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The largest rivers in developed countries have usually been turned into waterways by straightening them and removing large bedforms hampering navigation. For river restoration and their sustainable management it is important to know how large bedforms support biodiversity, whether they could be protected and what potential conflicts in river management they can pose. We have addressed these questions by studying the role of large bedforms in supporting populations of two inland tern species Sternula albifrons and Sterna hirundo. We spatially analysed the behaviour of these two species with reference to the bedform structure mapped over a long semi-natural reach of the River Wisła (Vistula) (S. Poland). The results show that radiotagged terns breed on islands within the aggradation reaches, foraging in the adjacent shallows inhabited by populations of small fish. For Little Terns, the more complex the water line of emergent forms, the greater their foraging intensity. The islands do not pose any flood risk to human settlements. The whole geofeature forms an integral habitat for fish and birds; it is maintained by its geographic settings and so is stable over long periods of time (over 200 years). Protection of such habitats is thus feasible. [ABSTRACT FROM AUTHOR]

There is growing evidence that the fitness of birds in temperate zones depends strongly on the match between the timing of breeding and local phenology. We have analysed data collected from a 15-year study on a Sedge Warbler ( Acrocephalus schoenobaenus) population in its natural habitat. The highly skewed distribution of arrival dates of males indicated that they competed intensely to be the earliest arrivals. The distribution of mating dates, unlike arrival dates, was not skewed, rather it formed a bell-shaped distribution. Because females arrived much later, they could not base their mating choices on the arrival dates of males. Females, however, could use male song repertoire, a trait we found to be correlated with male arrival date. Double-brooded females mated early in the season, exactly within the peak of mating date distribution. Polygynous females, on the other hand, mated later in the season, choosing high-quality older males which had arrived significantly earlier. Male territory quality did not differ between double-brooded and polygynous females, nor did the quality of the territories occupied by an individual female change during her lifetime. Although longer lifespan and double-brooding influenced a female's fitness over the course of her lifetime, polygyny had no significant effect. We conclude that Sedge Warbler females do not compete for territorial resources, but they do prefer to mate with high-quality early-arriving males. Polygyny is an effective strategy used by females to compensate for their late arrival and breeding onset, since they pair with high-quality males. [ABSTRACT FROM AUTHOR]

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A territorial male can shift the location of its territory from year to year in order to increase its quality. The male can base its decision on environmental cues or else on its breeding experiences (when territory shift is caused by breeding failure in previous seasons). We tested these possible mechanisms of territory choice in the sedge warbler ( Acrocephalus schoenobaenus), a territorial migrating passerine that occupies wetlands. This species bases its territory choices on an environmental cue: tall wetland vegetation cover. We found that the magnitude of territory quality improvement between seasons (measured as the area of tall wetland vegetation) increased throughout the early stages of a male's breeding career as a result of territory shifts dependent on the earliness of arrival. The distance the territory was shifted between seasons depended negatively on the previous year's territory quality and, less clearly, on the previous year's mating success. On the other hand, previous mating or nesting success had no influence on territory quality improvement between seasons as measured in terms of vegetation. The results imply that tall wetland vegetation is a long-term, effective environmental cue and that a preference for territories in which this type of landcover prevails has evolved into a rigid behavioral mechanism, supplemented by short-term individual experiences of breeding failure. [ABSTRACT FROM AUTHOR]