Common Buzzards do Better with Colder Environments and Greater Snowfall

by Hilary Bruegl

In Eastern Westfalia, Germany, the varying North Atlantic Oscillation (NAO), which characterizes atmospheric pressure in areas surrounding the North Atlantic Ocean, affects the habitat specifications of the Common Buzzard Buteo buteo, causing a range of survival factors key to this predator’s life cycle to adjust accordingly. Jonker, et al. (2014) discuss the possible factors involved in population survival rates and overall population size in four study locations including the Teutoburger forest, Kiefernheide, Ravensberger Land, and Lower-Saxony. These locations vary in humidity, foliage type, and presence of predators. The authors deduced that time, NAO, spring rainfall, availability of prey, physical appearance or morph, and birth year were the variables most responsible for survival within a buzzard population. A decrease NAO was found to be the overarching variable that ultimately affected prey availability and rainfall, and correlated closest with an increase in buzzard survival. Continue reading

Increased Residency in Short-Distance Migrant Raptor Species in Western Europe

by Cortland Henderson

Shifts in vertebrate and plant migration patterns have become a growing center of study for scientists trying to explain the consequences of climate change. Studies generally focus on birds due to their ability to migrate quickly and the large data sets that are collected by avid birders. Most research has concentrated on changes on spring migration, showing that migration shifts forward as temperatures increase. Jaffré et al. (2013) defined the period of time between spring and autumn migrations of birds as Breeding-Area Residence Time (BART). Although no link between autumn departure dates and changes in temperatures were found, increases in BART length are shown to correlate to increasing temperatures in breeding sites of Western Europe. The authors conclude that migration traits that evolved during prehistoric global cooling stages may fade as partial migrant raptor species increase residency in Northern sites. Consistent patterns of change in the phenology and biogeography of organisms are a result of current climate change, but knowledge of the extent of these patterns is often limited. Since most research has gone into raptor pre-breeding migration in the spring, little has been done to understand possible trends of increased residency in raptors in Northern breeding sites. By studying Mean Passage Date (MPD), or the average date of autumn departure, Jaffré and his colleagues were able to expand past studies of migration patterns. Past record of air surface temperatures from NOAA were compiled and compared against latitudinal abundances of several partial migrant raptor species in Western Europe. These species included Eurasian sparrowhawk Accipiter nisus, common buzzard Buteo buteo (subspecies buteo), marsh harrier Circus aeruginosus (subspecies aeruginosus), hen harrier Circus cyaneus, merlin Falco columbarius, common kestrel Falco tinnunculus and red kite Milvus milvus. The authors chose these birds due to their status as partial migrant raptor species and because they had a sufficient abundance on monitored watch sites that enabled statistical analyses. Continue reading