48 | Chapter 3
simply captured, by withdrawing them from their nesting burrow. At
the season of this project, incubation was nearing its end and small
chicks were hatching. Having attached GPS devices to 50 immatures
and 27 adults, Fayet then faced the need to recapture the birds to re-
trieve the devices. That was straightforward for the adults; the birds
returned to their marked burrow. For the immatures, it was anything
but straightforward. Imagine a pitch dark June night, with tens of thou-
sands of birds flying, calling, and landing with a thump. Which is the
one with the GPS device? To increase her chance of finding it, Fayet
stuck reflective tape on the GPS loggers, and also configured the loggers
to emit either a blue flashing light or a radio signal which alerted two
base stations, and hence the researchers, that a target bird was in the
vicinity that night.
Fayet summarizes the frustrations of her fieldwork, “We hid on the
colony dressed in dark clothing, armed with night- vision scopes and
walkie- talkies, slowly crawling towards birds to catch them by surprise
when they eventually returned to the colony. By the end I had spent so
much time desperately looking for blue flashes in the dark that I ended
up seeing them everywhere!”
Perseverance was rewarded by useful data from 20 immatures and
19 adults – and the results were striking.
The immatures made shorter trips than the adults, both in terms
of duration and maximum distance from the colony (over 200 km for
adults, an average of 135 km for immatures), and those trips took the
birds in markedly different directions. While the immatures concen-
trated south of Skomer, adults either headed west to waters off south-
west Ireland or north to the northern Irish Sea. (See Map 2.) As with
gannets, the Manx Shearwaters of different ages were spatially segre-
gated. But the icing on the study’s cake came when Annette Fayet used
the pattern of GPS fixes to determine for how long on each trip a bird
was feeding. Roughly speaking, the bird was reckoned to be feeding
when it was moving relatively slowly over the sea, and turning often.
This enabled her to calculate how much mass was gained per unit time
spent feeding. It was significantly less for the immature birds. They ap-
peared to be less successful foragers, even when feeding away from any
possible interference from adults. What remained unresolved was the