Search birdRS Box

Search birdRS blog posts

Browse the Blog Posts

Or scan through the blog archive below for items of interest as only the latest post is shown below, thanks.

Tuesday, 24 March 2015

Ibis, International Journal of Avian Science. April 2015, Volume 157, Issue 2






Cover image for Vol. 157 Issue 2

April 2015

Volume 157Issue 2


    © British Ornithologists' Union

    LINK

    REVIEW ARTICLE

    Abundance and abundance change in the world's parrots
    Stuart J. Marsden and Kay Royle

    Abstract
    Estimates of population density and abundance change (differences in density or encounter rates across land uses or time periods) form the cornerstone of much of our knowledge of species' responses to environmental conditions, extinction risks and potential conservation actions. Gathering baseline data on abundance of the world's c. 10 000 bird species and monitoring trends in the light of rapidly changing environmental and harvest pressures is a daunting prospect. With this in mind, we review literature on population densities and abundance changes across habitats in one of the world's largest and most threatened bird families, the parrots (Psittaciformes), to identify gaps in knowledge, model phylogenetic and other influences on abundance, and seek patterns that might guide thinking for data-deficient taxa and situations. Density estimates were found for only 25% of 356 parrot species. Abundance change data were similarly limited and most came from logged forest, with very few comparisons across different anthropogenic habitats. Threatened species were no more likely to have a density estimate than non-threatened species, and were less likely to have estimates of abundance change. Exploratory generalized linear mixed models indicated that densities are most influenced by genus, and are generally higher within protected areas than outside. It is unclear whether the latter effect stems from habitat protection, a reduction in poaching or both, but protected areas appear to be beneficial for parrots. Individual members of the ‘parakeet’ genera (e.g. Pyrrhura and Eos) were predictably abundant, whereas within larger-bodied genera such as Ara (macaws), species were predictably uncommon (< 10 individuals per km2) and there was a long tail of extreme rarity. Responses of parrots to habitat change were highly variable, with natural variation in parrot abundance across different primary forests as great as that between primary forest and human-altered forests. The speed at which environmental change is affecting the world's parrots far outstrips that of our current capacity to track their abundance and we assess the likely scale of data deficiency in this and other bird groups. Developments in survey and analysis methods such as variants of distance sampling and the integration of niche modelling with point density estimation may increase our effectiveness in monitoring parrots and other important and threatened bird groups.


    ORIGINAL ARTICLES

    Conservation

    Widespread supplementary feeding in domestic gardens explains the return of reintroduced Red Kites Milvus milvus to an urban area
    Melanie E. Orros and Mark D. E. Fellowes

    Abstract
    Reintroductions are commonly used to mitigate biodiversity loss. One prominent example is that of the Red Kite Milvus milvus, a charismatic raptor of conservation concern. This species has been reintroduced across the UK over the last 25 years following its near extinction after centuries of persecution. The species was not expected to recolonize urban areas; its historical association with human settlements is attributed to scavenging on human waste and refuse, a resource now greatly reduced on the streets of modern European cities. However, the species has become a common daytime visitor to a large conurbation centred on the town of Reading, southern England, approximately 20 km from the first English reintroduction site. Given a near-absence of breeding and roost sites, we investigated foraging opportunities and habitat associations that might explain use by Red Kites of this urban area. Surveys of discarded human foods and road-kill suggested that these could support at most 13–29 Kites per day. Face-to-face surveys of a cross-section of residents revealed that 4.5% (equivalent to 4349 households) provided supplementary food for Red Kites in their gardens. Using estimates of per-household resource provision from another study, we calculated that this is potentially sufficient to feed 142–320 Kites, a substantial proportion of the total estimated to visit the conurbation each day (between 140 and 440). Road transects found positive associations between Red Kites and residential areas. We suggest that the decision made by thousands of householders to provide supplementary food for Red Kites in their gardens is the primary factor explaining their daytime abundance in this urban area.

    Light grazing of saltmarshes is a direct and indirect cause of nest failure in Common Redshank Tringa totanus 
    Elwyn Sharps, Jennifer Smart, Martin W. Skov, Angus Garbutt and Jan G. Hiddink

    Abstract
    The Common Redshank Tringa totanus breeding population on British saltmarshes has declined by over 50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low-intensity grazing of less than one cattle per hectare, but Redshank have continued to decline, even in regions where light grazing was predominant. This study quantified effects of grazing intensity on Redshank nest survival over six lightly grazed saltmarshes with livestock densities between 0 and 0.82 cattle per hectare, in the Ribble Estuary, northwest England. We assessed whether grazing resulted in nest mortality directly through cattle trampling and/or indirectly through grazer modification of habitat that accelerates predation risks. Cattle density was recorded both during the Redshank breeding season and for 1 year prior to the study, to account for both short-term trampling effects and the longer term effects on vegetation. Results showed that risk of nest loss to trampling increased from 16% at 0.15 cattle per hectare to 98% at 0.82 cattle per hectare in the breeding season. The risk of a nest being predated increased from 28% with no grazing to 95% at 0.55 cattle per hectare based on all year grazing data. These results suggest that even light conservation grazing at less than one cattle per hectare can reduce Redshank nest survival rates to near zero. It may therefore be appropriate to reduce saltmarsh grazing intensities, or change the timing of saltmarsh grazing to reduce the number of livestock present during the Redshank breeding season.

    Effects of grassland intensification on Whinchats Saxicola rubetra and implications for conservation in upland habitats
    Gavino Strebel, Alain Jacot, Petra Horch and Reto Spaar

    Abstract
    Modern, intensive grassland management has led to strong declines in ground-nesting grassland birds, and is now increasingly threatening the last remaining strongholds of the Whinchat Saxicola rubetra in the Central European uplands. In this study, we assess key threats to Whinchat populations in these uplands in order to suggest appropriate conservation measures. We compared the direct threat of early mowing as well as the indirect threat resulting from a deteriorating arthropod food source in an inner-alpine valley. Five of our seven study sites were mown too early with respect to the chicks' fledging date. Such early mowing was particularly evident on the more intensively farmed, earlier mown valley bottoms than on the valley slopes. Arthropod abundance and biomass did not differ between valley bottoms and slopes. However, valley bottoms had a greater amount of unprofitable prey items such as flies. Breeding bird density was mainly determined by the degree of overlap between the mowing schedule and breeding phenology. These findings suggest that in upland grasslands at an early stage of intensification, early mowing is of greater importance for populations than possible negative effects of a reduced food source. We suggest that mowing is delayed until a sufficient proportion of nestlings are safely fledged.

    Home-range size and habitat use of European Nightjars Caprimulgus europaeusnesting in a complex plantation-forest landscape 
    Katrina Sharps, Ian Henderson, Greg Conway, Neal Armour-Chelu and Paul M. Dolman

    Abstract
    In Europe, the consequences of commercial plantation management for birds of conservation concern are poorly understood. The European Nightjar Caprimulgus europaeus is a species of conservation concern across Europe due to population depletion through habitat loss. Pine plantation-forest is now a key Nightjar nesting habitat, particularly in northwestern Europe, and increased understanding of foraging habitat selection is required. We radiotracked 31 Nightjars in an extensive (185-km2) complex conifer plantation landscape in 2009 and 2010. Home-range 95% kernels for females, paired males and unpaired males were an order of magnitude larger than song territories of paired males, emphasizing the importance of habitats beyond the song territory. Nightjars travelled a mean maximum distance of 747 m from the territory centre each night. Home-range placement relative to landscape composition was examined by compositional analysis. Pre-closure canopy forest (aged 5–10 years) was selected at all scales (MCP, 95% and 50% kernels), with newly planted forest (aged 0–4 years) also selected within 50% kernels. For telemetry fixes relative to habitat composition within 2 km of their territory centre, individuals again selected pre-closure and newly planted forest, and also grazed grass heath. Open ungrazed habitat was not selected, with implications for open habitat planning for biodiversity conservation within public-owned forests. Despite the Nightjars’ selection for younger growth, moth biomass was greater in older forest stands, suggesting that foraging site selection reflects ease of prey capture rather than prey abundance. Within large plantation-forest landscapes, a variety of growth stages is important for this species and our results suggest that grazing of open habitats within and adjacent to forest will additionally benefit the European Nightjar.

    Seabird Ecology

    Feather-based measures of stable isotopes and corticosterone reveal a relationship between trophic position and physiology in a pelagic seabird over a 153-year period 
    Graham D. Fairhurst, Alexander L. Bond, Keith A. Hobson and Robert A. Ronconi

    Abstract
    Diet during the non-breeding period influences condition and subsequent reproduction. Physiological mechanisms underlying such carry-over effects are poorly understood but could be clarified by studying physiological responses to variation in diet during non-breeding. The hormone corticosterone provides a functional link between diet and survival and reproduction, but methodological limitations have prevented previous studies from testing the hypothesis that, on an individual level, avian corticosterone levels during the non-breeding period reflect broader patterns in feeding ecology during that time. Using museum specimens (1859–2002) and live birds (2012), we found that corticosterone from feathers (CORTf) is negatively related to trophic position (TP) inferred from feather stable-nitrogen isotope values (δ15N) in Leach's Storm-petrels Oceanodroma leucorhoa. CORTf was not related to stable-carbon isotope values (δ13C). We detected no temporal trends in CORTf or δ15N, and neither was related to a large-scale index of winter climate, suggesting a general ecological phenomenon rather than a reflection of historical environmental changes. However, we detected a temporal trend in feather δ13C, and δ13C was related to δ15N. Our findings suggest a physiological benefit of feeding at higher TPs, either through increased nutritional value or reduced foraging costs associated with higher TP prey, and future research should aim to distinguish between these two explanations. Nevertheless, ours is the first evidence of a correlation between individual endocrine levels and foraging ecology, and demonstrates non-lethal variation in a physiological mediator in turn related to variation in resource use.

    Commercial fisheries, inter-colony competition and sea depth affect foraging location of breeding Scopoli's Shearwaters Calonectris diomedea
    Jacopo G. Cecere, Carlo Catoni, Giorgia Gaibani, Pedro Geraldes, Claudio Celada and Simona Imperio

    Abstract
    The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra-specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra-specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long-distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at-sea distribution and habitat preference of a seabird inhabiting the over-exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.

    Evolution and Taxonomy

    Interspecific competition affects evolutionary links between cavity nesting, migration and clutch size in Old World flycatchers (Muscicapdae)
    Sahas Barve and Nicholas A. Mason

    Abstract
    The ecology of cavity nesting in passerine birds has been studied extensively, yet there are no phylogenetic comparative studies that quantify differences in life history traits between cavity- and open-nesting birds within a passerine family. We test existing hypotheses regarding the evolutionary significance of cavity nesting in the Old World flycatchers (Muscicapidae). We used a multi-locus phylogeny of 252 species to reconstruct the evolutionary history of cavity nesting and to quantify correlations between nest types and life history traits. Within a phylogenetic generalized linear model framework, we found that cavity-nesting species are larger than open-nesting species and that maximum clutch sizes are larger in cavity-nesting lineages. In addition to differences in life history traits between nest types, species that breed at higher latitudes have larger average and maximum clutch sizes and begin to breed later in the year. Gains and losses of migratory behaviour have occurred far more often in cavity-nesting lineages than in open-nesting taxa, suggesting that cavity nesting may have played a crucial role in the evolution of migratory behaviour. These findings identify important macro-evolutionary links between the evolution of cavity nesting, clutch size, interspecific competition and migratory behaviour in a large clade of Old World songbirds.

    Taxonomy of the Narcissus Flycatcher Ficedula narcissina complex: an integrative approach using morphological, bioacoustic and multilocus DNA data
    Lu Dong, Min Wei, Per Alström, Xi Huang, Urban Olsson, Yoshimitsu Shigeta, Yanyun Zhang and Guangmei Zheng

    Abstract
    The taxonomy of the Narcissus Flycatcher Ficedula narcissina–Yellow-rumped Flycatcher Ficedula zanthopygia complex from East Asia has long been debated. Most authors recognize two species: F. narcissina, with the subspecies narcissina (most of Japan and Sakhalin Island), owstoni (south Japanese islands) and elisae (northeast China) and F. zanthopygia (monotypic), although species status has been proposed for elisae and sometimes for owstoni. Here, we revise the taxonomy of this complex based on an integrative approach utilizing morphology, songs and mitochondrial and nuclear DNA for all taxa. All taxa were diagnosably different in plumage, and there were also structural differences among them, although the northernmost populations of owstoni (sometimes recognized as jakuschima and shonis) were somewhat intermediate in plumage, structure and male plumage maturation between southern populations of owstoni and narcissina. All taxa had different songs, and a discriminant function analysis of four song variables correctly classified 100% of all songs. A strongly supported phylogeny was recovered based on three mitochondrial genes and three nuclear introns (total of 3543 bp), revealing a sister relationship between F. zanthopygia and the other taxa, between F. n. narcissina and F. n. owstoni, and between F. n. elisae and F. n. narcissina + F. n. owstoni. The corrected COI distances among the three F. narcissina subspecies ranged from 2.8% (narcissina–owstoni) to 8.2% (narcissina–elisae). We suggest that the congruent differences in multiple independent traits and the deep genetic divergences among the four taxa in the F. narcissina–F. zanthopygia complex support treatment of all of these taxa as separate species. However, we acknowledge the paucity of data for F. owstoni and recommend further studies of this taxon. We suggest listing both F. elisae and F. owstoni, which have small and fragmented populations, as globally threatened.

    Migration and Moult

    Patterns and correlates of songbird movements at an ecological barrier during autumn migration assessed using landscape- and regional-scale automated radiotelemetry
    Bradley K. Woodworth, Greg W. Mitchell, D. Ryan Norris, Charles M. Francis and Philip D. Taylor

    Abstract
    Departure decisions of songbirds at ecological barriers they encounter en route can strongly influence time, energy and survival costs of migration. To date, most field studies of departure decisions and their correlates have used indirect methods and followed migrants at a single stopover site, with limited information on what happens to individuals after they depart from the site. We used an automated radiotelemetry array extending 350 km from southwest Nova Scotia to southern Maine to study the migratory and stopover movements of Northern Waterthrushes Parkesia noveboracensis, Red-eyed Vireos Vireo olivaceus and Yellow-rumped Warblers Setophaga coronata in relation to fuel load and weather at the northeastern edge of the Gulf of Maine. From the 105 radio-transmitters we deployed in southwest Nova Scotia, we recorded 42 landscape-scale stopover flights and 47 migratory flights by 75 individuals. Of the migratory flights, 57% were orientated southwest, a trajectory that, if held, would require individuals to complete a 350–440 km overwater flight. The remaining 43% of migratory flights were orientated northwest, away from the Gulf of Maine, and 15 individuals were confirmed to have detoured around all or a portion of the barrier, as evidenced by their being re-detected over the Bay of Fundy and/or along the coast of Maine between 4 h and 15 days later. Across all individuals, initial fat score had a positive effect on departure probability, especially for individuals that made stopover flights. Among weather variables, tailwind assistance was the best predictor of migratory departures but did not appear to be the main factor determining whether individuals orientated towards or away from the Gulf of Maine. Weather had little effect on departure decisions of individuals that made stopover flights. These differences in the correlates of migratory departures and stopover flights would probably not have been distinguishable had our study been restricted to a local scale. Therefore, our findings highlight the importance of expanding the scale at which departure decisions and the ecology of stopover in general are studied.

    Flexibility in the timing of post-breeding moult in passerines in the UK 
    Catriona A. Morrison, Stephen R. Baillie, Jacquie A. Clark, Alison Johnston, David I. Leech and Robert A. Robinson

    Abstract
    Higher temperatures resulting from climate change have led to predictions that the duration of the breeding season of many temperate bird species may be changing. However, the extent to which breeding seasons can be altered will also depend on the degree of flexibility in processes occurring at other points in the annual cycle. In particular, plasticity in the timing of post-breeding moult (PBM) could facilitate changes in the timing of key events throughout the annual cycle, but little is known about the level of within- and between-species plasticity in PBM. As part of the British Trust for Ornithology (BTO) Ringing Scheme, many ringers routinely record moult scores of flight feathers, and these can be used to provide information on the annual progression of PBM for a range of species. Here we use ringing data to investigate patterns of PBM in 15 passerines, as well as data from the BTO Nest Record Scheme to relate these differences to the timing of breeding of these species across the UK. We find considerable variation in both the mean start (19 May–29 July) and duration (66–111 days) of PBM between species, but find no evidence that species starting PBM later in the season complete it any faster. However, there is considerable within-species variation in PBM, particularly for multi-brooded species; PBM starts later and is completed in less time when the duration of the breeding season (difference between first and last nests) is longer. This implies that a later end to breeding can be compensated for by faster PBM, and that advances in breeding could lead to earlier and slower PBM. Our findings suggest that adaptation of PBM in response to climate-mediated changes in the timing and duration of the breeding season is possible. However, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.

    Breeding Ecology

    Early morning fledging improves recruitment in Great Tits Parus major
    Reinder Radersma, Jan Komdeur and Joost M. Tinbergen

    Abstract
    A potential key event linking the nestling phase to first-year survival is fledging (nest leaving) because this process is characterized by a major change of environments and therefore a sudden shift in selective forces. Here we assessed whether different facets of fledging predicted subsequent survival (measured as local recruitment) in Great Tits Parus major. Nestlings had a higher recruitment probability when they fledged early in the morning and when they were heavy. The existence of selection for fledging early in the day has been suggested before, but here we provide the first empirical evidence in support of that prediction.

    Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators
    Ewa Węgrzyn and Konrad Leniowski

    Abstract
    Nest predation is a major source of reproductive failure in birds and thus it can exert selection on both parental and offspring strategies. Begging calls are known to be a powerful component of parent–offspring communication but these calls can also increase predation risk. Here we demonstrate a sophisticated strategy for the development of begging vocalization in a species under high nest predation. Blackcap Sylvia atricapilla nestlings spend most of their nesting period silent, and develop begging calls just before they are able to fledge. The onset of begging vocalization matches the onset of endothermy, which enables Blackcap chicks to leave the nest. We demonstrate experimentally that begging calls function as a signal of the increased needs of homeothermic nestlings. Playback of begging calls conducted in nests with silent nestlings resulted in a significant increase in feeding rates and a decrease in brooding. Development of begging calls only at the age of endothermy allows species under high nest predation to keep the risky period of begging vocalizations and frequent feeding to a minimum. This strategy may constitute an evolutionary solution to high predation pressure in some open nesting passerines. This is the first study to demonstrate the existence of silent begging in a passerine.

    Reproductive responses of temperate and boreal Tengmalm's Owl Aegolius funereus populations to spatial and temporal variation in prey availability
    Markéta Zárybnická, Ondřej Sedláček, Pälvi Salo, Karel Šťastný and Erkki Korpimäki

    Abstract
    Environmental variation across space and time can strongly influence life-history strategies in vertebrates. It has been shown that the reproductive success of birds of prey is closely related to food availability. However, relatively little is known about intraspecific differences in reproductive success of birds in relation to varying ecological conditions across environmental gradients. We investigated the reproductive performance of Tengmalm's Owls Aegolius funereus in a temperate (Czech Republic, 50°N) and a boreal (Finland, 63°N) population in relation to long-term variations in the abundance of their main prey (small rodents). Prey densities at the northern site were much higher, but there were also large inter-annual fluctuations and years with steep summer declines of vole densities. Northern owls laid larger clutches but offspring production per nest was similar at both study sites. This resulted from higher nestling mortality in the northern population, especially in nests established later in the season. Despite much greater nesting losses due to predation by Pine Martens Martes martes, productivity at the population level was about four times greater at the temperate site, mainly due to the much higher breeding densities compared with Finland. Tengmalm's Owls at the temperate study site may benefit from relatively stable prey abundance, a more diverse prey community that offers alternative prey during vole scarcity, longer nights in summer that allow more time for foraging, and a lower level of interspecific competition with other vole-specialized predators.

    SHORT COMMUNICATIONS

    Quantifying the robustness of first arrival dates as a measure of avian migratory phenology 
    Anne E. Goodenough, Stacey M. Fairhurst, Julia B. Morrison, Martin Cade, Peter J. Morgan and Matt J. Wood

    Abstract
    As the climate changes, many long-term studies have shown that the timing of bird migration is shifting, increasing the need for reliable measures of migratory phenology. Ideally, daily counts of birds at a site are used to calculate the mean arrival date (MAD) but, as this approach is not always possible and is very labour-intensive, simpler metrics such as first arrival date (FAD) have commonly been used. Here, we examine the relationship between FAD and MAD in 28 summer migrant bird species over a 42-year period (1970–2011) at Portland Bird Observatory, UK. Although significant correlations between FAD and MAD were detected, relationships were weak, particularly in long-distance migrants. We suggest that FAD, although a simple and straightforward measure, is not particularly robust as a proxy for overall migratory phenology at a population level.

    Age-ratio bias among hunter-based surveys of Eurasian Wigeon Anas penelopebased on wing vs. field samples
    Anthony D. Fox, Kevin Kuhlmann Clausen, Lars Dalby, Thomas Kjær Christensen and Peter Sunde

    Abstract
    We compared age and sex ratios among Eurasian Wigeon Anas penelope derived from Danish field observations and hunter-based shot samples throughout an entire winter. Sex ratios did not differ significantly between the two samples. Overall, first-year males were more than three times more likely to be represented than adult males in the hunter sample compared with field samples and were 7–20 times overrepresented in the hunting sample at the beginning of the season. These results confirm the need to account for such bias and its temporal variation when using the results of hunting surveys to model population parameters. Hunter-shot age ratios may provide a long-term measure of reproductive success of dabbling duck flyway populations given an understanding of such bias.

    Experimental enlargement of nest size does not increase risk of predation or brood parasitism in the Great Reed Warbler Acrocephalus arundinaceus 
    Václav Jelínek, Petr Procházka and Marcel Honza

    Abstract
    We assessed whether nest size affects the probability of nest loss using dyads of large and small (large being twice the size of small) inactive Great Reed Warbler Acrocephalus arundinaceus nests placed at similar sites in Great Reed Warbler territories. Large nests were not predated significantly more frequently than small nests. Experimentally enlarged active Great Reed Warbler nests suffered non-significantly higher predation compared with non-manipulated control nests. Our experiments did not support the nest-size hypothesis and suggested that nest size does not appear to be a factor affecting the risk of nest predation in this species. The probability of brood parasitism by the Common Cuckoo Cuculus canorus was also unaffected by experimental nest enlargement, supporting the commonly accepted hypothesis that the Common Cuckoo searches for suitable host nests by host activity during nest building rather than nest size.

    No evidence for sex bias in winter inter-site movements in an Arctic-nesting goose population 
    Mitch D. Weegman, Anthony D. Fox, Stuart Bearhop, Geoff M. Hilton, Alyn J. Walsh, Ian R. Cleasby and David J. Hodgson

    Abstract
    Understanding movement of individuals between sites is necessary to quantify emigration and immigration, yet previous analyses exploring sex biases in site fidelity among birds have not evaluated remigration (the return of marked birds that moved to alternative areas from the site at which they were marked). Using novel Bayesian multistate models, we tested whether between-winter emigration, remigration and survival rates were sex-biased among 851 Greenland White-fronted Geese Anser albifrons flavirostris marked at Wexford, Ireland. We found no evidence for sex biases in emigration, remigration or survival. Thus, sex biases in winter site fidelity do not occur in any form in this population; these techniques for modelling sex-biased movement will be useful for a better understanding of site fidelity and connectivity in other marked animal populations.

    Optimal habitat conditions for the globally threatened Aquatic Warbler Acrocephalus paludicola in eastern Poland and their implications for fen management 
    Janusz Kloskowski, Franziska Tanneberger, Piotr Marczakiewicz, Anna Wiśniewska and Agata Choynowska

    Abstract
    To identify optimal habitat for the Aquatic Warbler Acrocephalus paludicola, a flagship species of fen mires, we related numbers of singing males to habitat variables in all core breeding sites in eastern Poland. The density of male Aquatic Warblers increased with increasing ground cover by water and mosses and litter layer height, and was highest where vegetation was 60–90 cm tall. Male densities also increased with the biomass of arthropods > 10 mm length, estimated by sweep netting, and with the abundance of spiders, estimated by pan trapping. We suggest that habitat management should take into account species-specific morphological adaptations, nest safety and arthropod productivity. Prevention of vegetation succession is a conservation priority for open fen mires. However, modern management practices to achieve this, especially mowing using tracked vehicles, should be evaluated and optimized to ensure that such practices do not adversely affect the long-term development of moss cover and litter structure.

    No comments:

    Post a Comment