Short-eared Owls: ringing reveals mysterious migration
A century of Short-eared Owl ringing has shown differences in this species’ migration over space and time, providing clues about how population sizes may have changed during that period. A candidate for red-listing (based on declines apparent from the Atlas) analyses of ringing recoveries have found that birds originating from Scandinavia and Central Europe travelled the furthest on migration, while those from Britain and the North Sea area made the shortest journeys. More surprisingly, distances travelled tended to increase from the 1920s through to the 1960s and 1970s, but have since fallen. These patterns might be associated with changing population sizes. Further, these trends may have contributed to breeding declines in more southern and isolated parts of this species’ range, where populations are compromised without periodic immigration. The analyses also highlight the particular potential of Britain, with its shorter distances between breeding and wintering grounds, to facilitate the conservation of this vulnerable species.
Increases in browsing deer depress woodland bird populations
Newly published work by BTO scientists in the Journal of Applied Ecology indicates that the increasing abundance of three widespread deer species is contributing to declines in breeding populations of woodland birds found in dense understorey habitats. Using data from the Breeding Bird Survey, this research suggests that the impact of deer is greatest for two species of conservation concern, the Willow Tit and the Common Nightingale.
Are uplands a good refuge for declining farmland birds?
Like several species, the Whinchat was once common across lowland Europe, but has recently suffered substantial declines as agricultural practices have intensified. Populations are now increasingly concentrated in more upland areas, where agriculture is of a lower intensity, but where environmental constraints, such as low ambient temperatures, may limit habitat suitability. Recent research by BTO Scotland has explored the habitat requirements of Whinchats breeding in British uplands. As these areas represent a refuge for a number of declining bird species, this work has important conservation implications.
Crossing the Sahara desert: migratory strategies of the Grasshopper Warbler
Although a quarter of Europe’s breeding bird population crosses the Sahara on spring and autumn migration, when, where and how species prepare for and recover from this difficult and dangerous part of their journey remains poorly understood. Recent work by the Wetland Trust and the BTO has used ringing datasets from Portugal and Senegal to explore these questions in the Grasshopper Warbler.
Trichomonosis spread by migrating finches
Since its emergence in 2005, the parasitic disease trichomonosis has caused epidemic mortality and significant population declines in British Greenfinches and Chaffinches. This began in western England and Wales, but spread to eastern England, and more recently, southern Fennoscandia.