JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Ornis Scandinavica. . 1991. Survival and population dynamics of Nuthatches Sitta europaea breeding in natural cavities in a primeval temperate forest. -Ornis Scand. 22: 143-154.Data on breeding densities of Nuthatch were collected in three types of mature tree stands in Bialowieza National Park, E Poland, during 1975-90. Detailed observations on breeding and survival were made during 1987-89. The highest densities occurred in swampy stands (max. 4.8 territories per 10 ha), they were 10-47% lower in oak-hornbeam stands, and in coniferous stands densities did not exceed 1.2 territories per 10 ha. Nuthatch numbers reached a low in 1979, then increased over fourfold to a maximum in 1990. In contrast to the situation in Scandinavia, Nuthatch numbers in spring were not significantly correlated with the severity of the preceding winter, though their numbers seemed to be influenced by autumn seed supply and availability of caterpillars in the preceding spring. Yearly survival rates were close to 50%. Winter survival equaled that in spring and summer, and was even higher in the unusually mild winter of 1989/90 which had a rich supply of hornbeam seeds. Egg-laying in BNP commenced between 5 April and 26 April in different years. Clutches usually contained 6-9 eggs. On average two thirds of the nesting attempts resulted in fledged young, though nesting success varied much between plots. Nest losses were among the highest reecorded in European populations. Nests containing young were destroyed two to four times as often as nests with eggs, suggesting that the losses were mainly due to predation.

Geographic variation in the plumage pattern of birds is widespread but poorly understood, and in very few cases has its evolutionary significance been investigated experimentally. Neotropical warblers of the genus Myioborus use their contrasting black-and-white plumage to flush insect prey during animated foraging displays. Although previous experimental work has demonstrated that white plumage patches are critical to flush-pursuit foraging success, the amount of white in the plumage shows considerable interspecific and intraspecific geographic variation. We investigated the evolutionary significance of this geographic variation by experimentally decreasing or increasing the amount of white in the tail of slate-throated redstarts (Myioborus miniatus comptus) from Monteverde, Costa Rica, to mimic the natural extremes of tail pattern variation in this species. In addition to measuring the effects of plumage manipulation on foraging performance, we performed field experiments measuring the escape response of a common insect prey species (an asilid fly) using model redstarts representing four different Myioborus plumage patterns. Our experiments were designed to test four hypotheses that could explain geographic variation in plumage pattern. Compared to controls, experimental birds with reduced-white tails that mimic the plumage pattern of M. miniatus hellmayri of Guatemala showed significant reductions in flush-pursuit foraging performance. In contrast, the addition of white to the tail to mimic the plumage pattern of M. miniatus verticalis of Bolivia had no significant effect on foraging performance of Costa Rican redstarts. In field experiments with asilid flies, model redstarts simulating the plumage of M. miniatus comptus of Costa Rica and M. miniatus verticalis of Bolivia elicited greater responses than did models of other Myioborus taxa with either less or more white in the plumage. The results of our experiments with both birds and insects allow us to reject two hypotheses for geographic variation in plumage pattern: (1) that geographic variation is a nonadaptive result of genetic drift, and (2) that selection for enhanced flush-pursuit foraging performance generally favors increased white in the plumage, but evolutionary trade-offs constrain the evolution of extensive patches of white in some geographic regions. Instead, our results suggest that geographic variation in the plumage pattern of Myioborus redstarts reflects adaptation to regional habitat characteristics that enhances flush-pursuit foraging performance.

The Whiskered Tern population in Poland has rapidly increased from 40 breeding pairs in 1990 to over 1,600 in 2007, with strongest local population in the Upper Vistula River Valley. Owing to rather low pre-breeding and adult apparent survival rates estimated for this population (0.54 and 0.80, respectively) and a delay in accession to reproduction (recruitment completed at age 3), matrix modelling indicated an intrinsic growth rate of k calc = 1.02. Observed growth rates of both the Polish and the Upper Vistula River Valley populations was k obs = 1.29. Using the deterministic population projection matrix including immigrant class, we estimated that, on average, 44 immigrants should enter the Upper Vistula River Valley population annually to match the observed growth. With survival rates increased (U P = 0.63, U B = 0.90) as to mimic no emigration and reduced dispersal, the estimated number of immigrants was only eight, indicating that substantial emigration rates are likely. A majority of the breeding sites were recorded in man-made water bodies. Colonisation has started in the southeast and proceeded towards the northwest. The strong, stable population in western Ukraine may explain high numbers of immigrants that could originate from there. Other factors favouring quick colonisation of Poland include availability of suitable breeding sites, the wide flexibility of the species with respect to breeding habitat, plentiful food, and high breeding success in the Upper Vistula River Valley. It also seems likely that westward shifts in both breeding and wintering ranges could add to the strong population increases in Eastern Europe.Die Ausbreitung der Weißbart-Seeschwalbe (Chlidonias hybrida) in Polen: Rolle der Zuwanderung Die Population der Weißbart-Seeschwalbe (Chlidonias hybrida) in Polen ist von 40 Brutpaaren (1990) sehr rasch auf über 1600 Brutpaare (2007) angewachsen, mit der stärksten örtlichen Population im oberen Weichseltal. Wegen der für diese Population geschätzten, ziemlich niedrigen Ü berlebensrate junger und adulter Vögel (0,54, bzw. 0,80) und der Verzögerung, mit der das Reproduktionsalter erreicht wird (mit 3 Jahren), legen MatrixModelle eine intrinsische Wachstumsrate von k calc = 1,02Communicated by C. Barbraud. Electronic supplementary materialThe online version of this article

Abstract. Geographic variation in the plumage pattern of birds is widespread but poorly understood, and in very few cases has its evolutionary significance been investigated experimentally. Neotropical warblers of the genus Myioborus use their contrasting black-and-white plumage to flush insect prey during animated foraging displays. Although previous experimental work has demonstrated that white plumage patches are critical to flush-pursuit foraging success, the amount of white in the plumage shows considerable interspecific and intraspecific geographic variation. We investigated the evolutionary significance of this geographic variation by experimentally decreasing or increasing the amount of white in the tail of slate-throated redstarts (Myioborus miniatus comptus) from Monteverde, Costa Rica, to mimic the natural extremes of tail pattern variation in this species. In addition to measuring the effects of plumage manipulation on foraging performance, we performed field experiments measuring the escape response of a common insect prey species (an asilid fly) using model redstarts representing four different Myioborus plumage patterns. Our experiments were designed to test four hypotheses that could explain geographic variation in plumage pattern. Compared to controls, experimental birds with reduced-white tails that mimic the plumage pattern of M. miniatus hellmayri of Guatemala showed significant reductions in flush-pursuit foraging performance. In contrast, the addition of white to the tail to mimic the plumage pattern of M. miniatus verticalis of Bolivia had no significant effect on foraging performance of Costa Rican redstarts. In field experiments with asilid flies, model redstarts simulating the plumage of M. miniatus comptus of Costa Rica and M. miniatus verticalis of Bolivia elicited greater responses than did models of other Myioborus taxa with either less or more white in the plumage. The results of our experiments with both birds and insects allow us to reject two hypotheses for geographic variation in plumage pattern: (1) that geographic variation is a nonadaptive result of genetic drift, and (2) that selection for enhanced flush-pursuit foraging performance generally favors increased white in the plumage, but evolutionary trade-offs constrain the evolution of extensive patches of white in some geographic regions. Instead, our results suggest that geographic variation in the plumage pattern of Myioborus redstarts reflects adaptation to regional habitat characteristics that enhances flush-pursuit foraging performance.