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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.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The frequency of cuckoo Cuculus canorus L. parasitism of reed warblers Acrocephalus scirpaceus Hermann, was investigated in the south-eastern part of the Czech Republic in relation to the distance of the nest from the nearest tree, and to the distance of the nest from that of the nearest active conspecific neighbour. 2. We also investigated whether any differences in egg size, clutch size and laying dates existed between the reed warblers breeding at different distances from trees, and if breeding reed warblers avoided choosing nesting sites near trees. Differences in clutch size and laying date between parasitized and unparasitized birds were also investigated. 3. The frequency of parasitism was higher close to trees and far away from the nearest active neighbour. 4. Our data support the prediction that reed warblers should avoid nesting near trees. The density of breeding birds were higher further away from trees. The egg-laying dates of reed warblers breeding further away from trees were earlier. Finally, we found that reed warblers breeding further away from trees laid significantly larger eggs than birds breeding closer to trees.

The Arctic is entering a new ecological state, with alarming consequences for humanity. Animal-borne sensors offer a window into these changes. Although substantial animal tracking data from the Arctic and subarctic exist, most are difficult to discover and access. Here, we present the new Arctic Animal Movement Archive (AAMA), a growing collection of more than 200 standardized terrestrial and marine animal tracking studies from 1991 to the present. The AAMA supports public data discovery, preserves fundamental baseline data for the future, and facilitates efficient, collaborative data analysis. With AAMA-based case studies, we document climatic influences on the migration phenology of eagles, geographic differences in the adaptive response of caribou reproductive phenology to climate change, and species-specific changes in terrestrial mammal movement rates in response to increasing temperature.

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The Cuckoo (Cuculus canorus) is an interspecific brood parasite that mimics the eggs of its hosts. In this study we tested the resemblance between Cuckoo and host eggs in four host species breeding in sympatry: the Reed Warbler (Acrocephalus scirpaceus), Great Reed Warbler (A. arundinaceus), Sedge Warbler (A. schoenobaenus), and Marsh Warbler (A. palustris). According to the “gentes theory,” individual Cuckoos lay eggs that mimic those of a single host species, and they parasitize only that species. We therefore expected the Cuckoo eggs to more closely resemble the eggs of their respective host species than eggs of sympatric hosts. However, analyses showed no such resemblance; test subjects were not able to distinguish Cuckoo eggs taken from nests of different host species. The most common Cuckoo egg type resembled the eggs of the Garden Warbler (Sylvia borin), a frequent European Cuckoo host which, however, has not been found parasitized in the study area. A possible evolutionary origin for this resemblance is discussed. Results from radio-tracking of Cuckoo females in the study area have shown that host preference does exist. This preference has not yet been manifested in the evolution of clear Cuckoo egg morphs adapted to the different host species.Imitación de Huevos por Cuculus canorus que Parasitan Cuatro Especies Simpátricas de AcrocephalusResumen. El cuco (Cuculus canorus) parasita los nidos de varias especies imitando los huevos de sus especies hospederas. En este estudio cotejamos la similitud entre los huevos de cucos y los huevos de cuatro especies hospederas que crían en simpatría: Acrocephalus scirpaceus, A. arundinaceus, A. schoenobaenus, A. palustris. De acuerdo a la “teoría de gentes” los huevos que pone un individuo de cuco imitan sólo a los huevos de una especie hospedera, y por lo tanto parasita sólo a esa especie. Debido a esto esperábamos que los huevos de cucos fueran más similares a los huevos de sus respectivas especies hospederas que a los huevos de las demás especies hospederas simpátricas. Sin embargo, los análisis no mostraron dicha similitud; los individuos testeados no fueron capaces de distinguir entre huevos de cucos tomados de nidos de diferentes especies hospederas. El tipo de huevo más común de cuco se asemeja a los huevos de Sylvia borin, una especie hospedera frecuente para los cucos europeos, la cual, sin embargo, no ha sido encontrada parasitada en el área de estudio. Se discute el posible origen evolutivo de dicha similitud. Los resultados de telemetría de hembras de cucos en el área de estudio han mostrado que la preferencia de hospedadores existe. Esta preferencia no se ha manifestado aún en la evolución del morfo claro de huevo de cuco adaptado a las diferentes especies hospederas.