Tropical forests are becoming increasingly fragmented, threatening the survival of the species that depend on them. Small, isolated forest fragments will lose some of their original species. What is uncertain is how long this process of faunal relaxation will take. We compiled data on birds in five tropical forest fragments in Kakamega Forest, Kenya, of known date of isolation. We then predicted the original and eventual species richness of these fragments and, from this difference, the eventual species losses. Expressing the losses to date as a fraction of eventual losses suggests that faunal relaxation approximates an exponential decay with a half‐life of approximately 50 years for fragments of roughly 1000 ha. In other words, in the first 50 years after isolation, tropical forest fragments of this size suffer half of the total number of extinctions that they are likely to experience. This result sets the time scale over which humanity must take conservation action in fragmented tropical forests, may aid efforts to set priorities, and indicates how high the future global extinction rate will be.

We examined tree species diversity, density, dispersion patterns and size class distributions in Brachystegia woodland of Arabuko-Sokoke Forest, Kenya. The metrics varied with human disturbance (disturbed versus relatively undisturbed areas). Julbernardia magnistipulata Harms occurred only in the undisturbed site. Brachystegia spiciformis Benth. had the highest importance value (IV) at both study sites, whereas the IVs for the other tree species were greater within the undisturbed than the disturbed sites. Simpson's Diversity Index and tree densities were greater in the undisturbed site than in the disturbed site. All seven tree species exhibited random dispersions in the disturbed site, but three species were clumped in the undisturbed areas. Smaller individuals of B. spiciformis were over-represented in the disturbed habitat relative to the undisturbed habitat. In contrast, J. magnistipulata, Lannea schweinfurthii Engl. and Mimusops obtusifolia Wall. exhibited a greater proportion of smaller trees in the undisturbed site. The tree size class distributions may provide an index of regeneration for these four tree species in the disturbed and undisturbed sites respectively. Active management and restoration may be desirable for J. magnistipulata but appears unnecessary for the remaining common tree species. Illegal logging has persisted in the forest despite its conservation status over many decades. If logging activities cease, it would be instructive to document changes in vegetation composition and structure over time.Key words: Arabuko-Sokoke Forest, Brachystegia spiciformis, diversity, Lloyd's index, size distribution RésuméNous avons examiné la diversité, la densité, les schémas de dispersion et la distribution des classes d'âge de différentes espèces d'arbres dans la forêt à Bratystegia d'ArabukoSokoke, au Kenya. Les données mesurées varient avec les perturbations humaines (zone perturbée vs. relativement non perturbée). Julbernardia magnistipulata Harms ne se trouvait que dans la zone non perturbée. Brachystegia spiciformis Benth. avait l'Importance value (IV) la plus grande dans les deux sites d'étude tandis que l'IV des autres espèces d'arbres était plus grande dans le site non perturbé que dans le site perturbé. L'Indice de diversité de Simpson et la densité des arbres étaient plus grands dans le site non perturbé que dans le site perturbé. Les sept espèces d'arbres présentaient des dispersions aléatoires dans le site perturbé, mais trois espèces poussaient en groupes dans le site non perturbé. Les individus plus petits de B. spiciformis étaient sur-représentés dans l'habitat perturbé par rapport à l'habitat non perturbé. Par contre, J. magnistipulata, Lannea schweinfurthii Engl. et Mimusops obtusifolia Wall. présentaient une plus grande proportion de petits arbres dans le site non perturbé. La distribution des classes de taille d'arbres peut donner un indice de la régénération de ces quatre espèces dans les deux sites respectivement. La gestion et la restauration actives peuvent être souhaitab...

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In a field experiment, we measured the giving-up densities and activity of co-occurring American Robins (Turdus migratorius) and European Starlings (Sturnus vulgaris). Across six distances from cover, both species had lower giving-up densities near cover (safe) than away (risky). In terms of activity, both species were more active near than away from cover. Preference for cover was more pronounced for robins. Both species foraged more in the morning than in the afternoon. This pattern was more pronounced for starlings. Relative to the background environment (mowed grass), robins favored the food patches more than starlings. For starlings and robins, respectively, it took 72.6 m2 and 382.3 m2 of background environment to generate the same feeding activity in a 1-m2 food patch filled with 210 mealworms (Tenebrio molitor). The greater degree of herbivory by starlings may explain the robins' greater affinity for food patches (invertebrates only) relative to the background environment (both invertebrates and plants).Densidades de Abandono y Preferencias de Hábitat de Turdus migratorius y Sturnus vulgarisResumen. En un experimento de campo, medimos las densidades de abandono (i.e., “giving-up densities”) y la actividad de individuos simpátricos de Turdus migratorius y Sturnus vulgaris. A través de seis distancias a sitios cubiertos, ambas especies presentaron menores densidades de abandono cerca de sitios cubiertos (seguros) que lejos de éstos (riesgosos). En términos de actividad, ambas especies fueron más activas cerca que lejos de sitios cubiertos. La preferencia por sitios cubiertos fue más pronunciada en T. migratorius. Ambas especies forrajearon más en la mañana que en la tarde, siendo este patrón más pronunciado en S. vulgaris. Con relación al ambiente de fondo (pasto cortado), T. migratorius prefirió los parches de alimento más que S. vulgaris. Generar la misma actividad de alimentación en un parche de 1 m2 con 210 gusanos de la harina (Tenebrio molitor), tomó 72.6 m2 de ambiente de fondo para T. migratorius y 382.3 m2 para S. vulgaris. El más alto grado de herbivoría de S. vulgaris podría explicar la mayor afinidad de T. migratorius hacia parches de alimento (sólo invertebrados) con relación al ambiente de fondo (invertebrados y plantas).