How to hatch from an egg of great structural strength. A study of the Common Cuckoo

Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus . Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.     

Nest defence,enemy recognition and nest inspection behaviour of experimentally parasitized Reed Warblers Acrocephalus scirpaceus

Capsule Reed Warblers in a regularly parasitized population do not recognize Cuckoo Cuculus canorus as a special enemy and do not change their behaviour at nest immediately after being parasitized.

Aims To assess if an intruder near the nest influences the behaviour of the Cuckoo host.

Methods Host responses to Cuckoo, control Pigeon dummies and human intruder were observed. Host behaviour at 71 nests was video-recorded for 30 minutes at four experimental groups of nests: Cuckoo dummy, Cuckoo dummy + Cuckoo egg, Pigeon dummy, human intruder.

Results Reed Warblers did not respond differently to the Cuckoo and the control species. The experimental procedure had no significant effect on the behaviour of hosts during the study period. We were unable to find any differences in the time spent at the nest, clutch inspection behaviour and nest defence behaviour between morning and afternoon experimental groups. Our results do not support the hypothesis that afternoon laying by the Cuckoo is maintained by a selection pressure from the host. We observed no ejection or egg-pecking during the 30-min period after the experimental parasitism.

Conclusions Low aggression and non-specificity of host responses in our study area are in line with the fact that the Reed Warbler is an intermediate rejecter of Cuckoo eggs as expected from the spatial habitat structure hypothesis.     

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.     

Geographic variation in parasitism rates of two sympatric cuckoo hosts in China

Rates of brood parasitism vary extensively among host species and populations of a single host species. In this study, we documented and compared parasitism rates of two sympatric hosts, the Oriental Reed Warbler (Acrocephalus orientalis) and the Reed Parrotbill (Paradoxornis heudei), in three populations in China. We found that the Common Cuckoo (Cuculus canorus) is the only parasite using both the Oriental Reed Warbler and Reed Parrotbill as hosts, with a parasitism rate of 22.4%-34.3% and 0%-4.6%, respectively. The multiple parasitism rates were positively correlated with local parasitism rates across three geographic populations of Oriental Reed Warbler, which implies that higher pressure of parasitism lead to higher multiple parasitism rate. Furthermore, only one phenotype of cuckoo eggs was found in the nests of these two host species. Our results lead to two conclusions: (1) The Oriental Reed Warbler should be considered the major host of Common Cuckoo in our study sites; and (2) obligate parasitism on Oriental Reed Warbler by Common Cuckoo is specialized but flexible to some extent, i.e., using Reed Parrotbill as a secondary host. Further studies focusing on egg recognition and rejection behaviour of these two host species should be conducted to test our predictions.     

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.

     

European Cuckoo Cuculus canorus parasitism and host's rejection behaviour in a heavily parasitized Great Reed Warbler Acrocephalus arundinaceus population

An unusually high frequency (64%) of European Cuckoo Cuculus canorus parasitism was found in Great Reed Warbler Acrocephalus arundinaceus clutches in central Hungary. Sixty-four per cent of the parasitized clutches contained one Cuckoo egg, 23% contained two, 10% had three and 3% had four. This means that 58% of the Cuckoo eggs were found in multiply parasitized clutches. In multiple parasitism the laying second Cuckoo removed an egg from the clutch randomly, so preferred neither the host eggs, nor the concurrent Cuckoo egg. Host response towards the parasitic eggs showed 66% acceptance, 12% ejection, 20% desertion and 2% egg burial. We found great variation in both the host and the parasitic egg colour and pattern. This reduces the chance that the parasitic egg's appearance matched that of the hosts' but, in spite of this, almost perfect mimesis was found in 28% of the Cuckoo eggs. Poorly mimetic Cuckoo eggs were more frequently rejected by Great Reed Warblers than parasite eggs that were very similar to the host eggs. This high level of mimicry sometimes makes it difficult for the observer to identify the parasitic egg, especially when it is similar in size to the host eggs. It is also difficult for the host, as shown by the relatively high recognition error and ejection cost.     

Common Cuckoo Cuculus canorus and host behaviour at Reed Warbler Acrocephalus scirpaceus nests

This study is based on continuous video recordings made at 53 Reed Warbler Acrocephalus scirpaceus nests each day during the laying period. Egg-laying by the Common Cuckoo Cuculus canorus was recorded in 14 (26.4%) of these nests. By analysing the activity of the host birds around and at the nest, we found that this is probably not the only cue used by the Common Cuckoo when locating suitable nests to parasitize. Furthermore, in most cases there was no significant difference between the length of time the host birds spent at the nest in the morning and afternoon, thus providing little support for the hypothesis that the Common Cuckoo lays in the afternoon because it is less likely to be seen by the nest owners then. Parasitized Reed Warblers rejected the Common Cuckoo egg more frequently when they observed the parasite at their nests. However, contrary to what should be expected, most Common Cuckoos laid their eggs in the presence of the host(s), and in general their egg-laying behaviour (for example duration of stay at the nest) was less secretive than described earlier. When partially depredating host clutches, Cuckoos showed the same behavioural pattern at parasitized and unparasitized nests, indicating that the latter may act as a potential reserve for egg-laying.     

CuckooCuclus canorus parasitism onAcrocephalus Warblers in Southern Moravia in The Czech Republic

Summary The Reed Warbler,Acrocephalus scirpaceus, in the Lednice area, Southern Moravia in the Czech Republic, was parasitized by the Cuckoo,Cuculus canorus, at a rate of at least 18.0 %. The Cuckoo eggs showed poor mimesis with the Reed Warbler eggs, but showed a greater resemblance to the eggs of other species breeding in the area, including the Great Reed Warbler,A. arundinaceus. This latter species was also parasitized, but we did not find enough nests to obtain a reliable estimate for the rate of parasitism. The parasitized Reed Warblers rejected the Cuckoo eggs at a high rate (42.1 %) and therefore both the hatching success and the breeding success of the Cuckoo was considerably lower than shown by comparable results from Britain. On the background of these results (poor mimesis of the Cuckoo eggs and a high rejection rate by the hosts) the question of the degree of specialization versus generalism in the Cuckoo's host preference is discussed.

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Zusammenfassung Teichrohrsänger im Gebiet von Lednice (Südmähren, Tschechei) waren mindestens zu 18 % vom Kuckuck parasitiert. Die Kuckuckseier glichen jenen der Teichrohrsänger nur wenig, waren jedoch den Eiern anderer im Gebiet brütender Arten einschließlich des Drosselrohrsängers ähnlicher. Drosselrohrsänger waren auch parasitiert; wir fanden jedoch nicht genug Nester, um eine Parasitierungsrate ermitteln zu können. 42,1 % der Kuckuckseier wurden vom Teichrohrsänger nicht angenommen; daher waren Schlüpf- und Ausfliegerate des Kuckucks merklich geringer als in vergleichbaren Ergebnissen aus Großbritannien. Vor dem Hintergrund unserer Ergebnisse — geringe Angleichung der Kuckuckseier und hohe Ablehnungsrate durch die Wirtsart — wird die Frage von Spezialisierung und Generalismus in der Wirtswahl des Kuckucks diskutiert.

     

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.     

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.     

Changes in migration phenology and biometrical traits of Reed,Marsh and Sedge Warblers

Global environmental processes like climate change could severely affect population level migratory behaviour of long range migrant birds. We analyzed changes in migration phenology and biometrics of three closely-related long-distance migrant Acrocephalus species. We used the records of 12 063 Sedge, 12 913 Reed, and 5 409 Marsh Warblers caught and ringed between 1989–2009, at a Hungarian stopover site. Quantile regressions were used to analyse the changes in spring and autumn migration phenology. Median spring arrival date of Sedge and Reed Warblers shifted 6.5 and 7.5 days earlier, respectively. Autumn arrival of all species shifted one (Reed and Marsh Warblers) or two (Sedge Warbler) weeks later. Mean body mass of adult Reed and Marsh Warblers decreased in spring (by 0.3 and 0.2 grams, respectively) and in autumn (by 0.8 and 0.2 grams, respectively) while body mass of adult Sedge Warblers decreased only in autumn (by 0.4 grams). Mean wing length of all species increased significantly (range of change: 0.6–1 mm). Despite the fact that the studied species are closely related, all three have remarkably different migration strategies. However, similar patterns can be observed in the studied parameters, indicating that global processes may have general effects on these species, albeit through markedly different mechanisms.     

Experimental enlargement of nest size does not increase risk of predation or brood parasitism in the Great Reed Warbler Acrocephalus arundinaceus

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.     

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.     

Responses of breeding Reed Warblers Acrocephalus scirpaceus to mounts of Sparrowhawk Accipiter nisus, Cuckoo Cuculus canorus and Jay Garrulus glandarius

Mounts of a Cuckoo Cuculus canorus , a Sparrowhawk Accipiter nisus and a Jay Garrulus glandarius were presented at nests of Reed Warblers Acrocephalus scirpaceus at all breeding stages. Response strength could best be classified according to approach distance (to the mount) and vocalizations used. Warblers reacted much more aggressively to a mount on the nest than to one 3 m adjacent; they approached much more closely, were less likely to sing but often gave a frenzied-sounding rasp (which was never given to an adjacent mount). Reaction was more aggressive to a Cuckoo, which was often attacked, than to a Sparrowhawk, of which they were wary; response to a Jay was intermediate. Reaction was more aggressive after the clutch had been completed than before. After the brood had fledged, parents still responded strongly to the Jay and Sparrowhawk, but responded to the Cuckoo only briefly before ignoring it. These results are consistent with the Reproductive Value-Stimulus Value hypothesis. They also demonstrate that Reed Warblers can tell Cuckoos from Sparrowhawks, as can many non-host species. The close resemblance of these two species is often suggested to be mimicry of the Sparrowhawk by the Cuckoo but, if this is so, it is not successful. Alternatively, the similarity could be mimicry to reduce predation on the Cuckoos themselves, a chance resemblance, or due to similar selective forces acting on both species, as each would presumably benefit from reduced conspicuousness.     

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.     

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.     

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.     

Vocal mimicry by the Black-browed Reed Warbler Acrocephalus bistrigiceps: objective identification of mimetic sounds

Vocal mimicry by the Black-browed Reed Warbler Acrocephalus bistrigiceps was investigated. To identify mimicry objectively, we measured similarities between the sounds of models and those of Warblers by means of Principal Component Analysis (PCA) using a set of acoustic parameters. Of the sounds suspected of being mimicry according to visual inspection of sonagrams, only 57% were identifiable as mimicry according to PCA. Previous studies have not included quantitative criteria for assessing vocal mimicry, and our results suggest that judgements might not be reliable in the absence of objective criteria. Male Warblers incorporated the mimetic sounds into their songs, and each male mimicked 2–5 species. We found no evidence that females preferred males with large mimetic repertoires. This suggests that vocal mimicry has not evolved in response to selection by females in this species, although our analysis did not reveal entire mimetic repertoires in the Warbler songs.     

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.