Capture and marking One of the main methods we use in our project is marking birds with unique wingtags and radiotransmitters. This permits identification of individual birds in the field with telescopes and the tracking their movements with telemetry receivers. Each summer we capture and tag 2-3 months old young birds, when they are still flightless and dependent on their mothers. Wingtags are covered with paper to minimize their visibility during the first weeks after marking. This eventually falls off to reveal the wingtag.

These two pictures represent the start and the present of more than 20 years of research, with over 600 bustards marked and tracked in several Spanish regions. Left, the first young bustard we marked at Villafáfila Reserve on 16th July 1987. Right, the last young we marked in Madrid province in July 2006.

The radiotransmitter enables tracking the marked bird over a period of 4-5 years. The male “White Star on Red”, marked at an age of two months in Villafáfila in July 1991 (left picture), established as a breeding adult in the Reserve three years later (central picture). The female chick “White Band on Red”, marked in the same year was photographed twelve years later in the same area.
Birds with wingtags can be identified using telescopes once the batteries of the radiotransmitter are exhausted, or, as in the birds of the pictures above, the transmitter is lost as the harness material is worn.

These pictures show another bird marked as a three-months-old chick in Sevilla province, southern Spain, and 30 months later, as an immature male. Today this bird is a breeding male of one of the bustard groups still surviving in Andalusia.

Besides juveniles, we also capture adults using rocket-nets. The birds are quickly removed from the net and immobilized with special jackets. Their heads are covered with hoods to ensure they remain calm.

Ground and aerial radiotracking

Each transmitter sends a signal on a different frequency, which makes identification possible just by hearing the signal with the receiver. The signal can be received at ground level at distances of just a few kilometres. When birds disperse further, the use of aircraft is necessary to locate the birds. The pilots of the Getafe Air Base of the Spanish Air Forces (Base Aérea de Getafe) collaborate with us in the project. The E-24 Bonanza aircraft have proved effective for these aerial searches. Using a GPS and a directional yagi antenna mounted at the wing end we can locate each signal with high precision. This method has enabled tracking long-distance dispersal and migratory movements of many bustards, and thus facilitated the study of their ecology, behaviour and life histories.

The collaboration of the Spanish Air Forces has been fundamental to obtain excellent results on dispersal and migration of the Great Bustards in Spain. During the last fifteen years we have collected over 2000 aerial locations of dispersing birds that were lost during ground tracking.

Adult Great Bustards may perform seasonal movements of up to 250 km between their breeding areas and the sites they use in summer or winter. They follow the same flight routes year after year. Juvenile birds also carry out dispersal movements of several hundred kilometres before establishing as breeding adults at an age of 3-4 years.