Andrzej Dyrcz

Factors affecting facultative polygyny and breeding results in the Great Reed Warbler (Acrocephalus arundinaceus)

In a population of Great Reed Warbler (42–53 stationary males) the sex ratio was balanced and occurence of polygynous males (on average 15 % of the males) was more or less compensated by respective number of unmated males. Prospective polygynists arrived earlier in spring on average than monogamists, and got the first female quicker. Their territories were larger (statistically insignificant) and more often situated close to good foraging grounds. The reeds around primary female nests were on average thicker (and taller) and not so dense as in the case of monogamous, secondary and tertiary females. The intensity of nestling feeding (no. of visits per nestling per hour) was higher in the nests of monogamous females, than in primary females, and lowest in secondary and tertiary females nests. Nestlings in secondary and tertiary female broods were on average lighter than in monogamous and primary female broods. The male helped feed nestlings in secondary female nest only exceptionally. In monogamous situation their share in feeding was ca. 50%, and less so in primary female nests. Production of fledglings per female was highest in primary females and lowest in secondary and tertiary females, mainly due to the high starvation rate in the nests of secondary and tertiary females. Generally, collected data strongly suggest that female choice is determined by territory quality, and polygyny threshold hypothesis cannot be rejected. The “deception” hypothesis cannot be rejected as well in some observed special situations (disruptive territories or polyterritoriality; four cases). Das Geschlechterverhältnis in der untersuchten Drosselrohrsänger-Population von 42 bis 53 ♂ war ausgeglichen. Das Auftreten polygyner ♂ (durchschnittlich 15 % der ♂) wurde mehr oder weniger durch eine entsprechende Anzahl unverpaarter ♂ kompensiert. Prospektiv polygyne ♂ kamen durchschnittlich früher an als monogame und waren schneller verpaart. Ihre Reviere waren (statistisch nicht signifikant) größer und lagen näher zu günstigen Nahrungsgebieten. Das Schilf in der Nähe der Nester von Erst- ♀ war durchschnittlich dicker (und höher) als und nicht so dicht wie bei Einzel- oder Zweit- und Dritt- ♀. Die Fütterungsfrequenz der Nestlinge (Anzahl der Besuche beider Altvögel mit Futter pro Nestling pro Stunde) war bei Nestern von Einzel- ♀ höher als bei Erst- ♀ und am niedrigsten bei Nestern von Zweit- und Dritt-♀. Nestlinge von Zweit- und Dritt- ♀ waren durchschnittlich leichter als solche von Einzel-und Erst- ♀. ♂ halfen nur ausnahmsweise bei der Fütterung von Nestlingen von Zweit- ♀. Bei monogamen Paaren beteiligten sich die ♂ ungefähr zur Hälfte an der Fütterung der Nestlinge, bei Nestern von Erst- ♀ in geringerem Umfang. Der Ausfliegeerfolg war am höchsten beim Erst- ♀ und am niedrigsten bei Zweit- und Dritt- ♀, hauptsächlich bedingt durch Verhungern der Nestlinge. Allgemein legen die Daten nahe, da\ die ♀ die ♂ nach der Revierqualität auswählen und daß das Polygynieschwellenmodell vonOrians undVerner nicht abgelehnt werden kann. Einige Beobachtungen stützen die Hypothese, daß ♂ in bestimmten Situationen (unübersichtliche Reviere, Polyterritorialität) durch Täuschung polygyn werden.

Multiple Vaterschaften in Bruten des SeggenrohrsängersAcrocephalus paludicola: Erste Ergebnisse des DNA-Fingerprintings

Beim SeggenrohrsängerAcrocephalus paludicola ziehen die Weibchen ihre Brut allein auf. Offensichtlich ermöglicht der hohe Nahrungsreichtum des Lebensraumes Seggenwiese die uniparentale Aufzucht der Jungen. Sowohl die Männchen als auch die Weibchen streben Kopulationen mit mehreren Partnern an. Um den reproduktive Erfolg der Männchen zu ermitteln, sammelten wir 1990 in der Biebrza-Niederung in NE-Polen bei 70 Nestlingen in 18 Bruten, den zugehörigen 18 Müttern und 32 Männchen der weiteren Nestumgebung Blut für DNA-Fingerprinting-Analysen. Wir fanden eine große Ähnlichkeit aller Fingerprints, die auf einen gewissen genetischen Verwandtschaftsgrad innerhalb der Population schließen läßt. In keinem Fall konnte intraspezifischer Nestparasitismus nachgewiesen werden, d. h. die Weibchen, die am Nest fütterten, waren immer die leiblichen Mütter. In der Hälfte der Bruten war nur ein Vater, in der anderen Hälfte waren zwischen 2 und 4 Väter beteiligt. Alle Bruten mit 5 und 6 Jungen hatten mehrere Väter. Die Nestlingszahl in Bruten mit nur einem Vater war signifikant kleiner als bei Bruten mit mehreren Vätern. Wir kennen bisher kein Beispiel unter den Passeres, in dem 58 % aller Nestlinge aus Bruten stammen, die mehr als einen Vater haben, und in dem in 44 % aller Bruten 3 oder gar 4 Väter beteiligt sind. Bezogen auf alle untersuchten Jungvögel lag die Rate der „extra-pair paternity“ bei 36 %. Female Aquatic Warblers always care alone for their broods, whereas males are obviously emancipated from any duties. Prerequisite for the uniparental care of the nestlings is the high abundance of arthropods in theCarex vegetation inhabited by Aquatic Warblers. Both sexes strive for copulations with several partners. The reproductive success of the males, which advertize constantly throughout the entire breeding season, was analyzed in this study by DNA-fingerprinting. Blood samples were collected in 1990 in a study plot on the Biebrza marshes/NE-Poland from 70 nestlings of 18 broods, their respective mothers and 32 males. DNA-fingerprint analysis was performed with synthetic multilocus probes ([CAC]5 or [GAA]5) and immunological methods (anti-digoxigenin antibodies coupled to phosphatase) were employed to visualize hybridized DNA bands. Analyzing 70 nestlings, intraspecific nestparasitism could not be detected in any case, i.e. the female feeding at a nest was always the corresponding mother. Nine of 18 broods originated from one single father, while the other nine broods had two to four fathers respectively. Multiple paternity occurred in all broods with five and six nestlings, whereas we found single paternity exclusively in broods with two to four nestlings (p<0.01; Fishers exact test). In most broods with multiple paternity the involved males fathered only just one nestling. The degree of multiple paternity in Aquatic Warbler broods was very high: 58 % of nestlings origined from multiple paternity broods and 44 % of all broods were fathered by 3 or even 4 males. Taking all nestlings into account, the ‘extra-pair’ paternity rate was 36 %.

MALE REPRODUCTIVE SUCCESS IS CORRELATED WITH BLOOD PARASITE LEVELS AND BODY CONDITION IN THE PROMISCUOUS AQUATIC WARBLER (ACROCEPHALUS PALUDICOLA)

Abstract The Aquatic Warbler (Acrocephalus paludicola) has a unique mating system. Males are free of any parental duties and can fertilize many females during a single breeding season. Females also usually copulate with more than one male, and nestlings in a single nest may be sired by as many as five males. Paternal success of 33 Aquatic Warbler males in a Polish population was determined by microsatellite polymerase-chain-reaction analysis. Males infected by blood parasites (trypanosomes) sired fewer offspring, weighed less, and probably arrived later to breeding grounds than uninfected males. Number of nestlings sired by a male correlated positively with its fat deposits and wing length. These findings indicate that male body condition directly influences paternal success. Number of sired nestlings per individual male ranged from one to eight. Reproductive success among males was uneven, with six males (18%) fathering 44% of nestlings in the study area. Males with high reproductive success arrived at the breeding grounds earlier in spring than males with low reproductive success.

Brutzeitliche Beutewahl beim SeggenrohrsängerAcrocephalus paludicola

Aquatic Warblers inhabitCarex Marshes (Magnocaricia) exceptionally rich in arthropods. Contrasting with the otherAcrocephalus species their mating system is some form of polygyny resp. promiscuity and the female alone feeds her nestlings. At 17 nests females fed large prey items compared with the arthropod fauna of the vegetation. Food was collected close to the nest and feeding rate proved to be high. Therefore richness of arthropods in the vegetation seems to form a prerequisite to this mating system untypical amongAcrocephalus warblers.

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.

Responses of Reed Warblers Acrocephalus scirpaceus to Non-Mimetic Eggs of Different Sizes in a Nest Parasitism Experiment

Abstract. Host rejection of parasitic eggs is the most important defence against avian brood parasitism. Here, we examined the influence of egg size differences between host and parasite eggs on egg rejection behaviour in a population of Reed Warblers Acrocephalus scirpaceus parasitized by Common Cuckoos Cuculus canorus. To this end, we experimentally parasitized host clutches using real Chinese Quail Coturnix chinensis and conspecific eggs. Both egg types were painted immaculate blue. The Chinese Quail eggs differed from host eggs in both size and colour, while the conspecific eggs differed only in colour. There were no differences in the rate of rejection rate of the two types of experimental eggs. However, Chinese Quail eggs were rejected primarily by nest desertion, whereas conspecific eggs were mostly ejected. Moreover, clutches with Chinese Quail eggs were deserted significantly sooner in comparison with the ejection of conspecific eggs. Therefore, egg size differences apparently affect the mode and speed but not the rate of egg rejection in this host population.

Breeding statistics of the Aquatic WarblerAcrocephalus paludicola on the Biebrza marshes, northeast Poland

The study population of the Aquatic Warbler showed a low proportion of unfertile eggs (8.6 %), very low nest losses (17.9 %), including losses from predation (11.1 %), and high average production of fledglings per nest (3.25 ±1.9) compared with populations of its congeners and other related species. As adult mortality also seems low, it is concluded that the main threat to this endangered species in the study area may be change of habitat. Eine Population des Seggenrohrsängers in Polen wies im Vergleich zu Gattungsverwandten und anderen nahe verwandten Arten geringe bis sehr geringe Anteile an unbefruchteten Eiern (8,6 %) und Nestverlusten (17,9 %; einschließlich 11,1 % Verluste durch Nesträuber) sowie hohe Jungenproduktion pro Nest (3,25 ±1,9) auf. Da auch die Adultmortalität ziemliche niedrig zu sein scheint, ist zu schließen, daß eine Gefährdung der seltenen Art im Untersuchungsgebiet hauptsächlich von einer Habitatänderung ausgeht.

Great reed warbler Acrocephalus arundinaceus and reed warbler Acrocephalus scirpaceus respond differently to cuckoo dummy at the nest

A cuckoo Cuculus canorus dummy was exposed at 24 nests of great reed warbler Acrocephalus arundinaceus (GRW) and 34 nests of reed warbler Acrocephalus scirpaceus (RW) during the egg-laying stage. The eight GRW pairs attacked the cuckoo directly, striking the dummy, but such a behaviour was not recorded in RWs. Also, other behavioural measures (closest distance from the model, duration of distress calls and number of excitement calls) indicated a lower level of defence by RWs compared to GRWs. In the study area, the parasitism rate was much lower in GRWs (1.7% of nests) than in RWs (11.3%). We suggest that one of the reasons for the lower level of cuckoo parasitism on GRWs is its stronger nest defence and hence higher risk of injury or even death for the cuckoo during egg dumping.

Effect of mowing on productivity in the endangered Aquatic Warbler Acrocephalus paludicola

The Aquatic Warbler Acrocephalus paludicola is a globally threatened habitat specialist that breeds in open fens in Central and Eastern Europe. Because bush and reed encroachment threaten many suitable breeding areas, habitat management is necessary to maintain the open wetlands that Aquatic Warblers require for nesting. The effectiveness of mowing as habitat management has so far only been assessed by counting the number of singing males. To assess whether mowing also affected vital reproduction parameters, we analysed Aquatic Warbler productivity in the Biebrza National Park, Poland, on plots in four different successional stages after mowing. Our study showed that productivity was lowest in the first year after mowing, but increased to the highest levels in the second year after mowing. The productivity differences between areas at different stages after mowing resulted from differences in nest density, since we found little evidence for an effect of mowing on nest survival or the number of fledglings produced per successful nest. Nest survival was highly variable between years and varied mostly with nest age and nest initiation date. The density of singing males was positively correlated with both the nest density and the number of fledglings produced in an area, suggesting that this simple indicator could be used to rank the quality of Aquatic Warbler habitats. We recommend that in mesotrophic fen mires, such as the Biebrza valley, mowing as habitat management is applied less frequently than every second year.

Nestling food of the congeneric and sympatric Rusty-margined and Social flycatchers

Abstract We studied the food of nestling Rusty-margined (Myozetetes cayanensis) and Social flycatchers (M. similis) in 1998 and 1999 at Barro Colorado Island, Panama. Food samples were taken from nestlings by fecal analysis and the neck-collar method. In both species most food items were beetles, winged ants, dragonflies, spiders, and seeds of Miconia spp. Water animals (mainly backswimmers, freshwater snails, and dragonfly larvae) constituted 7.8%–13.5% of animal prey. The nestlings of the Social Flycatcher received significantly more flying insects, while the proportion of fruits and seeds was significantly higher in the diet of Rusty-margined Flycatcher nestlings. Length of animal prey varied from 4–25 mm in the Rusty-margined Flycatcher and 2–50 mm in the Social Flycatcher, and the length of fruits and seeds were 4–11 mm and 2–19 mm, respectively. The average length of animal food was larger in the Rusty-margined Flycatcher despite its slightly smaller size. The number of broods with nestlings or fledglings present in the study area was positively correlated with the abundance of fruits in the Social Flycatcher.