Migrant declines linked to wintering grounds
Many UK-breeding birds that migrate to Africa for the winter have undergone dramatic declines in recent decades. New BTO research shows that both winter habitat and the geographical regions visited had a significant effect on population trends, as measured by BBS. Species overwintering in the tropical Humid Zone of west and central Africa declined more rapidly than migrants wintering elsewhere. Species affected included four on the Birds of Conservation Concern Red List: Turtle Dove, Tree Pipit, Spotted Flycatcher and Cuckoo. However, generalist species did well no matter where they wintered, because their ability to adapt to a wide range of habitats allows them to cope with changes to land use (e.g. deforestation) in their wintering grounds. Conversely, habitat specialists are likely to be adversely affected by accelerating changes in their wintering grounds. This research highlights the difficulties and complexities in defining the numerous and often interacting factors underpinning population changes.
Food for thought: studying foraging to protect seabirds at sea
The UK government is committed to establishing an ecologically coherent network of Marine Protected Areas (MPAs) to manage and conserve marine ecosystems. Although seabirds are vital to such ecosystems, there is scant information available on the oceanic regions they use. A new study led by the BTO has sought to address this by bringing together work on how far UK-breeding seabirds travel from their colonies during the breeding season. This study used results from tracking, indirect measures and survey-based observations to calculate ranges over which seabirds might forage, and also assessed the validity of these ranges based on the quality of the methods underpinning them. Manx Shearwater, Northern Gannet and Northern Fulmar had the largest maximum foraging ranges, while Red-throated Diver and Little Tern had the smallest. The approach taken in this study can be used as a first step in identifying areas of ocean that may be crucial for sustaining seabirds.
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.