In order to study the neurophysiology of large-scale spatial cognition, we analyzed the neuronal activity of navigating homing pigeons. This is not possible using conventional radio-telemetry suitable for short distances only. Therefore, we developed a miniaturized data logger ('neurologger') that can be carried by a homing pigeon on its back, in conjunction with a micro-GPS logger recording the spatial position of the bird. In its present state, the neurologger permits recording from up-to eight single-ended or differential electrodes in a walking or flying pigeon. Inputs from eight independent channels are pre-amplified, band-pass filtered, and directed to 8-channels 10-bits analog-digital converter of the microcontroller storing data on a 'Multimedia' or 'Secure Digital' card. For EEG, the logger permits simultaneous recordings of up to eight channels during maximally 47 hours, depending on memory, while single unit activity from two channels can be stored over 9 hours. The logger permits single unit separation from recorded multiunit signals. The neurologger with GPS represents a better alternative to telemetry that will eventually permit to record neuronal activity during cognitive and innate behavior of many species moving freely in their habitats, but will also permit automated high-throughput screening of EEG in the laboratory.