Many migrating animals, belonging to different taxa, annually move across the globe and cover hundreds and thousands of kilometres. Many of them are able to show site fidelity, i.e. to return to relatively small migratory targets, from distant areas located beyond the possible range of direct sensory perception. One widely debated possibility of how they do it is the use of a magnetic map, based on the dependence of parameters of the geomagnetic field (total field intensity and inclination) on geographical coordinates. We analysed temporal fluctuations of the geomagnetic field intensity as recorded by three geomagnetic observatories located in Europe within the route of many avian migrants, to study the highest theoretically possible spatial resolution of the putative map. If migratory birds measure total field intensity perfectly and take the time of day into account, in northern Europe 81% of them may return to a strip of land of 43 km in width along one of coordinates, whereas in more southern areas such a strip may be narrower than 10 km. However, if measurements are performed with an error of 0.1%, the strip width is increased by approximately 40 km, so that in spring migrating birds are able to return to within 90 km of their intended goal. In this case, migrating birds would probably need another navigation system, e.g. an olfactory map, intermediate between the large-scale geomagnetic map and the local landscape cues, to locate their goal to within several kilometres.

Relatively few geophysical surveys have shown how buried traces of agricultural fields can be revealed. An ancient Greek vineyard on the Crimean peninsula was first suggested in a satellite photograph; however, it was discovered only with a magnetic survey. This survey found a 5.7‐ha field that is crossed by about 80 buried stone walls that are parallel and spaced by 2.6 m; this pattern is found only in the vineyard. Later excavations revealed underground walls in this vineyard. The magnetic survey also detected simple magnetic anomalies at three of the four corners of the vineyard. Excavations found that these anomalies are caused by pits that were dug by the ancient Greeks into bedrock to a depth of 2.5 m; the purpose of these pits is not known. The magnetic properties of soil and stone were measured in the excavations, and the magnetic anomalies of the features were calculated. These calculations agree with the measurements, and this means that the entire source of the anomalies was discovered. The interpretation of the magnetic map was adaptive, and it improved as excavations added more information. The archaeological importance of the Ortli vineyard is described along with the efficient procedures that allowed its discovery and mapping. Using the same techniques that were applied at Ortli, another ancient Greek vineyard and farmhouse was later found 1.5 km away. This vineyard has dimensions that are 25% larger than those of the first vineyard. Copyright © 2015 John Wiley & Sons, Ltd.

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