Tuesday 2 October 2012

Results from the Landbeach Geolocator Swift

by Dick Newell

We previously reported on the behaviour of one of the Landbeach Swifts, Swift 396, in its nest-box on the day that it was fitted with a geolocator, 21st July 2011.  We recorded it again on its last day, 28th July 2011, having successfully raised 2 chicks. We were therefore delighted when it reappeared in the box on 12th May 2012. It settled down to breed and we retrapped it to retrieve the geolocator on 21st June. About a week later, the chicks died, probably through lack of food, but both birds continued to visit the nest-box until 28th July, the same date as the previous year.
Since that time, the BTO has published the results of one of the Fowlmere birds retrapped in 2011, and results from birds fitted with geolocators in Sweden have also been published. So now, we can tell the story of the Landbeach geolocator swift.
click image to enlarge
The route taken by Swift 396. The red line marks its journey south and green the return journey.
The dotted green section is around the spring equinox, when positions are unreliable. 
The bird was in the Congo for the autumn equinox.
[Data shown courtesy British Trust for Ornithology]
The journey followed by Swift 396 resembles quite closely a number of other British Swifts. The following is a paraphrase of Chris Hewson's analysis and account of Swift 396 (thank you Chris):

"The positions (yellow symbols) are averages for day & night positions for three day periods, this smooths the data and also compensates for movement between successive dawn or dusk events.  Points within 20 days  of each equinox are removed, because the determination of latitude cannot be achieved reliably. After 21 April, daily 3-day running averages are shown (i.e. the three day periods overlap by two days) to give a clearer idea of the migration from central through to west Africa. It probably arrived back in Landbeach sometime on 12 May but didn't go back into the box until after dark. The first time one can be sure it was back in the box was 0728 on 13 May but it was probably there in the evening of 12 May. 

It left on 28 July 2011. It then spent about 8 days in southern Spain but still managed to be in the Congo in less than 4 weeks. There is a nice cluster in the western part of the Democratic Republic of Congo, where it spent the time from around 24th August until it left on its winter 'excursion' to Mozambique around 10th December.  After the spring equinox 'blackout', it looks like it is in northern Angola before moving into Gabon then across the Gulf of Guinea to Ivory Coast / Liberia. This bird seems to cross the Gulf of Guinea from near the equator with the first positions in West Africa off Ivory Coast. While at first sight, this may be hard to believe, tracks of other birds also show birds arriving off Liberia from the south-east, which indicates an oversea approach and gives confidence that these birds fly over the Gulf as does the fact that no tracks have been seen with a bird hanging around further east than the Ivory Coast."

As if a 2000km journey across the ocean was not enough, the bird refuelled for a week in Ivory Coast and Liberia until 5th May, and then it was back in its box in Landbeach on 12th May, that is over 5000 km in 7 days!

1 comment:

  1. Dick, the link to the Swedish results is not correct I suppose (The link "published" goes to the BTO-story again). Should it be ?: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041195

    Jaap Langenbach at : http://members.ziggo.nl/jaaplangenbach/Gierzwaluwwoudsend.html