first to show an association between edge-related landscape features and blood parasitism in an open habitat bird. This finding will support informed conservation measures for avian species of the globally shrinking marshland and other treeless habitats.

Identifying migration routes and non-breeding staging sites of adult males of the globally threatened Aquatic WarblerAcrocephalus paludicola

SummaryBirds that are long-distance migrants partition their annual cycle among a number of locations over a large spatial range. The conservation of these species is particularly complex because it requires attention to a number of different and distant habitats based on knowledge of migratory phenology, routes and staging areas. In the case of the globally threatened Aquatic WarblerAcrocephalus paludicola, a habitat specialist that breeds in Europe and spends the boreal winter in sub-Saharan Africa, non-breeding staging areas were widely unknown until recently. We applied light-level geolocators to adult male Aquatic Warblers at breeding sites in Belarus and Ukraine. Data from eight retrieved geolocators confirmed a south-west and then westward migration route through Europe via the northern Mediterranean with staging sites on the Iberian Peninsula and occasionally France and north-west Africa. In sub-Saharan Africa, final staging areas were in Mali, either in the Inner Niger Delta or at (presumably) small water bodies in the desert, with one bird most likely staying in the north of Ivory Coast south of the previously assumed range. The birds probably stayed in the final staging areas for most of the non-breeding season, but the logger on only one bird provided data throughout the entire migration cycle. Pre-nuptial migration of the latter was by a more easterly route than the southward migration. Our study suggests that conservation strategies for Aquatic Warbler north of the Sahara should include consideration of unknown staging sites in the northern Mediterranean as well as on the Iberian Peninsula and in north-west Africa. South of the Sahara, our study demonstrates the importance of the Sahel for the conservation of the Aquatic Warbler, including both the major floodplains of the Niger River and small Sahelian wetlands that are under pressure from human development.

Conservation of disappearing cultural landscape\u2019s biodiversity: are people in Belarus willing to pay for wet grassland restoration?

Abandonment of traditional farming practices, such as hay-making and pasturing, has resulted in rapid loss of open wet grassland habitats in Europe. The globally threatened Aquatic Warbler (Acrocephalus paludicola L.) is a bird species that occurs almost exclusively in open fen mires, which have virtually disappeared in Western Europe, but still persist locally in Eastern Europe. Focusing on the world’s most important breeding site for Aquatic Warbler, the Zvaniec fen mire in Belarus, we estimated Belarusian citizens’ willingness-to-pay for adequate conservation management of this fen mire and its focal species the Aquatic Warbler. Results from a discrete choice experiment indicated that Belarusian citizens were willing to pay for appropriate conservation programmes of the Zvaniec fen mire. Scything and mechanical mowing were preferred compared to controlled burning, and especially over herbicide treatment of encroaching shrubs. Conservation management was preferred over legal protection of wetland areas without management. Respondents considered such passive conservation to be insufficient to maintain open fen mire habitat and gave a higher priority to active conservation management programmes. These preferences are consistent with evidence-based knowledge about what is effective conservation management for the Aquatic Warbler. Given the gradual disappearance of Europe’s traditional cultural landscapes, we discuss the challenge to fund the maintenance of this biocultural biodiversity legacy.

The importance of the management of small reed patches for the conservation of endangered passerine birds linked to wetlands

Reed patches around wetlands have been proved to be important to enhance dispersal of vertebrates particularly medium size birds However the importance for small size endangered passerine birds some of them totally or partially endangered e g Acrocephalus paludicola Acrocephalus melanopogon Emberiza schoeniclus Panurus biarmicus is not completely assessed This mini review highlights some physiological mechanisms used for reed bed specialists to move in reed patches and emphasizes the importance of management peripheral areas of wetlands to ensure dispersal

Mercury contamination, a potential threat to the globally endangered aquatic warbler Acrocephalus paludicola

Mercury (Hg) contamination is considered a global concern for humans and wildlife, and although the number of studies dealing with that issue continues to increase, some taxonomic groups such as small passerine birds are largely understudied. In this paper, concentration of mercury in the aquatic warbler (Acrocephalus paludicola) feathers, a globally threatened passerine species, was examined. The concentration differences between two ages and sexes were investigated. The comparison of feathers taken on autumn migrants of two age categories act as a comparison of the species’ exposure within the two different areas (European breeding or African wintering grounds). The average Hg concentration for all sampled individuals [2.32 μg/g dw (range 0.38–12.76)] is relatively high, compared with values found in other passerine species. An age difference was found, with first-year individuals displaying higher mercury concentrations than adults. This indicates that birds are exposed to mercury pollution during the breeding season, i.e., in the continental floodplains of eastern Europe. The average Hg concentration in feathers grown on the breeding grounds was 3.88 ± 2.59 μg/g dw, closer to the critical value of 5 μg/g dw, which is considered to impair the health of individuals. The findings suggest that mercury pollution may constitute a threat so far neglected for the endangered aquatic warbler.

Water on the Fen Mire as a Problem in the Protection of Globally Threatened Species: Long-Term Changes in Aquatic Warbler Numbers

Water on the Fen Mire as a Problem in the Protection of Globally Threatened Species: Long-Term Changes in Aquatic Warbler Numbers

Diet Selection of the Aquatic Warbler Acrocephalus paludicola During Its Post-Nuptial Migration Stopover in NW Spain

Food availability and diet are two key issues in understanding the ecological requirements of a migratory species in stopover sites and in taking effective conservation measures. In the case of the globally threatened Aquatic Warbler, there have previously been no studies examining diet selection in the Iberian Peninsula, a key region for their post-nuptial movements. In this context, the availability of arthropods in different habitats (reeds, rushes and grassland), the composition and biomass of prey in faecal samples, and diet selection were all investigated in a wetland in northwest Spain. The results showed a higher total abundance of arthropods in grassland and rushes: habitats which were more similar to each other, in terms of vegetation physiognomy and composition of invertebrates, compared with reeds. In terms of prey abundance, diet was dominated by Araneae, Heteroptera and Homoptera. However, the groups that contributed most to the ingested biomass were Diptera (Tipulidae), Odonata and Orthoptera, followed by Araneae. Prey selection indices showed a preference for these groups, which all contain insects with a large body length. These diet characteristics showed many similarities with studies in other stopover and breeding areas, but differ in that Araneae were the main arthropod prey at this stopover site.

Spatial Variation in Long-Term Trends in a Metapopulation of the Globally Threatened Aquatic WarblerAcrocephalus paludicolain Poland

Abstract. The Polish breeding population (3,200–3,250 males) of the globally threatened Aquatic Warbler Acrocephalus paludicola represents almost 25% of the global population. Except for the relatively stable large population in the Biebrza valley in north-east Poland less is known about population trends of peripheral populations in western, central and south-eastern regions of the country and whether trends differ depending on region. We investigated the long-term population dynamics in 38 small populations between 1969–2013 in the four Polish regions. Summarizing the trends of all small populations of Aquatic Warblers showed a significant decline in total number of individuals and declining number of populations over time. However, population trends were distinctly different in the different regions, with stable dynamics in south-east, moderate decline in north-east and sharp decline in the central and western regions. During the study period 19 out of 38 populations became extinct (11 populations in t...

Extracting historical population trends using archival ringing data—an example: the globally threatened Aquatic Warbler

Understanding how animal population size changes over time is one of the key means to identify threats and facilitate the successful implementation of conservation measures. The globally endangered Aquatic Warbler has undergone a major decline throughout its range. While in the first half of the 20th century, it was still an abundant species across major parts of Central and Western Europe, over the last century the size of its European population is considered to have declined by more than 90 %. However, little is known of the historical changes in its population size. Here we model the past population size of the Aquatic Warbler using historical ringing records of European ringing schemes and population monitoring software (TRends for Indices and Monitoring). We found that during the short 30-year period between 1950 and 1980 the European Aquatic Warbler population underwent a dramatic 95 % decline. According to this model, the population has recently been stable, no further decline was observed between 1980 and the late 1990s.

Hydrological Management in a Restored Wetland Affects Stopover Ecology of Aquatic Warbler: The Case of La Nava Wetland, Northern Spain

Abstract The Aquatic Warbler (Acrocephalus paludicola) is one of the most threatened migratory passerine birds in the world. The species stops over at both European and African wetlands during its migration. Using data from a long-term ringing program in the restored wetland of La Nava (Spain), we describe several aspects of the species' stopover ecology at this site with special focus on juveniles: (1) timing of migration, (2) population size, (3) fuel reposition rate, (4) stopover duration and (5) site fidelity. We elaborated two Multiple Linear Regressions and a Generalized Linear Model to estimate the determinants of migration phenology, daily fattening rate and abundance of captures in addition to minimum observed stopover duration. Finally, we calculated return rates to estimate stopover site fidelity. We determined that: this stopover site belongs to an Atlantic migration route; juveniles experience delayed migration; and that reduced captures are associated with more restrictive hydrological manag...

Prevalence and diversity of Plasmodium and Haemoproteus parasites in the globally-threatened Aquatic Warbler Acrocephalus paludicola.

The diversity and prevalence of malaria parasites of the genera Plasmodium and Haemoproteus were determined in the globally-threatened Aquatic Warbler Acrocephalus paludicola. Birds were sampled during migration in Portugal and at the wintering quarters in Senegal and parasites were detected using molecular methods. Only three generalist parasite lineages (Plasmodium) were found. There were no significant differences in the prevalence of parasites between sexes in Europe, but adults had higher prevalence than first-year birds, and birds in Europe had higher prevalence than those captured in Africa. When comparing with other Acrocephalus species and taking sample size into account, Aquatic Warblers had the lowest prevalence and, together with another threatened species, the Seychelles Warbler Acrocephalus sechellensis, the lowest diversity of malaria parasites. We hypothesize that the low diversity of parasites and absence of specialist lineages of Aquatic Warblers are caused by its small population size and fragmented distribution. Furthermore, Aquatic Warblers' extreme habitat specialization may decrease their exposure to malaria parasites, but other explanations such as high mortality (which would constraint the sampling of infected birds) or, in contrast, very efficient immunological system in clearing the infections cannot be ruled out. This study contributes to explain variation in prevalence and diversity of malaria parasites among hosts.