SeyCCAT project: update on satellite tracking of juvenile Sooty Terns from Bird Island

Since our arrival on Bird Island on 20 August, and Rachel Bristol’s arrival the following day, our main activity has been to prepare the 15 satellite tags (five made by Microwave Telemetry Inc. (MTI) and ten manufactured by Lotek in UK that have been bought for the SeyCCAT-funded project. This is aimed at investigating the movements and feeding areas used by juvenile Sooty Terns in the months following their departure from the island, and at the time of gaining independence from their parents (see blog posts of 20 June and 5 July 2019). This is likely to be a critical time in their survival and at a location where food is easily obtainable.

The tags relay location information from the tag to satellites from the Argos constellation that orbit the earth. This satellite system is widely used for the long-term tracking of a wide variety of animals, both marine and terrestrial, and of sizes from whales down to increasingly small birds as the technology becomes ever more miniaturised. The tags we are using on Sooty Terns weigh 5-6 grams but Microwave Telemetry Inc. now produce a satellite tag weighing only 2 grams.

Rachel loading our transmission schedule on to a Lotek tag; Chris ensuring the tag remained connected to the laptop (Photo: Christine Larose)

Our preparatory work has involved much reading of manuals to teach us the intricacies of what to us is new technology. Having digested as much as we can, Rachel (who is leading the satellite tracking project) has taken the lead in scheduling the tags to communicate location information to the satellites at intervals that will provide the information we need, without draining the solar-charged batteries on the tags to excessive extents. From her laptop we have initially prepared brief schedules to test that the tags are working correctly in transmitting information to the satellites, and that we can then access. To achieve this, we have set up the tags, as instructed by the manufacturers, in an open area of the island as far as possible from trees and with a clear view of the sky. The tags must be separated from each other by at least one metre and be supported off the ground. With the limited resources available on Bird Island we found the ideal supports – plastic crates from the Seychelles brewery that produces the local (excellent) beer “Seybrew”!

The array of tags during testing: each tag on top of a Seybrew case and separated about 3 metres from the nearest tag
Recommended test method for the Lotek tags, placed on a flat surface ad exposed to sun.
Recommended test method for MTI tags, attached to a full soda can!

After the test period we shall programme the tags to report locations daily up to 31 December this year, by which time we expect the young birds to have become independent of their parents. Thereafter we shall programme them to relay the birds’ positions every three days for the following two years to show us the places in the wider Indian Ocean that are of importance to the maturing birds.

This will provide us with the most comprehensive information so far on the travels and feeding areas of Bird Island’s juvenile Sooty Terns. During this time, they have to become independent of their parents, learn how and where to locate and capture their own food, and learn to avoid adverse weather systems and predatory fish that lurk below the ocean surface. This is therefore a crucial time for their survival, and where they make these accomplishments could be an important marine area for the youngsters, and also for other marine life. At some stage during their immaturity they will moult their feathers from the dark spotted patterns that we see in the colony now, to attain the striking black backs and white underparts of adult birds. From our ringing (banding) studies, we know that many juveniles fail to survive this period, and that those that do survive will not return to breed until they are about 5 years old. This suggests that they have a lot to learn before they are ready to join the Bird Island’s breeding population.

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