Both humans and animals are known to select resources at different spatial scales. For example, when choosing a city in which to live, I might consider weather patterns, local amenities, and job availability. When purchasing a home, I would want to know a house’s square footage, yard size, and safety. Animals respond to environmental conditions at different scales in similar ways. When selecting a home range, a bird might prioritize food resources, water availability, and nearby competitors. When selecting a nest site within a home range, ease of entry and shelter from predators may be more important. These habitat selection processes, combined across many individuals, determine a species’ local distribution.
The first step in studying scale-dependent occurrence patterns is to measure the scales where habitat selection takes place. One method uses movements made by individuals over long time periods. Places where animals move short distances and turn in many directions likely contain important resources like food; places where animals move long distances over short time periods might be dangerous or contain less food or water. Recent technological developments make it possible for very small GPS tags (less than 20 grams) to collect a precise GPS location every 20 minutes, and run for months on solar-powered batteries. During August – October 2012, my team attached GPS tags (built by the University of Konstanz, Germany) to six adult Von der Decken’s hornbills at Mpala. One tagged hornbill often flies by the research station and dining area, showing off his GPS “backpack.”