Why Seychelles Warblers fail to recolonize nearby islands: unwilling or unable to fly there?

The Seychelles Warbler Acrocephalus sechellensis is a rare island endemic which, from 1920 to 1988, occurred only on Cousin Island (29 ha) in the Seychelles. Despite the saturated nature of this population and the possibility of obtaining higher reproductive success on new nearby islands, inter-island dispersal by Seychelles Warblers is extremely rare (0.10%). We test the hypothesis that Seychelles Warblers show an adaptation typical for island birds: a low-cost reduced-size flight apparatus. We compared the anatomy of the flight apparatus (wing shape, wing loading, skeletal parts and musculature) of Seychelles Warblers with that of three closely related migratory Acrocephalus species (Eurasian Reed Warbler A. scirpaceus , Australian Reed Warbler A. australis and African Reed Warbler A. baeticatus ). Seychelles Warblers do not differ from the migratory warblers in pectoral mass and skeletal attachment area relative to body mass, wing shape and wing loading. Seychelles Warblers show the morphological structures required for sustained flight, but may have the behavioural reluctance to cross what they may regard as extensive bodies of water.     

Apomorphine as an emetic for insectivorous songbirds: effectiveness and post‐release effects on survival and mass change

Emetics can be used to obtain food samples from birds, but they can harm birds during or after treatment. Studies to date suggest that apomorphine is a safe emetic for songbirds, but information is needed about possible post‐release deleterious effects. From March to July 2012, we collected food samples from insectivorous songbirds using apomorphine. We treated 67 Moustached Warblers (Acrocephalus melanopogon), 56 Reed Warblers (Acrocephalus scirpaceus), 15 Great Reed Warblers (Acrocephalus arundinaceus), and 12 Savi's Warblers (Locustella luscinoides). Effectiveness in inducing regurgitation was high (76.7%) and varied among species, being significantly more effective with Reed Warblers (91.1%). No birds died during treatment. To check for possible post‐release negative effects, we considered 53 treated Moustached Warblers and 37 treated Reed Warblers and selected an equal number of untreated individuals (simply captured, banded, and measured). We found no support for differences in survival or recapture probabilities between treated and untreated birds of either species within 21 d after administering apomorphine. We calculated body mass changes of all Moustached Warblers subsequently recaptured (within 21 d) and found no difference between treated (N = 8) and untreated (N = 22) birds, suggesting normal foraging activity after release. Our results suggest that apomorphine is a safe emetic, with no negative effect on survival at least in the short term. The effectiveness of apomorphine with insectivorous songbirds in our study contrasts with the results of some previous studies and confirms the differences in effectiveness among different taxa of songbirds. As with differences in effectiveness among species in our study, this variability in sensitivity to the emetic could be caused by morphological and physiological differences among different taxa.     

Prey abundance and male parental behaviour in Acrocephalus warblers

This study examined the prey abundance at nesting sites of five different Acrocephalus warbler species. Intraspecific variations in prey density were analysed to determine the relative significance of this ecological factor for different mating systems and components of male parental behaviour. The Great Reed Warbler Acrocephalus arundinaceus, a facultatively polygynous species, nested in areas with the highest insect abundance. Its intraspecific variation in prey density (between different territories) was the highest while the male: female offspring feeding ratio was the lowest. At the other extreme, the monogamous Moustached Warbler Acrocephalus melanopogon and Reed Warbler Acrocephalus scirpaceus nested in areas with the lowest prey abundance and lowest intraspecific variation. Males of these species had the highest involvement in feeding young. In the Moustached Warbler and Marsh Warbler Acrocephalus palustris, an intraspecific comparison revealed a negative correlation between insect abundance and the male feeding component; a tendency in this direction was found for the Reed Warbler, while no correlation was evident in the polygynous Great Reed Warbler. These data demonstrate a general pattern relating prey abundance, mating systems and male parental investment on an interspecific level. However, intraspecific correlations revealed a net of complex interdependence. One of the factors which may be important is resource predictability. We found a significant correlation between certain vegetation types and insect abundance. The vegetation composition of territories is further influenced by interspecific dominance relationships whereby the dominant Great Reed Warbler occupies territories with the vegetation type which correlates with high prey abundance while the overlapping Moustached Warbler and Reed Warbler are restricted to areas with lower insect density.     

Stable isotope ratios in winter‐grown feathers of Great Reed Warblers Acrocephalus arundinaceus,Clamorous Reed Warblers A. stentoreus and their hybrids in a sympatric breeding population in Kazakhstan

Analyses of the stable isotope composition of feathers can provide significant insight into the spatial structure of bird migration. We collected feathers from Great Reed Warblers Acrocephalus arundinaceus, Clamorous Reed Warblers A. stentoreus and a small sample of their hybrids in a sympatric breeding population in Kazakhstan to assess natural variation in stable isotope signatures and delineate wintering sites. The Great Reed Warbler is a long‐distance migrant that overwinters in sub‐Saharan Africa, whereas the Clamorous Reed Warbler performs a short‐distance migration to the Indian sub‐continent. Carbon (δ¹³C), nitrogen (δ¹⁵N) and deuterium (δD) isotope signatures were obtained from winter‐grown feathers of adult birds. There were highly significant differences in δD and less significant differences in δ¹³C between Great and Clamorous Reed Warblers. Thus, our results show that the stable isotope technique, and in particular the deuterium (δD) signal, resolves continental variation in winter distribution between these closely related Acrocephalus species with sympatric natal origin. The isotope signatures of hybrid Great × Clamorous Reed Warblers clustered with those of the Great Reed Warblers. Hence, a parsimonious suggestion is that the hybrids undergo moult in Afrotropical wintering grounds, as do the Great Reed Warblers. The observed δD values fell within the range of expected values based on available precipitation data collected at precipitation stations across the wintering continents of each species. However, the power to predict the winter origin of birds in our study system using these data was weak as the expected values ranged widely at this broad continental scale.     

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.     

Breeding phenology,reproductive traits and apparent survival of sympatric Marsh Warbler Acrocephalus palustris and Blyth’s Reed Warbler Acrocephalus dumetorum

Capsule: Sympatric Marsh Warblers Acrocephalus palustris and Blyth’s Reed Warblers Acrocephalus dumetorum differ significantly in their life history traits.

Aims: To provide a direct comparison of demographic parameters among two sympatric populations of the closely related Marsh Warbler and Blyth’s Reed Warbler.

Methods: We examined breeding phenology and reproductive traits at a 25?ha study plot. We use program MARK to estimate daily nest survival and adult apparent survival rates.

Results: On average, Marsh Warblers laid the first eggs 3 days later than Blyth’s Reed Warblers. Mean clutch size in the Marsh Warbler was significantly lower than in the Blyth’s Reed Warbler. There are no significant differences between the two species for nest daily survival, duration of incubation and nestling periods. Apparent survival of adults was slightly higher in Marsh Warblers than in Blyth’s Reed Warblers.

Conclusion: Our findings suggest that two ecologically similar sympatric species differ significantly in terms of life history traits. We assume that observed differences could be the result of adaptations to environmental factors in the central parts of the species’ ranges or due to differences in mortality on migratory pathways or wintering grounds.     

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.     

THE BREEDING BIRDS OF THE HULEH SWAMP AND LAKE (NORTHERN ISRAEL).

1. The Huleh swamp and lake, which are now under a draining scheme, are described in relation to their vegetation habitats and the birds breeding in them.
2. Data are presented on the breeding birds, concerning their distribution within Israel, laying season, nest site and clutch size.
3. The Common Heron, White-tailed Eagle, Marsh Harrier, Mallard, Baillon's Crake, Yellow Wagtail, Moustached Warbler and the Great Reed Warbler are here first recorded as breeding in Israel.
4. The relationship between Acrocephalus arundinaceus and A. stentoreus is discussed.
5. Some remarks are made on habitat selection of the warblers breeding in the area.     

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

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

Survival of Reed Warbler Acrocephalus scirpaceus clutches in relation to nest position

Nest survival was studied in relation to nest position of 164 nests of the Reed Warbler Acrocephalus scirpaceus in the Southeastern part of the Czech Republic in 1993. Breeding was successful in 91 (55.5%) cases, whereas 40 (24.4%) were predated, 19 (11.6%) were parasitized by the Cuckoo Cuculus canorus and 14 (8.5%) were destroyed by other causes. Of the predated nests, small mammals accounted for 26 (65.0%) and unknown predators for 14 (35.0%) nests. Rates of predation and parasitism varied in relation to a series of habitat factors and Reed Warblers avoided nest sites most vulnerable to predation or parasitism. Concealed places in the vegetation far away from trees were the safest nest sites.     

Song in two cryptic species: comparative analysis of Large-billed Reed Warblers Acrocephalus orinus and Blyth’s Reed Warblers Acrocephalus dumetorum

Capsule: Songs of Large-billed Reed Warblers Acrocephalus orinus and Blyth’s Reed Warblers Acrocephalus dumetorum differed in quantitative parameters. Blyth’s Reed Warbler used different modes of singing on breeding grounds and migration stopovers.

Aims: To compare the songs of two cryptic species of reed warblers. To compare Blyth’s Reed Warbler songs in different parts of the breeding range and on migration stopovers in central Asia. To investigate the status of Blyth’s Reed Warblers in central Asia.

Methods: We analysed song recordings of individual singing males and conducted field observations of singing behaviour at migration stopover and breeding sites. The status of Blyth’s Reed Warblers in central Asia was reviewed from the historical Russian literature and other sources.

Results: We found differences between six out of eight variables in songs of Large-billed and Blyth’s Reed Warblers on breeding sites. Blyth’s Reed Warbler songs recorded on migration stopovers showed differences in five variables from Large-billed Reed Warblers and in six variables from breeding Blyth’s Reed Warblers. On migration stopovers, Blyth’s Reed Warblers sang actively but did not stay more than 1–2 days. The evidence suggests that Blyth’s Reed Warbler does not breed in central Asia.

Conclusion: Songs of Large-billed and Blyth’s Reed Warblers could be distinguished by quantitative analysis. Blyth’s Reed Warblers used different modes of singing on breeding sites and migration stopovers. We believe vocalizations of Blyth’s Reed Warblers on migration to be plastic song.     

Provisioning of nestling Cuckoos Cuculus canorus by Reed Warbler Acrocephalus scirpaceus hosts

Reed Warblers Acrocephalus scirpaceus fostering a single nestling Cuckoo Cuculus canorus bring food to it at roughly the same rate as they do to an average-sized brood (three or four) of their own young. The food brought, mostly flies and beetles, is also similar. We conclude that the Cuckoo does not provide a supernormal stimulus. We show that Reed Warblers, given experimentally-enlarged broods of seven or eight, can substantially increase their feeding rate. This raises the question of why the young Cuckoo does not exploit this 'spare' feeding capacity of the Reed Warbler hosts. We offer three explanations', (i) that the increased begging necessary would attract predators, (ii) that the young Cuckoo is unable to grow faster, and (iii) that it would not be to the advantage of a young Cuckoo, dependent on its foster parents for about 5 weeks (cf. 3 weeks for Reed Warbler young), to provoke a feeding rate that the warblers could not sustain.     

Parasitierung und Brutverluste durch den Kuckuck (Cuculus canorus) bei Teich- und Sumpfrohrs?nger (Acrocephalus scirpaceus,A. palustris) in Mittel- und Westeuropa

Zusammenfassung Nach 52 brutbiologischen Untersuchungen und Angaben der Parasitierung durch den KuckuckCuculus canorus bei Teich- und SumpfrohrsängernAcrocephalus scirpaceus,A. palustris wird für Mittel- und Westeuropa eine durchschnittliche Parasitierung von 8,3±7,8 % bei Teich- und von 6,3±6,6 % bei Sumpfrohrsängern berechnet (Tab. 1). Wegen der hohen Streuung beträgt der Median beim Teichrohrsänger 9 % und beim Sumpfrohrsänger nur 1,2 %. Selbst unter der Annahme einer gewissen Unausgewohgenheit des Datenmateriales übertreffen diese Werte bei weitem die aller anderen häufigen Kuckuckswirte in Mittel- und Westeuropa. Die Parasitierung des Teichrohrsängers ist fast flächendeckend, beim Sumpfrohrsänger dagegen mehr lückig über die Region verteilt (Abb. 1). Die Parasitierungsfrequenz scheint im Osten und Süden geringer als im Nordwesten. Ihre hohe Brutbestandsdichte macht die beiden Rohrsänger zu idealen Kuckuckswirten. Es gibt Hinweise, daß die Parasitierung bei beiden Arten zunimmt (Abb. 2). Darüberhinaus werden auch zahlreiche Gelege von den Kuckucksweibchen geraubt. Diese Verluste können viermal so hoch sein wie die durch Parasitierung (s. auch Abb. 3). Beide Arten haben zahlreiche Abwehrmechanismen gegenüber dem Kuckuck, wobei die Eiablehnung durch den Sumpfrohrsänger viel heftiger und effektiver ist als beim Teichrohrsänger. Möglicherweise steht der Sumpfrohrsänger unter einem höheren selektiven Druck für erfolgreiches Brüten.

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Parasitism and egg losses due to the Cuckoo (Cuculus canorus) in Reed and Marsh Warblers (Acrocephalus scirpaceus,A. palustris) in central and western Europe

Summary Both Reed and Marsh Warblers are common Cuckoo hosts. In this paper the frequencies of Cuckoo parasitism in 52 studies dealing with breeding success as well as parasitism in both warblers over a wide range of central and western Europe are analysed. Average parasitism rates are 8.3±7.9 % in Reed and 6.3±6.6 % in Marsh Warblers (tab. 1). Taking the high variation coefficient into consideration the median of Reed Warbler parasitism is 9 % and of Marsh Warbler parasitism only 1.2 %. Due to the uneven distribution of the studies over the region analysed and due to the preference by the researchers for smaller study plots vs large habitats there might be some bias towards higher parasitism figures. Nevertheless, both warblers range on top of the list of Cuckoo hosts and have much higher parasitism rates than other common hosts. Parasitism of the Reed Warbler does occur over the whole region, whereas in the Marsh Warbler it is more unevenly and patchily distributed. Parasitism seems to be higher in the northwestern than in the eastern and southern parts of central and western Europe. Both warblers are ideal hosts due to their high population densities in good habitats. There are indications for an increase of parasitism in both species during the last 30–50 years. Besides parasitism, many clutches of both warblers are predated upon by female Cuckoos. The number of predated nests can be four times as high as the number parasitized (see also Fig. 3). Both species exhibit a broad array of counter-reactions against the Cuckoo. The egg rejection by Marsh Warblers is much stronger and much more effective than in the Reed Warbler. Probably Marsh Warblers are under a higher selection pressure for successful breeding than Reed Warblers or have a different strategy to avoid losses.

     

Philopatry of winter moult area in migratory Great Reed Warblers Acrocephalus arundinaceus demonstrated by stable isotope profiles

Stable carbon- (δ¹³C), nitrogen- (δ¹⁵N) and hydrogen (δD) isotope profiles in feathers of migratory Great Reed Warblers Acrocephalus arundinaceus recaptured for 2 or more years in 6 successive years were examined to test whether the isotope profiles of individual warblers appeared to be consistent between years. Similar isotopic signatures in successive years suggested that individual birds tended to return and grow their feathers in Afro-tropical wintering habitats that generate similar δ¹³C, δ¹⁵N and δD signatures. Previous studies have shown that Great Reed Warblers exhibit strong natal and breeding philopatry, with most of the surviving birds returning to the breeding site. The present study of feather δ¹³C, δ¹⁵N and δD isotopic values demonstrate the year-to-year fidelity might also include the African moulting sites in this migratory species.     

Philopatry and natal dispersal of Montagu's harriers (Circus pygargus) breeding in Spain: a review of existing data

Natal dispersal is an important component of bird ecology, plays a key role in many ecological and evolutionary processes, and has important conservation implications. Nevertheless, detailed knowledge on natal dispersal is still lacking in many bird species, especially raptors. We review and compile existing information from five tagging programmes of juvenile Montagu's harriers (Circus pygargus) in different Spanish regions, with PVC rings or wing tags, to provide an assessment of philopatry and natal dispersal of the species in Spain. Only 7% of all tagged harriers were observed as breeders in subsequent years. The percentage of philopatric (i.e. breeding within 10?km of the natal site) males and females was lower that 5%. Overall, there were no sexual differences in percentage of philopatric birds or dispersal distances, but we found study area differences. The low philopatry observed suggests a high capacity for natal dispersal in this species, for both sexes, and therefore high genetic mixing between populations. Differences in philopatry between study areas may be influenced by the different observation effort or detectability, or else reflect different philopatric strategies among populations. Finally, we found no significant differences in philopatry rate or dispersal distances related to tagging method, suggesting that tagging technique has a smaller effect than monitoring effort or observation ease on observation probability. Developing tagging programmes at a small scale and without procuring very large-scale and intensive subsequent monitoring is not worthwhile for evaluating philopatry and natal dispersal in this species.     

WEIGHTS OF SOME PALAEARCTIC MIGRANTS IN SOUTHERN UGANDA

Between March 1966 and May 1968 Palaearctic passerines were mist-netted in thick bush and lightly wooded savannah habitats near Kampala, on the northern shore of Lake Victoria. This paper reports weights of the seven principal species involved. Most migrants appeared to be in a lean condition during the winter months, when weights were relatively low and varied little in each species. Birds were not particularly light on arrival. In fact, autumn Garden Warblers Sylvia borin and Willow Warblers Phylloscopus trochilus were sometimes markedly heavy, and for the former species there was some evidence that the individuals concerned were passage migrants. Autumn weights of Swallows Hirundo rustica, Reed Warblers Acrocephalus scirpaceus and Yellow Wagtails Motacilla flava were similar to those recorded in winter. The mean weight of all species rose during late March or early April. Although most Garden Warblers and Willow Warblers trapped at the time of spring migration were within the normal winter weight range, many Acrocephalus warblers and the majority of Sand Martins Riparia riparia and Yellow Wagtails were rather heavy. Spring weights 40% or more above mean winter weight were not uncommon in the Sedge Warbler Acrocephalus schoenobaenus, but were recorded only occasionally in other species. Although most passerine migrants evidently left Kampala with substantial fat reserves, it was concluded that a considerable number of warblers departed at rather low weight. High spring weights were mainly confined to a period of two or three weeks in each of the warbler species. Locally wintering Acrocephalus warblers must have attained full premigratory weights within three weeks, and a number of spring retraps showed substantial gains at minimum mean rates of between 0–1 and 0–35 g per day. Most heavy Garden Warblers were probably on passage. Significant correlations between weight and wing-length were obtained for all species investigated, regressions of weight on wing-length being in the range 011-0-25 g/mm. Spring weights are briefly compared with data from Nigeria, and the northward migration of passerines from Lake Victoria is discussed.     

Individual patterns of habitat and nest-site use by hosts promote transgenerational transmission of avian brood parasitism status

Brood parasitic birds impose variable fitness costs upon their hosts by causing the partial or complete loss of the hosts' own brood. Growing evidence from multiple avian host-parasite taxa indicates that exposure of individual hosts to parasitism is not necessarily random and varies with habitat use, nest-site selection, age or other phenotypic attributes. For instance, nonrandom patterns of brood parasitism had similar evolutionary consequences to those of limited horizontal transmission of parasites and pathogens across space and time and altered the dynamics of both population productivity and co-evolutionary interactions of hosts and parasites. We report that brood parasitism status of hosts of brown-headed cowbirds Molothrus ater is also transmitted across generations in individually colour-banded female prothonotary warblers Protonotaria citrea. Warbler daughters were more likely to share their mothers' parasitism status when showing natal philopatry at the scale of habitat patch. Females never bred in their natal nestboxes but daughters of parasitized mothers had shorter natal dispersal distances than daughters of nonparasitized mothers. Daughters of parasitized mothers were more likely to use nestboxes that had been parasitized by cowbirds in both the previous and current years. Although difficult to document in avian systems, different propensities of vertical transmission of parasitism status within host lineages will have critical implications both for the evolution of parasite tolerance in hosts and, if found to be mediated by lineages of parasites themselves, for the difference in virulence between such extremes as the nestmate-tolerant and nestmate-eliminator strategies of different avian brood parasite species.     

Auswirkung der Jugenderfahrung auf die Wahl von Habitatstrukturen und auf das Erkundungsverhalten des Mariskens?ngers (Acrocephalus melanopogon)

Ohne Zusammenfassung

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The role of early experience in the selection of habitat structures and in exploratory behaviour of Moustached Warblers (Acrocephalus melanopogon)

     

The response of the Great Reed Warbler Acrocephalus arundinaceus to climate change

We examined long-term responses in the breeding performance of the Great Reed Warblers Acrocephalus arundinaceus to climate change. The study took place in various years from 1970 to 2007. During the study period, mean temperatures in the breeding season of the species increased and precipitation decreased significantly. We found evidence for the significant advancement in both earliest and annual median first-egg-laying dates. This advancement correlated with temperature increases early in the season. The latest first-egg laying dates, however, remained unchanged. Other breeding statistics: clutch size, nest losses, and production of young per nest, did not change significantly over the study period. Precipitation did not affect any of the analysed measures. It is important to note, though, that during dry seasons, the production of young per successful nest was higher. In contrast to some woodland species, the Great Reed Warbler seems to adapt well to climate change by shifting laying dates. The reason for this is probably to optimise food resources.     

Dates of first arrival and song of birds during 1974–99 in mid-Deeside,Scotland

We studied the wing-length and body mass of the two populations of Reed Warblers (summer breeders and transients), and that of the resident Clamorous Reed Warbler, which exist in Israel. We found that, in all three groups, wing-length increases significantly with age for several years. Body mass also increased slightly (but significantly) with age. These differences were not caused by differential survival of juveniles, but appear to be a general phenomenon, possibly related to better nutrition of the adults. The autumn migration of transient Reed Warblers lasted from August until November, but no adults were captured during October and November, while 29.3% of the first-year birds were captured during these months. This suggests that adults can afford to start migration earlier, perhaps due to their greater experience.