An exceptionally high diversity of hoverflies (Syrphidae) in the food of the reed warbler (Acrocephalus scirpaceus)

Despite being considered a classical example of protective Batesian mimicry hoverflies (Syrphidae) are known to be preyed upon by various passerines. The aim of the present study was to examine in detail food brought by reed warblers Acrocephalus scirpaceus to their nests to better understand the importance of hoverflies in the diet of small passerines. Using neck collars, 273 food samples containing 8,545 food items delivered to reed warbler and parasitic common cuckoo Cuculus canorus nestlings in warbler nests were recorded. The study was conducted during three breeding seasons in South Moravia, Czech Republic. An unusually high diversity of hoverflies was found — 27 species, including Mesembrius peregrinus (critically endangered species in the Czech Republic) and Mallota cimbiciformis (endangered species) — a new taxon to the Czech Republic. This indicates that nestling diet analyses may provide not only information on avian foraging behaviour but also important faunistic data. Thus, without the detailed identification to species level of material from foraging behaviour studies valuable scientific information may be lost. Overall dominance of Syrphidae was 3.7%, the most common species being Episyrphus balteatus (55.7%, n = 318). However, this number seriously underestimates the importance of hoverflies in the diet of reed warblers as hoverflies are one of the largest prey taken by warblers. Both larvae and pupae were rare, imagines strongly dominating (92.7%). Both specific wasp mimics (e.g., Chrysotoxum verrali) and bee mimics (e.g., Eristalis spp.) were not avoided by foraging reed warblers. The presence of a parasitic cuckoo chick did not affect host foraging behaviour with respect to overall dominance of hoverflies in the diet (warbler 3.3%, cuckoo 3.8%).     

Infanticide in great reed warblers: secondary females destroy eggs of primary females

In 1994–1995 artificial nests with attached model eggs were put into territories that were known to have been occupied by male great reed warblers,Acrocephalus arundinaceusin previous years. Because the eggs were made of soft plasticine, predators left peckmarks in them and this enabled us to identify predators by comparing peckmarks with reference marks made by various species. Previous field data had suggested that infanticidal behaviour existed in our study population, as nests of primary females suffered a three times higher rate of nest loss during the egg-laying period than nests of secondary and monogamous females. The presence of infanticide was supported by the experiment. Small peckmarks resembling those of a great reed warbler occurred almost exclusively in territories occupied by great reed warblers, in particular when a new female settled in the territory. The newly settled females built nests closer to depredated than non-depredated nests. That small peckmarks occurred when new females settled strongly suggests that it is secondary female great reed warblers that commit infanticide on eggs of primary females. Females of low harem rank are expected to gain from infanticidal behaviour because a low ranked female gets a higher proportion of male parental investment when the nest of the primary female fails.     

Habitat selection and polygyny in breeding Corn Buntings Miliaria calandra

Unlike many other polygynous passerine species, female Corn Buntings Miliaria calandra apparently do not suffer costs by pairing polygynously, yet it is unclear whether this is because polygynous males hold the highest quality territories or because pairing with polygynous males is unimportant in determining female reproductive success. Male Corn Buntings on North Uist, Scotland, consistently defended territories which contained nesting habitat, and females often foraged outside male territories when provisioning nestlings. Females showed strong preferences for nesting in uncultivated land, and 80% of nests were under Hogweed Heracleum sphondylium, possibly because this provided cover against predation and the weather. When provisioning nestlings, females showed strong preferences for foraging in cereal crops, probably because this habitat provided better food resources and/or better cover from predators. Males were unpaired or paired with one to three females per breeding season, but variation in territory size or vegetation composition did not explain differences in the number of females paired with individual males. We suggest that when females neither gain benefits nor suffer costs by breeding polygynously, and males do not differ greatly in the areas of habitat selected, polygyny can arise through random female settlement within the nesting habitat.     

Space and habitat use by Red Kites Milvus milvus during winter in the Guadalquivir marshes: a comparison between resident and wintering populations

Differences in habitat selection, diet and behaviour of resident and wintering Red Kites Milvus milvus were studied in Donana National Park, southwest Spain. Adult resident Red Kites roosted at their nests, while immature residents and wintering birds gathered at communal roosts. Individuals remained on average for two consecutive nights (range 1–8) at the same communal roost. Wintering kites spent significantly more time foraging gregariously than residents. The use of the marsh was greater by wintering kites while residents more often used the forest. Wintering birds consumed more goose carrion than the residents. Wintering kites had larger core areas, moved farther from their roost sites to feed and changed foraging areas more frequently than residents. Among residents, adult females had the smallest home ranges (core area, distances travelled and time spent flying). We suggest that Red Kites wintering in Donana occupy the marsh because it provides high food availability, and is vacated by Black Kites M. migrans which exploit this profitable habitat during the breeding season.     

Predation risk affects trade-off between nest guarding and foraging in Seychelles warblers

The fitness costs of egg loss for Seychelles warblers (Acrocephalus sechellensis)on Cousin Island are considerable because warblers have a single-eggclutch and no time to lay a successful replacement clutch. Onthe islands of Cousin and Cousine, with equal densities of Seychellesfodies (Foudia sechellarum), nearly 75% of artificial eggs placedin artificial nests were predated by fodies after 3 days. OnAride Island with no fodies present, loss of artificial eggswas not observed. Female warblers incubate the clutch, and malewarblers guard the clutch when females are absent. Deterrenceof fodies by male warblers is efficient: loss rate of eggs fromunattended warbler nests was seven times as high as from attendednests, and the more nest guarding, the lower the egg loss andthe higher the hatching success. Egg loss is independent ofthe amount of incubation by females. There is no trade-off betweenincubating and foraging by females. Nest guarding competes withforaging by males, and this trade-off has a more pronounced effecton egg loss when food availability is low. The transfer of breeding pairsfrom Cousin to either Cousine with egg-predating fodies or toAride without fodies allowed us to experimentally investigatethe presumed trade-off between nest guarding and foraging. OnCousine, individual males spent the same amount of time nestguarding and foraging as on Cousin, and egg loss was similarand inversely related to time spent nest guarding as on Cousin.Males that guarded their clutch on Cousin did not guard theclutch on Aride but allocated significantly more time to foragingand gained better body condition. Loss of warbler eggs on Aridewas not observed. Time allocation to incubating and foragingby individual females before and after both translocations remainedthe same.     

Restricted dispersal in a long-distance migrant bird with patchy distribution,the great reed warbler

In patchily distributed species dispersal connects local populations into metapopulations. Reliable quantifications of dispersal are therefore crucial to understanding the population dynamics and genetic structure of such metapopulation systems. The great reed warbler (Acrocephalus arundinaceus) inhabits eutrophic lakes and has a patchy breeding distribution. In this study we investigated the dispersal pattern of the great reed warbler based on an extensive capture-recapture effort covering a large census area (22,500 km²). At two adjacent breeding sites (10 km apart) in southern Central Sweden, the "main study area", we ringed the majority of adult and nestling great reed warblers between 1992 and 1999. In 1998 and 1999, we opportunistically searched for territorial males at the majority of the Swedish breeding sites, and were able to examine about 56% of all males in the region. Analyses of recaptured males demonstrated that philopatry predominated. Sixty-nine percent of the recruiting nestlings returned to breed in the main study area (their natal area), and 92% of the resighted adults were found at the same breeding locality in both study years. Breeding dispersal was significantly more restricted than natal dispersal. Additional data on natal and breeding dispersal within the main study area in 1992-1999 suggested that females were as philopatric as males. The overall high level of philopatry, with only occasional longer dispersal distances documented, yielded a root-mean-square dispersal distance of 33 km per generation. High philopatry, short dispersal distances and similar dispersal patterns of male and female great reed warblers contrast the findings among birds in general, but conform to data of species having patchy breeding habitat and isolated populations. Restricted dispersal suggests limited gene flow even among several Swedish populations, which is in line with some previous findings of the population ecology of the great reed warbler: (1) structured mtDNA lineages among European populations; (2) small-scale population differences in song patterns; and (3) low genetic variation and occurrence of inbreeding depression in our main study population.     

Sex ratio variation among broods of great reed warblers Acrocephalus arundinaceus

The sex of 746 great reed warbler fledglings (from 175 broods) was determined by the use of single primer polymerase chain reaction. The reliability of the technique was confirmed as 104 of the fledglings were subsequently recorded as adults of known sex. The overall sex ratio did not differ from unity. Variation in sex ratios between broods was larger than expected from a binomial distribution. Female identity explained some of the variation of brood sex ratio indicating that certain females consistently produced sex ratios that departed from the average value in the population. The theory of sex allocation predicts that parents should adjust the sex ratio of their brood to the relative value of sons and daughters and this may vary in relation to the quality of the parents or to the time of breeding. In the great reed warbler, the proportion of sons was not related to time of breeding, or to any of five female variables. Of five male variables, males with early arrival date tended to produce more daughters. The sex ratio of fledglings that were a result of extra-pair fertilizations did not differ from that of legitimate fledglings. Hence, there is currently no evidence of that female great reed warblers invest in a higher proportion of sons when mated with attractive males.     

Untersuchungen an Drossel- und Teichrohrs?nger(Acrocephalus arundinaceus, A. scirpaceus): Bestandsentwicklung, Brutbiologie, ?kologie

Zusammenfassung Von 1973–1978 wurden systematische Beringungen und regelmäßige Nestkontrollen einer Drs-Population im Fränkischen Weihergebiet (Nordbayern) durchgeführt (Auswertung von 487 Nestkarten). Die vorhandene Trs-Population wurde nicht systematisch erfaßt (645 Nestkarten).Der Bestand der einzelnen Teilpopulationen des Drs schwankte im Untersuchungszeitraum; die gesamte Population blieb annähernd konstant.Die Nestabstände benachbarter Drs-Bruten innerhalb eines günstigen Schilfstreifens lagen zwischen 7 m und ca. 300 m. Das kolonieartige Brüten der Trs wird mit Beispielen belegt.Medianer Legebeginn des Drs war der 29. Mai, der des Trs der 13. Juni. Der nach Erreichen des Maximums im Legemuster folgende Abfall war beim Drs deutlich steiler als beim Trs. Die mittlere Gelegegröße des Drs betrug 4,73, die des Trs 3,85 Eier. Bei beiden Arten fand eine Gelegegrößenreduktion mit fortschreitender Brutzeit statt.Das Schlüpfen der Jungen erfolgte beim Drs überwiegend am 12. bis 14. Tag nach Ablage des letzten Eies, beim Trs am 11. bis 13. Die Brutdauer betrug meist 14 (Drs) bzw. 13 (Trs) Tage.Beim Drs waren 59,7 % der Nester erfolgreich. Der Ausfliegeerfolg, bezogen auf erfolgreiche Nester, betrug 73,2 %, der Gesamtbruterfolg demnach 43,7 %. Beim Trs ergaben sich entsprechend die Werte 66,6 %, 82,9 % und 55,2 %. Auch die durchschnittliche Anzahl flügger Jungvögel pro Brutnest lag beim Drs mit 2,00 etwas niedriger als beim Trs mit 2,15. Als Reproduktions-rate des Drs wurde ein Wert von 2,24 flüggen Jungen pro errechnet. Für den Trs wird die Reproduktionsrate wesentlich höher geschätzt.Die Verluste wurden nach Ursachen aufgeschlüsselt, wobei besonders verglichen mit gleichaltrigen Trs die vielfach größere Empfindlichkeit nestjunger Drs gegen Regen und Kälte auffiel.In zwei Fällen konnten für Drs- Zweitbruten mittels Beringung nachgewiesen werden. Beobachtungen an Trs gaben zu Vermutungen von Zweitbruten bei dieser Art Anlaß.Bigamie wurde beim Drs mehrfach mittels Farbberingung nachgewiesen. Aus den Nestabständen konnte im Untersuchungsgebiet nicht auf monogames oder polygames Verhalten der Drs geschlossen werden. Es werden Angaben über Alter und Verhalten polygamer in verschiedenen Jahren gemacht. Paarzusammenhalt am Vorjahresbrutplatz wurde beim Drs mittels Beringung einmal nachgewiesen.Die meisten überlebenden der als Brutvögel beringten Drs kehrten ins Untersuchungsgebiet zurück, von den überlebenden nestjung beringten dagegen etwa ein Drittel. 3 nestjung beringte Trs wurden nach 1 bzw. 2 Jahren im Untersuchungsgebiet zur Brutzeit kontrolliert.Ein Drittel der Drs-Population stammte aus dem Untersuchungsgebiet. 2 nestjung beringte aus 78 km und 500 km Entfernung wurden als Brutvögel kontrolliert. Alter der Brutvögel 1–9 Jahre.An Beispielen wird die räumliche und zeitliche Einnischung beider Arten beschrieben.

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Studies onAcrocephalus arundinaceus andscirpaceus: Population trends, breeding biology, and ecology

Summary Results of 6 years (1973–1978) of systematic ringing and regular nest controls of a great reed warbler population in Northern Bavaria are given (data of 487 nests) as well as results on a population of the reed warbler (data of 645 nests).Numbers of great reed warblers fluctuated in different parts of the study area. The whole population, however, remained fairly constant.Data on the arrival of males in the breeding area are given.Distances between neighbouring nests of great reed warblers varied from 7 to about 300 m. Differences in nest densities in the reed warbler could be found.The mean first egg laying dates in the great reed warbler and the reed warbler were May 29 and June 13 respectively. The great reed warbler showed a distinct steeper decrease in its egg laying pattern than the smaller species. Average clutch size in the great reed warble was 4.73 eggs and 3.85 eggs in the reed warbler. In both species clutch size decreased during the season.Great reed warbler nestlings hatched on the 12th to 14th day after the last egg had been laid, reed warbler nestlings on the 11th to 13th day. The incubation period was mainly 14 days in the great reed warbler and 13 days in the reed warbler.In the great reed warbler 59.7 % of the nests were successful. The fledging success of successful nests was 73.2 %, accordingly the total nest success was 43.7 %. The corresponding data in reed warbler were 66.6 %, 82.9 % and 55.2 %. On average great reed warblers produced 2.00 fledglings per clutch, reed warblers 2.15. In the great reed warbler a reproduction rate of 2.24 fledglings per female was calculated. The reproduction rate in reed warbler was estimated substantially higher.Great reed warbler nestlings were much more sensitive to rain and cold weather than reed warbler nestlings of the same age.Two great reed warbler males were proved to make a second brood. The same is supposed for the other species but could not be proved so far.Polygyny was proved several times in the great reed warbler. Age and behaviour of polygynous males in different years are reported. Two great reed warblers were found breeding with their former mates at last year's breeding place.Most of the great reed warblers ringed as breeding birds returned into the study area. Nearly one third of the great reed warbler nestlings returned for breeding. Three reed warblers ringed as nestlings could be controlled in the study area during breeding period after 1 year and 2 years respectively.Distances of returned great reed warblers in relation to their birth places and their former breeding places are specified.One third of the great reed warbler population originates from the study area. Two females breeding in the study area were ringed as nestlings 78 km and 500 km apart.One-year-old to nine-year-old great reed warblers were found breeding. Data on the age composition of breeding birds are given.Plant species supporting the nests of great reed warbler and reed warbler were investigated. Differences in the spatial and temporal habitat selection of both species are described.

     

Breeding ecology of the Aquatic Warbler Acrocephalus paludicola on the Biebrza marshes, northeast Poland

Aquatic Warblers Acrocephalus paludicola were studied in a natural fen mire in the Biebrza River valley, the main breeding ground of the species in its entire distribution range. The number of males present and singing at the sample plot changed considerably during the breeding season. Individual identified colour-ringed males sang with unchanged intensity throughout the breeding season. The period of daily singing activity differed from other species of Acrocephalus ; males sang at dusk rather than at dawn. Males took no part in rearing nestlings but remained on territory and showed vigilance behaviour. The density of males in the breeding season ranged from 1.0 to 10.9 per 10 ha. The density of nesting females ranged from 1.3 to 15.7 per 10 ha. In the most suitable habitat females were more numerous than males. The distribution of females (nests) was clumped where potential food resources were higher. Nests were well hidden in places with deeper water between sedge tufts and an abundance of old dry sedge. Females feeding nestlings collected most food within a 5–60-m radius (mean 31.7 m). The return rate of males was higher than that of females. The results suggest a mating system that is intermediate between facultative polygyny and promiscuity.     

Breeding success of common cuckoos Cuculus canorus parasitising four sympatric species of Acrocephalus warblers

We investigated the level of parasitism, egg mimicry and breeding success of cuckoos parasitising four sympatric species of Acrocephalus warblers in southern Moravia, Czech Republic. The parasitism rate was highest in the marsh warbler Acrocephalus palustris (44.8%) followed by great reed warbler A. arundinaceus (33.8%), sedge warbler A. schoenobaenus (26.5%) and reed warbler A. scirpaceus (11.6%). Although the cuckoo eggs showed a high level of mimicry the eggs of the marsh warbler this host species rejected 72% of the cuckoo eggs, resulting in a cuckoo breeding success of only 4.3%. Cuckoo eggs laid in great reed warbler and reed warbler nests showed a similar hatching success, but the cuckoo chicks survived better in great reed warbler nests, resulting in a breeding success of 30.4%, as compared to 16.4% in nests of the reed warbler. The relationship between the level of parasitism, host rejection of cuckoo eggs, cuckoo chick survival and breeding success is discussed for the four host species.     

Male parental care promotes early fledging in an open-nester, the Willow Warbler Phylloscopus trochilus

The importance of male parental care to female reproductive success was investigated in the monogamous Willow Warbler Phylloscopus trochilus by removing the male parent at two different stages of the breeding cycle. Females that were widowed at the start of egg-laying continued breeding and managed to raise their brood on their own with no apparent reductions in numbers fledged or fledgling body-mass. The widowed females compensated for the loss of male assistance by increasing their own food provisioning rate as compared with control females. However, widows spent less time brooding the small young, and the growth rate of nestlings was reduced. In nests where the male parent was removed 7 days after the eggs hatched, the subsequent growth rate of nestlings was still affected, which suggests that male care is influential throughout the nestling period. On average, broods reared by widows fledged 2 days later than did broods of control females. An extension of the nestling period may appreciably affect reproductive success, since 68% of nests failed due to predation, mostly during the nestling period. We suggest that the main role of male parental care in the Willow Warbler is to assure a high growth rate of nestlings, which leads to early fledging and hence a reduced risk of nest predation.     

Habitat use by three Acrocephalus warblers in an intensively used farmland area: the influence of breeding patch and its surroundings

Habitat use by the sedge warbler Acrocephalus schoenobaenus, reed warbler A. scirpaceus and marsh warbler A. palustris was studied during 1998–2000 in an intensively cultivated agricultural landscape in western Poland. The birds occupied mid-field marsh patches (0.05–9.84 ha) and drainage ditches. Using logistic regression models, habitat preferences for particular patch type, characteristics of breeding patch vegetation and surrounding crop type were investigated. All habitat measurements were done within 50-m radius circles around breeding territory centers. The most important factors that influenced species distributions were the proportions of particular habitats within patch area and the type of surrounding crops. Sedge and reed warblers preferred areas with a high proportion of reeds and meadows. Marsh warblers avoided emergents other than reeds, and favored herbaceous vegetation and bushes. Open water areas positively affected reed warbler distribution. Crop type had a significant influence on within-year territory distribution and changes in between-year occupation pattern. In general, birds preferred to settle near fields of oil seed rape, while root crops and spring cereals were avoided. Breeding patch type and structure of reedbeds had relatively little influence on the distribution of breeding territories. The results obtained show that the surrounding landscape may significantly influence habitat use of species breeding in habitat islands in farmland. Depending on their structure and food resources, crops might have different value to the birds.     

The significance of seed food in chick development re‐evaluated by tracking day‐to‐day dietary variation in the nestlings of a granivorous passerine

The dietary adjustment of nestlings of granivorous birds to a seed diet and the different morphological characteristics of ingested food have rarely been examined in natural conditions. It has been suggested that the provision of cereal grains to nestlings of some seed‐eating bird species in modern agroecosytems is the result of poor food conditions after agricultural intensification. We analysed the abundance of invertebrate prey in the main foraging habitat of parent birds, daily changes (from hatching to fledging) in the efficiency of cereal seed digestion, and the dietary characteristics, diet composition and prey type delivered to nestlings of the Yellowhammer Emberiza citrinella. Analysis of faecal sacs from nests located in breeding habitat with an abundant invertebrate fauna revealed no relationship between the proportion of cereal seeds in the diet of nestlings and the food supply in the main foraging sites of the parents. Neonate nestlings (1 day old) exclusively received weakly chitinized invertebrate prey (arachnids and flies), but from the second day of life the nestlings were fed a variety of highly chitinized invertebrate prey, the percentage biomass of which did not change for the remainder of the nesting period. Cereal grains started to be delivered to 3‐day‐old nestlings and were already efficiently digested, and the percentage biomass of this food type increased progressively with nestling age. We suggest that the provisioning of cereal grains to nestlings is not forced by external factors, such as modern agricultural intensification; rather, it is an intentional behaviour of parent birds aimed at achieving physiological adjustment to seed food in the early stages of ontogeny.     

Polygyny and the breeding success of the great reed warblerAcrocephalus arundinaceus

Settlement date, mating status, and breeding success of individually marked great reed warblers, Acrocephalus arundinaceus, were studied during the 1980–84 breeding seasons in Kahokugata, Ishikawa Prefecture, Japan. Twenty-five per cent of the territorial males were polygynous, of which the majority were bigamous. The settling periods of both sexes were long, extending for 65 days in males and 49 days in females. About 80% of males and females settled in the first half of the settling period, and the settlement date of 28–54% males overlapped with that of females. Many of the late settlers were bachelors and the males which mated earlier tended to be polygynous. The timing of a male's settlement is important in acquiring mates. Fifty-five per cent of eggs laid were lost before fledging, mainly due to predation. The mean number of fledglings was 3.19 per primary female, 2.41 per secondary female, and 2.80 per monogamous female. Comparison of the number of fledglings of females which mated during the same period showed that the presence of another female in the same territory did not adversely affect the breeding success of either of the polygynous females. Polygynous males have the advantage of decreasing the risk of breeding failure under high predation pressure.     

黄河三角洲东方白鹳繁殖期觅食栖息地的利用

2008和2009年3—6月,在黄河三角洲自然保护区采用定点观察、GPS定位、样方调查和逐步判别分析等方法对东方白鹳(Ciconia boyciana)繁殖期觅食地的利用进行了研究。共测定了75个觅食利用样方和74个对照样方的14个生态因子。结果表明,东方白鹳繁殖期倾向于在明水面、芦苇沼泽和滩地中觅食,对草地和农田利用极少。偏向于食物丰富度较高的觅食点;对隐蔽级高低没有明显的偏好。对利用样方和对照样方进行比较,发现利用样方具有植被高度和植被盖度较低,觅食地水深相对较浅,距明水面、芦苇沼泽、树林等距离较近,距重度干扰源较远等特征。逐步判别分析表明,距芦苇沼泽距离、样方内水深、距重度干扰源距离、食物丰富度和明水面距离具有重要作用,由这5个变量构成的方程在对繁殖季节东方白鹳觅食地利用样方和对照样方进行区分时,正确判别率可以达到95.5%。东方白鹳繁殖期觅食地的利用主要与水源、人为干扰和食物条件有关。     

Islands in a desert: breeding ecology of the African Reed Warbler Acrocephalus baeticatus in Namibia

The continental African Reed Warbler Acrocephalus baeticatus, like its relative the Seychelles Warbler Acrocephalus sechellensis, breeds in isolated patches. We studied the mating system of the African Reed Warbler to see whether this species, like the Seychelles Warbler, shows co-operative breeding. The African Reed Warbler is not polygynous. The majority breed monogamously (88%, n = 65), however in 12% of the territories three adult unrelated birds (mostly males) were observed participating in the brooding and feeding of nestlings, suggesting a polyandrous breeding system. Multilocus DNA fingerprinting revealed that the helping bird was unrelated to the pair birds. The percentage of nests with helpers was low compared to rates found in the Seychelles Warbler or Henderson Reed Warbler Acrocephalus vaughani taiti. This could be due to the scarcity of potential helpers or to the fact that, although limited, birds still had the opportunity to disperse within a meta-population structure in search of vacant territories. The presence of helpers was associated with increased hatching success due to lower predation rates, but not with increased fledging success. Another possible benefit of helping behaviour in this species could be improved predator detection and mobbing. Nest predation was high and warblers tended to build their nests in the highest, most dense reed patches available in their territory. There was no relation between habitat quality, measured as insect food availability, and the occurrence of helpers.     

Behaviour of female common cuckoos, Cuculus canorus, in the vicinity of host nests before and during egg laying: a radiotelemetry study

We radiotracked 13 common cuckoo females in the southeastern part of the Czech Republic. Seven females laid eggs in the nests of reed warblers, Acrocephalus scirpaceus, sedge warblers, A. schoenobaenus, and marsh warblers, A. palustris. We observed 53 nest visits, of which 26 involved egg laying. Cuckoos spent significantly more time within 50 m of the host nest on the laying day than on the 5 prelaying days. The vantage point used when parasitizing or visiting a nest was on average four times further from the nest than the closest possible vantage point, but there was a positive correlation between these two distances. Cuckoos spent on average 20 min observing host nests from their vantage points before they visited a nest. Comparison of cuckoos' visits to host nests with and without egg laying revealed no significant differences in the duration of visits or in other measures of behaviour. There was significant variation in behaviour between cuckoos, particularly in the time of day when eggs were laid in host nests. This variation can be attributed to the strong, but not absolute, host and habitat specificity of individuals. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Management of reedbeds: mosaic reed cutting does not affect prey abundance and nest predation rate of reed passerine birds

Reed passerine birds are strict habitat specialists inhabiting reedbed habitats. In Europe, many of these species are threatened due to loss and degradation of natural reedbeds. Another important factor that can negatively affect the abundance of reed passerines is commercial reed harvesting. Previous studies have shown negative impacts of large-scale winter reed cutting on passerine breeding assemblages and arthropod communities. The effect of reed cutting on a small scale, however, has not been studied experimentally to date. The aim of this study was to investigate whether and how small-scale, mosaic reed cutting influences prey abundance and nest predation rate of reed passerines. In June, after the reed had reached maturity, we conducted nest predation experiments with artificial nests and arthropod sampling using pan traps in cut reed patches, adjacent uncut reed patches and unmanaged reedbed. We found no differences in the risk of egg predation between three types of reedbeds. In contrast, the abundance of arthropods in cut and adjacent uncut reed patches was significantly higher than that in unmanaged reedbed. We assume this was caused by habitat heterogeneity, small size of cut patches and their rapid recolonization by arthropods from adjacent uncut patches. Our results suggest that in contrast to large-scale reed cutting, small-scale, mosaic reed cutting has no negative effect on nest survival and food abundance of reed passerine birds. However, given that we performed all experiments in June, i.e., when the reed was mature, our findings cannot be generalized to whole breeding period of all reed passerine birds. Therefore, temporal variation in nest predation rate and arthropod abundance in managed and unmanaged reedbeds during the entire breeding season should be examined in future studies.     

Seasonal home range dynamics and sex differences in habitat use in a threatened,coastal marsh bird

A comprehensive understanding of spatiotemporal ecology is needed to develop conservation strategies for declining species. The king rail (Rallus elegans) is a secretive marsh bird whose range historically extended across the eastern United States. Inland migratory populations have been greatly reduced with most remaining populations inhabiting the coastal margins. Our objectives were to determine the migratory status of breeding king rails on the mid‐Atlantic coast and to characterize home range size, seasonal patterns of movement, and habitat use. Using radiotelemetry, we tracked individual king rails among seasons, and established that at least a segment of this breeding population is resident. Mean (±SE) home range size was 19.8 ± 5.0 ha (95% kernel density) or 2.5 ± 0.9 (50% kernel density). We detected seasonal variation and sex differences in home range size and habitat use. In the nonbreeding season, resident male home ranges coincided essentially with their breeding territories. Overwintering males were more likely than females to be found in natural emergent marsh with a greater area of open water. Females tended to have larger home ranges than males during the nonbreeding season. We report for the first time the use of wooded natural marsh by overwintering females. Brood‐rearing king rails led their young considerable distances away from their nests (average maximum distance: ~600 ± 200 m) and used both wooded natural and impounded marsh. King rails moved between natural marsh and managed impoundments during all life stages, but the proximity of these habitat types particularly benefitted brood‐rearing parents seeking foraging areas with shallower water in proximity to cover. Our results demonstrate the importance of interspersion of habitat types to support resident breeders. Summer draining of impounded wetlands that are seasonally flooded for wintering waterfowl allows regrowth of vegetation and provides additional habitat at a critical time for wading birds.     

The common cuckoo Cuculus canorus is not locally adapted to its reed warbler Acrocephalus scirpaceus host

The obligate avian brood parasitic common cuckoo Cuculus canorus comprises different strains of females that specialize on particular host species by laying eggs of a constant type that often mimics those of the host. Whether cuckoos are locally adapted for mimicking populations of the hosts on which they are specialized has never been investigated. In this study, we first explored the possibility of local adaptation in cuckoo egg mimicry over a geographical mosaic of selection exerted by one of its main European hosts, the reed warbler Acrocephalus scirpaceus. Secondly, we investigated whether cuckoos inhabiting reed warbler populations with a broad number of alternative suitable hosts at hand were less locally adapted. Cuckoo eggs showed different degrees of mimicry to different reed warbler populations. However, cuckoo eggs did not match the egg phenotypes of their local host population better than eggs of other host populations, indicating that cuckoos were not locally adapted for mimicry on reed warblers. Interestingly, cuckoos exploiting reed warblers in populations with a relatively larger number of co-occurring cuckoo gentes showed lower than average levels of local adaptation in egg volume. Our results suggest that cuckoo local adaptation might be prevented when different cuckoo populations exploit more or fewer different host species, with gene flow or frequent host switches breaking down local adaptation where many host races co-occur.