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onsdag 29 juli 2009

The pigeon project

Since 1996 a variety of species of raptor birds has been tracked by satellite telemetry by the migration ecology group in Lund. The first species that was tracked was the Osprey, a large fish-eating raptor that winters in West Africa. Other species that were tracked by satellite were the Honey Buzzard, the Marsh Harrier, and the Buzzard (a short distance migrant). The main reason to focus on raptor birds was simply that they are relatively big, and can thus carry devices that weigh several tens of grams. Recently satellite transmitters have become small enough to follow smaller birds, which has allowed us to record the incredible migration of the Hobby between breeding sites in Skåne to wintering sites south of the equator in Angola/Zambia.

The satellite tracking program still continues. Currently we focus on obtaining more detailed tracks by combining satellite telemetry with GPS technology. Nowadays we can follow migrating Ospreys in such detail that we can see exactly where they catch their fishes! A consequence of tracking only raptor birds is that one might get a somewhat biased view on migrating birds, as raptor birds only represent one type of migrant. One very typical aspect of raptor birds is that they frequently soar in thermals, a very energy efficient way of travelling. Even the small Hobby might be able to profit from these columns of raising air, although it is unknown to what extent. It would therefore be very interesting to track a species that does not soar, but still flies during the day. A species that is big enough to carry a 22g transmitter. That is how we ended up with Wood Pigeons.

The Wood Pigeon is a strong flyer that only flies during the day. They make considerable migrations; birds ringed in Sweden were recovered from wintering sites in France and Spain. In October, one can witness an impressive Wood Pigeon migration at Falsterbo, where flocks of sometimes thousands of birds congregate before the water crossing.

So the task was to catch 4 Wood Pigeons for GPS satellite transmitters. We decided to focus on birds breeding outside towns and villages as this presumably reduced the risk that we tag a bird that stays the winter in Sweden (small numbers of Wood Pigeons can be found in towns in the winter). The idea was catch them near the nest using mistnets. As we cannot easily raise the nets very high above the ground we were searching for nests in bushes or low in the trees. Early in the season a considerable number of suitable nests was found. However, at the time the transmitters had arrived all these ‘low nests’ had disappeared, and the pigeons were laughing at us from their safe nests high in the trees...

At the end, one very good candidate nest was still active. Upon approach, with the satellite transmitters in my backpack, I was pleased to see a large young sitting on the nest! A closer inspection however revealed two furry ears, characters unknown to birds... No, it was a Marten sleeping on the pigeon nest! Two predated eggs were lying under the nest, and a tail feather from one of the parents...

Marten on the pigeon nest, looking anxiously at frustrated pigeon catcher.

Predated eggs and Wood Pigeon tail feather under the nest.

As the breeding season progressed it became more and more challenging to obtain birds. No birds were caught despite several attempts in Skåne and even near Grimsö. When we were visiting the bird observatory on Öland we explained for the young but experienced bird catchers that we were in need of Wood Pigeons. They unanimously reported that the Wood Pigeon is a very difficult species to catch. The last time Wood Pigeons were ringed at the station was almost 2 years ago... The next day we were out in the field, when we received a phone call that they had just caught two Wood Pigeons at the ringing station! We thus rushed back to apply transmitters on these birds. We are very grateful to the staff that they remembered us talking about pigeons and thus not had released the birds directly after ringing!

A happy researcher with the first Wood Pigeon with a satellite transmitter.

Wood Pigeons being released!

The very first results are already very interesting. The birds are commuting between some resting place at Ottenby and foraging fields just northeast of the area. The flight speeds are different from what we observe in raptor birds. The pigeons regularly fly about 60 km/h, which is in the upper range of flight speeds as we have recorded for raptor birds.

GPS locations for a Wood Pigeon on Öland. The birds rest in the southern forested area and feed on field in the north.

We are now anxious to see the migration. Let’s just hope that these individuals will not be one of the 15 million (!) pigeons that are shot every year in Europe...

söndag 26 juli 2009

Light-logger plovers breed successfully

In the previous item we reported on the successful light-logger deployment on little ringed plovers. The last pair was outfitted with loggers while they were still incubating eggs in late June. Upon returning back to Dalby after some time of vacation the breeding site was checked, and we immediately observed the adult birds (easily identified by their colour bands, while the light-loggers are quite hard to observe). The behavior of the adult birds (calling when approaching them and wounded bird display, or rodent run as it is also called) suggested the presence of young. After observing the birds from a distance when they resume undisturbed behavior, the young could be seen feeding when being overlooked by the parents. All four, now more than 10 day old, young could be ringed on the 25 July. On evening of the 26 July the birds could still be heard calling from the Hedenström/Åkesson garden as the plover family resides only about 100 yards away. This observation is encouraging since it shows that light-logger birds apparently are capable of breeding successfully. Now we only have to hope the birds return in 2010 after a successful migration, to where we do not have a clue yet.