Tailwind for animal migration
A computer model links migratory movements with environmental data from satellites
No hiking without a reliable weather report - a rule that also applies for animal species which sometimes migrate thousands of kilometres along their given routes. It is not only the weather that governs their movements, however, but also other environmental factors. Working with colleagues from the Ohio State University, USA, scientists from the Max Planck Institute for Ornithology in Radolfzell have developed the Env-DATA system to link patterns of movement with hundreds of environmental datasets. This enables researchers to access global satellite data at the click of a mouse and track, for example, how Galapagos albatrosses (Phoebastria irrorata) fly from their Pacific island home to the coast of Peru to make the most of the nutrient-rich ocean currents. In doing so, they take different routes on the outward and homeward journeys to minimise the need to fly against headwinds.
Animal migrations are among the most fascinating spectacles on Earth. At any given time, countless species are moving around the globe, some covering only short distances and others crossing entire continents. GPS transmitters now enable scientists to track their movements with great accuracy. Movebank (www.movebank.org) is a freely accessible online database developed by Martin Wikelski and his colleagues at the Max Planck Institute for Ornithology in Radolfzell, which documents the migrations of over 300 different species, making it the biggest compilation of its kind in the world.
The reasons for animal migration are many: mating, the search for food, or protection from predators. However, animals are exposed to a wide variety of environmental factors as they travel, and these play a major role in shaping their journeys. Birds and whales, for example, select their routes in such a way that the wind and ocean currents are with them, so they expend less energy.
Satellites and stations on land and at sea measure these factors. Until now, however, it was a very laborious task to link the data on migratory patterns to the corresponding environmental conditions. Consequently, the scientists developed a software module for Movebank that automatically links the migratory data to the corresponding measurements for environmental conditions on the ground. They can thus observe the temperatures, wind speed or ocean currents applying at every stage of a particular migratory movement. “The application makes it possible for scientists around the world to link movement patterns to this type of data. In the past, projects of this kind comprised doctoral theses, whereas now a click is all that is needed”, says Martin Wikelski. The program uses computer capacity from the Max Planck Society’s computing centre in Garching near Munich, and accesses various sources of environmental data, including NASA and ESA measurements of vegetation, ice cover, geography and rainfall.
The Max Planck scientists together with Gil Bohrer from Ohio State University and his colleagues used the new computer models to analyse the conditions on the flight paths of the Galapagos albatross. These seabirds breed on various islands in the Galapagos archipelago during the summer months, setting out from there on long flights to provide their young with food. The scientists fitted nine birds with GPS transmitters and tracked them for four months. “By linking in with the data gathered by Oregon State University on primary production in the ocean, we found that the albatrosses fly to areas off the Peruvian coast that have high concentrations of chlorophyll.” This indicates that the areas are rich in phytoplankton, and thus in fish - the main food of the albatross.
The birds follow a clockwise route that enables them to benefit from tailwinds for most of their journey. First, they take the shortest route to the mainland, then turn south along the coast in their search for food. Only when they turn back to the north do they ‘sail close to the wind’, and must struggle against the prevailing winds on the homeward leg. “The albatross case study shows how important it is to analyse migratory and environmental data together. The prevalent environmental conditions at any given time determine when animals set out on their journeys and which route they select”, explains Wikelski. In future, this data will make it possible to predict the influence of global environmental changes on animal migrations and human activities.