Northeastwards Shifts of Waterbird Species’ Wintering Range in European Flyways

by Cortland Henderson

Several studies of bird range shifts have found northward shifts in wintering distributions. However, these studies have been limited by studying the limits of bird migrations, rather than distributions of whole ranges or populations. Research on European butterfly species has found southern boundary retraction in addition to northern boundary expansion, which calls for further examination of whole bird ranges in European flyways. Using survey data from nine countries over a three-decade period, Lehikoinen et al. (2013) track the centers of gravity of three common waterbird species in Europe to determine spatial shifts of entire ranges. They found that a 3.8 °C increase in early winter temperatures in northeastern sites of the European flyway has been linked to north-eastwards shifts in the entire wintering range of all three waterbird species. In addition to overall shifts, they detected that northern boundaries of bird ranges experienced higher rates of expansion than the rates of retraction of southern boundaries. For the first time at the larger flyway level, wintering distribution changes have been linked to rising temperatures. 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

Disequilibrium between Tree Species Distributions and Regional Temperatures

by Cortland Henderson

Correlations between geographic distributions of plant species and the current climate have been identified, suggesting that species ranges will shift upwards if global temperatures rise. These links, however, are based on models that do not establish whether or not plant species are at equilibrium with the current climate, and are incapable of differentiating between naturally occurring shifts and climate-induced shifts. García-Valdés et al. (2013) examine the ten most common tree distributions throughout the Iberian Peninsula by creating a new species distribution model that relaxes built-in assumptions that tree species and climate are currently at equilibrium. Their model successfully removed previous biases and found that tree species are not at equilibrium Continue reading

Turnover versus Migration: Forest Responses to Climate Change

 

by Cortland Henderson

Studying fluctuations in biogeography–or the distribution of species and ecosystems–has been an effective alternative to viewing real life effects of climate change in short time scales. Although there is a large volume of research on the biogeography of animals, there is an inadequate amount of study into the change of forests despite vast amounts of data and the ability to check for age distributions, environmental effects or stressors. Zhu et al. (2014) assert that studying forest biogeography is important because species often fulfill different niches dependent on their life stage. Most models of species migration assume that juveniles and adults have the same environmental requirements, but by studying different life stages of trees, these models might prove inaccurate. One untested theory is that as temperature and precipitation increase, juvenile trees will develop rapid growth, increased mortality, and increased recruitment. This study found that forests in the Eastern United States have increased turnover rather than migrating North as a result of climate change suggesting that climate models need to be modified.

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